DIY Remote Controlled Lawn Mower

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DIY Remote Controlled Lawn Mower

#1  Postby theropod_V_2.0 » Mar 07, 2020 8:41 pm

Hey all,

In my boredom, and associated laziness, I have begun the task of building a remote controlled lawn mower. For now the Briggs and Stratton will remain the prime mover, but with future plans for a brushless electric motor to spin the blade. I expect this to be an ongoing project, and input is invited.

Since I have a little exposure to the Arduino environment I am using a pair of Nanos and a pair of NRF2L01 WIFI modules to send joystick inputs from a hand held “master” to an onboard “slave”. The slave will drive 2 X BTS7960B, 43 amp @ 24 V Pulse Width Modulation (PWM) brushed direct current motor drivers.

I have already sourced most of the electronic stuff, and have a handle on the code. I still need to find/buy/salvage 2 robust geared down brushed DC motors, which I hope to attach a bike sprocket. Then maybe I can use 2 kiddie bike rear wheels with big sprockets from the pedals adapted to rear wheel use.

I am planning on rear wheel drive with independent speed/reverse control, and this means the front wheels must pivot, like castors. This, along with the drive/battery/control stuff, will require a subframe from which the mower and deck is suspended. If I added actuators I could adjust the cut height on the fly.

Eventually I want to replace the small gasoline engine, an old school “flat head” <4 HP type, with a brushless DC motor. To help sustain a flow of power a 10 amp 24 v solar panel with an MPPT (Maximum Power Point Tracking) controller that will remain affixed, and keep the battery pack topped up when parked.

As far as batteries go I am looking at gel cell lead/acid batteries for 2 reasons. Cost and availability. With proper care that tech can do the job, and I have learned a little about lead/acid batteries in 21 years of living off grid with the flooded versions. Never let them remain discharged, never let them get dry, never let them get too hot, never over charge them, never subject them to high G shocks and never let them freeze. Gel cells just need the proper charge rate, and voltage control, and they are perfectly happy. These batteries won’t spill no matter what the mower does, and will be easily recycled at the end of life. Every Wal-Mart in Arkansas has a sporting goods section, and among the items on the shelves are 12 V gel cells I can series/parallel to get the target 24 V for the drive motors.

Surplus/salvage wheel chair drive motors/gear boxes seem to be the “go to” solution as far as the drive wheels are concerned. These are horrible expensive new, and certified rebuilt are just barely less so. One can find them on fleabay for between $50 and $100 used. I’ve been thinking of 2 heavy duty cordless drills with the drill switch(es) disabled/bypassed, with a mounting bracket fabricated to clamp them down firmly in a cradle. The mower will not be that heavy, and I am not out for speed. Geared down even further via the tiny drive sprocket to huge driven sprocket I think they would suffice. Perhaps a computer cooling fan ducted to force air over each motor would help them last. The drills could just be chucked down on a drive shaft with the little sprocket, and this would allow some in/out position adjustments to align the chain and driven sprocket.

On both the controller and the mower will be a big easy to reach emergency stop button, which will kill all the electric functions and stop the gas engine. To reset the use of the system in the event of an emergency stop everything will have to have a hard reboot with a power down of all components.

Anyway, the idea is to not sweat my guts out trying to keep the jungle at bay, and eventually stop burning gas to have a lawn. With just a few more goodies and I could feed video to a set of VR goggles and “ride” the mower around as it went about its work.

RS
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Re: DIY Remote Controlled Lawn Mower

#2  Postby laklak » Mar 07, 2020 9:21 pm

That sounds pretty cool. I'm lazy and just hire some Mexicans, they drive themselves.
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Re: DIY Remote Controlled Lawn Mower

#3  Postby theropod_V_2.0 » Mar 07, 2020 10:10 pm

laklak wrote:That sounds pretty cool. I'm lazy and just hire some Mexicans, they drive themselves.


That defeats the purpose of being an antisocial grump, and I’m doing this as cheap as possible. The Arduino micro controllers were about $3 shipped, and I got 2 sets of WIFI boards for less than $5. The motor drivers were $5.50 each. I plan on about $50 in batteries and maybe that much for motors. The sprocket/chains I have, and a couple kiddie bikes ought to be easy to come by. I figure bed frame will work for the brackets and such. This leaves me front pivoting wheels, and I happen to have connections at Bad Boy mowers where all their mowers have these type front tires/wheels. I bet a “defective” set can be found.

