Battery Powered Radio Controlled Lawnmower From a Kids Ride-on Toy

Welcome reader. This Instructable will show you how I made my very first radio controlled lawnmower, which is aptly named "The Mow-tivator".

The Project:

I have taken a second hand 24v kids ride-on vehicle which had 2 wheeled skid/tank/zero-turn steering and a 36v battery powered lawnmower I already owned, stripped them down, and with a few extra bits, combined the pieces to make a cordless radio controlled lawnmower with variable grass cutting height adjustment, and optional grass collection. The radio control unit controls the drive/steering, cutting height adjustment, and powers the mower deck blade On and Off. Whether driving around or cutting grass, there is a three speed forward and reverse movement, and keeping the skid steering idea, free wheeling rotational castor wheels are mounted at the front while the rear drive wheels steer the mower.

The Inspiration:

This idea came from my Mobility scooter/mower conversion project and it's something I always wanted to try building. Many of the DIY RC lawnmowers I have seen either don't have a grass collection option or have grass cutting height adjustment, so I wanted to give this a try. While designing and building my RC mower, I was always thinking of this as a prototype (and still am at time of writing), but with using this proof of concept for a while, I'm really actually pleased with how it performs. Read the concluding step to see some of my future improvement ideas. I have also made this for health reasons as I have a lower spine condition and cutting my friend/neighbor's lawn causes me a lot of discomfort using a standard mower, and the RC design really helps with that. And the name, it give the motivation to mow the lawn because it is now something fun to do, having fun driving an RC vehicle while doing something practical.

What's Involved:

I acquired the non working RC kids ride-on toy vehicle a friend gave me for parts figured out what the issue was (a loose wire and batteries not charging to full capacity), so it was a case of stripping it down, buying new batteries, then stripping down the lawnmower so I was left with just the deck. Making a framework, figuring out the cutting height adjustment mechanism were the main things to work out, then sorting out the electrics using the original ride-on motor controller, and adding a couple or relays to power the motor and changing the deck cutting height gave me a functional mower. Finally, instead of having just a frame on wheels, a bit of dressing up to give it a nice look finished the job. The video shows me cutting my friends back yard which was in desperate need of mowing, and I'm happy to say that The Mow-tivator actually handled the thick long grass really well.

Tools:

1. Cordless drill/driver and bits
2. Hand held circular saw
3. Jigsaw with wood cutting blade
4. Pencil and ruler
5. Spanners (I needed a 10mm and a 13mm)
6. Sockets (As above, I needed a 10mm and a 13mm)
7. Wire cutters/strippers
8. Electrical Screwdrivers
9. Tape measure

Materials:

1. 24V Radio Controlled Electric Dodgem Waltzer Car or similar
2. Cordless lawnmower (I used a 36V Mac Allister push mower)
3. Two 38mm x 63mm x 2400mm CLS timber lengths
4. A sheet of 12mm x 610mm x 1220mm Plywood
5. External wood sealer
6. External wood/metal paint (I used a satin black brush on and red spray paints)
7. Paint brush
8. Masking tape
9. 4 x 25cm draw runners
10. Linear actuator (mine has a 10cm extended shaft, can lift a max of 90KG, and is 12 volt)
11. Remote Linear actuator relay with momentary control (push button =On, release button = Off)
12. Remote 30A relay (to power the mower deck On/Off)
13. 2 x heavy duty 150mm rotational castor wheels
14. Various nuts, nyloc nuts, bolts and external use screws

There were a few things to consider in regards to the design, the cutting height mechanism, easy fitting and removal of the grass collector, a drivetrain that could work on long grass and the safety aspects.

Height adjustment: As I mentioned before, one of the key design factors was to have the grass cutting height adjustment. I used the lowest height of 25mm from the original mower, but decided to go up to 125mm at the highest setting. Using a linear actuator with a 10cm extended shaft fixed to the framework would lift and lower the mower deck, and four draw runners would keep the mower deck secure and allow smooth movement. Finding the balance point for the mower deck with the battery inserted is important so the anchoring point for the actuator would be directly over the balancing point so both the front and rear of the deck hangs evenly. The added weight of increasing grass collection was taken into account and is helped by a rear frame platform/drivetrain which the bottom of the collector would sit on, and a full grass collector doesn't actually weigh very much. A remote momentary switch would be used to adjust the height while cutting which would save on stopping, adjusting and restart cutting, it could be adjusted on the fly.

