Sunday, September 19, 2010

My primary Ph.D projects

It gets pretty confusing about what I do for Ph.D. I am in the Biology Department at Tufts University, getting my Ph.D in biology. However, I've worked with people from biomedical engineering, mechanical engineering, electrical engineering, and computer sciences in the course of my Ph.D training. In fact, most of my colleagues start to think that I'm from "their department" (whatever it is). What exactly am I? That's a very good question which I actually does not have an answer to. Perhaps after I summarize my primary Ph.D research projects below, you may call me whatever you wish with a better understanding of what you are referring to.

My first project at Tufts was to design a force beam array to collect ground reaction forces from all the leg contacts from Manduca caterpillars in two directions simultaneously. This system involves synchronized video tracking and alternative force transducer design. The results suggested that caterpillars may use the substrate to transmit force much like an external skeleton. I'm currently working on the manuscript for the second part of the animal study.

For soft-bodied animals, tissue material properties can contribute greatly to the overall behaviors. My second project at Trimmer Lab was to instrument a lever-arm system to perform uniaxial tests on soft cuticle from the Manduca caterpillar. These soft specimens were often 5mm long and less than 1mm wide. Real-time video extensometry was necessary to control the strain. We then attempted an constitutive model for the material.

To understand how tissue mechanical properties affect the overall animal behaviors, one must go to the structural level. My third project was to investigate the overall structural properties of the Manduca caterpillar over a scaling range. We tracked down all the body tissue that could take mechanical loads and simulate the hydrostatic skeleton in a FEA model. We found a dramatic increase of flexural stiffness associated with body miniaturization. This implies several evolutionary constraint on caterpillar body plans.

Going beyond the Manduca crawling, I wanted to explore some clues about how caterpillars developed inching gaits in the course of evolution. I first simulated different crawling and inching gaits in my first soft-bodied robot lineage. Then I created a second robot lineage to simulate some ballistic behaviors which were supposed to derive from the normal locomotor patterns. Finally, I conducted a field work in Costa Rica to examine all these caterpillar behaviors in nature across different species.

In summary, my practical skills in the lab allowed me to design systems, acquire all the parts/supplies, manufacture/implement devices, and program systems to execute experiments. I would summarize my scientific contribution in my little niche in three statements.

1) During locomotion, soft-bodied animals can use the substrate as their external skeleton, and therefore gain stability and robustness.

2) The mechanical scaling of hydrostatic skeleton may limit the prolegs configurations and locomotor modes in caterpillars.

3) Soft-bodied robots, by definition, cannot rely on exact postural control. The very minute such a robot force a conformation, it becomes rigid.

Wednesday, September 15, 2010

Mechanics of a ballistic roll - Part 2

GoQBot is a soft-bodied robot designed to simulate the ballistic rolling escape behavior in caterpillars. The robot mimics the scale, timing and morphing of the behavior while allowing us to explore the control parameters and perform dynamics tracking. Please refer to earlier posts for more background information.
Kinematics tracking can be very tricky especially with high speed erratic movements. In order to compute the angular momentum of GoQBot, we must know the mass distribution of the robot as it deforms quickly within the 0.2 second window. One way to do it is to break down the body into many segments and track each segment individually. However, that requires installing more than twenty 1-mm size IR emitters on a small soft body no longer than 12cm. The soldering would be simply a torture, not to mention the wiring. Luckily, there is an alternative: kinematics-based model extrapolation.The idea is to constrain a virtual model of the GoQBot using the five IR-marked coordinates as the reference. By applying some deformation characteristics on the model, I can easily extrapolate the positions of every bit of the robot. This is exactly what I have done.

Monday, September 6, 2010

Sharing research tools and links

Hi there,

A new section has been added to my blog called "Huai-Ti's research tools". There you would find some useful links from general referencing to good online stores. There are also some good deals such as a free SEM imaging program (but the image will be public). In addition, you may find some useful software for making presentations or publications. For example, there is a Screen Capture Software that streamlines the print-screen function in most computers. Anyways, stuffs like this could be useful when you need it. I will populate this list gradually.

Over the past four years of my R&D, I have designed over 12 instruments, written more than 5 systems of feedback control programs, placed more than 85 orders for supplies and parts. I guess the number of projects and pet projects in experimental science directly correlates to the spending and instrumentation. Also, people in my research team tend to leave purchasing jobs to me since I've been really good at communicating with vendors and company associates to get the right parts for laboratory research. But I have to say such job is really stressful, although all the spending came from various research grants and not from my pocket.

Friday, September 3, 2010

Mechanics of a ballistic roll - Part 1

First off... I would like to remind you of the behavior that I'm studying. See the ballistic rolls and flips in some leaf roller caterpillars, and check out my biomimetic GoQBot's performance.

