# Reasonable design?



## erikg (Feb 21, 2012)

Hi, everyone;

I'm new here, and I want to say I've enjoyed reading all the stories about EV conversions. It's great to see that do-it-yourself innovation is alive and well, at least in cities with less restrictive laws that the one I live in 

That said, I'm planning on doing some work on a small EV in my home shop with the doors closed... I've got enough space to build a go-kart sized vehicle, or a small garden tractor.

I'm trying to do a build as cheaply as possible using mostly salvaged parts. I am not expecting super performance. What I'm hoping for is a four wheel drive skid steer type tractor.

What I have to work with are parts salvaged from a set of floor scrubbers I bought at an auction.

Parts include:

2x 24volt curtis controllers, model 1208

2x 3/4 horsepower 24vDC PM motors

2x 1/3 horsepower 24vDC PM motors tied to gearbox/transaxle set-ups and axles.

2x vacuum motors (from the wet/dry vac portion of the scrubbers)

2x brush gearboxes, driving 2 200 rpm brushes from a single shaft input/worm gear setup. Designed for up to 3 hp input.

2 sets of 6 volt x4 (24v pack) trojan deep cycle batteries

2 24volt chargers

Lots of cables, switches, vacuum hoses, etc.


What I want to do is buy a set of 4x 15" rototiller type wheels and tires, weld together a frame set up so that all four are on bearing supported half shafts with a sprocket on each, and use the brush drive gearboxes with the 3/4 horse motors to make each side (left/right) turn in sync via short chain runs. I could adjust sprocket size a little to tweak gear ratio as needed.

Then I'd set up the motor controllers with joystick input, one joystick per side, with a seat in between. One four battery 24v pack for power mounted low in the frame (that should give me about 300amp-hours of power at the 20 hour rate).

Running the motors with the joysticks should let me skid steer, and at 200 rpm I should move about 2-3 mph, which is plenty. The curtis controller will allow a pot with a knob to adjust overall speed limits, and it has safety features and soft start, so that should be easy to work with.

My question is, is this a sort of reasonable plan? I'm not expecting the final tractor to move mountains, I'd just like it to move carrying me and with enough extra force to push a simple blade for scraping and pull a wagon full of dirt or a lawn roller.

I saw online that one guy selling plans for a backhoe and tractor made one work with a single 1.5 hp motor here:
http://www.youtube.com/watch?v=knCmpSplxow&feature=channel

Something with that level of performance is fine with me.

Opinions on this idea are requested.

Thanks,
Erik


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## Woodsmith (Jun 5, 2008)

Sounds like a plan!

Hi and welcome.

If you click on the 'Me Wee Beastie thread' link in my sig you will see my tractor project. It sorta grew a bit over time.

Your plan sounds good and you seem to have the right starting point, two of everything.
The rest is much easier to find on a small budget to make it work.

If you can set up a 'wigwag' joystick control then you can have forward and reverse on each joystick with a return to centre off position. You can then turn on the spot.

It is a good learning curve as there is nothing too complicated about the electrical aspects and the rest is mechanical work.

Good luck with it.


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## erikg (Feb 21, 2012)

Yep, I took a good look through your tractor thread, looks really nice. I admire your ability to do tasks by hand that I'd only attempt with a big machine myself 


One more point I forgot to add on to my ideas above... since I have more than one controller and more than two motors, would it make any sense to try to use one motor per wheel? Put the right side motors on one controlller and the left side on the other, then I could skip the mechanical linkage between the half axles and I'd get 3 hp total?

Assuming the controller could handle the additional draw (looks like they can) would the motors sharing a controller sync up well enough to work this way?

Erik


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## Woodsmith (Jun 5, 2008)

I would guess that if you had four matching motors you could have two motors per controller but not if the pairs didn't match.

I think I would work with one motor per side. Use the motor to connect directly to a wheel and then a chain or toothed belt to the other wheel on that side.
The motorised wheel could be fixed to the chassis and the chain driven one on a moveable mount for tensioning the chain.
The chain could be outboard of the chassis and the sprockets could be bolted directly to the hubs behind the wheel mounting. That reduces the components required to get the drive to all the wheels.

How big do you want the vehicle to be? What you can do will depend on the size of the vehicle. Too small and space is an issue, too big and weight may be too much for the motors/controllers.

Mine was supposed to be ride on garden mower size and is now compact tractor size!


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## erikg (Feb 21, 2012)

Basically, I'm going to build as large as needed to fit the motors, batteries, and drive train, then put a seat on top and a roll bar/cage.

If I go with the 3/4 hp motors in two pairs and two controllers, that means I'll need four of the 6 volt batteries I've got mounted on the chassis centerline or under my seat, the two controllers somewhere they can get cooled, plus enough structure to support it all. 

Assuming all that, I'd use a steel box for a base, reinforced with welded tubing and/or angle. Probably about 2.5-3 or so feet wide and 4-5 feet long, with the axles as far forward and back as possible. Motors mounted above each half axle with a short chain loop connecting them. 

Probably I'd have the steel box be the main support for the thing... I'd probably use 1/4 inch plate, and weld on strips for the sides about 4-5 inches high. I'd reinforce those with 3/8 plate where the axles pass through, plus reinforce across the length and width of the bottom with tubing welded in a # shape to prevent flexing. Suspension would have to come from the tires, no springs or shocks. Reinforcement points at front and back also for mounting tools.

I'd install the motors and axles first, then mount the batteries and do the wiring for them and the controllers, then do a seat mount with the joysticks. Finally I'd weld on a roll bar and some kind of sheet metal or fiberglass housing to cover the batteries and controllers, and a simple dashboard for status info on the controllers and batteries, and a key.

Of course, all this depends on the size of motors I use. I did find a matched pair of 3/4 hp motors, so that's one side. I have another 3/4 hp that I'm hoping to find a match for, otherwise I may have to go with a matched 1 hp pair... uneven power, but as long as they're on the same side it should work.

I haven't figured out the weight of the proposed idea above, this is the first time I've dumped it out of my head. I wouldn't be surprised at all if it's 500-600 lbs of stuff not counting 250 lbs of batteries and 300(ish) lbs of me. That's a lot to move and still get work done.

I'm also looking for forklift type motors... if I can find a pair of 3-4 kw (about 4-5 hp) motors locally then I can use them with gearboxes and not worry about weight so much.

Erik


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