### Author Topic: design help  (Read 959 times)

0 Members and 1 Guest are viewing this topic.

#### mblackwolf

• Beginner
• Posts: 6
##### design help
« on: September 30, 2011, 12:50:35 PM »
Hey guys,

So i recently planned out a hexapod but have run short on money. Therefore I dont think I can afford all 18 servos(it was gonna be 3DOF/leg). Now I am thinking of a quadropod. The trouble I am having is the walking sequence. In a hexpod you can move 3 legs at a time with ease due to the remaining three forming a tripod of sorts. I can't really figure out a quad walking sequence though. One leg at a time would be complicated and slow. I have seen videos of some moving front left and back right together followed by front right and back left. I would think that this would case the robot to be off balance though due to only having two points of contact with the ground. Can anyone help me by explaining the walking sequence of a quad. Thank you very much!

P.S. Sorry if this is in the wrong place I just assumed it was mechanical since I am not asking about programming the walking sequence.

#### hamzaman

• Jr. Member
• Posts: 9
##### Re: design help
« Reply #1 on: October 01, 2011, 05:39:17 AM »
If the weight of your robot is distributed fairly equally on all legs and your walking motions are fast enough, the robot will not go off balance.
Also try not to raise the legs too high above the ground while walking because that can shift the center of gravity too much. Also it will decrease the chance of robot actually toppling over in case it loses balance.

#### waltr

• Supreme Robot
• Posts: 1,944
##### Re: design help
« Reply #2 on: October 01, 2011, 07:03:15 PM »
You could also use active balancing using accelerometer and gryo.

#### Fr0stAngel

• Full Member
• Posts: 96
• [O_O] what??
##### Re: design help
« Reply #3 on: October 03, 2011, 11:02:16 AM »
like hexapod, quadruped has different gaits.... the most easiest to implement is to lift one leg at a time in a sequence  like !: front right- back left -front left -back right :! and repeat.  this way three legs are always on ground (tripod stand).
try searching quadruped gaits on the internet , you'll find interesting works people have done.
'crazy' is the new hype! =)

#### Gertlex

• Supreme Robot
• Posts: 761
• Nuclear Engineer · Roboticist
##### Re: design help
« Reply #4 on: October 03, 2011, 03:26:48 PM »
The secret with two-legs on the ground at a time gaits is a combo of having wide feet, how big the steps are, and how fast the bot walks.

...Thus with the wide feet, you really have 4 points of contact.  You might not actually have the CoG within those points at all time, but it works when moving.  My bot can actually stand on two feet because it's centered well enough.  Two sucessful 4DoF quads using this approach are Immortal and Numa (mine...).  Immortal is small quick steps, while Numa takes bigger steps (I'll probably go smaller quicker steps once I finish IK coding...)
I

#### Conscripted

• Robot Overlord
• Posts: 291