To study the the dynamics of such impressive behavior, the robot has been a great tool to test hypotheses and facilitated the collection of mechanical and control data. Back in April this year, I successfully collected the kinematics of GoQBot using my own adaptation of the VICON motion capture system. However, the kinematics data alone only tells half of the story. We could compute the angular momentum as well as the linear momentum from pure motion tracking. However, there is no data on the mechanical power output and loading condition. To extend the analysis, I took one of the force beams I used for caterpillar ground reaction forces measurement and implemented it for robot GRF collection. In fact, VICON system has built-in capabilities to take in force-plate measurements and any other analog signals.With some modification and instrumentation, I obtained GRF in two directions from the head anchor and simultaneous recording of the actuator current draw during the high speed kinematics recording. Here are some very preliminary data.I'm currently processing the data to calculate the center of mass and the development of angular momentum. More results are coming!!

Wednesday, August 18, 2010

Stop crawling... pace up!!

My Ph.D defense is coming up in December. I better hurry and pace up. When I was 7, I thought about a great deal of things about academic research and becoming a Ph.D. But I always thought of them in future tense. Time is truly incredible.

In any case, I just sent out another manuscript to Journal of Experimental Biology about my studies on the hydrostatic skeleton on caterpillars... three chapters of my thesis done... now onto the fourth one: soft-bodied robots.

Well, thesis writing requires a lot of integration and I've been organizing all my research files in my multiple hard drives as well as lab notes on paper. It's a very tedious yet enlightening process. I realize that my blog updates have been slowing down and infrequent. Well, that's because I begin to invest most of my writing power on my publications and thesis. Sometimes, after going through so much organization, I am left with no energy and patience to write anymore.

Nevertheless, hosting a blog is a commitment. I will post some update on my kinematics-dynamics simultaneous recording of ballistic rolling caterpillar robots in a week. In the mean time, I just release the Costa Rica Fieldwork Journal Part 3, which has been in my draft box for months. Sorry about that!! I will do better...

Monday, July 26, 2010

Quick clarification for the media

I got some inquiries regarding the recent press release on caterpillar gut movement. It is entirely my colleagues' X-ray work and I have not taken any part in that project. Thus I am not responsible for any claims in the NPR interview or other press manuscript. Many online media translations started to deviate from the original release and the announcement does not have any bearing on the on-going or past soft robotic projects.

If you really want to see something in the news, the Boston Globe has a more conservative release, and the NSF promotional video was roughly accurate. As a scientist, I am always concerned about interviews from the mass media because the public can always see sciences in some funny ways. Want the real story? Go straight to the researcher(s) who work(s) on the specific project that interests you. You might be surprised!

Saturday, July 24, 2010

A short review of my European resonances

I've been away for three weeks in Europe for the Society for Experimental Biology annual meeting and several academic visits . I met quite a few cool people on the road and in meetings. Here I would only highlight a few topics that I found relevant to my current research theme.

At the SEB conference, there were a significant number of people involved with the EU project "Locomorph". I found this new term intriguing. It has been widely recognized that morphology plays a key role in locomotion, and many studies have focused on how the default body configuration function and coordinate to produce desirable kinematics. Well, this project combines "locomotion" and "morphing" into a word so to emphasize the effects of "changing" body morphologies during locomotion. For soft-bodied animals, morphing can be a means to locomotion, but that is the extreme case I'm currently concerned with. For most skeletal systems, coping with a changing morphology is a process of adaptation, and it is this very strategy that biologists and roboticists are interested in. To find out more about this huge collaborative project, see the project website. It sounds awful lot like a DARPA project in the US. I wish good health and good progress to all the people who are involved.

My visit to the EPFL in Switzerland was quite an experience. I heard so many things about it even since I started following robotics stuffs. That's when I was still a teenager. It's quite amazing that I actually get to visit and actually gave a talk about my work. Again, I won't even attempt to summarize people's research, in case I don't do a good job. But one recurring concept in many robotic efforts was localized intelligence and the emergent properties. Indeed, intelligence does not have to live in a central processing unit. Localized simple logic goes a long way when certain information sharing occur between the functional nodes. This can be seen at the sensory reflex level such as the optical flow control drones, or on the coordination level as in the salamander robot's coupled oscillators, or at the navigation level where swarms of MAVs create a communication network. In a way, I think this is how intelligence arise in any systems. Even our complex brain employ millions of neurons to generate a gross computation. Each single neuron has its own logic depending on the excitability and pre-conditioning. To exchange information, neurons rely on the varied synapses which can be modulated dynamically as well. In fact, I would go so far to say that all forms of intelligence are emergent properties of certain collection of simple logic units. This subject is indeed fascinating and I think using robots is often a more efficient way to study it. Browse their website to find out more.

