converting small pit bike from petrol to electric.

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Jessiedog1234567
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converting small pit bike from petrol to electric.

Post by Jessiedog1234567 » Sep 21, 2017 2:33 pm

I want to convert the pit bike shown or similar to electric so that my 10 -11 year old son son can ride it without disturbing the neighbourhood. There are kids electric motorbikes out there for sale ready made but they are all too small for him and a bit "toyish"
The pit bike is not very large, weight without engine is about 120lbs and he is not heavy . I have a few questions about the conversion.

1.) What sized motor wattage and voltage would be an ideal size to give it a good but safe turn of speed and make it perform well over cross country.I am thinking 48v 800w?

2.) Can I use a twist throttle and speed controller etc kit suitable for an electric bicycle/ quad bike obviously for this wattage.

3.) If I keep the rear wheel exactly as it is would an ideal sprocket on the motor be 14 tooth or should it be less or more?

4.) I plan on using a 48v 13ah lithium battery(suitable for an ebike) because of the smaller size/weight over lead acid. Should this battery have enough"whoomph" to drive this bike at a reasonable speed for the flat and cross country.
Thanks in advance

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Re: converting small pit bike from petrol to electric.

Post by Jessiedog1234567 » Sep 21, 2017 2:35 pm

pit bike (1).jpg
pit bike (1).jpg (39.85 KiB) Viewed 485 times
Sorry this is the sort of bike, its not very big.

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Re: converting small pit bike from petrol to electric.

Post by marty » Sep 21, 2017 4:14 pm

Jessiedog1234567 wrote:10 -11 year old son son
Recommend a bicycle with pedals. Safer and better exercise.
MARTY
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Re: converting small pit bike from petrol to electric.

Post by Jessiedog1234567 » Sep 21, 2017 4:46 pm

Thanks for that but that doesn't really answer my question.
He gets plenty of exercise playing rugby, football, cricket and athletics. He has asked me if I can put a scrambler together for him so he can have some fun on it. Really just need technical advice. Thanks

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Re: converting small pit bike from petrol to electric.

Post by e-beach » Sep 21, 2017 5:00 pm

Jessiedog1234567 wrote:I want to convert the pit bike shown or similar to electric so that my 10 -11 year old son son can ride it without disturbing the neighbourhood. There are kids electric motorbikes out there for sale ready made but they are all too small for him and a bit "toyish"
The pit bike is not very large, weight without engine is about 120lbs and he is not heavy . I have a few questions about the conversion.
If you trust your 11 year old son to ride around on a 30 mph bike, then put a motor on that bike. I would recommend a full face helmet as well.
Jessiedog1234567 wrote: 1.) What sized motor wattage and voltage would be an ideal size to give it a good but safe turn of speed and make it perform well over cross country.I am thinking 48v 800w?
120lbs is a lot of weight for a bicycle motor, however 48v 800 watt will get it moving around the neighborhood. I am not sure how you intend to put a motor on it and keep the breaking system intact as most motors are built for bicycles. Or if you go with a mid drive motor then you will have to get some custom mounting brackets for the motor. I always recommend putting the batteries in the "triangle" section of a bike for the best balance, so consider a custom battery mount where the ice motor now goes.
Jessiedog1234567 wrote: 2.) Can I use a twist throttle and speed controller etc kit suitable for an electric bicycle/ quad bike obviously for this wattage.
Yes. They will come with the kit if you buy a e-bike motor kit with a twist throttle.
Jessiedog1234567 wrote: 3.) If I keep the rear wheel exactly as it is would an ideal sprocket on the motor be 14 tooth or should it be less or more?
That depends on things like the electric motor torque, watts, and rpm. Since you will be building a one of a kind e-motorcycle you might have to experiment with the setup until you get it right.
Jessiedog1234567 wrote: 4.) I plan on using a 48v 13ah lithium battery(suitable for an ebike) because of the smaller size/weight over lead acid. Should this battery have enough"whoomph" to drive this bike at a reasonable speed for the flat and cross country.
Thanks in advance
Different lithium chemistry's give different "whoomph" results. RC lipo has relitive low cost and high energy release "C rating") but if mis-handled will burn your house down....literally. High discharge 18650's will give you a good "C" rate but can be pricey. LiFePO4 is one of he safest chemistry's, lasts a long time but has low "C" ratings.
If this is new information to you please do your research. Battery safety is super-super important. If a kid mis-handles his battery pack and it burns your house down you will be very sad! :cry:

