Introduction: Remote Control Lawn Mower
Just like Honey I Shrunk The Kids - who doesn't want a remote control lawnmower!?
This mower is made for a wheelchair user (and dear friend) so that he can keep his lawn looking sharp without having to rely on someone else. In fact, this is his second one - we made the first RC mower in 2016 on the cheap - it was reliable and is still working fine, but I wanted to add a couple of improvements and really enjoy projects like this.
Step 1: Design Choices
What is the purpose of this project?
In this case I had three goals, and they influenced the rest of the decisions I made:
- Give a wheelchair buddy a way to mow his lawn and stay independent
- Learn something new (particularly TIG welding practice)
- Have fun
What is your budget?
A project like this can be done on the cheap, or it can cost a whole bucket of cash. I included a photo above of the original mower I built, on that one we were resourceful and spent about $200 including a used mower, free power chair, new RC gear and new motor controller. In this current build I started with a new mower and we purchased the chair (used); in total the materials cost was somewhere around $600-700. We had already proven that a mower like this can work (the original has done every mowing on his lawn for 3 years), and spending more to get a mower that might last 10 years seemed reasonable.
What tools and skills are at your disposal?
This kind of project is a great opportunity to learn something new. Welded steel makes a great structure for the mower, but also requires a lot of tools to work with. There are other ways to assemble a frame (aluminum extrusion for example) that may cost more in materials but require less in the way of equipment to build. This project is also electronics-intensive, but you may be able to get away with minimal soldering if you buy pre-made modules. I recommend designing your project around what materials and gear you have available, or alternatively use your project as an excuse to get more tools!
What could go wrong?
Safety is obviously a concern when you use a lawnmower, doubly so when you give it the ability to run without anyone holding onto it, not to mention making it able to move around on it's own. Naturally as a stranger on the internet I don't want to be responsible for your accident, so here are some things to consider before you start:
- What happens if the mower is moving and goes out of controller range?
- What happens if the controller batteries die?
- What happens if the mower is running and the main batteries die?
- What happens if there is a short circuit?
- What happens if the wire to the mower ignition coil (kill switch) are pulled out (maybe by a branch)?
- What happens if the mower is powered up before the controller?
- What happens if the controller is powered up and one of the control sticks is off-center?
- What happens if the mower runs away? Is it contained in a fenced yard, or will it go into the street, into a lake, into a park full of children, etc?
For all of these the best outcome is for it to stop moving and have the motor shut off, but that might be hard to guarantee. For example, the ignition circuit on most small engines is ON unless the ignition coil is grounded; normally this is done with a spring loaded mechanism and the operator presence lever, but we're replacing that with a relay. Using the normally closed relay contact means that the coil will be grounded when power to the relay is lost (this is good), but if the wire between this relay and the mower is severed then you may have no way of turning the motor off!
What I picked:
Here's a list of what I wanted to have for this build:
- Gas powered mower
- Electric start - better for a wheelchair user and fairly common these days.
- Alternator for self charging - runtime can be unlimited as long as you have fuel.
- First-person camera, transmitter, and screen. We learned that depth perception makes it challenging to mow a consistent pattern the further away the mower is when you move across your field of view.
Step 2: Ingredients
Main components
- Mower
- I ended up getting a "new" mower from craigslist. I used online manuals and parts diagrams to figure out which mowers met my requirements which were that it was electric start, didn't have a manual choke/primer, and was self propelled in such a way that I could drive an alternator. Some mowers drive their wheels through a flexible shaft (like a speedometer cable), but this one used a v-belt directly from the crankshaft, and even better it came out of the front which would leave me room to put the motors and batteries in the back. This mower's starter ran on 18 volts from a power tool battery, but it functions just fine on 24 volts as well. If it were a 12 volt starter I would have tapped between the batteries to get 12 volts for starting. Bagging is out, mulching is the plan - there really wasn't room for all the equipment and the bag, not to mention that the whole rear was plastic.
- Motors
- Power wheelchairs/mobility scooters are a great source for motors and wheels. Most of these are extremely robust and are probably overkill for a project like this, but they're pretty easy to find. Getting a complete chair is recommended so that you can re-use the battery wiring and casters. Most of these motors are 24v, so this will impact your battery options.