U. Jena Lauflabor is known for the development of the SLIP (Spring Loaded Inverted Pendulum) model for biped locomotion. More specifically, this group of physicists attempt to find dynamic stability in a open-loop control scenario. In contrast to the reflex model for locomotion as employed in many traditional robots, researchers at Jena really investigate how inherent walk-run mechanics and leg properties can produce stability. Implementing robots from these simulations may lead to much more elegant solutions to legged locomotion, far from the reflex control as demonstrated by Boston Dynamics' "Big Dog" (which is very impressive, but not very smart). Their goal is actually similar to my soft-bodied robotic trials, except that our subjects are really quite distinct.

In any case, these are only three things that seem the most relevant to my current research goals. The field of biomechanics is really growing bigger each year and the use of robots has become a standard procedure now (for one purpose or the other).

Wednesday, July 14, 2010

The European Tour

Sorry everybody!!

I've been traveling across Europe for more than two weeks already. The internet access and schedule doesn't really allow me to do any serious blogging. However, I will be reviewing some of the things I learned from all the amazing biomechanics researchers in Europe next week when I go back to Boston. Stay tuned!!

Huai-Ti (YT)

Saturday, June 12, 2010

Field Work Journal (Part 3)

Working in reverse, I started to examine how inching caterpillars may revert to crawling gait. Behaviorally it's quite feasible and we've observed some tiny step crawling when inchworms adjust their bodies on the foliage. My discovery of the day was that by constraining the uplifting body bend, I can actually induce crawling in many caterpillars that inch as their default gait. What I did was a very simple behavioral experiment: take a sheet of heavy duty plastic bag and lay it on top of a inching caterpillar on a flat surface. The result was quite stunning: the weight of the plastic prevent body upward bulking, so the inchworms start the stereotypical anterior-grade crawling. The very second plastic sheet constraint is gone (when I remove the plastic sheet or when they simply crawl out from under the sheet) they start inching again. This transition can happen at any phase of a gait cycle and so reversible that I can't imaging any other gait transition mechanism other than a biomechanical one. The implication is quite mind-bogging: inching gaits came naturally when mid-abdominal segments are not locked down to the substrate.6/8
I went back to the memorial behind the casona today for the sunset. Actually I went with my friend Ian. The casona is a big historic farm house that has been converted to a little museum to document the development of ACG. The memorial was built for many worriers and political leaders who defended Costa Rica against an ambitious Nicaragua war-lord in 80's. This memorial is about two stories high at the top of a hill, overlooking the entire Santa Rosa sector and the two main volcanoes on the other side of the intercontinental highway. We walked up there briskly right after dinner and caught glimpse of sunset. Before it became pitch-dark, I looked around and wonder where the scorpion I met earlier went, and whether it also lingered around at sunset.
My Costa Rica stay is drawing to an end, but I feel that everything has just become part of my life... three meals of rice and beans everyday, new trails everywhere, mosquito swarms at certain spots, incomprehensible language that sounds very familiar, WiFi domain guided by the trees, checking e-mail late at night in pitch-dark with some frogs as companies. The list goes on and on, making my experience quite unforgettable.
Today I decided to stop looking for caterpillars, otherwise I can't really wrap up the study. I went back to the caterpillar barn to examine all the caterpillars I've been working with and start to let them lose. If there is a video that is so amusing and that I can release freely, it is this video that I captured today of two noctuidae inching along a jar cover. Why is it funny? Well, I love the way they negotiate with each other. This circular walk lasted for about 6min until I got tired of filming. Apparently, you don't need very fancy enclosure to keep inching caterpillars. They would happily stay on a nice upright track even if it has a periodic boundary -- never ending. Isn't that what we call "inertia"?

Field Work Journal (Part 2)

I started another day with fried rice and beans plus scramble eggs and cheese. Just when I got to my second coffee around 7:30am the bus brought in all the park rangers in for breakfast. People streamed into the Comidor with greetings and jokes. I watched them eat and talk and set out to work with a mouthful of Costa Rican rice coffee aroma. Somewhere in my heart, I envied such life: so simple, so natural and communal.
It’s time to organize data and find out what and what else can I get out of this trip. I started up with three aspects: Biometry, Kinematics, and Behavior. The biometry project was targeted to compare the biometry proportions of different caterpillar species as well as tracking down the ontogenetic scaling of some species. The only way to perform measurements on soft-bodied animal is to use photography. Unfortunately, caterpillars are wild animals after all. There is no easy way to get them to sit still in a specific posture while I photograph. Weighing them is also impractical because many of them do not relinquish their substrate (often their food as well). Brute force can injure caterpillars and decrease their survival rate dramatically, making ontogenetic tracking impossible. However, the general biometry can be still obtained from the video frames I collect in the kinematics project. One of the measurements I was looking for is the aspect ratio of the cylindrical body. Compare the two caterpillars before and after this paragraph to see what I mean.

