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3DOF Mini Quadruped

by tmbg, published

3DOF Mini Quadruped by tmbg Feb 13, 2013
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18901Views 4105Downloads Found in Robotics
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I printed TheCase's excellent mini-quadruped design, and I love the simplicity of the parts, but I wanted a third degree of freedom in the leg for more complete kinematics, so I slightly redesigned the leg parts.

This also results in a slightly less bulky leg.

For now, I've left off the servo buttons at the coxa joint, but I may go back and add them back in for smoother motion.

If there's interest, I may workup a PCB which carries a Teensy 2.0 microcontroller board and provides power and support for twelve servos.

Update: Video of its first gait!


Parts needed:

1 backbone
2 hips
2 coxa_right
2 coxa_left
4 femur
4 tibia

12 9g servos. Design is optimized for Turnigy TG9e servos: http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=22928

However, any 9g servo will work, but the printed parts may need to be tweaked a bit.

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where can I find the code at? thanks.

Hello, print files of 2 coxa_right 2 coxa_left, and noticed that one of the thighs not Coincide with the design of its assembly.

Can you share your code and wiring diagrams?

Can you share your code? if you have any, i love the design.

Can you post a Youtube video of it in action? I would love to see how it moves.

Here you go :) https://www.youtube.com/watch?v=VsHNA3oLXC8https://www.youtube.com/watch?...

Mind you, this is my first shot at walking bots, and the gait is kinda naive, but it works!

In my opinion, that is an awesome start! It looks to me like you have the basic timing down for a 4 legged bot. My initial impression is to put some "shoes" on the bot for better grip. I suggest Sugru. There might be a better choice though. Here is one source: https://www.adafruit.com/products/436https://www.adafruit.com/produ...
I teach an engineering course at a community college and have been looking for a cheap, open source, easy to replicate quadruped design for my students to build. Yours is very impressive. I look forward to see how it progresses. Awesome work.

I don't have anything yet. I'm working on IK now, and I'm basically teaching it to myself from scratch, so it's taking some time :) I'll certainly put up videos as soon as I have something.

That looks great! Let me know about your power source and how many servos you can power with it at the same time. And I like that direct connection of two servos without the clamp bracket. The servo's gears are powerful. But can the servo's axis handle the weight without a clamp?

tmbg - in reply to Ablapo

For the moment I'm running off USB, and it's plenty of power. I haven't tried measuring draw yet. The servos handle the static weight of the bot without issue. It's designed such that the force is mostly up from the foot through the tibia directly into the femur, and not much twisting moment. If you twist the tibia, it will pop the horn off over the screw, but for normal motion it's plenty strong enough.

With this many servos it would be extremely advantageous to use a switching regulator in conjunction with a 2S Lipo. This would greatly reduce weight over conventional batteries and provide ample power without straining the servos.

Right now I have a simple 7805 regulator on the board, and I can power it from a 2S lipo. If I end up spinning a board for it, I will likely do a small switcher for efficiency. Honestly, right now I'm just powering it off USB, and these little servos require little enough power that it's plenty.

Good to know, I only suggest the switching regulator as you can power an chip and the servos from a single switch in most cases. Otherwise with a linear regulator voltage dropout will occur well before the battery is drained.

Thanks for the tip on USB, are you powering from a 1+ amp charger or from a 500ma computer output?

off a powered hub, and I'm not sure what it supplies. I'll try to rig up a current measuring rig here soon.

If it is a powered hub then you are getting much more power than what a PC USB port can supply. Typically 1 amp unless you are using a larger than normal wall adapter for the hub.

Exactly what I had in mind for getting a 3rd servo on each leg, thanks for making this.