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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pretty soon you will be making the big bucks... lol

keep up the great work. You are one of my priciple inspirations with some of the... "Odd" bots you come up with. no pun intended lol 

very cool. im going to try and make one of these.


I would like to see what you can do. In a few weeks you will be able to buy them here at LMR from DAGU at a discounted price. The body will be clear plastic.

I do not want to put you off making one for yourself, I am just letting you know you will have a choice soon.

I am always amazed by the robots you create! Great write-up, & video as always. Another great example of why I now visit LMR almost daily to see (and be inspired) by the amazing projects posted here. Thanks for posting Caterpillar!
That is truely awesome oddbot. love the design, love the music(what is it btw?!?!  :D) and love the creativity of this place. I really need to avoid being gone for so long....

Congrats on a commercial design!

Which processor is DAGU using on their version?

The Caterpillar will come with a picaxe 28X1 for beginners and an atmega 8 for University students as far as I know.
pretty tricky to program. I reckon i could control 8 servos with code, but to get them to work together like that would be something that i could only imagine to be mind boggoling. 
The code is attached and dead simple. It does take a lot of experimentation to work out each move though. There are three moves stored as subroutines. The whole program is only about 300 bytes.
Still getting used to the site lol