In a forest full of activities, it is very difficult to stay put for more than a day. Although I haven’t finished the image organization on my two EEE PCs, I decide to head out to the field anyways. As the sun journeyed pass 10am, the wet “dry forest” turned into a steamer. I could smell many things around me, from fresh leaves to fermentation in the rotten woods. The strongest of all was a pungent smell that reminded me of steamed peanuts. I never figured out what that was, but it definitely imprinted in my memory of Santa Rosa. Anyways, the most memorable discovery from today’s field work was a leaf craftily “eaten” into a beautiful symmetric pattern. I couldn’t help but respect the "minds" of these wild caterpillars.

Over time, I found myself very tuned in to looking for caterpillars. I could distinguish leaves damaged by caterpillars from those eaten by ants or beetles. I was able to spot the caterpillar feces and trace the source to a plant, and I became pretty picky about what caterpillar I get. One of the tasks for today’s field work was to collect some cydista plants for my Manduca lanuginose. This was the only Manduca I found so far so I really should keep them alive. Just as I was full with plastic bags of caterpillar and plant harvest, something lighted up my eyes. It was a huge Manduca sexta gorging up a Solanum hayesii. I was very excited to see such a familiar body even though my memory of Manduca has been this obstinate stupid animal in the lab. For some reason, the wild type looked much brighter in color. It’s got a puffy body with clear healthy white lateral strips. Maybe the organic food really made a difference.

The English speaking researchers tend to cluster in one table at dinner, although many of them speak perfect Spanish. I have been meaning to learn to speak a few words, but the data organization work every night really crushed my ambition. Over some rice and beans with pork stomach, we talked about what we encountered during the day and frustration with the animals. Indeed, field work is a very different mode of research. We are studying the organisms in the great nature which is beyond our power to control. We cannot force any activities or interactions. We must let them come to us. Patience is the key and letting things be is the attitude.

Due to my field work during the day, I started to shift my caterpillar photography work to after dinner. Tonight, I found a keystone to solving the gait transition mystery in caterpillars. So far I’ve found caterpillars that inch with reduced prolegs and caterpillar that crawl with full prolegs. This caterpillar I picked up today inches with full prolegs, displaying how exactly a inching gait can be derived from a crawling pattern. This spotted caterpillar had a full set of functional prolegs from abdominent 3rd. However, when it picked up speed to run away from me, it lifted very large proportion of its body and actually cut under itself to gain the maximum step length. The whole gait pattern resembled a very conservative inching which can be shifted into a crawl at any moment in a cycle.

Thursday, June 3, 2010

Field Work Journal (Part 1)

Part 1 --- 6/1~3

I was so busy figuring out experimental protocols and data analysis during the first week of my stay. Every night I barely had energy to brush my teeth, not to mentioned writing in my journal book. My advisor left yesterday so I’m literally on my own now. But I think I am in good hands. The dormitory house keeper Lily helped me with my laundry on Sunday even though I didn’t have any soap. When I came back in 40min, she was already folding my clean dried clothes in the laundry room. The cook Aida came up with some food for me tonight when I worked overtime and forgot about the dinner time. Somehow I think they could empathize this poor young Asian kid who doesn’t even know how to say “por favor”. Of course, Dan and Winnie continued to bring me interesting caterpillars when they encounter them. What more could I wish for in the care of these people.
All the inching caterpillars I worked with so far tend to be very active. Some of them moved with impressive speed (up to ~4cm/s). In addition, they can also perform various acrobatic moves especially in the situation of disturbance. This Anomis I picked up today demonstrated one of the most memorable moves in front of my camera. It simply “disappeared” when I poked it on the rear back. 300fps high speed video showed exactly what it did. The caterpillar first span some silk around the thoracic legs, then it flip its whole body sideway with extremely high speed. The prolegs release was nicely coordinated to let go of the momentum it built up. The result was a ballistic lateral jump. The caterpillar landed on another leaf below the substrate I provided. It then used the silk line to climb back to the exact same spot where it jumped off. I simply couldn’t say a word but marvel such innate skill.