Grass collection: The framework was built around the use of the grass collector that came with the mower. The rear of the frame was left open so the collector could easily be fitted and removed, not be obstructed by anything during height adjustment, and the length of the mower deck and collector fitted would dictate the overall length of the frame.

Drivetrain: With the ride-on car being 24 volt, having two 55 Watt motors, and a maximum load weight of 50KG, I had no worries about it coping with a larger frame made from wood and running on grass. But steering was something to decide on, do I add front wheel steering, or use the zero turn element the ride-on already had? So I decided to use the zero turn setup to have rear wheel skid steering with rotating castor wheels of the front... less complexity and sharper turns.

Drive wheel location: I decided to mount the drive wheels at the very back of the frame to eliminate steering over-swing. By this I mean if the mower is going along a fence or around a tree or other obstacle and I then steer the mower, the grass collector won't swing out and hit anything as it would if the wheels were mounted further forward.

Control: The ride-on car has a radio controller for forward, reverse and steering, so I wanted to control the height adjustment, blade operation by remote as well. So instead of handling three different remotes, I knocked up a quick design to add the three remotes into one controller. A possible future addition I was thinking of was to add a wireless camera to the mower that would stream to my phone that would fit to the controller too.

Safety: While designing this and because I completely stripped the lawnmower including the safety control, I decided on adding a safety cut off switch for the mower deck which would completely isolate the battery for safe cutting chamber cleaning. In regards to mower blade motor operation, I decided on remote start and stop so if anything happened, I wouldn't have to chase after the mower to turn the blade off. As I mentioned for the cutting height adjustment, I used a momentary remote actuator relay. Using a momentary relay instead of a latching one makes for easier fine height adjustment, but also is safer should something happen.

I admit that the overall design does loose edge grass cutting because of the drive wheels width and frame, but I'm fine with that as I can use a strimmer afterwards (maybe adding a strimmer head could be a future addition?). And why did I use wood instead of metal, simply because I'm comfortable using wood, I don't really have any metalwork tools, the frame would still be lightweight yet strong, and as this as a sort of prototype, wood was my preferred choice which would be treated to protect it.

As I mentioned in the intro, the lawnmower was one I already owned and used, and although I had initial reservations about stripping apart an perfectly working £300 mower, the fun and enjoyment of making and using an RC lawnmower won me over pretty quickly.

Measurements: The first thing I did before getting the spanners and screwdrivers out, was to take measurements of the physical adjustable cutting heights, the lowest one and the highest. Then I took the overall size of the mower deck itself so I could work out how much wood I would need for the frame and deck base.

Disassembly: As I only needed the mower deck and power cable for the control handle, I removed the wheels which were press fit into a couple of plastic clips, height adjustment assembly held on with a couple of screws, and the control handle assembly which was held on with a couple of bolts while disconnecting the control handle from the power cable. Instead of just cutting the power cable, I took apart the lever/safety switches to see the insides just in case there was something inside I might need, like an unexpected wire, a small PC board etc., but there were none, just two wires as expected.

All the unused parts were stored away just in case I ever wanted to put the mower back together again, or to use on another project. Now I was ready to spice the scooter and mower deck together.

I was careful when stripping apart the lawnmower because there were parts I could use for future projects, but I took extra care taking apart the rind-on car because I was going to use many of the parts and the wiring loom. I removed the batteries, wheels, motors, motor control module, and the switch gear and wiring loom.

While disconnecting anything electric, and I advise you do this too, I took reference photos of everything. Even though the wiring was pretty straight forward in regards that the wiring loom was colour coded and wires had their own separate sized plugs so you can't plug things into the wrong sockets of the control module, having the reference photos would be a big help identifying things if needed. Anything not needed was put in a supply cupboard for future projects.

The drivetrain is made using a piece of 12mm thick plywood, the ride-on cars motor mounts, axel, motors and wheels. The width of the ply would be the width of the entire framework and would be the platform the grass collector sits on. Having the wheels under the platform would have interfered with the height adjustment with the grass collector fitted so they had to stick out the sides. The depth of the plywood platform was the length of the motor mounts.

With the plywood piece cut to size, Sand down the edges until nice and smooth, then cover the piece with a couple of coats of external wood sealer. Although we wouldn't be cutting the grass in the rain or if the grass is soaking wet, there is still moisture in play, and also where it is stored when not in use (a shed for example) is also a factor where the wood could get a little damp.