Anyway, I’m laying out the hardware right now, and a PlayStation layout with a thumbstick (which I also have) for each drive wheel driving should be familiar to anyone that’s driven a skid-steer vehicle, like a Bobcat. This can house all the “master” components, including the battery, in a compact form. Push both sticks forward and the mower should move forward in proportion to the input. Pull back and the mower should back up, and pushing one while pulling the other should induce turns up to zero radius.

I’ve seen an example on YouTube where a dumping wheel borrow pan was attached, and that would make my life much easier. All sorts of little loads could be shuffled around, like the propane bottle that got away from me and snapped my ankle.

RS
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Re: DIY Remote Controlled Lawn Mower

#4  Postby Fenrir » Mar 07, 2020 11:36 pm

Yay!

I gots a half- finished (more like 1/10th finished) ardumower on my random unfinished projects bench (actually that's the entire garage).
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Re: DIY Remote Controlled Lawn Mower

#5  Postby theropod_V_2.0 » Mar 08, 2020 4:27 am

Fenrir wrote:Yay!

I gots a half- finished (more like 1/10th finished) ardumower on my random unfinished projects bench (actually that's the entire garage).


Nice!

Maybe we can compare notes.

I have feelers out for a used wheel chair. If I can score one of those I’m set.

I think the trick might be weight distribution, and speed control. Examples on YouTube all seem to be to fast, and twitchy. I want smooth steady movement that tracks well. Some of those mowers also spin the drive wheels too easily, and seem to lose traction quite often. My solution is a bike tire with screws shot through the tube side, the heads slathered in silicone, a strip of old tube covering the screw heads/silicone and assembled with a new tube with minimal inflation before the silicone cures. 3/4”-1” screws should provide ample “bite” to keep the loss of traction to a minimum. Something like the tires used on ice racing motorbikes.

I’ll probably play with the PWM mapping/upper limits in software to keep my speed limits within my desired range. I’m sure it will require a lot of trial and error to get the gearing, wheel speed and cutting abilities to match up. I’m also considering a stepper motor driven throttle control for even more adaptive capabilities. If the grass just needs trimmed the engine need not run wide open, but during those months when we have a 4 day rotation, and the grass grows at night, I might need to crank the throttle to munch the stuff.

I have finalized my controller layout, and all that remains is some epoxy work and soldering. I’m going to play around with adding an external antenna to the RF modules of the correct length and embedding that in a rigid epoxy rail in both master and slave. This could extend the master battery life by using low power mode, and extend the range (not that I expect to need it on my small lawn). I just want to make sure not to lose comms between the modules with a running mower. Of course this too will have to be tested extensively without the engine running! I don’t want a running mower set loose on the world to follow its own devices.

My test bed, well before 24 volt motors are powered up, will be 4 LEDs. Two for each motor. One red for reverse, and one green for forward for each motor lead. The drivers I’m using need a PWM signal for forward and another for reverse. So, the simulation of the correct signals will be two green LEDs full bright for as fast forward as possible, and two red LEDs full bright for full reverse. A mix of the two, at various brightness, will indicate that the slave WIFI device/Arduino/coding is functional. This will allow me a preview of the functionality without having to spin high torque DC motors, and make corrections as needed.

RS
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Re: DIY Remote Controlled Lawn Mower

#6  Postby Fenrir » Mar 08, 2020 5:22 am

I'm aiming much smaller and a lot less techy.

It doesn't need to be big or beefy coz of being mowing continuously on a fairly small area. More breadbox than wheelchair.

Also have quite a small lawn and will use detection of buried wires to constrain it from wandering off into the untamed wilds of the rest of our block. Bumpers and ultrasonic detectors for navigation. Physical barriers like existing walls and garden edging will stop it wandering far anyway.

Not planning on having it go home and charge itself, figure it shouldn't be too hard to find a bright red box on the lawn and charge it occasionally. Step 2 would be adding a bit of on-board solar charging.

Ardumower uses a blade off a box-cutter type knife thingy. That seems a bit of a joke so I'm planning on uppening that a bit. More robust, less razerblade cutty seems more practical.
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Re: DIY Remote Controlled Lawn Mower

#7  Postby Fenrir » Mar 08, 2020 5:27 am

The trick with ardumower (and there are many similar jobbies) is it is self-controlling, not remote controlled.