I took today off for a hike with my new friends, mainly to explore the conservation area and also to get some exercises. The focus of field collection was never about walking, and I found myself so out of shape. Nevertheless, I carried my big CASIO EXLIM camera in case my SONY Cybershot can’t do some animals justice. Field exploration is very much part of the field work. You never know what you would find by wondering about without a particular search criterion in mind. We started out right after breakfast at 7:30am and headed straight down to the valley. It was a pretty damaging road for most cars, but an easy one for hikers.
I met more butterflies than caterpillars on my way down to the coast line. They all cluster under the sun sucking liquid on the mud or some rocks. Wing flaps by wing flaps just like having group meetings. The blazing sun started to steam up the water from yesterday’s rain. Each water puddle contained thousands of tadpoles and supported tens of water surface insects. I found another beetle larva moving upside down by peristaltic on the rocky ground. I wonder why they still keep their thoracic legs if they don’t even use it for locomotion. At the bottom of the valley we crossed two rivers. We met a gang of monkeys after we waded across the second one. My friend was somewhat aggressive on photo shooting, that the monkeys decided to protest. Several of them started breaking branches to drop on top of us, and many more gather over. We left soon after these demonstrations. Sometimes, communication can be so effective. We were caught in the pouring rain when we reached the beach. It didn’t bother us much since we were all soaking wet in sweat anyways. Sweat, rain, and Pacific Ocean all mixed together as we headed back to the research station.

Today I had to move out of my room to stay with other researchers. It was a bit of a hassle, but I don't mind joining the party. Having a room with four double bunkers for myself is too luxurious out in the forest. It was always an adventure to interact with the ACG staffs, because I pretty much don't speak Spanish and many of them don't speak English. In any case, we all managed to came to the same conclusion on our subject whatever it was. Still, I wish I spoke Spanish. I’m missing so much.
My caterpillars in the barn are doing pretty well now. But I need to finish up filming these caterpillars before I can get more. I can never predict when I will lose them to stress, parasite, or pupation. The inchworm Sphacelodes I picked up before breakfast was the largest geo I’ve even seen. It’s about 3.5 cm long and weighed 0.146g. However, it had every bit of athleticism of Geometridae. Most geo’s preferred to inch on top of the branches if possible, but this one had much stronger preference. When I turned it upside down on my dowel, it started to have trouble pulling the body in. After a few steps it just spiraled around to the top of the dowel again. Well, counter-levering a hydrostatic body up to 3.5cm long does become pretty difficult with only ~0.5cm leverage.

Sunday, May 30, 2010

Costa Rica Field Work

It's been over a month since I last updated my blog. I truly apologize for those who follow my blog. But honestly, this is my first chance since mid April to catch a breath and log in to my blog. In any case, I'm currently in Costa Rica for a field work, tracking down an amazing collection of caterpillars in the tropics. Pictures and field work journals will follow. Stay tuned in the next 10 days.

The week before I set off to Costa Rica, I questioned myself once about this trip. What exactly do I expect to get out of the forests? Do I really need so many projects for my Ph.D? With two manuscripts pending and an international conference travel coming up, setting up my first field work at a distant foreign place was the last thing I needed. However, as my adviser and I arrived at the Area de Conservación Guanacaste, Costa Rica, my doubt dissolved instantly. It is totally worth the sleepless April and May. For the following week, I will be posting my field work journal. They all consist of two paragraphs. The first one contains something about my field experience. In the second paragraph you will find some portraits of what I saw in the field and animal interactions. For my research, I will focus on locomotion in different caterpillars and some associated behaviors.

Tuesday, April 20, 2010

For those who track 3D

Folks in the field of animal locomotion would know how kinematics data are usually obtained. But allow me to summary the general procedure in a few sentences. To track anything in 3D, at least two camera views have to be available at all time. After space calibration, one can calculate the 3D configurations of the objects in the analysis software of his/her choice. Ideally, video tracking can use any inherent features of the subject. However, to facilitate automatic tracking, high contrast makers are often attached to the subject. Infrared markers offer a way to highlight the features of interest without compromising the lighting for the normal video acquisition. After I created two families of soft-bodied robots, I was challenged by the need of quantitative data. These kinematics data are critical for any mechanical analysis on the robot locomotion.I set up our VICON 3D system to track my robot kinematics at Tufts Advanced Technology Laboratory. VICON is a company that makes 3D tracking systems for research in locomotion and animation industry. It employed several near infrared high speed cameras which would detect the IR signals coming off the retro-reflective markers attached to the subject. Unfortunately, retro-reflective marking is really not the way to track small animals such as insects or robots of the same scale. After going through many types of IR florescent chemicals, I finally decided to go with semi-conductor IR emitters (or infrared LEDs).
This works out really great for my application because I do not need to worry about IR light flooding or bad camera focus. These surface mount IR emitters produce point-source lighting smaller than 1mm. The IR cameras pick them up like many distant stars. In fact, a little out of focus actually increase the pixel numbers from which the centroid positions are derived.
Data are coming alright, but my data crunching techniques are still too slow for the rate by which these high speed cameras acquire data. I better work on that!

