Pololu Simple User Manual
Page 50
They are called Hard Limits because they are stored in non-volatile memory and they are always obeyed. However,
all of them except Starting Speed can be temporarily modified using the appropriate USB or serial command. Only
modifications that make the system safer are allowed. These temporary changes will only last until the next time
the device resets, at which point the hard limits will be reloaded. See
for more details about setting
temporary motor limits.
If you want to enter different limits for the reverse and forward directions, check the Asymmetric checkbox.
Max speed is a number between 0 and 3200 that specifies the maximum speed at which the motor controller will
ever drive the motor. The default value is 3200, which corresponds to 100% and means there is no limit. A value of
0 means that the motor will not be allowed to drive in the specified direction. This setting also affects how the Target
Speed is computed in RC and Analog modes: after mixing is optionally performed, a scaled value of 3200 or -3200
maps to the Max speed. The Max speed should be zero or it should be greater than the Starting speed.
Starting speed is a number between 0 and 3200 that specifies the minimum speed at which the motor controller will
ever drive the motor. The default value is 0, which means there is no minimum, so this setting has no effect. This
setting also affects how the Target Speed is computed in RC or Analog modes: after mixing is optionally performed, a
scaled value of 1 means the Target Speed equals the Forward Starting Speed and a scaled value of -1 means the Target
Speed equals the inverse (negation) of Reverse Starting Speed. The starting speed parameter allows you to save some
energy by never driving the motor at speeds that are too low to actually make the motor turn. It can also make your
joystick control be more accurate and responsive, because the motor can start moving as sooner as the stick leaves the
neutral area.
Max. acceleration is a number between 0 and 3200 that specifies how much the magnitude (absolute value) of the
motor speed is allowed to increase every speed update period. The default value is 0, which means there is no limit.
An acceleration limit can help reduce mechanical stress and help reduce current spikes when the motor is starting
up. If an acceleration value of 1 is too fast for your application, you can increase the Speed update period to make it
slower.
Max. deceleration is a number between 0 and 3200 that specifies how much the magnitude (absolute value) of the
motor speed is allowed to decrease every speed update period. The default value is 0, which means there is no limit.
A deceleration limit can help reduce mechanical stress and help reduce current spikes when the motor is decelerating.
Note that deceleration limits apply even when there is an error stopping the motor; depending on your setup, it might
not be a good idea to use deceleration in conjunction with a limit switch because the motor will not stop as fast
as possible with the limit switch is triggered. If an deceleration value of 1 is too fast for your application, you can
increase the Speed update period to make it slower.
Brake duration is the time, in milliseconds, that the motor controller will spend braking the motor (Current Speed =
0) before allowing the Current Speed to change signs. The Forward Brake Duration is the braking time required before
switching from forward to reverse (from positive to negative speeds). The Reverse Brake Duration is the braking time
required before switching from reverse to forward (from negative to positive speeds).
The Speed update period is the time, in milliseconds, between consecutive updates to the Current Speed. The default
is 1 ms, which is the lowest allowed value. By increasing the Speed update period, you can decrease the effective
rate of acceleration and deceleration because the updates will be applied less often. The slowest possible acceleration/
deceleration can be achieved by setting the Speed update period to 100 ms and the acceleration/deceleration limit to
1; with this configuration it will take 320 seconds to accelerate from speed 0 to speed 3200 (100 %) or decelerate
from speed 3200 to speed 0.
The Invert motor direction option lets you switch the meanings of forward and reverse. By default, Forward means
the average voltage on OUTA is greater than the average voltage on OUTB (and reverse means the opposite). With the
Pololu Simple Motor Controller User's Guide
© 2001–2014 Pololu Corporation
5. Configuring Your Motor Controller
Page 50 of 101