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Dual Motor controller selection advice

(Christopher Milner) #1

Building a robotic lawn mower, skid steer. Propulsion with Electric Wheelchair Motors. 24V system for the motors. All up weight about 250 lbs.

I’ve combed through the forums and it seems that either a RoboClaw 2x30A Motor Controller or a Sabertooth dual 32A will work with my Pixhawk 4 running Rover 3.5. Aside from price it seems the Roboclaw has integrated decoders, hence off-the-shelf closed loop control, while the Sabertooth requires the Kangaroo x2 motion controller if I decide I need the controller to do the closed loop control. I’m planning on building encoders on the motor shafts directly (shafts turn 3600rpm). My thinking is to build and run without closed loop control, then, start by feeding encoder data directly to Rover (which I understand it will use in position estimation if I’m running EKF3).

Aside from price, does anyone know of any pluses or minuses or considerations I should be aware of when choosing the motor controller? Any experience with cheap no-name brands?

Thanks in advance…

1 Like
(Christopher Milner) #2

After sifting through the overwhelming number of votes/opinions (not…) I went with the roboclaw.

(RoboBill) #3

Some years back I had a smaller 10 pound robot driven by fours craftsman drill motors and experienced some sort of clipping with the 2X25 .

My current robot is 75+ pounds. I went with the 2X60. I wanted the driver to be something I would never worry about.

Their customer service is great. Just be careful to avoid ground loops. The folks at Dimension Engineering can help you with this.

(Jeffrey Berezin) #4

Dimension Engineering has great support. They have helped me multiple times since I started using them in 2011. I use both the Sabertooth and Syren series and have fried things with “ground loops”. Now I know how to design better thanks to their tech support team. I can’t say anything about Roboclaw because I haven’t used them. Let us know how it goes!

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Control with two DC motors using ardurover
(Christopher Milner) #5

The Roboclaw 2x30a is working fine. In fact the whole mower is working fine - I mowed my first 1/2 acre or so this evening. A video from a few days ago is here https://photos.app.goo.gl/rrNTHjFD2JTFJ7Kt6

The details

  • 42" 2-blade deck off a donor mower driven by a Motenergy ME0709 motor powered by a 13S (about 48V) 100Ah pack of Thundersky LFP100s, an Elithion Lite BMS and an Alltrax controller. About 25amps (x50v=1250 watts) to run the deck blades @ 2,000 rpm. I expect about 3-4 hrs runtime.
  • DIY chassis
  • Wheelchair motors powered by a 24V, 15ah SLA battery pack and a Roboclaw 2x30.
  • Yes there are 2 separate battery systems onboard, one for the autopilot+motors, and one for the blades.
  • Pixhawk4 running Rover 3.5.1. No encoders.
  • Ardusimple GPS, receiving RTK corrections sourced from an NTRIP caster about 21km away (giving about 10cm accuracy, plenty for my application), forwarded to the Pixhawk using Mission Planner.

385 lbs all up weight. All those batteries are heavy. I think the 2x30 roboclaw may be slightly underpowered for this vehicle and am considering upgrading to the 2x60HV.

Next: The Rasbperry PI to control the deck (via the Alltrax) and the BMS and the Pixhawk 4…

Thanks @rmackay9 @ktrussell @Jeffrey_Berezin @RoboBill for your help thus far.

4 Likes
(Kenny Trussell) #6

Looking good! Thanks for sharing your progress.

(Terrance Loughlin) #7

Thanks for sharing @Christopher_Milner

(Jad) #8

Hi Christopher,
I am trying to connect pixhawk4 to pmb of pixhawk and from pmb to roboclaw would you help pls with any hint or pictures, my background is IT with very basic background in electronic, I am trying to build a rover to transport some veggies in a small farm…Thank you already

(Christopher Milner) #9

In my photo album https://photos.app.goo.gl/rrNTHjFD2JTFJ7Kt6 there’s a picture of my setup that you may be able to zoom in to see what’s going on. (2nd row, 2nd from the left). In that pic I had the power going from the PMB to the Roboclaw but I have subsequently changed my setup to have the PMB and the roboclaw in parallel with each other, i.e. power goes to both. Aside from that I’m using the same set up as here https://docs.px4.io/en/assembly/quick_start_pixhawk4.html. I myself was confused about which plug on the PMB to use for the incoming signals, IO PWM In or FMU PWM In. I am using FMU PWM IN on the PMB (those signals get forwarded to the servo pins on the header labeled FMU-PWM-OUT).

If you want to power your Roboclaw from the PMB then you need to pull power off of one of the B+/GND pairs on the PMB (like is diagramed for ESC motor 1 in https://docs.px4.io/assets/flight_controller/pixhawk4/pixhawk4_power_management_board.png)

I think the main reason to power the roboclaw from the PMB is that the PMB can report current consumption by your motors.

Which part are you having trouble with?

2 Likes
(Jad) #10

Thank you Christopher you have done a great project, in fact in term of power I don’t have problem and my intention to power both PMB and Roboclaw separatly (in parallel as you mentioned).
the part that is confusing me is the wiring between PMB and Roboclaw
IO PWM out —> IO PWM in and then (how I connect to Roboclaw S1 & S2? I did figure it out (could be wrong) I should be soldering the edge of M1 on the PMB (Yellow,Black,Red) to S1 pins on Roboclaw and same will be from M2 to S2 on Roboclaw
or FMU PWM out---->FMU PWM in and then (how I connect the pins on PMB to S1, S2)
I am trying to run away from soldering,…
thank you again your replay made it more clear in my head the option between IO PWM in and FMU PWM in :smiley:

(Christopher Milner) #11

between the PMB and the roboclaw, there are 2 servos connections (each w 3 wires)… I used the FMU PWM out pins on the PMB. I didn’t use the I/O PWM out signals to connect the PMB to the Roboclaw.

Did your PMB come with headers on the FMU PWM out pins? Mine did. Like in this image https://www.3dxr.co.uk/wp-content/uploads/2018/06/Holybro-PM07-02.jpg . So it was easy to use female-to-female servo connectors to make that connection.

2 Likes
(Jad) #12

Hi Christopher,

yes it has the headers on the FMU PWM out pins but here you are another hassle " the power rail needs to be connected to a BEC equipped ESC or a standalone 5V BEC or a 2S LiPo battery" good luck for me I will use a BEC this is the plan I want less gadgets on board…by now connection btw pixhawk4, PMB and Roboclaw are clear for me so now I will try to configure and connect and I will see how I go …:crossed_fingers: and thank you again

(Christopher Milner) #13

I didn’t use a separate BEC; I used the power from the Roboclaw. Works fine. PMB’s PWM outputs 0 and 2 are connected to the S1 and S2 inputs on the roboclaw. Close-ups of this wiring are the most recent 2 pictures in my photo album https://photos.app.goo.gl/rrNTHjFD2JTFJ7Kt6

1 Like
(Jad) #14

Thank you again for the hint I will do this,:slightly_smiling_face: you are a great helper