Friday, April 2, 2010

Gait transition and embeded AI

A couple of years back, I was deeply impressed by probably the most well-known bio-inspired robot which demonstrated the effects of central pattern generator on gait transitions. This is the EPFL salamander robot with coupled non-linear oscillators. In this research amphibious robot, smooth gait transitions were accomplished by tuning the gain of oscillators coupling.

As I started working on soft-bodied robots, I discovered that many non-linear characteristics of the soft materials and actuators can be exploited to engineer behaviors. So I took a completely different approach to robot control. Instead of programming complex behaviors on a micro-processors, I "tuned" the body and actuators so they create desirable behaviors when I switch on a behavioral circuit. Amazingly, when the motor variations and body properties reach a certain domain, the robot was able to achieve gait transitions with a simple scaling of motor-pattern. This is a very intriguing demonstration because it provokes a rather radical inquiry: how much logic/intelligence can we embed in a piece of material? To what extent can we use morphing morphologies to perform computation (or thinking if you will)?

Thursday, April 1, 2010


A lot has happened in the past few weeks. Besides my secondary injury during my recovery of my bone fracture, everything else seems to progress in a positive direction.

First of all, my paper on caterpillar ground reaction forces was finally printed. It's been really over-due for a year now. Most data were collected by Christmas 2008, and I actually presented the major finding at the SICB 2009 January. I felt pretty bad about this delay but the robotics project last year really took my life from March through October. To summarize the findings in a few sentences: large caterpillars such as Manduca sexta load their bodies in constant tension when they are attached to a substrate. Locomotion was achieved by progressing the body tension/deformation forward. Biomechanically speaking, these critters use the substrate as their external skeletons. We call this strategy: environmental skeleton. For more details on this radical view of soft-bodied animal body control, check out the April 1st issue of the Journal of Experimental Biology. If you would like a PDF copy of my paper, simply e-mail me at and I will gladly send you one.

Besides my old new paper, I've been planning a field trip to Costa Rica for this May and June. Last spring at the SICB conference, I bought a few books about caterpillars. Among them, I was really impressed by a couple of books regarding tropical caterpillar diversity. So I contacted the authors Dr. Daniel Janzen et al and was struck by the idea of visiting the home of caterpillars in the wild. Lab animals are always somewhat unnatural. This idea was incubated in the back of my mind for many months until I finally formulated it into a more concrete field study project. My mentor Dr. Barry Trimmer was very supportive of the idea and quickly decided to make it happen. In any case, we have now arranged a 17 days field work at a conservation in Santa Rosa, collaborating with Dr. Janzen's team from UPenn.

Finally, to continue the imaging theme from last time, let me share a few images from our histology for Manduca caterpillars. Working together with my great undergraduate lab-mate Dan, we've been able to produce very clean cross-sections of caterpillar abdomens.Through some imaging techniques, we can enhance the cuticular folds.Or we can also highlight the muscles! So awesome... the biology I mean (but we're not bad either)

Monday, March 15, 2010

Take a hard look at the soft morpholgies

Every so often when I need to get some details about the caterpillars, I would do some electron microscopy. I especially love to browse specimens under a good scanning electron microscope (SEM). It feels like entering a different world: a microscopic one.

Recently I decided to look at more surface features of Manduca caterpillar bodies with SEM. This time I wanted to explore the folding structures on the soft cuticle.

The first thing I noticed was how hairy these cute caterpillars really are. No wonder people call caterpillars "fussy worms" in tropical Taiwan where I grew up. If vision is weak and proprioception is irrelevant, then tactile sensing must be dominant.

Then I couldn't help focusing my electron beam on the spiracles.... well, they look like tiny stadium to me. This the the hairs around the air slit can't be for tactile functions, or are they?
I think these are hairs that help repel moisture and particles to keep the air flow smooth. Maybe I should look into the literature.

Finally, I must show you at least one image of the crochets (microscopic claws) on the caterpillar prolegs. They are simply gorgeous!! I got many more images with higher magnification, but it's hard to explain what you are looking at in such close-up photos. This image was actually taken three weeks ago.
These caterpillars relay on these double array of crochets to grip on to any substrate. When a proleg retracts, these crochets are pulled into the cuticle pocket on the left side of the image. And the whole leg closes like a purse to prevent any unwanted hooking. It's so simple but reliable. I wonder if there is any better strategies for controlling these hooks array with large surface deformation... (another long night of restless dream)

Monday, March 1, 2010

Morphing Morphologies...

