0
\$\begingroup\$

My goal is to control two DC motors using the Sabertooth 2x32 motor driver with the driver's DIP switch settings set on analog mode. I read the driver's manual, but there is a couple of things I don't understand with the documentation on the analog mode DIP switch settings.

There are two DIP switches which confuse me: the DIP switches 4 and 6. I tried to understand them and at first I thought I understood how they work so I tried something but it didn't work. So I tried playing with the switches to find a configuration which would work but each time the motors ended up acting weirdly and far from what I was expecting. Then I decided to focus on a single position of the DIP switches. So I tried to understand how the motor would behave with the DIP switch 4 ON (Mixed) and the DIP switch 6 OFF (Unidirectionnal). Though I ended up getting even more confused, but at least I knew why I was confused.

So here is what I understand: image

At this point, I'm not even gonna try to understand how the other configurations work since they seem even more confusing. So I guess I'm just gonna keep trying things until I understand or until a very kind person explain me how it works. ;)

I know there are libraries available but I don't want to use them.

Note: I have a background in computer programming and not in electrical engineering. I do this as a hobby and I'm a complete beginner in electrical engineering. So please apologize for my lack of knowledge.

\$\endgroup\$

1 Answer 1

1
\$\begingroup\$

I shall define the control signal as follows: The control signal would be an voltage if you chose the analog version. If you chose radio then it would be a pulse of a width of (probably) 1000us (0%) to 2000us (100%) being the extremes, with 1500us being the center (50%).


DIP Switch 6 determines whether the motors are allowed to reverse direction.

DIP Switch 4 is responsible for independent and mixed:

Independent: Each motor has its own control signal. Simple.

Mixed: Both motors SHARE TWO control signals. Conceptually each signal determines the following:

  • the first control signal (which I will call the throttle) will determine the average RPM of both motors.
  • the second control signal (which I will call the differential) determines the difference in RPM between the motors (direction included so -100RPM or +100RPM difference).

In effect, one signal determines how fast you move and the other determines how much you are turning.


I would expect the following:

Independent Unidirectional: A control signal of 0% to 100% maps to 0% to 100% in only one direction.

Independent Bidirectional: A control signal of 0% to 100% maps from 100% throttle CCW to 100% throttle CW, which would mean that a control signal of 50% is required to keep the motor at stand still.


Things get interesting when you turn mixing on.

In mixed bidirectional, I would expect a throttle signal of 50% keeps both motors at an average RPM of zero.

In mixed unidirectonal, I would expect a throttle of 0% to keep both motors with an average RPM of zero.

In mixed bidirectional, I would expect a differential signal of 50% to keep both motors turning in the same direction, if they are turning at all.

In mixed unidirectional mode it gets a bit fuzzy how the differential signal behaves. I am unsure whether a motor can actually reverse if you have zero speed on the throttle and change the differential. But it makes the most sense (and the manual seems to imply) that it can reverse allowing for a vehicle that can only go forward but truly turn on the spot.

Otherwise you have a vehicle that tries to spin around one static wheel when you try turn at zero speed. But it's possible the controller enforces the unidirectional setting that strongly.


The auxiliary inputs are on page 18. They are not the control inputs. They just allow you to tune sensitivity and rate of resposne on the control inputs.

enter image description here

\$\endgroup\$
9
  • \$\begingroup\$ Ok but what about the two auxiliary inputs? (A1 and A2) \$\endgroup\$
    – Elie G.
    Apr 10, 2020 at 0:07
  • \$\begingroup\$ @ElieG. Was editing. Edits are all done now. \$\endgroup\$
    – DKNguyen
    Apr 10, 2020 at 0:25
  • \$\begingroup\$ I'm pretty sure that in unidirectional mode the auxiliary inputs are control inputs. They do not behave the same as they do in any other mode and that is what confuse me the most. You can see this in the second paragraph of the DIP switch 6 documentation. \$\endgroup\$
    – Elie G.
    Apr 10, 2020 at 0:39
  • \$\begingroup\$ Yes it does. It says «The direction the motor runs can be controlled by the A1 and A2 inputs. If you connect a switch between 5V and A1, it will act as a forward/reverse switch for the signal being fed into S1. » \$\endgroup\$
    – Elie G.
    Apr 10, 2020 at 0:47
  • \$\begingroup\$ @ElieG. It sounds like A1 lets you reverse the mapping on the throttle (or independent signal). I'm guessing A2 does the same for the other motor in independent and for the throttle on mixed, \$\endgroup\$
    – DKNguyen
    Apr 10, 2020 at 0:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.