4WD RC Lawn Mower

In am currently building a 4WD RC Electric Lawn Mower using 4 wheelchair motors. I am hoping to wrap it up very soon but had a few questions about the electronics. I will pose my questions first and then include supplemental information about the build for those who may be interested. Any advice is greatly appreciated. And I am happy to answer any questions anyone has for me.


I am using a Sabretooth 2x60. Batteries for the drive motors are separate from the mower/accessory batteries. For the drive motors, I have two 12v 35ah batteries and I am wondering if this is enough for, or if I should add 2 more batteries. If yes to using more, curious if the recommendation is two more 12v 35ah, or could I go smaller (and if so, what amperage). While I would love to not spend more on batteries, I likewise don’t want to have issues with performance/damage the Sabretooth.

Fuses/breakers—I am curious if any are necessary. Found a post from Dimension Engineering (linked below) seeming to imply they aren’t, but not sure if my build is big enough that they will be. Also found a post from SuperDroid Robots (linked below) showing a breaker between the battery, which conflicts with the Dimension engineering article. Would welcome any links/ recommendations of ones to buy (if applicable) and instructions on how they would be wired into the project.

Note: I do have a Duralast battery shut off that I use to turn on and off power from batteries to Sabretooth. I would also welcome any suggestions/links on a remote start/stop for the drive motors and/or for the mower. The mower is powered separately by a 24v battery and I have it wired to a cheap 60amp PWM. I also have a battery disconnect for that 24v system.


Details of the Build
2 motors from a Jazzy 1113
2 motors from a Jazzy Select
John Deere RX73 mower - stripped down.
4 16x6.50-8 wheels. Two from the RX73 and two purchased separately.

Black and Decker CMM1200
Sabretooth 2x60
Flysky FS-i6s

This project started in July of 2020. I originally wanted to build a rideable 4WD skid steer. I acquired two wheelchairs and at one point even bought a used swisher bucket. Problem was, I knew nothing about electronics, robots, welding, etc. Basically, I did not one who have the skills or knowledge to tackle this project.

So, although I was learning, I eventually decided to scrap the idea of the skid steer and just build a riding mower. I acquired a cheap John Deere RX73 for the project. Stripped down the RX73 and picked up a cheap welder from Harbor Freight. With enough YouTube videos, I learned to weld decently enough to stick metal together.

At one point I had all 4 motors mounted to the RX73 frame. I had a joystick communicating through and Arduino/simplified serial signals. Problem is mechanically the design was poor and a weld ended up failing. I was trying too hard to use the existing wheelchair motor mounts and weld them to the RX73 frame and hope it would all line up. This was not the case - especially since the front motors mounted differently from the rear motors.

I scrapped the front wheels and decided I could do two motors on the back with front casters. While this worked fine on flat ground, I was not able to climb the steep slope of my yard. I also didn’t want to just scrap the 4WD idea. I cut the project apart and decided to start again.

I built a steel tube frame to mount all motors. Using this method, I was able to accommodate for the mounting style differences of the motors much easier.

I trimmed off lots of the CMM1200 plastic and mounted it under the steel tube frame. I added a linear actuator to raise and lower the deck. Currently lifts from one side (which I reinforced with some flat bar bolted through). Design wise I realize this might not be the best way of lifting the deck, but it works for now. I realize I can continue to upgrade/tweak the design as I go.

I will use the frame from the RX73 which I have stripped down to basically nothing. It’s fairly light and will sit on top of my steel tube frame to give me a platform to mount the batteries and electronics. Previously I used a cheap toolbox from Harbor Freight to hold the batteries.I decided to go RC to reduce the load on the motors and because my yard is very steep (so also seemed safer).
Final note—wasn’t sure where this detail fit best. I kept the brakes from the Jazzy Select motors but wired them directly to the 24v system. This allowed me to use the power switch to apply brakes. I did this when it was still going to be a riding mower so I could use the power as an emergency stop. Now doesn’t seem like it will be as helpful unless I have power controlled remotely. I am open to any ideas on this.

For those who are still reading, I’m happy to share any info I can. Biggest takeaway for me was learning that I could pick up so many new skills thanks to the countless Youtube videos/forum posts/etc. I appreciate how much information was available, so I am happy to share any information in return.

@Maxg That’s quite the chassis!

(1) The battery voltage should match the motor’s nominal votlage (12V?), the discharge current available from the battery needs to be beyond the “worst case” scenario of all four motors (add the current draw at max power for all four motors, and compare that to the max continuous discharge current on the battery’s spec sheet). Last, the capacity will determine how long the robot will operate between charges.

(2) Fuses 9and related) are there to help save the battery and moreso the electronic controller. The choice is yours if you want that layer of protection, but you can imagine the potential costs / losses of not having it.

Additional thoughts:

(a) I assume all four motors operate at the same speed, and if not you’ll adjust accordingly?
(b) The cutting diameter seems so much smaller than the width of the frame - how effective will it be? Won’t the wide wheels simply flatten the grass to prevent it from being mowed? it looks like you could fit two side by side.
(c) Nice job on the welding!

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Hey Fellas,
New to Robotshop…I guess that’s why my post here the other day didn’t show up?..
I realize Wheelchair motors are often hard to get data for…But do you have any idea the wattage, or FLA?
I couldn’t find any for my motors, so I went with the value of 20A/ea with main overcurrent protection of 60A.
But i have watched several videos of 4x4 mowers and the batteries “look” around the size of 18AH batteries. Video posters aren’t clear as to the power demands.
I’m very curious…Without any feedback from the motors for speed correction…how are you going to match the rpms?

A few rpm different will lead to “motor fighting motor”…Or “drift”, using tank style steering. (i assume you are using)
2 motors with chain drive is always an option.

On to your questions:You absolutely should have over current protection!
And i’m not sure what that switch in the schematic is…But you better have something beefy that can make/break the amount of current you’re pulling.
And consider your voltages/devices needed for the rest of your build…Arduino has several input options, some better than others.
After my mistake of purchasing a 2a 24-5v convertor…I recommend against using the the unfiltered 5v Arduino pin to power it.
Also I don’t recommend using “Brake power” as an E-stop…A hardwire system that cuts mains is a better option …imho.
As @cbenson mentioned…Good work on the frame structure, but perhaps narrow it up front and rear.

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Hey @cbenson - wanted to thank you for the help. I “finished” the project and posted about it at the other post below. Long story short - I got it finished but encountered turning issues. Not too disappointed as I’ve enjoyed learning and building along the way. Will keep chopping and rebuilding but with more knowledge.

Also you were right about the frame. Was way bigger than it needed to be. I sort of knew this ahead of time, but I wanted to make it big just because I thought it would look cooler. Probably would be cooler if it worked in the end, but like I said, I’ll just keep rebuilding!

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I’ll guess it can turn, but has a very large turning radius? It look professionally made, so I hope you’ll take the time to correct the issue.

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