Some people asked me how I got into rolling locomotion from soft-bodied animals. This is actually a subtle point which perhaps I didn't make it explicit in my previous post. Although my current study system is one without any well-defined articulation, my interest is really about morphologies that function through morphing. All animals in the wild have to undergo dramatic transformation to switch the mode of locomotion (e.g. from crawling, swimming, running or whatever to wheeling/rolling). Their bodies are definitely morphing morphologies.

Similarly, soft-bodied robot can be defined by its ability to morph regardless of its material. Indeed, the definition of "soft-bodied robot" has been a indefinite argument in my research group. What is really considered "soft"? Isn't it all relative?

After four years of contemplation, I have only recently come to the conclusion that a soft-bodied robot is a robotic device that can conform to the environment without active control. In other words, soft-bodied robots do not maintain any definite posture. Instead they allow the environment to determine its shape in conjunction with the internal control of body properties. This definition was really an inspiration from my study of caterpillar locomotion. Proprioception (perception of body posture) is therefore insignificant by definition. If we translate this definition of soft-bodiedness back to the animal kingdom. A true soft-body is one that does not force any posture. This will exclude all the hydrostatically controlled bodies especially muscular hydrostats. How heretic? Octopus arms are not soft? Well, we must also recognize that tissues can be tuned to different states. An octopus arm can be a very well-controlled muscular hydrostat when performing a manipulative task but highly compliant when relaxed. From this concept, I urge the biology community to take on more specific terms when describing animals or organismic bodies:

Articulated body [lever-linkage system with joint actuation]
Celumic hydrostat [the pressurized fluid-filled body as a skeleton]
Muscular hydrostat [muscles as the skeleton and actuators]
Environmental skeleton [substrate as skeleton on which muscles act]

Sunday, February 14, 2010

A short review of rolling locomotion

For my rolling GoQBot publication, I've been doing literature reviews and dug out some interesting information about animals with rotary locomotion. While I wrote a formal literature review in my manuscript, here allow me to share my thrills in a visually guided relaxed format! For in depth information, see my list of references at the end of the post.

The earliest documented rotary locomotion I could find was from this shrimp like creature living on sandy beaches. It has short legs specialized for swimming. So when there is no water, they flip on their backs and performed a slow body rolling motion (Caldwell 1979).Of course, a much more dynamic gymnast has to be this somersaulting spider in Sahara desert. This little guy can perform amazing somersaults across the dessert sand after a running start up to 2 m/s, according to the discoverer Dr. Ingo Rechenberg. Check out some of his videos on YouTube: Short intro; Extended
Despite the amazing gymnastic moves, the above two creatures don't really roll in a circular form. The stomatopod really just flips its body by reaching the head with the tail, and the somersaulting spider actually got airborne in their strides. A true wheel is one that relies on the continuous contact of same radius spokes. The following two examples are animals that form quite perfect circles for downhill passive rolling. They are really very cute and circular... (Henschel 1990, 1995; Garcia-Paris et al 1995)Finally, the true powered wheeler is still my favorite rolling mother-of-pearl caterpillar. These caterpillars would curl into a wheel ballistically and catapult themselves into free-wheeling objects when disturbed (Bruckenbury 1997, 1999). According to the scientist who characterized this motion Dr. John Bruckenbury, there are a few more species of caterpillars that perform this behavior. It's really quite an effective way to escape. [pictures below are from Bruckenbury 1997 publication]
Armour, R. H. and Vincent, J. F. V. (2006). Rolling in Nature and Robotics: A Review. Journal of Bionic Engineering 3, 195-208.

Brackenbury, J. (1997). Caterpillar Kinematics. Nature 390, 453.

Brackenbury, J. (1999). Fast Locomotion in Caterpillars. J. Insect Physiol. 45, 525-533.

Deban, S. M. (1995). A Novel Antipredator Mechanism in Salamanders: Rolling Escape in Hydromantes Platycephalus. J. Herpetol. 29, 149-151.

Full, R., Earls, K., Wong, M. and Caldwell, R. (1993). Locomotion Like a Wheel? Nature 365, 494.

Gould, S. J. (1981). Kingdoms without Wheels. Natural History 90, 42-48.

LaBarbera, M. (1983). Why the Wheels Won't Go. Am. Nat. 121, 395-408.

Siegwart, R., Lamon, P., Estier, T., Lauria, M. and Piguet, R. (2002). Innovative Design for Wheeled Locomotion in Rough Terrain. Robotics and Autonomous systems 40, 151-162.

Saturday, January 30, 2010

Biomimetic vs. Bio-inspired Robots

Whenever I tell people that I do robotics, the first question that bounces back is: "That's the application?" Then I would have to start making things up quickly...