- Motor Controller
- Dimension Engineering makes a tried-and-true motor controller that is very easy to use in projects like this. I used the 2x32, but the 2x25 should be more than adequate. There are other options to control large DC motors, but I really like the fact that I can plug an RC Receiver directly into this and it just works. Specifically it allows you to mix two channels to make differential steering work easily.
- Alternator
- First challenge is finding a way to drive the alternator. The mower I chose had a v-belt drive for the original transmission that came out the front which was perfect. Check the direction of rotation for your motor and the alternator. Also check the diameter of the pulleys on the mower and alternator and the acceptable RPM for the alternator. Typical mowers run the crankshaft/blade between 2700-3200 RPM.
- Second challenge is finding an affordable 24v alternator. Sort by price is a joke on Amazon, but I eventually found a replacement for a small diesel engine for less than $50. Unfortunately the most common and easy to find alternators are all 12 volts.
- If you have 24 volt motors you should run 24 volt batteries. I found the cheapest way to achieve this was with two "lawn and garden" U7 batteries in series. Sealed lead-acid deep cycle batteries are usually used with power chairs, but the most affordable U7 batteries are plain flooded lead-acid. This isn't ideal for an application like this because they are starting batteries and aren't designed for sustained lower current output and greater discharge. I can get away with these for a few reasons: we learned with the previous mower that they have more than enough capacity to mow the lawn once or twice, they're less than half the price of a deep cycle battery so it's easier to afford replacements after a few years, and with an alternator we won't be discharging them much in the first place. The weight of a lead-acid battery is a benefit in this application as well. With that said, any battery chemistry is just fine, but this was the easiest choice.
- The basic requirements were to have four channels: one forward/reverse, one left/right, one switch for the ignition, and one switch for the starter. On the previous mower I used the Flysky FS-i6 with receiver and had no problems, this time around I picked up the FS-i6x which has 10 channels, but was the same price.
- Went with the cheapest 5.4 ghz camera and screen I could find on ebay. Mounted it with a RAM mount so that it could be repositioned until we were happy.
Electronics
- Some kind of enclosure, I used a Harbor Freight "Apache" pelican case knockoff.
- Low current relay for the ignition circuit
- High current relay for the starter circuit
- Way to convert RC PWM signal to switch a relay
- I used an Arduino Nano
- Could also use Dimension Engineering's "Pico Switch"
- Or hack a hobby servo, I may document this some day but there are quite a few tutorials online
- Anderson Power Pole 30 are great for the motors
Other things
- Front wheels (casters)
- Steel for the frame
- Nuts/bolts/fasteners
- Paint
Step 3: Mechanical Design
Key points
I feel that these are the most important points in order:
- Minimize width so that you can mow against edges/fences
- Minimize length to reduce steering effort
- Balance more weight on the drive wheels, but not so much that the front won't stay on the ground. Probably 70-30 is good.
Other points:
- Secure the batteries extremely well. Bouncing around is bad for them, and if they bounce and short out explosion is a very real danger. If they crack and leak you will have to deal with a sulfuric acid spill, plus the damage it does to the rest of the machine.
- Height adjustment is still required, but may not needed much. I've made it inconvenient enough that you won't want to do it very often, and if you don't do it often it won't matter that it's inconvenient. Problem solves itself!
- Make a strong frame. If you use the mower itself as the frame and still have height adjustment then good job! Also, make sure that the torque from the motors in the back doesn't bend or destroy the mower deck. The one I got was all plastic in the back so I had to weld up an entire new butt-flap for it.
Modifying the mower
- Remove or disable the blade brake
- Take off the wheels, handle, control cables, everything that isn't an RC mower
- Find the ground, starter, and ignition kill wires and label them for later
Mocking things up is really important. I won't provide measurements or drawings for this, and even if I did it means that you would have to source the same parts that I did. There are a lot of photos on this step. A better approach is to take the key parts and try to arrange them where they go in relation to each other. I first worked out a way to hold the alternator in space where I thought it should go. The original belt that came on the mower actually worked out perfectly, and there was only one practical spot where the alternator could be, so everything else had to work around that. I laser cut two wooden boxes in the same size as the batteries to use in the mockup as well. Once things were in place I started fitting together the frame. Start with the known part locations and work from there.
