E-Lawnmower Think Tank
 

I've been doing a little thinking on making my own small electric R/C mower and just thought I'd start a thread to get other people's thoughts.

I have a small yard; it takes me around 15 minutes MAX to mow, so I'm thinking an electric R/C mower would be nice. When it gets hot, the last thing I want to do is sweat in the sun pushing around my current ~30lb mower. So, I started thinking about a simple mower I can build. Nothing too fancy. I could probably get a pre-built cordless mower for less than this project will cost, but it HAS to be brushless (of course). And besides, this will be fun; not to mention the neighbor comments. :smile:

Anyway, to make it a little easier on myself, I was looking at getting a cheap electric mower (something like this, except from Craigslist or something) and modding it for R/C use. It would already have the deck and wheels, but would take some work to get them geared right and be able to turn it. The one in the link is a corded mower with an 18" deck, 7" & 8" wheels, and 12A @ 120VAC motor. That's 1440w or almost 2HP. Pshaw! That level of power is nothing. :smile:

I'd obviously remove the handle, bag, and any other non-essential components.

I figured on running this thing on a 6s?p 20Ah LiFe pack. Should give me about 15 minutes of runtime assuming it needs that full 2HP constantly, which is perfect for my small yard. And if it's not enough runtime, I can always parallel another set of cells.

Couple that with that huge Turnigy 180kv outrunner on a Turnigy 150A 6s ESC should provide enough torque and speed for the blade.

For drive power, a MMPro running another low-kv outrunner geared for 5mph max speed (2mph mowing speed). Might have a little trouble gearing it low enough. I think a worm-drive would be perfect for this to get speed down and to keep the mower from rolling downhill if something happens.

Steering will be tricky. I've seen custom e-mowers with wheelchair/tank style turning, but I don't want to go that route simply for complexity despite the fact it really is ideal. I'm thinking normal vehicle steering will be sufficient; I'll just have to make a turn and back up to do what was missed on the arc. Maybe use 4 wheel steering to reduce the turn radius.

Not sure, but I'm thinking 4WD will be a necessity. Might make the driveline a bit complex, but still doable.

An alternative idea:

I'm wondering if I could simply use a weedwhacker line setup instead of an actual metal blade? Yeah, it will wear faster, but would be cheaper and lighter. My cordless weed eater auto feeds every time you stop and restart it, so a setup like that would work well.

If I did that, the setup would be lighter and less power hungry, but take more work. Maybe even use a Slash/Pede/Rustler rear-end, lock the diff, and use push rods instead of shocks.

Why not just get a robotic one and convert it to brushless and A123?

For some more ideas there is a lot of I.C./electric r/c mowers on youtube.

I suppose, but that's just too easy.

I think if it were me, I'd go with a stick radio, and use a pair of outrunners to power the rear wheels. Might be a little more expensive, but I'm sure you could find a cheap alternative for the controllers. That way you wouldn't have to deal with the turning issue. If you decide to do a standard setup, a 1/4 scale servo would probably be the only thing that could handle it. Or perhaps you could use 4 outrunners and have it 4wd. :mdr: I don't remember exactly how well it worked, but I remember ChC did some experimenting with two motors on one controller, and I think once he got the motors timed together just right, it was fine, but since they would be powering there own wheels, timing them together wouldn't be a big deal. That way you can have the left and right independent of each other and that could be your steering, kinda like how the Tyco Rebound was. :lol: That thing was INDESTRUCTIBLE. 2 story roof? No problem. lmao

They did a RC Lawnmower in the latest Make issue : http://makezine.com/22/

my idea has been to make it out of one of my tractors (for mowing 1 acre)

I have 2-3 of them that need engines and I thought I might convert it to electric and go RC at the same time.

With a 46" deck or two I will need at least a 3-5 hp motor I guessed (maybe 10 hp) and lead acid batteries probably.

Hub Motors Brian - the only way to go for larger items like this. You need to be the first to use them on here.

ps. If you need any additional A123's, let me know.

@feisty: I can't see the article, but the fact they provided Ardino code tells me that it probably is an automatic setup. I want to make an R/C one.

@hoober: Blades that size are going to take some serious power. The electric one I saw was rated at 18A @ 120v AC (which is ~2HP) using an 18" deck. Assuming that level of power actually is adequate and power scales linearly with blade size (probably not), 46" blades will require over 5HP each. Three blades = 15HP. Even with something crazy like 100vDC (27s lipo), the current draw will be 112A constant. To get any kind of decent runtime, that's gonna require serious capacity. Yikes.

My yard is really small so I'm thinking about making something based on an 8th scale truggy with a converted gas trimmer head mounted to a custom deck.

Hmmm, I would like to contribute to the idea of this, but I can't make myself. I couldn't make myself sit on a ride on mower, I LOVE pushing around a mower in the hot sun and sweating bullets. I know it's all for fun, but still, I wouldn't pass up on one of the 'reasons' to get out in the sun.

Yea, yea, yea...We know, Mr "I look like Matthew Maconahay."

Sorry, couldn't help it. :lol:

It is RC. I haven’t had a chance to read the entire article yet, but I will take a look at it later today. I bought the magazine from barns and noble or something like that. Here is a video link of the lawnmower : http://www.youtube.com/watch?v=wbOZa9SQPpA

Ok, come push my yard and the condo association I take care of. That'll make you want to ride a mower in no time. :whistle:

O I forgot to throw in the word, acreage. :surprised:

Okay, okay, that's enough! :mdr: You know I just got called Mcconaughey again the other day when I was out of town believe it or not! :neutral:


If you want a battery suggestion, I would use the A123 15 or 20Ah prismatics, that is, if you weren't already thinking of using them.

http://www.cloudelectric.com/category_s/385.htm

There is a link to some DC motors that should work with a mower blade, there is a nice 24v 900watt unit that should be just right for the job, $150. IMO better than using a BL outrunner, all you need is a contactor, and probably more durable for sure, built for the type of duty.

Hmm, I was putting some thought back into my rc weedeater the other day.

Still set on using 2 outrunners with custom gearboxes for wheel drive. Setup like a zero turn mower, independent drive wheels on the back and swivel casters on the front.

Decided that a semi floating deck would be a good idea. My design has a central backbone chassis, and the deck would pivot off that in the center. The deck would have the ends cut off so the weedeater blades (plan to use those plastic blades that they sell to use on a weedeater) could stick out 2 inches or so. That way I can cut around trees, etc. The deck would have rollers on each corner so that it would remain at a fixed height, so no grass gouging.

I planned to use a stick radio, and have each stick control the rear wheels. So it would "feel" like my gravely zero turn.

I agree that worm drive would be nice, but making the gearbox to hold it all would be complex to say the least. My gearbox idea uses 4 gears riding on 3 shafts to get enough reduction to use a axi 2826 (660kv) outrunner with a 40 series mulcher tire to get around 5-10 mph. I plan to run 4s lipo as it fits the motor requirements and allows for cheaper escs. I would also use the gearbox as a stressed member of the chassis.

As for the blades I have a pair of axi 4130 outrunners that could be directly driven to power the blades. A pair of inexpensive air escs would be used for them, as they would be controlled by the 5th channel knob on my dx6 transmitter. Knob would give me variable speed as well. Might even set it up so I can switch off either side when just cutting down a fence line or around a tree?

This will be used primarily to weed eat around trees, poles, etc. So not as much as you plan Brian.