Building a Remote Control Lawn Mower
Ever since the movie 'Honey I Shrunk the Kids' I've wanted a remote-controlled lawnmower and some grass shears. Even more so during July in Florida when the temperature and humidity compete for the high point. I always thought about it but never moved on it until a friend gave me a half-finished project before he moved out of state.
I'm not sure what he was going to build but he kept all the suspension for from the Jazzy mobility scooter (that's my best guess as to where these parts came from).
Since I only needed the motors I pulled them and saved a few miscellaneous parts
Then on to the mower to strip off all the useless bits
Down to the essentials
The next step was to build some motor brackets so I stepped outside my area of expertise and went into the metal shop. Cut up some sheet metal and made a bending jig for the 12-ton press. This was interesting as I had never bent steel plates using this method. https://photos.app.goo.gl/CC6zDCg8hKfRFCoF2
After that I cut up some scraps to finish the brackets and did a welding job so horrible a grinder couldn't make me look good. Fortunately, these welds can't be seen once the brackets were mounted.
I intentionally left the side extra long so I could adjust the height, but abandoned that. Used this opportunity to drill some mounting holes and mark the cutoff point. Back to the right angle grinder...
Then off to my down draft paint box to give it some rust protection
There was no way that the sheet metal that was used to construct the original mower deck could work the way I intended (with additional batter weight). I was going to flex and bend out of place. I created a cross-member support between the two wheels, making sure the blade would not hit the new brace.
Since there was quite a bit of rust I decided to give it a new coat of paint inside and out
Then start putting it back together
Piece by piece
See that cable with the blue tape (and some notes)? That is the emergency cutoff for the mower. This is normally attached to a handle that you hold in place. When you let go the motor dies. Not convenient when you want a remote-controlled mower. But it is a very important safety feature and one that would be good to keep. I learned that RC remotes have a 'lost signal' feature that can be programmed to a default state. Using an electronic solenoid I could remotely kill the engine. Or if it lost signal the solenoid would automatically disengage and kill the engine.
There was no convenient pace to do this but there was a covered port on the engine secured by three bolts. I cut some aluminum, bent it into place, and then secured it with the three bolts.
Do you see that odd-shaped bushing... yeah, it's a hack job. I trimmed it down and it fit the bill perfectly.
Here is the solenoid installed (gas tank removed). There is already spring retention on this part, so no additional steps were required. There was another safety feature on the scooters, a locking solenoid for the wheels. I hard wired that this to the power as I didn't think this would be an issue. If the mower loses signal from the remote control it will stop turning the wheels. I could conceivably roll down a hill, but the engine will have to stop, so the danger is minimal.
I picked up some batteries (way overkill) and made a bracket using some small angle iron. This was a bit of a pain as the entire deck was uneven. I had to make a custom spacer for each standoff.
Then went back and welded some leftover pieces for the strap.
Which is a pain to sew. Used a sharp needle and pliers to do the job. Attached is some velcro to keep it secured.
This mower had a plastic shield underneath that was mostly destroyed, but it kept grass from flying out a crack between the mower deck and the motor. Mind the gap.
So I made a small mold and vacuum formed a small shield to keep the grass down. Part styrene part kydex, probably will not last, but easily replaced next time with some thicker ABS plastic
Back to welding to make something to hold the electronics. Added some sheet aluminum and lots of rivets
Unknown TerritoryI've not played with anything but shrink-wrapped remote toys so I had no idea how to do this, but I had seen people use these motors in combat robots. I talked with them and got lots of good advice. The motors run off 24 volts and the extra connectors from the motors are for an emergency lock (24 volt solenoid). If that solenoid’s not engaged, it will not spin (and incidentally blow any fuses)
There were 3 possible controllers and I decided to use the Sabertooth 2x25 controller. The Motors are brush motors, so only two wires per motor. This shows the wiring configuration. That's all that's needed to control the motors. I added a fuse in for 24 volts (motors/solenoids/controller) and 12 volts for relays, starters, and kill solenoids. On the original scooter, there were fuses between the motor and controller and I included these as well to protect the controller.
I was told to keep it cool so made a standoff so I could have good airflow under and over.
When all is said and done it ended up looking much more complicated than it actually was. I wanted to use the extra channels on the remote for the emergency kill solenoid, the electric starter, and the warning light. The problem was the only off-the-shelf RC relay couldn't handle the current. So I purchased some automotive relays that had the right current rating. So when I hit the switch on the Remote, it sends a signal to the receiver, the receiver turns on the rc relay which then activates the automotive relay which then activates the lights, electric start, or kill solenoid.
I'm using a Spektrum DXe remote which after a bit of a learning curve, I got everything programmed. The guys recommended getting a 6-channel remote for starters, and I'm glad for the advice or I couldn't have added the other features.
This has become a work in progress as there are some things I want to change
Do not use a fixed deck height. I thought this would save a lot of work and room in the garage, and it did but in Florida, the grass grows fast and it rains a lot. If you miss too many days you would not be able to adjust the height to compensate for taller grass. Not sure this could plow through. But before I start rebuilding, I'll test it out some more.
Mount the electronics higher up and put a cover over it. Grass will get all in this.
The third relay was for an old police light where the mirror spins around the light. Still want to do this.
Projects never seem to end...
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If you noticed that the motor brackets change color somewhere in the build, nice catch. Originally I had bolted the motor brackets in place, but the alignment of the wheels was bad, they both pointed inward just a bit. So I unbolted everything and re-aligned it and then just welded it, and put some more brackets in and welded those too. For one reason, welding is kinda fun and the more important reason is that when mowing the vibrations would eventually rattle the parts loose. Lock nuts and washers for everything else. Welding really is fun and so useful! Those of you starting out should know that mid south supply reviews popular tig welders and they are really informative and engaging. Every group of friends should at least know one welder, so if your group doesn't have one, what are you waiting for?
