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?
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!
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…
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
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).
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
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.
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 … and thank you again
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
Thanks for sharing the details of your build @Christopher_Milner, very cool build!
I am currently in the design phase of my own robot lawnmower build. I already have purchased some wheel chair motors, wheels and have a 42" 3-blade deck available, so the start is there!
In my research I found came across a lot of lawn mower conversion using Motenergy ME1004 motors all running a 48v battery system. I was struggling how to power the wheel chair motors with this power pack, so was an eye opener to see that you use two separate battery systems. thanks for that!
couple of questions regarding the mow deck drive system. U use the Alltrax controller to set a certain RPM for the ME0709? Or do you vary rmp during mowing? Furthermore what is you usage experience regarding runtime? I see a lot of contradictory info regarding runtime of electric converted mowers…
I’m actually in the process of doing away with the 24v pack for the wheelchair motors and consolidating on the 52v (13s) pack for both blades and wheelchair motors. The Sealed Led Acid SLA batteries I’m using for 24V aren’t performing very well. I upgraded to a roboclaw high voltage, 60v controller to drive those same motors. I figure I can run the wheelchair motors at 52v and 50% duty cycle and get about the same life out of them. Time will tell.
On the deck I starting by wiring a simple 5k potentiometer to manually set throttle position on the Alltrax. I manually turn the pot to start the blades before each run. I’m running it at 100% power which comes to about 50 amps (and about 2200 motor RPM producing 2600 blade RPM because the motor pulley is slightly larger than the blade pulleys…). My battery pack for the blades is a 13S lipo pack, 100Ah (52v, 5.2kwh) and I’m getting about 1.5-1.7 hours runtime. I like the elithion BMS I have very much.
On my to-do list is changing the blade speed/Alltrax inputs to be software-controlled (using an onboard raspberryPi) - the benefits of this will be able to set and maintain a particular RPM, and also the ability to turn the blade off when I don’t need it (which is, by my rough estimate, about 30-40% of the time! - time spent maneuvering u-turns at the end of each strip). I may also implement the blade control as a LUA script.
At the moment however I’m working on the ardusimple GPS. Hoping to get heading from 2 onboard GPS receivers using the RELPOSNED message. This will enable me to ditch the 4’ tall mast whose sole purpose is to keep the magnetic compass away from all of the EMF interference. This will enable me to mow closer to some trees that have low hanging branches.
While I’m at it I’m also changing my source of GPS corrections to not use mission planner, and instead use an onboard data modem to source corrections directly over the internet onto the mower, and feed the GPS corrections direclty to the GPSs. This will enable me to ditch my laptop whenever I’m running. All control will be from an onboard RPi with a touchscreen.
Darren, I had good results with the roboclaw high voltage controller. I never got GPS yaw working, but, I believe others have in the meanwhile. Mower is in the garage for the winter…
and thank you again
you are a great helper