https://endless-sphere.com/forums/viewt ... tery+fires

Also, most e-bike motors and kits are made to fit bicycles. You could build a good mountain bike into a good e-bike more easily then converting a motorcycle into an e-motorcycle. So I agree with the above suggestion. Leave the motorcycle as it is and build a good e-bike.

Edit:https://endless-sphere.com/w/index.php/Main_Page

Edit: Something like this might be an option as well....Razor MX650 17 MPH Steel Electric Dirt Rocket Motor Bike for Kids
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Re: converting small pit bike from petrol to electric.

Post by flat tire » Sep 21, 2017 5:14 pm

I think you need way more than 800W unless your son has never ridden a bike before. 800W will be RIDICULOUSLY boring. Regular pitbikes have around 10 times that much power from the gasoline engine and they are not that fast. Kids his age who race ride machines of the same weight with over 20 horsepower.

A hub motor like a cromotor would probably be adequate, of course then you need to spend decent bucks on a battery for it to have worthwhile range at good power.

Now, if you are unwilling to put more than 800 watts in the thing, forget aboutit and just get a bicycle. Much better platform for that power level and your son will have just as much fun, can ride ANYWHERE and not get hassled by law enforcement.
marty wrote:
Jessiedog1234567 wrote:10 -11 year old son son
Recommend a bicycle with pedals. Safer and better exercise.
Ha wow what a stupid suggestion. Moto is as safe as you make it and if you think it's not good exercise you've never ridden.
Orange DH w/ Cyclone mid on 6kw
Gary Fisher w/ Leaf hub on 6kw
RC Lipo and domino throttles only!

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Re: converting small pit bike from petrol to electric.

Post by SlowCo » Sep 21, 2017 5:30 pm

https://www.youtube.com/watch?v=BCKP_2Ndzjw

I have a 2016 model Kuberg Cross that I converted to off road mobility device for myself (adult, 80kg/178lbs). The new 2017 model has better rear suspension and is less 'toyish' than you might think. An upgrade from SLA to Li-Ion battery with a little more volts and Ah would be nice though:
https://www.kuberg.com/young-hero


https://www.youtube.com/watch?v=REeeYtp-8qE
Other great bikes would be the Oset 20.0 and 24.0 with a padded seat added. They are already with Lithium batteries and have more power and speed:
https://osetbikes.com/us/2017-oset-bike ... -0-racing/
https://osetbikes.com/us/2017-oset-bike ... -0-racing/
https://osetbikes.com/us/us-oset-latest ... available/

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Re: converting small pit bike from petrol to electric.

Post by Jessiedog1234567 » Sep 22, 2017 2:51 am

Thanks for your replies and concerns, appreciated. I haven't intended on him racing around at 30mph anywhere, I am aware of the dangers of any sort of quad/ motorbike etc. He already has a 1000w 48v electric quad that travels at about 30 kmh and so has had plenty of experience of handling such a vehicle. He already naturally has full faced helmet.The first thing I would install would be a speed restricter until he felt comfortable with it and to be honest all he wants to do is do some cross country but not necessarily fast.
Like wise I know a bit about batteries as my son has a powerful RC car that runs of Lipo batteries and so we know all about the dangers of those but good advice thanks
I had looked at the Kuberg bikes but to be honest they are too expensive but great and second hand ones are not available , the Razor 650 is not available in the UK.
I have a friend who is a qualified welder and so creating a plate or other sort of fixing plate for the motor should be no problem especially as the bike fixings have to hold a heavy engine anyway originally. The braking system would not be touched as the only change would be replacing the petrol motor with an electric motor in its place.
All the technical advice is really useful and I am taking that on board but with respect I don't really need the pros and cons of safety, health etc as I have taken all of those on board already. I just want to build a small electrically powered scramble bike for my son to have a bit of fun with in our back field , not to take part in competitions.
Thanks again.
Last edited by Jessiedog1234567 on Sep 22, 2017 3:09 am, edited 3 times in total.

