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I'm building a RC mower ( https://www.lawnmowerforum.com/show...rt-but-not-self-propelled?p=336699#post336699 ).

Decided to go with a 20" 40V Brushless as they were on sale and it has the one lever deck height adjustment which I am hoping to utilize with an actuator for remote control of cutting height. But we will see.

Anyways, does anyone have a wiring diagram for this model? There is a DPST switch with one side wired together, which seems odd. I removed the mechanical safety as I will be using a 10 Amp RC relay to replace the switch. Just seems odd why it would be wired this way. In the pics below, if you bridged the black and green wires it seems you'd have the exact same circuit and could use a SPST switch...so why is it wired this way? Any ideas?

Not sure yet which lead goes to battery +, but will post more once I get deeper into tear down so I can make the welded frame for drive motors, drive batteries, electronics, etc.

Any help appreciated....

my first thought, they utilized a part they already had in inventory for some other model instead of qualifying a new part?

and , maybe, some certifying agency doesn't allow an unterminated switch connection?

I think you are correct, or very close to correct. I can't think of an electrical reason to do this...especially having the power travel down two separate wires.

Thanks.

Just thought I would update this thread, if only as a record in case I forget....

Turns out there is a reason for wiring the switch this way. With the exception of paint and making the wiring neat, I finished the project and my RC lawnmower runs. But I left wiring the blade switch via an RC relay to the very end. Surprizingly it didn't work. So weird I thought...because when I tested it back in August it worked. When I wired the white and green wires together and connected them via a SPST relay it wouldn't start unless I removed the 40V mower battery pack and reinstalled it again. That got me thinking: something must need to be reset here first. So I reversed the wiring sequence such that the green and black wires are wired together, THEN these are connected to the white wire via the SPST relay. In other words, there's a controller board in this mower and unless the wires are connected in a certain sequence, the blade won't spin.

To confirm this I hooked up and oscilloscope to the terminals and ran a 10KHz square wave through both DPST contacts on the factory switch. Sure enough the one set of wires contacts slightly before the other, which starts the mower blade spinning. So interesting to learn this. Obviously a safety feature. If I were smart I'd add a push button switch on the mower so that when I switch on the blade from the RC transmitter, I have to have my other hand on the pushbutton and not near the blade. But that kind of defeats the purpose to being able start it remotely. So instead I'll think of another failsafe.

Anyways, here's a pic of the final project. As I write this the unit has been taken apart and I am waiting for the paint to dry before reassembly. Also, here's a link to the test run in my driveway. Now, if only the snow would melt in Calgary and we'd have some grass to mow
(The rattling sound is just the electronics box that isn't yet fastened down.)

ho......ly........sh@%
wow, thats awesome
and i thought i was good when i built my racing electric scooter,
brownie points man good job

Thanks. It was a fun winter project.

what kind of batts you run on it?
what # of cell?
lipo, or micl hydrate

oh..... wait never mind, looking at the pic, are you running 2, 12v, 12ah, scooter batteries?

logert gogert said:

oh..... wait never mind, looking at the pic, are you running 2, 12v, 12ah, scooter batteries?

Click to expand...

Yup, you're right. That's exactly what they are. The differential drive system is two 250W 24VDC wheelchair motors. The batteries are 35AH sealed AGM deep cycles. By my calculations I'll get about 60-90 mins per charge. I built it because we have a lot of trees in our small back yard and my back has issues bending to get under them. I should have more than enough juice to do my yard, then sit back with an adult beverage and relax.

CalgaryPT said:

Yup, you're right. That's exactly what they are. The differential drive system is two 250W 24VDC wheelchair motors. The batteries are 35AH sealed AGM deep cycles. By my calculations I'll get about 60-90 mins per charge. I built it because we have a lot of trees in our small back yard and my back has issues bending to get under them. I should have more than enough juice to do my yard, then sit back with an adult beverage and relax.

Click to expand...

wait, so they are 35 ah? because i gussed they were 12ah and you said i was right. then you said they were 35ah.
okay besides that.
but yea you should have plenty of battery life to do your yard, are your batteries powering the blades to?
and with those 2 250 watt motors, you should be able to get over ANYTHING as long as you have grip,
when i built my electric scooter, i got a 500 watt 24 volt motor, a 36v 1000 watt speed controller, 3, 12ah, 12v batts,
totalling at 36 volts, giving the motor a 12v over volt,, putting out 750 watts in the motor, add that to a 80 tooth rear sprocket, i was doing 25 mph, and a but ton of torque, imm 13 and i have a lawn business and i have about 10 yards, so i would haul around my lawn care equipment in a mower trailer with ease, imagine seeing a kid going 20 mph on a scooter pulling 300lbs of lawn equipment down the road lol

logert gogert said:

wait, so they are 35 ah? because i gussed they were 12ah and you said i was right. then you said they were 35ah.
okay besides that.
but yea you should have plenty of battery life to do your yard, are your batteries powering the blades to?
and with those 2 250 watt motors, you should be able to get over ANYTHING as long as you have grip,
when i built my electric scooter, i got a 500 watt 24 volt motor, a 36v 1000 watt speed controller, 3, 12ah, 12v batts,
totalling at 36 volts, giving the motor a 12v over volt,, putting out 750 watts in the motor, add that to a 80 tooth rear sprocket, i was doing 25 mph, and a but ton of torque, imm 13 and i have a lawn business and i have about 10 yards, so i would haul around my lawn care equipment in a mower trailer with ease, imagine seeing a kid going 20 mph on a scooter pulling 300lbs of lawn equipment down the road lol

Click to expand...

Yeah sorry, I misread your post. They are 12VDC, 35AH AGM deep cycles x2. Series connected obviously. I have a 24V Battery Tender to charge from, but I also bought a 12V 15W solar panel with the intent of building a small garage/shed for the mower that it will pull into and charge itself from the panel on the roof. I'll use an Arduino and some code to alternate charging each 12 battery until both are at capacity, then trickle them. I need to design a mechanical switch that will separate the series bus under the mower when it drives into the shed. I've got a great hobby metal shop where I do all this stuff in my retirement. That will be fun I think.

The batteries aren't powering the mower blade because that's a 40V brushless motor with a Lithium pack. Originally the unit was going to be gas, but switched to this design for a few reasons. I actually had a linear actuator on it at one time that raised and lowered the deck height remotely for different grass lengths. But (sadly) the geometry sucked. It made the wheelbase so long the unit wouldn't be able to maneuver though my trees and bushes easily, so I had to scrap that mod. But it was fun to try at least.

I have some onboard Arduino circuits I am just putting the finishing touches on too. One is a tilt sensor safety switch, and the other uses a flex sensor in a piece of vinyl tube on the front of the mower. If it bends too much because it hits something...it shuts down the blade. From the two AGM batteries I also run both 5VDC and 12VDC Buck convertors to separate buses in case I want to add more features. Video is an option here obviously and I am looking around for the right wireless camera.

There is more detail on build on the Metal Working site I belong to if you are interested:


I'd LOVE to see some pics of your scooter. I think those things are so cool, and they look like fun to build. What did you use for your controller? I used a 2x60W Sabertooth for my build.

36 Volt 1000 watts Brushed Motor Controller. 36v 1000w 36volts 1000watts
i didn't really use anything for the controller, just bought it, and wired it up, but it wasn't as easy as it sounds when i said, "and wire it up" but if you have anymore questions about it id be happy to awnser, i love talking about stuff i built lol,
but obviously you're MUCH more inclined than me, i could never, do what you did, if it was something like my scooter, yea, i could build it.
but i don't think i could built it out of pretty much nothing like you did XD