still working on legs

Turns out, a step is much harder than first thought. A child is faster than I am at learning to walk!

The secquence:

Right ankle rotates to right and right leg bends down a little.

Bending down right leg forces the left leg to be longer, pushing over leg assembly to the right.

I bend the left ankle forward/down, increasing the push over.

Now leg assembly is balancing on right leg and foot.

Lift left foot by bending knee and moving ankle/foot up so toes do not hit floor.

Rotate left hip forward.

Put left knee and ankle down flat touching floor

Rotate left and right ankle sideways slowly shifting weight to left leg

Again right leg is higher helping pushing assembly over on left leg.

Lift right leg by bending knee and raising ankle/foot so toes do not hit floor

Rotate right hip.

Lower right leg to be on floor.

Rotate both hips back to start position.

Now all motor encoders should be back close to starting position for next step. I have a dead zone of 10 rpms set in PID. Legs have 6 DC motors with encoders running in position mode (or absolute mode) using 3 RoboClaw motor controllers. The 3 RoboClaw motor controllers share one serial port and have there own board addresses. I also have 2 servo motors for ankle rotation left to right on legs, a 9 axis sensor (gyro) on each foot, and servos to move the toes up/down. I will  post the current code in my mrl folder and  there is a new video on youtube. Not sure if it will ever really work but having fun building. 

(1) first steps - YouTube

Ray.Edgley's picture

Might need to put on some weight

Hello Harland,

Its just a thought, but for dynamic ballance, you might need a mass located above the waist.

That can be used as an inertial mass to help with the balance as the robot moves.

If you lift the left leg a small amount and as the mass start to move left you straighten the left leg while at the same time lift the right leg and move it forward, the mass will help with the lift until its mass is slowed down and the direction of travel changes back, by that time you should be putting the right leg down and forward of where it was, and be preared to lift the left leg as the mass moves right.

Process then repeats....

If you need extra weight, I sure could loose some from around the waist... :-)


harland's picture


Hi Ray, thanks for the idea

I am having trouble with trying to keep the electronics base stable. When one of the hip motors moves a leg most of the time the leg moves some an so does the base.  More weight should help. I also need to add another 9 axis sensor to that base so I know where it is.