Roomba's for grass.
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Re: DIY Remote Controlled Lawn Mower

#8  Postby theropod_V_2.0 » Mar 08, 2020 1:02 pm

If I can lay hands on a wheelchair all I will use are the geared brushed motors, and maybe the pivoting front wheels.

I hadn’t looked into the Ardumower, and the wire following is great. Not near so complex as remote control in either software or hardware. Box cutter blades might work well.

I considered using big stepping motors for this project, and I could write a program to map the lawn and keep track of the mower position using a scheme similar to a CNC plotter. Steppers that big are stupid expensive, and I might be able to do the same thing with encoders on the DC motors. I might try this, eventually.

RS
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Re: DIY Remote Controlled Lawn Mower

#9  Postby felltoearth » Mar 08, 2020 1:53 pm

:popcorn:
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Re: DIY Remote Controlled Lawn Mower

#10  Postby zulumoose » Mar 10, 2020 12:57 pm

I have begun the task of building a remote controlled lawn mower. For now the Briggs and Stratton will remain the prime mover, but with future plans for a brushless electric motor to spin the blade.


You don't need big blades and weight when time is not a factor.
Think more like a vacuum cleaner robot with a solar docking station and a tiny cordless weed-eater on the deck.
300W solar panel powering the docking/recharge station, and with cutting happening every day the clippings will be tiny and just mulch into the ground.
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Re: DIY Remote Controlled Lawn Mower

#11  Postby theropod_V_2.0 » Mar 10, 2020 1:46 pm

Yes, those ideas are workable, and have merit. My ultimate plan is to make the machine all electric and self recharging. I do want to have a machine that has more capability than just mowing. A dumping wheel borrow would be used a great deal around our home. This will require a more robust system than a simple autonomous bot. Having the ability to do things from hauling rocks and dirt to full 100 pound propane bottles would be a great to have around. Besides, this is as much about learning to use the RF devices, motor drivers and actually building the machine as anything. I also tend to think of this a making a big toy. Yes, I know all too well just how dangerous a gas powered mower would/could be if it went rouge, and extensive testing of both operational safeguards and a panic switch WHEN things go wrong will take place. As uneven and rough as our lawn is it will require a machine able to deal. The clippings never get raked up now, as I firmly feel than those clippings help build the soil/turf as they decompose.

There is also the size, and shape, of our lawn which I must consider. While not large by American standards our lawn is still pretty big, and far longer than wide. Over 20 years ago when the bulldozer cleared our house plot I didn’t consider the size very carefully. Some of that lawn is about to be removed by replacement with a crushed limestone parking pad. Right now we have to park our vehicles well up the hillside from our house, and carry down groceries and everything else. Sometimes this requires several trips, which gets old quickly. The projected parking pad will allow us to park very near the house, and take out a big chunk of the grass.

Yes, I will consider your idea very carefully, as there is no reason two, or more, versions of this remote controlled mower can be built. One I didn’t even have to think about sure has appeal.

RS
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Re: DIY Remote Controlled Lawn Mower

#12  Postby The_Metatron » Mar 10, 2020 3:53 pm

I think the problems you'll have are steering and positioning. Steering, because when driving or walking behind a mower, we're making constant corrections to keep straight lines. Positioning, because parallax is going to make it really hard to judge "lane positioning". You have to overlap a bit on each pass, but not too much. That's going to be hard to judge from anywhere other than the usual operating position.

Unless you're going for a random approach like a Roomba vacuum cleaner does to a floor. Then, it only needs to not mow things down or go off campus.
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Re: DIY Remote Controlled Lawn Mower

#13  Postby theropod_V_2.0 » Mar 10, 2020 7:52 pm

I’m seriously considering mounting a small wifi/bluetooth cam and feeding it to the laptop for now. A complete separate feed from the control modules, and cheap. With a visual feedback like that, slow speed by tweaking the PWM mapping/gearing and more or less straight line cuts ought to be manageable. A buried guide wire path is something I’m thinking about pretty hard. A spiral coil spaced just so would be easy enough to detect and follow. That wire system could also define the stop/turn point for a romba type mower.

