Hi All,
I recently build mini quadruped with 2DOF in each leg. I used following parts to assembly the robot.
lynxmotion.com/images/html/build081.htm
lynxmotion.com/p-435-quadrap … -mini.aspx
Each joint uses HS485 servo. I am using pololu mini maestro as servo controller. I am having difficulties to walk my robot. Is there any good tutorial for 4 legged 2 DOF robots? The problem I was facing is related with balance of the robot.
Ok two problems.
As you know quads are harder to get walking anyway. Possible but requires a few factors.
Second… im not even sure you can walk a 2dof quad due to it not being able to shift its body weight from side to side as each leg is lifed.
So you need to look at ways to shift its center of gravity, without having the ability to actually move its body…
You could used an un balanced servo in the center of the body with a weight attached to it so it rotates the weight away from the lifted leg, or add some kind of tail to act as a counterweight.
I have seen walking samples which have good balance. There must be a way without adding additional weight with unbalanced servo.
If I can see a good example of a 2dof quad?
One otherway without adding a counter balance is to give it a larger ground contact by making the surface of each foot bigger like a flate panel of some sort so it has a good solid footing.
It’s possible, and pretty cool:
youtube.com/watch?v=r4S6EGtkoCA
youtube.com/watch?v=LeaoEk8e7Tc
You could start with dynamic stability (two legs down, two legs up).
The two video examples seem to show 'bots that keep their feet very close to the floor, thus minimizing balance problems.
Alan KM6VV
I am trying to have dynamic stability, however when I move up two legs at the same time robot collapses to front or back depending on position and I don’t want the legs to rub the floor. Is there any tutorial which can become my starting point? Before I start building robot, I thought it would be much more easier.
Understandable. If you want the legs to raise higher id suggest widening the foot print so it can balance on two opposing legs.
Okay, I will ask my question in a different way.
I have 2DOF legs (Click to see) and body kit (Click to see). Each joint has HS-485HB (Click to see) servo motor. This robot is statically stable. Is it possible to make this configuration dynamically stable? or do I need more powerful servo motors on tibia joints? I might be wrong but I think tibia joints doesn’t have enough torque.
I can not say for sure, but if it were me, I would not try with less than HS-645mg. But I have never used those type of legs. I would also be tempted to add 4 more servos and make it 3dof…
Kurt
Use the '475 servos, minimum, per instructions. Better to use the 645s, as Kurt has recommended.
Alan KM6VV
Dynamic stability with suspension - not the easiest. This is not to say that an 8Dof Quad can’t be built - it has been done, but there are quite a few people working on 12DoF quads right now on this forum, so you might want to purchase 4x 645MG servos and join in with them. You could always fix the position of the knee later to revert back to an 8DoF quad.
