Let's Make Robots!

Wobbly, a MiniBiped robot

MiniBiped.zip3 KB

Long time ago I wanted to build a multi servo robot, like a biped or a hexapod. After seeing OddBot's Mini Biped robot, I wanted to build one just for fun until I could afford to get the number of servos required for a full robot. This is how Wobbly was born. He has 4 servos for the legs and one servo for panning a Sharp IR sensor. Needs a little bit more work until it will be able to walk and turn properly, but he's almost ready.

I have designed a 12 servo board just like the uBotino robot controller, but I am still waiting to arrive. Mean while, I started the work on the robot, since I had all the servos needed. I grabbed some scrap poplar plywood that I had from building MiniEric and quickly fitted 2 pieces to mount the hip servos, then I used 15mm plastic stand-offs to mount the neck servo and the servo board. 2 more pieces of plywood to mount the knee servos to the battery boxes and of course, 4 screws to mount the hip and knee servos together. Double sticky tape to mount the Sharp sensor as usual, and after a bit of soldering for the battery wires, the robot was ready for uploading the code.

See some pictures:


The easy part was done. Now comes the hard part. I have downloaded OddBot's code for the soccer robots and adapted it a bit to work with my setup. I still need to figure out how to steer the robot, but the forward-backward motion kind of works. I need to add some traction on the toes, otherwise the robot just skeeds in place. So, watch for a later update to see it in action.



Update Jan. 25th 2011:

After some more code tweaks, the robot kind of works how it's supposed to. Still way from being perfect, it proves the possibilities. At the moment, you can see it walking leaning a bit on the back and with the weight a little more over one foot, so it slowly turns right. The turning sequence is still slow, but it is an improvement. When I'll have more time, I'll play again with it's code and try to improve it further, but for now I am declaring it "Complete".

I have attached the current code of the robot. Perhaps anyone can give me hints on what can be improved?

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Because these robots need the toe to have traction and the heel to slide it can be difficult to get them working well. The Mini Biped allows you to fine tune the servo center positions via a remote control and store them in the EEPROM. This is an important part of getting the robot to walk well. Finding the right surface is another problem.

Try some silicone rubber on the toes. It grips pretty well.

Thanks for the tip OddBot,

I have been trying with a rubber ring like one of those "tires" for the servo wheels. But the robot loses it's balance and falls down. I think I'll add some plate on the foot sole to widen and flatten it. Somehow the bot walks with the weight more on the heel, if I could find a way to make it lean forward I think it will improve the walking. At the moment I'm not using the remote, although I have a universal remote that I use to drive my robots. But for the life of me I can't figure how to steer them. I guess I need to add and subtract an offset from left and right stride for a few cycles to make it turn, but first I need to improve on the stability. Oh well... It's been fun to see it walking like a country skier. 

Getting them to turn is not easy. My mini-bipeds look like they're doing the goosestep when they turn and even then they tend to turn in one direction better than another if the servos are not calibrated properly.

Nice design, I like how the batteries are used as feet to lower the center of mass.  On that note you may consider full battery enclosures although not really necessary.  Anyway it looks sweet!


although I did not invent anything, I merely adapted OddBot's design to my materials. Here is the Mini Biped robot by OddBot: http://letsmakerobots.com/node/22588?s=l

Oh, and here is the first robot of this type I have ever seen:


Are those servos you have been talking about in my topic "Best and Cheapest micro servo"?

And if they are what's your opinion are those better than the hxt 900?

Like I said in that post, I have been using same servos for the neck of my MiniEric robot. These 4 servos I got for MiniEric arms, but didn't had time to adjust the pieces to fit the new dimensions, as they are slightly bigger than the HXT900 servos. They work a lot better, as they do not jitter and they rotate correctly from 0 to 180 degrees with the middle at 90. The HXT900 servos have the middle at 80 and they rotate a bit odd between 80 and 180 degrees, and do not have a complete 180 degrees turn, it's more like 170 degrees. Again, these servos are Turnigy TGY-S3101S. I have an order of 10 servos on the way, can't wait to see how well they perform in a hexapod with 2 DOF per leg:


Nice to see you have your biped build. Waiting to see the video.