Keep left and right legs in lockstep

[steamboat]

For my RepWalker I am using hacked servos controlled by an Arduino and the Servo.h library.

You can control the speed and the direction of the servo by
Servo s_left; // create a servo object
s_left.writeMicroseconds(1400); // set pulse width in microseconds (ms)

Because the internal circuits of cheap servos differ in it's accuracy you will have different values for the zero position. With my servos this is 1200 ms and 1250 ms.

If you start running you have the same problem of different values! If you can not keep the right and left legs in lockstep, you will run in a circle! You can find the best values by try and error. But this can differ if you get some extra friction in the gear or if the battery tension drops maybe from 4.8 to 4.5 Volt. This is a general problem when steering a creature with two motors.

That is why I suggest to install two revolution sensors to keep track of the motor revolution and adjust it. With this you even can not only keep the rpm in sync but also can determine/control which leg went forward/up first and so on.

This will be a big field for experiments and theories. To enable the user to play with this "leged creature feature" we should find a good sensor and a place where to install it.

Regarding sensors I could imagine of dozens of alternatives but are they easy to source, to install and to understand?

Please tell me your opinion and ideas!