• 07-29-2011
blastdog
I have recently built a quad and I've figured out how to make it walk but it becomes unbalanced when it lifts up one of the legs and I was wondering how to fix that
• 07-29-2011
Gertlex
Quote:

Originally Posted by blastdog
I have recently built a quad and I've figured out how to make it walk but it becomes unbalanced when it lifts up one of the legs and I was wondering how to fix that

Do you have pictures? In general, you need to keep the center of mass in mind... namely the other three legs form a triangle on the ground. The center of mass needs to be within that triangle for static stability.
• 07-30-2011
blastdog
here are some pictures any suggestions?
• 07-30-2011
Gertlex
Since you're using wheels, you're essentially standing on 4 points, at most. With other quads, the feet have width so that there are multiple points of contact on the ground, and thus stability. What you could do is put 3 wheels on each foot and have the two outer ones be free-spinning, and unpowered. They could be ever so slightly smaller diameter than the center wheel too. Just an idea....

It sounds like you're starting with 1 leg off the ground at a time... This graphic for a walk with 2 legs off the ground at a time sort of illustrates the center of mass problem (note the intersection of red lines moves...)
http://forums.trossenrobotics.com/at...1&d=1308440074
• 07-30-2011
cire
Wider feet help because you get more then one contact point with the ground per foot. This does cause 'scrubbing" when the feet rotate though. Depending on the surface you are walking on, this may or may not be an issue.

If you want feet to be more like a point contact, you can program the center of mass of the robot to always be between the 3 legs contacting the ground. This is a common way to do it when using a ripple gait. But you need to be aware of the dynamic forces involved, if you lift one leg up quickly it will make the robot tend to fall. If you use a amble gait (2 legs moving at a time) you can somewhat balance this movement.

Another thing you can do is make the feet lift and return to the grounnd quick enough that it doesnt have time to fall over, the bot will rock a bit though.
• 07-30-2011
blastdog
Thanks for the advice and it will have treads on the wheels too
• 07-30-2011
Gertlex
Quote:

Originally Posted by blastdog
Thanks for the advice and it will have treads on the wheels too

It's a general concept to play around with and find what works well :)
• 08-10-2011
blastdog
Thank you sooooooo much :happy: I've fixed the wheels and made them a lot thicker and now it balances great :happy:
• 08-10-2011
Gertlex