problems. Because this
actuator uses a
potentiometer and runs
the signal wires parallel
to the motor power
wires, there is potential
for noise. The RoboClaw
motor controller is
specifically set up to take
ACD readings as far from
rising or falling edges of
the motor power pulses
as possible to limit this negative effect.
4. Backlash causes non-linear
issues when changing directions
(motor surge). A dead zone must be
added to eliminate hunting and limit
cycle action (± 4 minimum in this unit).
The second example is used as the
exception to the rule. This is a linear
actuator with a massive gear ratio (due
to its threaded rod actuator). It is slow
and has a large amount of backlash
due to this threaded rod. Note this
tends to be a property of all linear
You will find if you try to autotune
this actuator, your values are
completely wrong. If you then go
through the same steps as above to
manually tune for velocity and position
control, you will find that the best
option is to use P only. It’s rare, but in
this type of actuator, there is already
so much dampening due to the friction
in the threaded rod and slider — as
well as the backlash in the slider itself
— that integral has little good
effect. A P-P controller can be
used (or even a pure velocity P
only controller) since these
actuators have automatic
cutoffs at their limits.
The ideal manual tuning
method for these motors is to
find the best P for velocity and
then the best P for position.
Otherwise, the same tuning
steps apply: Check that the
encoder increases in value
when moving forward;
determine the QPPS (around
140); then, tune the velocity P
and the position P. Values will
be about 1000 and 2000,
So, there you have it. Now
that you have a grip on
encoders, position control, and
stiction, you can get the right
kind of motion out of your
robot’s motors. SV
Now that we’re able to get our bot from here to
there, I’ll leave you with a couple of techniques that can
help with all of your future motion control and motor
Use acceleration/deceleration curves. They can
reduce jerkiness on low resolution or slowly updated
controls (e.g., hand-controlled RC signals or slow serial
commands). Also, these curves can reduce power
surges at power supply limits.
Current/Voltage. How much is enough; voltage is a
killer. Always check your voltage limits. If you are using
a power supply, set the min and max voltage limits in
your motor controller to help prevent controller damage.
Never try to use a motor controller at a higher voltage
than its specified rating. Never run long wires from the
battery to the motor controller. The inductance in the
wire will cause large voltage spikes as the load changes
which can exceed the maximum voltage limit for the
controller or even cause negative voltages.
Contrary to popular songs, the heat is NOT on.
Current is all about the heat. Keep your controllers cool
and you will get longer life and more power.
Power contacts, fuses. Add a power switch or
contact on your final project that is rated for the
maximum current you will draw. Add a fuse as well. Note
that fuses do not blow at the rated amps. They blow at
much higher values. Look at the timing chart most
manufacturers have to see how long it will take a fuse to
blow at any given current range.
Figure 9. The linear actuator’s wiring harness.
Figure 8. The
12V- 20 linear
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