Quote:
|
Originally Posted by Rickertsen2
I am writing a java program to simulate PID contol of a robot drivetrain. For friction, i am including viscous and traditional friction, but i havn't clue what realistic values for these are.
|
Lets suppose that your robot weights 130 lbs, this corresponds
to a mass of 4.04 slugs. Suppose that the maximum speed of the
robot is 15 ft/sec. The energy of the robot is then 1/2 M V^2,
or 454 ft-lbf. Supposing that the motor controllers are wired to not
brake, and that the motors themselves do not generate any spurious
frictional forces when the controllers are not wired to brake, the
force of friction is what brings the robot to a stop when the power
is cut off. Supposing that the robot rolls about 20 feet if the power is
cut off at a speed of 15 feet per second, you can estimate the force
of friction in the drive train, assuming a constant force as a function
of velocity.
The total kinetic energy of the robot, 454 ft-lbf, is converted to
heat and noise by the frictional force, F, traveling a distance of 20 ft.
F = 454 ft-lbf / 20 ft = 22.7 lbf
This estimate assumes that the force of friction is a constant, as
a function of velocity of the robot. Your concern that the situation
might be more complicated, depending upon velocity,
is a valid one. The best way to really get a handle on this is a
measurement, you could pull a robot at a variety of speeds,
measuring the force required to pull it, and plot the results to
see how the frictional force depends upon velocity.