Like I keep sayin’, this is a toy project that will turn into a tool if I can make everything work. Just testing things is more than 3 weeks away. I have no drive motors, the master/slave hardware is just barely started and a thousand things stand in the way.
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Re: DIY Remote Controlled Lawn Mower

#14  Postby felltoearth » Mar 10, 2020 8:02 pm

What’s the terrain like? Flat? Rolling?
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Re: DIY Remote Controlled Lawn Mower

#15  Postby zulumoose » Mar 10, 2020 9:03 pm

If possible, one solution would be to have a wire or magnets just under the surface for it to follow on a set path.
All it would need then is a couple of sensors and some basic logic to make course corrections.
Other options would be for a laser pointer to trace the route for it, or for two visible markers to slowly move along the edges so that it just has to keep aligned between them and reverse direction when close enough.
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Re: DIY Remote Controlled Lawn Mower

#16  Postby theropod_V_2.0 » Mar 10, 2020 9:18 pm

felltoearth wrote:What’s the terrain like? Flat? Rolling?


A slope with bumps. Imagine a rectangle 120’ (40 meters) X 60’ (20 meters) with one long edge of the rectangle aprox 7% higher than the opposite. The bumps are not severe, but the lawn was never really smoothed after bulldozing cleared the house site. Mainly Bermuda grass, and surprisingly soft in most places. This slope, and the bumps, are a part of the consideration for oversized rear drive wheels, and spiked tires. My aim is to retain traction at all times, and limit bounce by keeping the speed low.

I really think a romba style mower would have issues with those bumps.

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Re: DIY Remote Controlled Lawn Mower

#17  Postby theropod_V_2.0 » Mar 10, 2020 9:31 pm

zulumoose wrote:If possible, one solution would be to have a wire or magnets just under the surface for it to follow on a set path.
All it would need then is a couple of sensors and some basic logic to make course corrections.
Other options would be for a laser pointer to trace the route for it, or for two visible markers to slowly move along the edges so that it just has to keep aligned between them and reverse direction when close enough.


You are correct. A buried guide wire would be simple to install and detect, and I just may resort to that. An inward spiral that was followed by the mower in a counterclockwise direction would allow clippings to be thrown free of the grass yet to be cut. No sense in cutting those clippings again and again. A magnet at the end of the spiral could serve as an end-of-task detector.

I just finished the first phase of soldering the jumper wires from the NRF24L01 wifi modules to the Arduino Nano, and installing a 10uf 30v electrolytic capacitor between the +/- pins on the wifi module to filter its power supply a touch. I yet have to install and wire up the two joysticks or battery clips. When those are done the Master will be ready to accept programming.

RS
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Re: DIY Remote Controlled Lawn Mower

#18  Postby felltoearth » Mar 10, 2020 9:55 pm

theropod_V_2.0 wrote:
felltoearth wrote:What’s the terrain like? Flat? Rolling?


A slope with bumps. Imagine a rectangle 120’ (40 meters) X 60’ (20 meters) with one long edge of the rectangle aprox 7% higher than the opposite. The bumps are not severe, but the lawn was never really smoothed after bulldozing cleared the house site. Mainly Bermuda grass, and surprisingly soft in most places. This slope, and the bumps, are a part of the consideration for oversized rear drive wheels, and spiked tires. My aim is to retain traction at all times, and limit bounce by keeping the speed low.

I really think a romba style mower would have issues with those bumps.

RS

Arkansas right? Looks like a lot of the state is silty and sandy loam from what I’m reading which is pretty soft indeed. Does fescue grow down there?

ETA just saw this blog post from 2009. Interesting
https://northwestarkansasaudubonsociety ... escue.html
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Re: DIY Remote Controlled Lawn Mower

#19  Postby theropod_V_2.0 » Mar 10, 2020 10:03 pm

That might hold for outside the Ozark region, but our ground is more clay rich and with sandstone base. It has taken 20 years to get this base to grow. Bermuda is less stem/stalk-like than fescue, and fills in via runners any bare/thin spots.

I’ll shoot some video in a few days to better describe what I have here.

I had a heart cath yesterday, and I’m supposed to stay planted on my ass for the next 6 days. The good news is I may get to stay off the blood thinners and anti cholesterol drugs, and the aorta hasn’t swelled even a little. The stent is “wide open” according to my cardio Dr.

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Re: DIY Remote Controlled Lawn Mower

#20  Postby zulumoose » Mar 11, 2020 7:09 am

Caterpillar tracks

Imagine a lawn being mowed by a WWII tank look-alike.

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