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Re: converting small pit bike from petrol to electric.

Post by Jessiedog1234567 » Sep 22, 2017 2:58 am

PS. Sorry meant to add. An ebike might weigh 50-60 lbs including motor etc and then another 160-180 lbs with rider (220-240 lbs all in). This project would weigh in at about 180 lbs altogether including my son and so relatively the motor and battery etc would not have to cope with any more weight than an ebike, actually quite a bit less.

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Re: converting small pit bike from petrol to electric.

Post by amberwolf » Sep 22, 2017 5:08 am

How quick an acceleration are you looking for? Zippy? Or just pokey? Better than the quad gets?

If you're planning on a hubmotor, you can play with the http://ebikes.ca/simulator and different motors and power levels (batteries and controllers), and see what kind of torque levels you'll get out of them at different speeds, which can give you an idea of how quick acceleration would be, and give you some ideas of combinations you could use to get that.

If it's only 180lbs total rider&bike, then you could get fairly zippy acceleration with 2kW+.

As an example, I have a bike that weighs (with me on it) about twice what yours will, and has about 4kw, 2WD, and reaches 20MPH from a stop in around 4 seconds. That's a bit less than "zippy", but it's still a little fun.


I'd make a guess that it'll be more like 8-10 seconds to 20MPh, depending on torque level, at only 800w. If torque is low, or there's hills, it'll be even pokier. :/

I'm guessing the bike you want to convert has a wide rear axle, probably wider than the typical ebike motors will fit. There are motors (like the QSmotors in the for sale section here) that would probably fit, but you'll need to measure the distance between the dropouts to make sure you get one that fits. You'll also want to get one with wide enough spoke flanges to be able to lace it into the existing rim.


You could go with a motor that drives the chain to the rear wheel instead, mounted in the frame, but then there's less (or no) space for the battery in the frame, which is probably the best place for it (keeps it safer when it gets crashed now and then).


Sprocket size on the motor will depend on the max speed you want out of it (or max torque), and the speed the motor is wound for at the voltage you want to run it at, and the sprocket size on the rear, and the wheel size. Smaller sprockets get you more torque, larger ones get you more speed.

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Re: converting small pit bike from petrol to electric.

Post by SlowCo » Sep 22, 2017 9:32 am

An alternative could be to buy a cheap second hand electric scooter with a 10" hubmotor rear wheel and broken SLA batteries. For 10" rims there are good off road tires and you would have everything you need in one go (Hubmotor wheel, controller, wiring and throttle).

Although a bit toyish I still like the Velocifero and would have really wanted one when I was 11...:
http://www.ebay.co.uk/itm/1600W-48V-Ele ... Swll1Wyet-

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Re: converting small pit bike from petrol to electric.

Post by craiggor » Sep 22, 2017 11:35 am

Does it have to be a pit bike.You could fit Any kit to a BMX or 24" wheeled mountain bike.

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Re: converting small pit bike from petrol to electric.

Post by Jessiedog1234567 » Sep 22, 2017 12:30 pm

Thanks for those suggestions and advice guys. The quad he has at the moment weighs about 145 lbs and has a 48v 800w motor running off a lead acid battery (4 x 12v). With him on it it takes off fairly fast and reaches about 30 kmh in a very short time and so I assume that a bike weighing less would be about the same or a bit faster. On that count I will probably use an 800w motor to begin with and then move up to a 1000w at a later stage. The plan as mentioned before is to have the motor fixed to a plate in turn welded or bolted to the bike frame where the original petrol engine was. The motor is very much smaller than the engine and so there would be plenty of room for the lithium battery.

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Re: converting small pit bike from petrol to electric.

Post by tigcross » Sep 22, 2017 12:45 pm

hey there,

IT sounds like you are committed to the 800 watt motor mounted to the frame, and that will work fine. You're right, it's a pretty small motor.