Place the motor mounts onto the ply with the axel fitted and wheels are on. Then line the mounts up until they are straight and equal making sure there is a 2 to 3cm gap between the inner side of the wheels and the edge of the plywood platform (see second photo), draw a pencil mark around the motor mounts, then drill and screw them into place. Then fit the wheels and tighten up the wheel nuts.

As with the drivetrain, cut to size a piece of plywood, Sand down the edges until nice and smooth, then cover the piece with a couple of coats of external wood sealer.

Line up the castor wheels so the are evenly spaced towards the outer edges, mark the drill holes, and remove the castors. Drill pilot holes then the correct size holes for the bolts to be used, then bolt on the caster wheels.

A little something to note, during the part of the build I used a pair of castor wheels (with the red rims), but when I was moving the frame around while working on it, I noticed the castors were not turning properly and were dragging on the ground (and would have added extra strain on the motors when steering). I though because they were new they may be a little stiff, but after adding some lithium grease which didn't help, I replaced them with another pair from a different brand which worked so much better. Bottom line, you don't want to use stiff castor wheels.

To work out the length and width of the frame, the mower deck base needed to be made first. The width needs to be shorter than the drivetrain width, and this is worked out using the thickness of the draw runners which will be used for the height adjustment. Start by laying the mower deck onto a sheet of 12mm plywood, draw around the deck, then measure, mark and cut out the ply so you're left with a rectangle.

Measure the diameter and location of the mowers cutting chamber, transfer this onto the plywood and cut out the circle with a jigsaw then sand around all of the edges, especially the circle. Ideally it needs to be rounded so no grass will catch on sharp edges.

Cut of four equal lengths of some CLS timber, apply external wood glue to one end of each length, attach to the plywood base and screw in using some galvanised screws. These uprights are what the draw runners will attach to and then attach to the inside of the framework which we make next.

The drivetrain and castor wheel panel will now dictate the height of the bottom of the framework, and the mower deck base, including the width of the left hand and right hand draw runner thickness, will decide the width. Start by laying the mower deck on the ground with the grass collector attached, place the drivetrain behind it and the castors in front, then line up a couple of lengths of CLS timber.

Measure, mark and cut the CLS lengths to size, screw one end of each to the top side of the drivetrain, and then the castor wheel panel. You want to make sure the front castor wheels have room to fully turn without hitting the front of the mower deck, and that the grass collector doesn't sit too high in the top of the drivetrain.

To decide the height of the frame itself, we need to factor in the highest point of the mower deck and when the deck is at its highest grass cutting position because we will be adding the electrical component board on top and we don't want the dop of the mower hitting the bottom of this panel. I placed some off cuts of some 12mm sheet wood on the floor and placed the mower deck on top. This would raise the bottom of the deck up 24mm of the ground and would be the lowest grass gutting height. Then using an angle measurer, I measured the highest point of the mower deck, then added 10cm to this measurement which would be the highest grass cutting height.

Using this measurement, cut four CLS lengths for the uprights, and two more for the upper frame. Line the uprights up to the uprights of the mower deck (these are where the backs of the draw runners will attach to), then glue and screw down and then attach the upper frame panels.

As the draw runners will guide the cutting height adjustment, a single linear actuator will do the heavy lifting. I worked out that the rough estimate of the mower deck with the ply base, CLS supports, mower battery fitted and a full grass collector would weight about 12kG to 15KG in total, so my 90KG max load actuator would be more than enough to handle the weight. But mounting the actuator would also need to cope with the weight as well.

Instead of a "How to do this" I will describe the following as "What I did was..." because you may want to use a different make of lawnmower which will be different in design to the one I used.

My mower had a plastic panel that covered the wiring, motor and held the battery meter. The balancing point was to the front of this panel (the weight of the motor and battery). Next to the heat sink, there was just enough room for a couple of bolt heads, but as this plastic panel was held on by only four screws, I was pretty sure that fixing the actuator just to this and for it to support the weight of the deck wouldn't last over time, so I decided to make a plywood bracket.

