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jimigunne 02-26-09 12:33 PM

Using a cordless drill for elctric bike conversion?
I think it should be possible to cheaply convert a mountain bike to electric with a Makita-type cordless drill. I checked ebay.... you can get a 18V drill, charger, and the new-type li-ion battery for 180.00. I am also thinking that you could use a cordless electric leaf-blower. I have seen simple designs where the motor and shaft are lowered onto the top of the wheel and held there by spring pressure. I think about 400 watts is needed, but i don't have a clue as to RPMs, torque, amperage drawn at cruise, etc. I know the knobby tire would have to be replaced with a smooth one. I am not sure how it would work out trying to remove the trigger/speed mechanism and remount on the handlebars. If anyone knows about this, and where I can get more info, please let me know.

daven1986 02-26-09 12:44 PM

I'm not sure but I don't think there will be enough torque, but I could be wrong.

Kingofgreens 02-26-09 12:56 PM

I have to agree. The motors used in a leaf blower were not built to handle heavy load. The drill motor can handle load but the RPMs will be a lot lower & if you try to gear it up, then you'll loose that torque.

jimigunne 02-26-09 01:43 PM

Well, you might be entirely right. Might need to employ a Dewalt 36 volt Li-ion battery pack and a 36 V motor. I can scratch-build a suitable MOSFET motor controller. But I lack the engineering background to figure out what RPM, torque, etc. is needed to drive a 26 in. wheel to 10 MPH or so. Also, you could greatly lessen the torque requirement by not engaging the drill/drive system until you have gotten the bike up to speed by pedal-power. Maybe in that case then, a Makita-type drill could handle the load?

karma 02-26-09 01:56 PM

cerewa 02-26-09 02:10 PM

The amount of thrust (forward force) you need in order to match a typical hub motor is something in the realm of 12 pounds to 20 pounds.

If you're talking about a motor built in to a 24 inch wheel, that should translate to 12 foot-pounds to 20 foot-pounds of torque. (because the radius of the wheel is one foot).

If you're talking about a motor with a friction drive system, driving a small friction-wheel, 2 inches in diameter, divide by 12 to find the foot pounds required but multiply by 12 to find the RPMs required.
if the small friction wheel is 1 inch in diameter, you'd divide by 24 to find the foot pounds required and multiply by 24 to find the RPMs required.

RPMs needed:
26" wheel at 10mph : wheel turns 129RPM
24" wheel at 10mph : wheel turns 140RPM

if you double the miles per hour, double the RPMs.

JinbaIttai 02-26-09 09:50 PM

FWIW, motors already designed just for ebikes are relatively inexpensive. By far the most expensive component will be the Lithium/NiMH/NiCad batteries. Going through the trouble of engineering a motor to work for your bike won't save you all that much money. Unless you're doing it for fun or using free stuff you already have, I'd buy an ebike motor for like $100 and piece together everything else.

kiwichris 02-27-09 05:05 AM

true that^

although there it's saying something to ride around with a drill stickin outa the back powering you along. :thumb:

safe 02-27-09 08:03 AM

Buy it.

Bolt it.

Use it.


jimigunne 02-28-09 05:50 AM

Well, the divide by 12, multiply by 12 rule you give, I guess, would only be valid for a certain size wheel....and my mountain bikes are 26 in. not 24. Are you referencing this to a 24 in. wheel? Also, the torque needed is going to be dependent on size/weight of the rider. Is that 20 ft-lbs figure sufficient for say a 200 lb rider assuming the motor is going to accelerate bike from a stop? Once I know what the max torque needed is, then I can figure out what the max amps required is, and build a controller of the appropriate rating. Motor hub conversion kits are expensive. I can mount a motor on a plate that rotates to drive the front wheel (I have rear racks/panniers on back wheel) and power with drill batteries like Dewalt for less, I think.

GeoffMarshall 02-28-09 09:37 AM

Motor Kit
You can get a complete electric bike motor kit with wheel and 36 V Lithium battery here:

raypsi 03-09-09 08:58 AM

I made my own electric bike conversion, I used a 3 inch grindstone mounted on an arbor shaft, mounted that to the front fork and directly drove the knobby tire with it. that gave me like 3:26 ratio to the motor. Top speed at 12.6vdc 15 mph, at about 1600rpm on the motor. If you go with a smaller drive like 2inch then the rpm will have to go up to increase the speed mph. And distance you can travel on a charge won't change no matter what, just the speed changes with the ratio of drive. I don't know if a cordless drill motor will get up to 1600 rpm.