Step 4: Electrical Design
Circuit Diagram
The diagram in the image above should be a good guide for how this all goes together. I did omit some details around the Arduino - particularly the transistors used to switch the relays, but the rest should be comprehensive. That detail can be found on the second schematic diagram for the circuit board that I created. This wasn't strictly necessary, but made it easier to make some of the connections. Note that there is one mistake in that circuit: I added headers thinking it would be easy to connect the relay contacts to ground/5v/24v, but I put them in the wrong spot. Simply don't use those and there should be no issues.
Main components
- Enclosure
- From past experience I've learned that too big is better than too small. Giving yourself extra space makes troubleshooting a lot easier in the long run. I actually didn't have enough space to lay all of my parts out at the same time, so I used a plastic sheet to make a two-tiered arrangement (see photos). The case I used is very robust. Consider checking how much heat is generated inside and adding vents or even a fan.
- Battery switch
- This needs to be able to switch or at least break the circuit while it's conducting it's full current. This could be as high as the sum of your fuse amperages, or as much as your wiring can take before it melts. Best is a switch that can easily be turned off in a hurry, like an emergency stop switch.
- Fuses
- Use a fuse for the main parts of the mower, particularly the motor, alternator, starter, and one for everything else. Any wires that carry current any distance outside of the nice enclosure are at risk of damage, and in the case of a short circuit the batteries may put out hundreds of amps and are likely to melt something or start a fire.
- Motor controller
- The Sabertooth 2x32 is very simple to hook up, it even provides 5 volts that you can power your RC receiver with. There may be other options, including creating your own H-bridge, but that might be an entire project on it's own, buying one was the easiest way in this case.
- Ignition kill relay
- This should use the normally closed contact so that the ignition defaults to off when no power is applied. Make sure that the wire to the mower is very secure and use a connector that can't be pulled out easily - if it is disconnected there will be no way to turn off the mower!
- Start relay
- This should have a large current carrying capacity, I used a 40 amp relay. In the diagram above you can see that I used a relay with a 24v coil, so I'm actually using a 5v relay to switch the 24v relay to switch the starter on/off.
- Microcontroller
- I used an Arduino nano in this case. The only function is to interpret the RC PWM signal into an on/off signal for the relays. Alternatively you could use the Pico Switch from Dimension Engineering, or hack a servo into a switch and skip the microcontroller entirely
Other stuff:
- Connectors
- I used Anderson Power Pole 30 connectors for the alternator, motors, and starter. The chair I got had suitable connectors for the batteries already, so I reused all of that. Inside of the enclosure I used a lot of crimp connectors and screw terminals. Make sure that everything is secure.
- Alternator
- This alternator has three connections: B+, W, D+, and Ground. B+ goes to the battery positive, the case ground goes to the battery negative. W is meant for a tachometer, so it can be ignored here. D+ is the winding - this alternator requires a small current through this terminal in order to energize the electromagnetic windings and actually generate power, without it there will be no charging. It needs 24 volts and roughly 4 watts, in "normal" use this is provided through a indicator lamp on the dashboard of a vehicle. You could use a 24v 4w bulb, or a resistor over ~150 ohms that can dissipate a few watts in heat.
- Camera
- This is a small FPV camera sold for drones. It only requires a 5v supply and the rest of the antenna and transmitter is self contained. We 3D printed an enclosure for it since it will be in a vulnerable position on the mower.
- DC power supply
- I decided to use a separate 5v buck converter to power the Arduino and RC receiver since I was concerned that the current to operate all of the relays would put an excessive load for the 5v provided by the 2x32.
- Charger
- The chair came with a charger, so I decided to add a connector so it could be used. Not strictly necessary because of the alternator, but it might be handy after winter storage. It has an XLR connector so I installed an XLR jack. Note that it is wired to the batteries directly before the switch so that charging will work while the mower is off.
Step 5: Firmware
This step can be optional - if you used an alternative way to drive the relays from the RC receiver then you can skip this.
The code I used was straight from this example:
https://create.arduino.cc/projecthub/kelvineyeone/...