Three plywood lengths were cut and fixed together using some steel angle brackets, two holes were drilled in the middle of the upper length and through the plastic cover, two bolts fed through the bottom of the cover, through the ply bracket, and the actuator bracket attached to the top. The plastic panel was then screwed back onto the mover deck, and two holes were drilled through the side supports of the ply bracket and into the mower deck in the upper area of the cutting chamber. The sides of the mower deck were thick double skinned plastic and very strong. Two more bolts were added feeding them through the ply into the deck and two nyloc nuts fitted. The nuts are well out of the way of the blade. So when the actuator would be fitted, the weight of the deck will now be supported by the four screws holding the plastic cover, and two thick bolts holding the ply bracket to the deck.

At this stage I decided to do some painting before parts started to be assembled. I did cut a piece of plywood for the electronic component platform, sanded the sides to make them smooth and set to work.

First off, sealing the wood. With a clean paint brush, apply two to three coats of clear external wood sealant waiting for each coat to dry, and the last coat leaving for 24 hours to cure.

In the mean time, I cleaned the mower deck and applied some spray paint. Using a direct to plastic spray paint (I used a satin black), spray the main part of the deck with a light dust coat and leave 20 minutes to dry. Apply another three to four coats leaving the final coat 24 hours to cure. To add another colour (I used red), mask off the areas not to be painted, then follow the previous instructions to apply the second colour to where you want it. When the paint is dry, carefully unmask.

Back to the wooden sections, apply a direct to wood external paint to cover all areas of the wood and leave for a couple of hours to dry. Then apply another two to three coats and leave to cure. The painting is not just for aesthetics, but it protects the wood as well because although I wouldn't be cutting grass in the rain, even on a dry sunny day the grass will be damp by nature, and if you would store the mower in a shed, there could be dampness during the cooler times of the year.

With the main part of the painting done, we can join the mower deck base to the frame. Line up, drill and screw in the four draw runners to the inside of the uprights of the frame.

Lay the frame onto its side, then insert the mower deck base (make sure it is facing the correct way as the hole we cut for the cutting chamber may be off centre). Extend the runners, line up the uprights, and start to drill and screw in the runners to the deck base.

As mentioned earlier, I am using a linear actuator with a 10cm extended shaft, and while I could have used 10cm extended draw runners, I decided to use 25cm ones for two reasons... 1: the longer runners would be more of a secure fit holding the mower deck while the mower is moving around, and 2: its better to have excess play on the runners so there is no strain on the actuator if there is a slight shift on the fittings. Better 'too much' than too tight or not enough in this case.

A relatively simple step, but an important one, fixing the mower deck to the deck base. This will stop the mower deck moving around and will keep it permanently lined up so there's no issues with cutting height adjustment and fitting the grass collector.

with the lawnmower on the ground, lay pieces of wood on the ground and lower the mower deck base on top so it's off the ground. Place the mower deck onto the base and line it up, then use some flat areas of the mower deck to drill some holes through the deck housing and through to the plywood base. Insert a bolt through each hole and fasten with nyloc nuts. I placed bolts to the left and right of the deck, and to the back just by the grass collection chute (third photo).

Here I was getting close to a first electronic test, the grass cutting height adjustment, but in order to do that, the actuator needed to be attached to the lawnmower. The actuator was going to do a dead lift for the mower deck so a strong bracket needed to be made that would be fixed to the frame. First thing to do was to connect the actuator to a battery and fully extend the shaft.

Cut three lengths of CLS timber, one the width of the frame, and two the height of the actuator top bracket fitted to the fully extended actuator. Then drill and screw the pieces together to make the support and make the holes on the centre of the long piece to attach the actuator bracket, then bolt it into place.

Place the support onto the frame and attach by screwing in a pre-drilled 70mm x 140mm steel fixing plate. Feed the fixing pin into the bracket and through the actuator mounting hole and fix into place with a split pin. Now you can attach the actuator to a battery to test the movement. As the actuator is essentially a DC motor, you can swap the polarity by switching the wires to the battery to change the actuator shaft direction.

The electrical components and batteries are fixed to a plywood panel that sits on top of the frame towards the rear. I cut a piece of plywood to size, sanded it down the edges, treated with wood sealer and painted when I did the frame.

Lay out the components to were you want them, including the batteries placing them in the centre for central balance and in from the edge so the sides of the cover can sit on the base (12mm each side). To secure the batteries, cut four lengths of some stick timber (I used 15mm x 22mm) to surround the batteries then screw in from underneath the panel. Then drill a couple of holes each side of the of the battery restraints, and use a jigsaw to cut out two slots to feed some nylon strap through. Feed the strap through, buckle it up around the batteries, cut off the excess strap and seal the end with a lighter to stop freying.

