Small ATV Gasoline -> Electric conversion
 

ERRR. I just closed the tab that I had this post made up on.
As a result, I'll be splitting this post in to several so I don't bone it up again.

I picked up a small china built 100cc gasoline children's ATV at a scrap yard with the intention of converting it to EV as a birthday present for a particularly small 7 year old boy.

http://farm9.staticflickr.com/8436/7...139ef89a_c.jpg

On disassembly I discovered that the motor had been previously dissembled and was obviously crap + shot. I did however find some nice features like hydraulic disc brakes and fluid fluid shock absorbers. Fairly ideal for the purpose.

I figured since it had a 100 cc motor previously it would likely need a fairly serious electric motor to do the stuff that little boys like to do on 4 wheelers.

I decided on a 1000 watt scooter motor and figured it should get about 1 hp to the ground. I picked a 48 volt version up from an online retailer and waited for it to arrive (today)

http://farm8.staticflickr.com/7122/7...c1d5a14d_c.jpg

I opted to wait until I received the motor to purchase a small sprocket due to lack of specs (shaft size / RPM range). So I hooked it up to my EV boat battery pack (also 48 volts) while in my vise only to have it fly out immediately, this thing has serious 0 RPM power! I re-clamped and continued testing with my "digital" optical tachometer. I got 6570 RPM no load at 48 volts (probably more like 52 volts) and 3240 RPM no load at 24 volts (probably more like 26). From that I guessed that I'd have about 3000 RPM at max load / power.
I also measured the Tire circumference to be 42" and the driven sprocket has 36 teeth.
From there I calculated that with the smallest ANSI 41 sprocket available (6 tooth) I should see 20 mph@ 3000 rpm, faster than desired, but slowest easily available gear ratio.

Batteries.
Not knowing the size of the motor I decided to wait until I had it in hand to choose batteries. As luck would have it the mail dropped off 2 18ah SLA's for an unrelated project just after UPS dropped off the motor + controller + throttle. They fit rather well and I guess now I need 4 more.


Forward 2
http://farm9.staticflickr.com/8306/7...2653a75f_c.jpg

Rear 2
http://farm9.staticflickr.com/8304/7...ecd33439_c.jpg

Sprockets are easy enough to come by for the rear wheel if you need to slow it down. Or, you can limit throttle input using the controller in most cases. Or just physically limit throttle until you're comfortable with above mentioned particularly small child giving it "everything".

When we bought my son a JD electric tractor, we limited him to 1st speed operation for all of 20 minutes before I was comfortable with him steering, etc. He now uses 1st speed for intricate maneuvers and 2nd speed for general operation. Talented 3 year old, he is.

Cost specs for this project would be nice, if you don't mind.

4 wheeler $30
Motor + Controller $150
Batteries ~$150
Sprocket $6

He has already had several plastic Powerwheels type toys ( Bumper car (~1 year old)John Deer tractor (2 ish), plastic 4 wheeler (4 ish), and now a proper framed 4 wheeler with 350 watt motor (about 15 mph max), but it isn't quite enough in the oomph department to give some real driving dynamics.

Any source for bolt to flange (I don't know the name) Sprockets would be highly appreciated.

try mc-mastercar

Northern Tool also has sprockets and hubs for go carts that they sell.

Make sure that the batteries are sized to handle the load, otherwise you are going to go thru batteries pretty quick, an hour of run time is almost what you want to aim for to get a slow enough discharge rate, also remember not to run your batteries dead or you will wear them out faster as well, gel batteries are a bit more forgiving but still don't like to be run dead.

If this was a 4 wheeler for an adult, I would say get lithium batteries right off, as the price of them is dropping so much it's worth it.

Took MY first ride today, basically just welded up a motor bracket + battery box.
Performance with an overweight adult is adequate, I'll have to add a pot for child use.
Also need to add a chain idler as my mounting didn't work out quite as planned (slight rubbing).

Any cheap ideas on adding reverse?