Rather than reproduce it here, I recommend reading that post and getting a copy there.
Step 6: Putting It All Together
If you've made it this far, you probably already have an entire mower already. After some brief testing, I disassembled the whole thing for paint, then did final assembly. This step is just a series of photos showing how this process went (click above to see more, usually only a few are displayed by default).
Step 7: Finished!
A couple finishing touches and then this is done:
- If your controller supports it, reduce the maximum limits for the right/left and reverse channels to a much lower percent. You may be surprised at just how quickly those wheelchair motors can move, it's almost violent. Reducing the throttle inputs makes steering and mowing a lot easier.
- Unplug the starter and test the kill and start relays
- Add some fuel and get it running
- Check the charging voltage of the alternator while the mower is running to verify that it is working
- Always turn the transmitter on first and off last

First Prize in the
Backyard Contest
47 Comments
Question 2 months ago on Step 7
Thanks for posting your setup and build. It inspired me to build one of my own. I am currently near completion on mine but have run into a snag. I decided to use 12 vdc wiper type motors mainly due to cost etc. My issue is when I reverse one motor while the other is going forward, it blows a fuse. I discovered that the reverse voltage (+) was traveling through the motor enclosure and so onto the frame. Did you have this issue with your motor choice?
Question 4 months ago on Step 6
Thank you so much for the design. I'm in the process of creating a version of it. Wondering you can share some photos of how the Alternator belt connects to the mower motor and what mods you did to fit it.
Question 8 months ago on Step 7
E possivel enviar um kit para Brasil sem o cortador de grama?
Ou qual seria o valor de um kit completo?
1 year ago
A couple of suggestions for builders of such a project like this one:
1) 24 volt wheelchair motors will run fine on 12 volts, just at approximately half the speed, and a reduction in torque. But keep in mind you don't need much speed for mowing a lawn, and that at 24 volts, such motors can easily move 300+ lbs at a brisk walking speed. The weight of the mower is not going to come close to that.
2) The output of a vehicle's alternator is limited by either an "internal" or "external" voltage regulator, which controls the current going into the field coils of the alternator. A regular 12 volt alternator, without regulation, can easily put out 10 times that voltage. So, if you can't easily find (or afford) a 24 volt alternator - consider getting a regular car alternator, and replacing the regulator with one meant for a 24 volt alternator.
Question 1 year ago on Introduction
Can you please tell me how much torque is on theese motors? I want to make something like u but I cant find any DC motor wich would look like yours
Answer 1 year ago
They are basically 24V worm-drive wheelchair motors. Something to keep in mind with such motors (if you pull them off a wheelchair especially): They have electromechanical brakes, and a manual clutch mechanism. You can easily remove the brake. The clutch mechanism can probably be removed as well, but it will be messy work (because you'll be removing it from a grease-filled gearbox). Or keep it as-is, and remember to put it in "motor drive" (versus free-wheel).
The torque of these are probably measured in 10s of foot-lbs, but I honestly don't know what that would be off-hand, in general. But as long as you get something meant for wheelchairs, you won't have to worry - these things are crazy powerful. I have a friend who I worked with (for his non-profit) where we repaired and donated out used wheelchairs. We usually had a surplus of old chairs that couldn't be used for anything other than custom projects; we made all kinds of things out them (in one case, we used them to create a custom 4wd chair for "off road" trail use).
If you use an old wheelchair for this project, you may be tempted to use the motor controller that came with the chair. Usually, this is decent enough to do, but interfacing to them can be a pain. They are designed to constantly test for faults, such that if anything fails (or has too low or too high voltage, etc) before or during operation, they'll go into an error mode (usually shutting everything down and locking the brakes) - this is because they are designed as a fail-safe medical device. If you attempt to do things like "create a virtual joystick" or whatever, keep this all in mind, because it can be a frustrating experience.
Those motor controllers also tend to be highly proprietary devices - forget even trying to get any information from the manufacturers, and if you open them up, you'll find they are potted in epoxy, or at least have a thick layer of conformal coating on every part. This, again, is because it's a medical device, and such coatings keep things stable under hard use. But they also make it near impossible to repair them easily, or do anything else with them.
