View Full Version : [Project] Biped Legs only

10-11-2010, 02:25 AM
Hey everyone, I've been working on this project for awhile now. My goal is to make a full bodied biped that can at the very least shuffle around and try to look cool. I thought I would post what I have so far and see what everyone's impression is. I'm coming from a more artistic background, I'm sure my design could be better. Let me know what you think!



here is an early test of the leg


I'm using AX-12 actuators controlled by an Arbotix controller. The leg is built from a combination of MicroRax aluminum beams, and parts from the servo erector set from lynxmotion.

I have loaded the joints with shocks to keep it from wiggling when it moves. Right now I can make shift around, but it can't take a step.

This is the first time I have attempted to make a robot like this, I'd like to know what everyone thinks, does it look like Im on the right track, or is my design already doomed to fail?



10-11-2010, 02:45 AM
That looks awesome. Good work! Overall about how high is it?

10-11-2010, 02:55 AM
It's about 20 inches tall, from foot to hip... I anticipate it being roughly 3 feet tall when I'm done. Now I'm thinking this might be a problem when it comes to mobility and weight.

10-11-2010, 07:38 AM
I think the legs look really cool. The springs and the material its made out of give it a very neat look.

Are you afraid of it being extremely top heavy though? If you are going for a humanoid, there will be quite a few servos making up arms and shoulders. I am definitely no expert, so maybe it would work, and those springs are strong enough to hold the legs in the correct positions. So I say keep trying, and continue to update your post so we can all see how it goes.

Can you get both legs moving at the same time? Have you tried holding them as they try to move on ground yet? I'd like to see more of your project.

10-11-2010, 04:46 PM
It looks like a nice design, although I hope the version in the photos is newer than that in the video. Relying only on an AX-12+/18F to hold a static pose in a large bot (especially in a bent knee) does not usually end well, but others seem to have had success using servos to change a static pose maintained primarily by a spring/shock. The two AX-18F I have used (without any springs to counterbalance the weight of the bot) absolutely love to overheat within minutes of use in a Bioloid Premium Humanoid knee (and almost constantly emit a high pitched squeal and/or a lower pitched groaning noise depending on loading, but that is hopefully the firmware).

Two possible sources of frustration that I can see may be the AX-12+ (may be too small/underpowered for the size of the bot) and the use of those small diameter rods to control the knee (given their length, they will probably deflect a bit under higher compression loading).

10-12-2010, 04:20 PM
The video is definitely older than the pictures. I had to double up the threaded rods on the knee, they were bowing out under the weight. The top most servos don't seem to have any problem moving the weight of the leg, they do emit that high pitch scream when holding the load. I do want to take the stress off the AX-12, is there a more efficient way to do this? Im putting shocks where I think they are needed, I'm wondering if there are good examples somewhere online?

I am concerned about the weight being too much when I add the rest of the body.

I'm using the AX-12 because of the price, I'm sure the higher end dynamixel servos would do a better job, I can see how, with unlimited funds, a project like this can reach the price of an automobile! :)

Thanks for the feedback. I will post my progress when I get this thing moving.

10-12-2010, 04:22 PM
I'd at least double up your AX-12+ on all pitch axis and make good use of leverage as you won't need the full 300 degrees of movement.

10-12-2010, 09:17 PM
Tyberius, which is the pitch axis?

sorry, noob here.

10-13-2010, 09:21 PM
Great project I think your moving in the right direction! Oh and can the leg bend so as the robot could set on it knees?

10-14-2010, 01:25 PM
Animeunplugged, It currently can't bend its knees that far. It has enough movement in the knee to lift the leg off the ground to take a step (hopefully)

10-14-2010, 04:03 PM
thanks for answering my question!

10-15-2010, 12:54 AM
What type of joints are you using?

10-15-2010, 10:08 AM
Tyberius, which is the pitch axis?

sorry, noob here.

Look up pitch, roll, and yaw axis in terms of aviation and navigation. They're commonly used to describe robot joints as well.

The more I look at this project, the more it seems you'd need to at least double up all of your weight bearing servos, and rely heavily on leverage to reduce range of motion of the servos and translate that to more torque.

10-15-2010, 01:09 PM
Thanks Tyberius, I looked it up.

Animeunplugged, the joints I'm using are ball bearing joints from lynxmotion.