I didn't have a controller. That's full speed on the motor only control was on or off. I had to pedal up to speed because it sux the power at low speed. And a momentary on off switch on the handle bars.

I found that 3 inch diameter drive is the best for a 26inch mountain tire.

Bottom line is a drill will only get 500RPM way to slow to drive the wheel, top speed would be like 5 MPH. you'd have to run a sprocket setup to the crank

24X18 04-20-09 02:57 AM

That's kinky--!!
First off..the electric drill wouldn't last 2-minutes..
and the Leaf Blower "shaft" would break off on torque..
You could try those things..
But they really won't last more than a second--/

rbelcher 04-05-10 06:24 PM

Sorry to bump this older thread, but I just found it and it's too cool. I love cordless drills and I love electric bikes and cars.

Looking at the Milwaukee V28 cordless drill you get 600 in-lbs of torque (50 ft-lbs) and 600 RPMs (on the low speed setting). So according to the calculations above that should be enough. The V28 system is the best I've found for price/power/weight.

The price is $365 at Amazon, but you get two batteries. I'm not sure how that would compare to the bike conversion kits around, probably about even I would guess.

But if you could find a V28 with a broken clutch, chuck, trigger or whatever, then you may have something more economical.

Azreal911 04-06-10 10:43 AM

I've looked at most of the drills in the store and it seems like all of them are on brushed motors. So with that the motor isn't going to last that long under such a constant heavy resistance to move an entire bike. Plus most of the bike kits out there nowadays are brushless, meaning you'll get alot more mileage on it before it dies. With a brushed motor you'll have to grind off a layer of that copper core shaft (after racking some miles on it) if you want to keep it a close efficiency as the brushless else there's even more power loss.

I've learned most of this from my RC car days playing with brushed motors and it got expensive even with my own truing machine carefully grinding my commutator.

rbelcher 04-12-10 09:12 AM

That's a good point. The only brushless cordless drills I know of are Festools and they're way too expensive to be taking apart to put in bikes.

But still I think if you got a V28 or even a good 18V model on the cheap because something else was wrong with the drill, it would make a good DIY project. Good quality cordless drills, even with brushed motors, will last quite a while.

GTALuigi 12-23-10 06:47 AM

did anyone seen this video ?

some one actually made it

there are a lot of great application for it.

and replacement batteries are affordable & easy to find on any hardware store :D

now if he could make it work by having the drill on the handle bar, then that will be even better, that way you can just accelerate or deaccelerate from the drill button itself :)

ariel cyclone 05-04-11 07:48 AM Sandy's BOSCH " BRUTE , 36 volt CORDLESS DRILL E - BIKE :





brianofvan 11-04-11 10:17 PM

Bosch and Hitachi and Makita also have new brushless cordless drills now. I saw a Makita for 1/4 the price of the Festool. My plan is to mount a freewheeling rear cluster on a 1/2" drive under the seat with a chain to the large front sprocket and leave the normal chain to the rear cluster on the two smaller sprockets. Thats 10 lowest speeds and it will free wheel when off. Then I'll own a new drill and a (slow) e-bike too. I'm disabled in the breathing department; there's a couple of low hills 'tween my house and the village. In calculation, the front crank does 60rpm.

brianofvan 11-04-11 11:25 PM

Slow is really good in my situation. 6mph is fast for me. and maybe you haven't met the torque of the new drills; they're like 50% everything better. And they're cheap like pasta. I don't think you can get a watt of lithium cheaper and the new brushless is so torquey. I don't want to do wheelies, I just need 4 minutes help up the hill. It's like a wheelchair.(that I can afford).
But thanks for responding. I'll think of a way to test it. Thanks again

christ0ph 11-11-11 01:04 PM

I don't know how durable the nylon gears in many power tools are but the economics of scale aspect does make total sense, and I can easily see how it might be possible to leverage the extremely affordable parts in a commodity product like an electric drill for transportation. People do it with other COTS products all the time. For example, a lot of consumer neworking products like wireless routers are basically very cheap, low powered computers and many of them are "hacked" almost as soon as they are released to have additional capabilities or do new things. I always try to buy products that have that kind of flexibility because you get much more value. For example, my wireless router running Linux based firmware is flexible enough to use it in a lot of different ways that until recently you had to spend at least $300 to get in a commercial router. Any manufacturer who made a drill that was easily harnessed for other tasks would sell a lot more of them, and batteries, too.

A series of legal decisions established the rights of people who own a product to modify it in any way they want.

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