Let's Make Robots!

Polymorph Caterpillar

Immitate a caterpillar
caterpillar.BAS1.88 KB

I'm trying to make a decent caterpillar style robot without a lot of mechanical complexity. I've had this idea ever since suggesting it to Thomas Countz who then made a carboard caterpillar.


This is the video of the caterpillar now that it's finished.

I've moved the processor to the centre to correct the

weight distribution problem.










The second video shows him in obstacle avoidance mode. No reverse yet!












The first video is my first attempt at moving straight ahead.

It isn't moving forward as much as I'd like.

Hopefully I will get it working properly this weekend.



To keep it simple the segments are made from a single polymorph bracket that joins two servos at 90 degrees. If you don't have polymorph then 3mm thick balsa wood sheet would be a good substitute. This is the pattern I used, the grey teardrop shape shows where the servohorn attaches.

After working out the shape of the bracket, I then printed it out with a laser printer and experimented with using that as an iron on transfer since both the toner and polymorph melt at a reasonably low temperature. I had the iron at its hottest temperature so the toner would melt as quick as possible. This meant I didn't have to keep it on the polymorph too long, just a few steady passes with the iron.

The sheet buckled slightly from the heat. I placed it between some books to keep it flat until it cooled. The paper stuck a little bit because I acidently melted the polymorph a bit but the pattern transfered well. By soaking in cold water and using a soft plastic scrubbing brush I removed the remaining paper.


I drilled 5mm holes where the servo horn screws into the servo and cut out the brackets with scissors and a sharp knife. I then bent the bracket as demonstrated in this walkthrough.


After mounting the servos and joining the segments together the design starts to make sense. The segments can pivot left and right for steering and flex upand down for locomotion.


This is his brain. The picaxe 20M has eight fixed outputs and eight fixed inputs. It's pins cannot be reconfigured and it has the same limited amount of memory that the 08M and 14M have. I may upgrade to a 28X1 later.





The rest of my servos finally arrived!

After mounting all the servos and battery holders I had a mess of wires. To tidy them up I used spiral binding. You can make your own by putting a plastic drinking straw through a pencil sharpener but it won't be as strong because drinking straws are made of thinner plastic.



After watching a video of a caterpillar walking I decided he needed feet.






I've posted a second video that shows the caterpillar in avoidance mode. He turns on the spot yet looks like a stretch limo doing a 30 point turn :) 

As pointed out by others, the head is too heavy. This is because of all the cables coonecting to the brain. I'm now going to rebuild him with the brain at the back.

I'll also upgrade to a 28X1 because I need more memory. This will allow other features to be added such as self correction if he rolls over.




I'm calling this project complete. I've changed to a picaxe 28X1 for the extra memory. With the processor mid-mounted I've eliminated 80cm of servo extension cable and the weight distribution problem. 




This is a 3D render of the caterpillar from DAGU electronics who are mass producing it.



Update: 20-5-2009

DAGU will be producing the caterpillar in the next couple of weeks. I am working on final improvements using a prototype hand built by their engineer.



I believe you will be able to buy it as just a body with servos allowing you to add your own sensors and processor. Later there will be picaxe and atmega8 versions available. I will make schematics and code available for those that want it.



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Hello oddbot, Great 'bot, love how clean and square the polymorph looks. The caterpillar is actually in the sparkfun (Chinese) polymorph manual: http://www.sparkfun.com/products/10950 (how to use polymorph), on the last page. (BTW. According to the manual, you should "stir well to become the state diagram").

I do not know why they used that badly translated instruction when I had a perfectly good tutorial here on LMR in English.

Wow! I can't believe I'm just now taking a look at this! 

I must say, I think my cardboard caterpillar (http://letsmakerobots.com/node/4468) is much better :p

On a serious note, this is great and I think it's awesome that it's available for purchase. The polymorph design that you constructed is very intelligent and innovative, I only wish I had that kind of creativity. 

It was inspired by your cardboard arm so in a way I have you to thank.
I wonder if covering it in some of that concertina`ed plastic pipe would work instead of a sock. Might be hard finding it in the right size though.

When I made caterpillar I did so from scratch having only seen robot snakes before. Now it seems my idea was not so original after all. I still haven't seen robot caterpillars on the market yet. At least I might be first there :D

At any rate my caterpillar is an LMR original. 


You will need to add a "skin"  to it, 

I put it in a sock but it restricted the movement a bit. The final version to go on the market is clear plastic so that the LEDs can form a pattern chasing up and down the length of the caterpillar. A skin would hide this pattern.

This will be on sale very soon with a discount price for LMR members so feel free to make a skin for your and show us how it looks :D


Nice. Sounds like a lot of thought went into the final design.

Not as maneuverable, but still fun to watch (when the makerbot site is back up).


The body parts on this one are made using a 3D printer. The brain is not on board. It has no sensors. It cannot turn. But still fun to watch. I forgive the video maker for the choice of music.

Video here: http://blog.makezine.com/archive/2009/06/3d-printer_robot_caterpillar_parts.html

Digital designs shared through thingiverse (also down?!): way cool.

More by this maker here.