Also - they are programmable - but the programmers for them are near impossible to get, unless you are a factory-authorized repair place. Sometimes you can find them on ebay, for a lot of money. They are kinda needed, though - because they allow changing settings, like upper-speed limits, acceleration/deceleration curves, braking response, etc. Most chairs are "tuned low" - we were able to reprogram chairs to the point where they were literally "burning rubber" from a start, and made them very dangerous to operate at times. Or we could set them to crawl at super-low speeds. Fun stuff.
Something to keep in mind about projects like these, when using such parts: Know that they are dangerous. If you don't follow the "turn on/off" instructions for the RC controller, they can go out of control. If you are using them for a robot, with programmed actions and such, be sure to design in both hardware and code some form of rapid shutdown system. Do all of your testing "up on blocks" before letting it "run loose". Especially if you are keeping and using the whole frame of a wheelchair - with motors, frame, and batteries installed, they can weigh quite a lot, and if they go out of control, can and will do some damage.
Question 2 years ago
Thanks for the reply on the kill switch. My lawn mower is now complete. Did you ever try fitting a gyro to get heading hold for cutting straight lines? I have been experimenting with a Helicopter gyro but am battling with the setup. I also tried a flight controller (CC3D) but am lost with the programming.
Answer 2 years ago
Wow, that is a really well thought out looking build, great job! I was considering the Pixhawk for an autonomous version. Google "ardumower", that project also looks promising.
2 years ago
Working on the same project with my kid. Have two alternator related questions:
1) what is the amp rating on the alternator that was used here? Or maybe share the model/brand of the alternator
2) engine rotation and alternator rotation direction, are they the same or do I need to make sure to buy alternator with a specific rotation direction?
Reply 2 years ago
I think it was this one, the cheapest 24v on amazon at the time. https://www.amazon.com/gp/product/B0081SBD9U/
One way to reverse the rotation of the alternator is just to flip it upside down, if you have room.
Reply 2 years ago
I have done some research on this, an alternator will generate electricity regardless of which way it spins. The rotation only matters for the fan, if it rotates in the wrong way it will just have the air flow in the wrong direction and have a slightly less cooling effect. As for the amps, still trying to figure that out, I will likely go with the cheapest option.
2 years ago
Thanks for the details, starting my project now, just picked up my power chair for $50. Hope you will comeback and help us. I love the idea of the alternator on the mower, looking for one of those mowers now. When you said limiting the speed with the controller, did you do that in the Sabertooth 2x32? Did you keep the brakes on the motors, it seems the Sabertooth 2x32 has the connections to release the motor brakes before attempting to move it, so that is my path.
Reply 2 years ago
If I remember right, I just limited the maximums on the transmitter for the speed. I threw away the brakes since they just seemed like a waste of electricity, but you're right, the sabertooth can do it for you.
Question 2 years ago on Step 3
Where can you buy this elliotmade circuit board? is the circuit board is already made?
2 years ago
Can you share the code you used?
Question 2 years ago
Can you share the code you used?
3 years ago
Hello,
I will be happy to understand the necessary characteristics of the motors, for exemple powered with DC12V.
- The RPM range (after reduction) ? arround 120 rpm ?
- The torque range ?
- The power in W ?
I have to way to get wheelchair motors, and I am searching on amazon or others web-stores. And I will be happy to have these criteria.
Best regards.
3 years ago
good job very entertaining must now be mowing the lawn
3 years ago
Well done and excellent post!
I am embarking on a similar project and was wondering about the engine kill switch. Usually the LT side of the ignition coil is grounded to kill the engine - I plan to do this with a relay as well. Is there a risk of back feeding current to the battery and electronics and causing damage considering that the battery and electronics share the same ground as the lawn mower chassis?
Reply 3 years ago
I haven't had any trouble with this so far. It's not super clear in the diagram above, but I didn't ground the coil inside of the control box near the rest of the electronics - the connection point to ground is right at the coil using the original wires from the mower, so current path is from the coil, in through the relay contacts (isolated from the rest of the board) and back out to the mower ground. I believe this is what prevents the current spikes while the mower is spinning but the coil is grounded from damaging the rest of the goodies.