For the cover, it's essentially a five sided box the width and length of the components base, held together with wood glue and nails. The holes for the switches were made by measuring the sizes, marked onto the box then drilled for the jigsaw blade to fit through, then cut out. Another hole on the side was made for the charging port for the motor controller batteries, and a large hole in the back where a metal air vent would be fitted, 1 to keep the batteries cool, and 2 to allow the wireless signals to be picked up from the remotes. The box was then treated and painted. When the paint was dry, the switches and vent cover were fitted.

Now fix the relays to the panel with some screws ready for wiring up.

I won't go into too much detail about the wiring up below as following the attached wiring diagrams I drew do that much better. But to explain the components...

The actuator relay is powered by one of the 12v lead acid batteries via a toggle switch to turn the relays power on and off. The actuator wires are connected to the "motor" terminals, but if you find that when you press the "Up" button on the control and the actuator moves down, simply swap the actuator wires on the relays terminals.

The mower deck relay is also connected to a toggle switch to power it off. The relay I'm using has variable operating voltage, so I've hooked it up to run off the combined 24v from the two lead acid batteries. The mower wires connect to the "Normally Open (NO)" terminals so when the "On" button is pressed on the controller, it closes the circuit and operates the mower. I also added a double redundancy toggle switch between one of the mower wires, so when the relay is off and this switch is off, there is two breaks in the circuit so it makes the mower safe to clear any grass blockages.

The rest of the switch gear is from the ride-on car... the power switch, speed select and the battery charge indicator. This is where I referred back to my reference photos I took when I stripped the ride-on car apart.

The components cover switches were connected and a couple of hinges were screwed to the cover and attached to the top of the frame.

This part is an optional step because the new RC mower is ready to get to work, but I wanted to dress it up a little, noting over the top but just a few 3mm plywood panels, painted and with a little bit of styling so it looks like a finished thing. A couple of side panels and something for the front area but still leaving access to the mower deck battery. Measure out the height of the frame and the length from the front to the forward facing part of the rear wheels, and draw this along with the front panels onto the 3mm plywood sheet. Now you can draw out your designs (curves, cutouts etc.) then cut them out with a jigsaw. Sand down the edges of all of the panels, give them a couple of coats of wood sealer, then three or four coats of paint and leave to cure.

For the styling, mask the panels, draw your patterns and cut them out with a hobby knife with a new blade fitted. You only need to apply light pressure when cutting the masking tape. Use the tip of the knife to lift the edges of the tape that needs to be removed, and carefully pull the tape off. Apply three or four coats of the second colour paint, wait for the last coat to dry and remove the rest of the tape.

To attach the panels, place into position and clamp them down, and fix into place with a nail gun (or hammer and tack nails).

Final job was to make a hand held controller to operate everything.

Charge up the batteries, insert, flip the switches to On, and get cutting.

Overall I am very happy with my first attempt at a radio controlled lawnmower, and the remote height adjustment and grass collection works really well. So after some use and taking notes, what would I change on my next version? First off, the one thing I'm not so happy with it the height of the mower itself, more precisely, the part of the frame that supports the top of the actuator. The actual function works really well but the actual support is just too high for my liking and would have preferred it to be a little more low profile. So I'm thinking that o my MK2 model, I may do away with the four draw runners and replace them with four smaller, identical linear actuators hooked up to a 4 channel actuator relay so they move in tandem.

Another thing I may change is the frame design. To get the edge grass cutting back I may do an up-and-over frame instead of the side-by-side frame I used here. That will take some working out as the outer edge of the drive wheels would need to be in line with the edge of the mower deck itself, but not obstruct the grass collector, especially when the mower deck is set to the lowest grass cutting height.

Some extra additions I am thinking of adding is a front bumper mounted on to a couple of springs, and two latching switches, so if the mower hits something, the bumper presses one or both switches which in turn turns off the blade motor and stops the drive motors. Once the mower or obstacle is removed, manually press the bumper to reset the blade motor and drive wheels. Another addition may be to add a wireless camera mounted to the front that will stream to my phone which would be mounted the handheld controller.

But for this MK1, prototype, working proof of concept, I will still use it for some time to come as it does exactly what I made it to do. You may have some different ideas or improvements in mind, but I hope this gives you the inspiration and motivation to give this a go yourself, or at the very least enjoyed seeing the process of my build.

Thank you for reading, and happy making.