K-Team Koala 2.5, Руководство пользователя

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Koala 2.5 User Manual Rev 1.1 27
4.9.1 Speed control (“D” command)
Both DC motors are controlled by a PID controller executed every 10ms in
an interrupt routine of the dsPIC. Every term of this controller
(Proportional, Integral, Derivative) is associated to a constant, setting the
weight of the corresponding term: Kp for the proportional, Ki for the
integral, Kd for the derivative.
The controller has as input the speed value of the wheels, and
controls the motor to keep this wheel speed. The speed modification is
made as quick as possible, in an abrupt way. No limitation in acceleration is
considered in this mode.
Be careful when using this mode; avoid a big difference of
speed order as the current drawn by the motor could reset
the Pico-ITX (battery voltage drops due to high current).
For example, do not change the direction of the two motors
at once.
The solution is to use the speed control with acceleration
ramp or use a weaker PID (decrease the Proportional part).
The speed unit corresponds to the difference measured in position between
the two controllers’ routine (10ms). Here’s the formula to convert the speed
unit to metric unit.
Refresh time: 10ms
Wheel diameter: 82.5mm
Revolution resolution: 23’400 [pulses]
[ ]
pulses
pulses
pulses
Wheel
fresh
pulses
v
v
Nb t
v
s mm Speed
• =
•
• =
•
• =
10761 . 1
23400
5 . 82
01 . 0
/
Re
π π φ
Formula to calculate real speed from the measured value
Note: this formula must be adapted if a payload is placed on the Koala.
The minimum speed order to ensure a correct control is 10 (=11mm/s).
Under this value, the control is not very stable with default PID parameters.
User can modify the PID to try to improve the behavior for this kind of very
low speed.
The maximum speed order is approximately 500 (=553mm/s). It’s still
possible to move the robot faster if the control mode is set to open loop. In
this case, the maximum speed will vary with the battery voltage and the
payload.