Well, to be honest, the true motive for my robotic effort was purely academic. I want to learn about how animals move by making physical models of them. That's why I insist to stick with biomimcry and try to be loyal to the biological system at least in the functional level. The ways biology deals with mechanics are not always optimal and often contain constraints, but I want to have those in my robots as well so I can discover them, feel them, and characterize them.

Recently the discussion of biomimetics came up in my research group because there are a good proportion of engineers who design for functions. Of course, in the name of good engineering, we should not make biomimetic robots but bio-inspired robots. The difference is that we could learn the principles of operations in biological systems and apply these ideas and only these ideas to robotic applications. In this approach, we can leave all the biological constraints behind and attempt to optimize specific functions in our devices. For example, Dr. Shimoyma in Japan has a project that aims to recreate the swallow tail butterfly wings on his micro-ornithopter (see below).

Taking the inspiration, they also created a tail-less micro-ornithopter with all the control electronics and sensors on-board. (very impressive works!!)

Of course, that's not to say I don't think about applications and moving on to bio-inspired robotics. Besides, my robots are still performing well beyond average among so many soft-bodied robotic platforms up to date. I believe that sticking to biomimetics would help us understand the nature of our biological inspirations. Surely, there is still much to learn from soft-bodied animals.

Monday, January 18, 2010

SICB 2010 Seattle

Welcome to the first post of 2010!!
I just got back from Seattle one week ago from the annual meeting for the Society of Integrative and Comparative Biology, or SICB in short. So here is a short report about some of the inspirations I received over the course of the 10 days Seattle visit. For the limited space, I will only mention three topics with: 1) ideas that resonates with my current research; 2) something about Manduca sexta; 3) the most entertaining contents.

To start with, I would like to acknowledge those researchers working on plant biomechanics. After staring at the quasi-static locomotion of caterpillars for 4 years, I can really appreciate the intricate movements without dynamics as also in plants. Really, caterpillar crawling is a "static problem" only that people don't like to hear about "static locomotion" so "quasi-" makes it sound better. Of course, plants movements are all driven hydraulically, but cellulose fibers can define the deformation. The morphology very much depends on the material properties and internal pressure. For climbing plants, stem development and attachment scheme are highly correlated. Those that attach to host substrate tightly can be soft, while the ones that hang on to forest tapestry loosely would need stiffer stems to self support. This principle of substrate interaction really resonates with the "environmental skeleton" hypothesis I proposed. For a big fat caterpillar with many prolegs attached to the substrate, no internal structural support is needed. In fact, compliance is imperative to allow conforming to the substrate, just like those tightly attached plants.

This year's SICB also had a lot of animal flight stuffs. In particular, Manduca hawkmoth flight has been a highlight. Thanks to the modern high-speed videography and kinematics tracking software, wing strokes can be digitized at many thousands of frames per second rate. Much attention has been delegated to turning maneuvers, especially in the yaw direction. In general, hawkmoth and other big insects create asymmetric effective wing angle of attack to turn. This change of stroke plane can generate a fairly acute turn, and we can find this strategy in many current radio controlled micro-ornithopters. After watching so many slow-motion of moth flying, it occurred to me that body weight shift must play a key role for stability as well. While most micro-ornithopters don't use tail for turning anymore, they still need it to smooth out the unsteady air flow from the wing. To create a tail-less flapping flight robot, we might want to model the body coordination as well. For any flapping flight agent on the order of a few grams, it seems to me that weight shift is as effective (if not faster) for stability compensation as wing stroke modification.

Finally for the topic with the most entertaining contents, I would like to mention some work on maximum performance of musculoskeletal systems. Although I am currently working with a critter without any skeleton, my original biology training was functional morphology of skeletal systems. In plain English, that means I held scalpels more often than pipettes. I was the student helper at this session called "Terrestrial Locomotion -- Jumping" with the session chair Steve Reilly. It's a strange feeling to see Dr. Reilly because I once read a lot of his work and almost did my undergraduate thesis on frog jumping. Anyways, the first talk of this session was probably the most entertaining talk I went to in SICB 2010. It was about why jumping frogs contests produced much better jump distance record than the scientific research. Well, apparently it's all in the arts of these professional "frog jockeys", which are unfortunately kept secret. However, the investigators in this research did find out one well-tuned factor that affects maximum muscle performance: temperature. This is probably a general issue for all poikilotherms (animals don't actively maintain a constant body temperature) which can be easily affected by climate change. In any case, although it's ambiguous what these "frog jockeys" were doing to their frogs, it was absolutely hilarious to see them "jump their frogs" with the utmost seriousness.

Of course, there was a lot more impressive research presented in this meeting. I was simply overwhelmed by Wednesday afternoon that I had to stop going to the talks in order to recall my own presentation scheduled on Thursday morning. It's good to be at a conference like this and feel connected to this fun community of scientists.