Some considerations:
- unless the 800 watt motor has reduction gears built in, you will probably need a much bigger sprocket on the rear wheel.
-that bigger sprocket will effect your chain line, so best to calculate what size of sprocket you will need to run at the desired top speed, and do a cardboard mockup to check out the chain line.
-don't forget you will have regenerative breaking available to you on the rear wheel.

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Re: converting small pit bike from petrol to electric.

Post by flat tire » Sep 22, 2017 1:20 pm

Consider getting your son a legit bike and going to the local motocross track. It will be approximately 10,000 times more fun than riding a slow, terribly crappy chinese electrified pitbike around the neighborhood, and he'll actually have motorcycle skills as a result.
Orange DH w/ Cyclone mid on 6kw
Gary Fisher w/ Leaf hub on 6kw
RC Lipo and domino throttles only!

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Re: converting small pit bike from petrol to electric.

Post by Jessiedog1234567 » Sep 22, 2017 1:22 pm

Untitled.png
That is really interesting Tig cross, thanks. I am certainly going to use a motor fixed to the frame but are you saying that when the throttle is let go off the motor should act as a sort of brake? I had an old beaten up electric single seater golf buggy once that had that function and braked really well but I am not sure if it had a special motor for this, does any motor work that way?
I was planning on using a motor similar to image (not necessarily that one) I am assuming that being geared it has more torque? If i am using the same back wheel set up (not touching it) with a motor like this what sort of sprocket size/teeth on the motor should give a good mixture of torque and reasonable speed or is a question of trial and error? Thanks again

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Re: converting small pit bike from petrol to electric.

Post by e-beach » Sep 22, 2017 3:11 pm

Regenerative braking is a matter of your motor and controller setup. Check this out for info.
https://endless-sphere.com/forums/viewt ... f=2&t=7891

Why go for 800w if you are only going to up it 200w later? Just go for 1000w and control the speed via the return voltage on the throttle wire. An inline resistor that cuts the 5v return voltage down so the controller thinks that you are only going at partial throttle.

Also try PMing liveforphysics in the members section of the board. He has a lot of experience in the type of motor setup you are thinking about. He might have an idea or two for you.
https://endless-sphere.com/forums/membe ... ile&u=7638
LPF Death Bike.jpg
LPF Death Bike.jpg (155.64 KiB) Viewed 361 times
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Current build: Liahona w/ cheap front suspension and suspension seat post. Yescomusa 36v 800w generic front hub motor. 15ah Headway triangle mounted pack. Tronsung 30 amp,

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Re: converting small pit bike from petrol to electric.

Post by Dauntless » Sep 22, 2017 10:28 pm

I'm not convinced the bike you have pictured is any bigger or more solid than the mentioned mx650. I have those. If its tough enough for 200 pound me, I'm sure it'll hold up under a preteen.

As he gets used to it, you can think of a 48v upgrade, a bit of a challenge in that tight fit. The other prospect is using equipment that'll fit the Curries and going 1000w.

I feel sure he'll be happy for awhile with the MX, probably for as long as he would with your conversion.
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Re: converting small pit bike from petrol to electric.

Post by tigcross » Sep 22, 2017 10:29 pm

Hi Jessie,

so what you're looking at is a DC gearmotor motor, meaning it does have a reduction gear built in. I expect it's a5 to 1 reduction, meaning for every five times the motor turns completely the output shaft turns once. I see it is rated for 600 rpm, that's how fast the output shaft will turn if given a full 48 volts.

Almost all electric motors have the capacity to generate electricity, it's the controller that has to be able to support it.

You will need a simple DC speed controller, and if you want to take advantage of the regeneration feature you''ll need to get one that can handle re-gen.

As for the gearing, I'd try that motor with the stock rear sprocket and see if you get the torque and speed you're looking for. Finding a gear for the motor that matches the motorcycle chain you are using might be tricky, the sprocket that's on there is probably for #25, or #35 roller chain. Check out Stanton sprocket.
http://www.staton-inc.com

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Re: converting small pit bike from petrol to electric.

Post by Jessiedog1234567 » Sep 23, 2017 10:12 am

Thanks again guys , great info . Regarding the Razor 650, I live in the UK and it is oddly not available here although the smaller versions are.
Cheers James

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