Do It Yourself Cheap and Easy Electric Bike

So, you want an electric bike but you don't want to spend a thousand bucks? Good news. It's pretty easy to convert any bike to an electric bike for well under $200. Depending on how much miscellaneous hardware you have on hand, and how much you shop around, it could be built for much less.
I was inspired by the concept shown on www.thestuffwebuild.com . It outlines a simple and cheap e-bike conversion that works great for his Trek bike. Unfortunately, it doesn't work at all on my particular bike.
He mounted the motor on the front fork and made it a front wheel drive.  But, there was no way I could make it fit the same way on my economy model Walmart mountain bike. So, with a little tinkering, I was able to do basically the same trick by mounting the motor on a seat post mounted luggage rack as a rear wheel drive instead.
It works great. The area where I live has a lot of steep hills. Putting a motor on my bike made using it as a commuter vehicle not only possible, but a blast.
I'll show you every step of the process I went through and hopefully save you some of the time and aggravation I went through to get a working design.

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The advantage of attaching the motor and batteries to a rear luggage rack is that you can easily remove the entire unit from the bike in just a few seconds.

Handlebar cam of my first test drive. Still a couple of bugs to work out...

First time hooking up all the electronics:

This is a Friction Drive setup, meaning that the power is transferred to the bike's rear wheel by the friction between a spinning drive wheel pressed against the tire.
The friction drive wheel is just an ordinary skateboard wheel. That was easy to get at a local skate shop. Another part is required to connect the skateboard wheel to the motor shaft, and unfortunately it isn't an easy item to find in a typical hardware store. It's called a motor arbor and it looks like this:

The barrel section with the set screws fits over the motor shaft and the skateboard wheel is tightened between the two washers on the threaded section. Here's a diagram if that isn't clear:

TINKERING NOTICE: YOU WILL PROBABLY HAVE TO FABRICATE A SPACER BETWEEN THE MOTOR SHAFT OUTSIDE DIAMETER AND THE INSIDE DIAMETER OF THE BARREL SECTION OF THE MOTOR ARBOR.
The motor shaft outside diameter is 8mm. The inside diameter of the barrel section most commonly available is 1/2".

The motor I ordered was intended as a replacement part for a motorized scooter, so it had a threaded section and a chain sprocket on it. Obviously, you'll have to remove the sprocket. The motor I received had a reverse thread, so pay attention when removing the sprocket. I got a head start on the spacer because there was a sleeve already provided on the shaft. The outside diameter of the sleeve was just a hair larger than 1/2", but I was able to file it down to make a tight fitting spacer for the motor arbor.
Once you get a tight fit between the motor shaft and the motor arbor, use loctite on the setscrews to make sure it doesn't work loose.

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Once you get the skateboard wheel firmly fastened to the motor, here's how I put the drive unit together:

I tried my best to make all these illustrations and descriptions self explanatory. If anything isn't clear please leave a comment on the blog: http://diy-ebike.webs.com/apps/blog/

Photograph from the motor side of the assembled unit.

Photograph from the skateboard wheel side of the assembled unit

Anti-Rotation Brace
Once you have the motor fastened to the rack, you'll need some kind of brace to prevent the drive unit from twisting on the seat post. Below are photographs from different angles to show what I came up with for my particular bike.
At this point you're on your own. Every bike is going to require a unique solution to this problem.

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Now put the electronics in the plastic box and tie it down tight to the rack.

I used old network cable I had around to tie the batteries down to the rack. That effectively locked it into one rock solid unit I can lift off the bike to carry inside to charge the batteries.

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Here's a list of the parts I used and where I got them:

Schwinn Multi-Purpose
Premium Rack
This is the foundation of the assembly. I got mine at Walmart for about $15.
1 -1/4" u bolts. You'll need 2 of these. I got them at Home Depot for about $1.50 each.
24 volt 300 watt motor, controller and throttle kit.
I got this kit on monsterscooterparts.com
I saved money by ordering on black Friday. The normal price is $89.99, but I got 15% off. This is a very good supplier to order parts from. The shipping is fast, the prices are reasonable and the phone support is good. They run discount specials often, so you can save a lot of money if you watch the site.
Two 12 volt batteries connected in series to provide 24 volts to the motor. There are many options when it comes to your decision on what batteries to buy. I bought 10 amp hour batteries because my commute to work is about 6 miles. Generally speaking, on flat ground you get about one mile of distance per amp hour. It depends a lot on how much you help out by pedaling, how much hill climbing happens, etc. I got this battery kit on monsterscooterparts.com. It ordinarily is about $50, but again, watch for discount specials. You can cut back on that cost by getting lower amp hour rating if you just intend to cruise around for a few miles.
Battery Charger
These are available on Ebay for around $10.
Charger socket
About $5
Motor Arbor
These are all over Ebay and Amazon for $5 to $10.
Skateboard wheel
You only need one, and it doesn't have to be perfect and new, just reasonably round. I got a leftover one at a local skateshop for a couple of bucks.

One on / off switch.

I got this at Home Depot for about $3

Miscellaneous items:
A small piece of 3/4" plywood (at least 5" x 24").

A plastic box to hold the electronics. If you don't have one lurking in the back of a closet they're only about a buck.

1/4 bolts, nuts and washers.

Some kind of 12 volt connector to connect the throttle to the drive unit. (I used a trailer light hookup)

I had all this stuff already in my junk hoard. I guess it would be five or ten bucks if you buy them.

Total cost:
Rack ............................. $15
Motor kit ...................... $80
Batteries ....................... $50 +/-
Charger ........................ $12 +/-
Motor Arbor ................. $8 +/-
Skateboard wheel ........ $2 +/-
Switch ......................... $3 +/-
Misc. ............................ $10 
Total ............................ $180
By shopping around on Ebay you could no doubt save quite a bit on each of these items.

Project notes

The size of the 3/4" plywood mounting platform for the motor isn't critical. It would be a good idea to wait until you have all the parts before you cut it, just to make sure there is enough distance from the center line of the rack (also the center line of the u bolt mounting holes) to the mounting holes of the motor. That distance depends on the final assembled dimension from the center line of the skateboard wheel (also the center line of the rack and the rear tire of your bike) to the face of the motor.


I got thrown a curve because the motor arbor I got was very different from the illustration on the Ebay listing where I bought it. I ended up having to shorten the motor shaft with a hacksaw to get a good connection because the arbor socket was too shallow.


You'll need to drill out the holes on the motor bracket before 1/4" bolts will fit. Use a 2 x 4 or something under the bracket as a support before drilling, like this:

just holding the motor and drilling out the existing holes might lead to the drill bit causing unfortunate scars on you motor like this:
oh well, no damage, just aggravation.

<---- This photo shows how I tied the batteries down to the rack. I punched some holes in the bottom of the plastic box to allow the tie down wires to wrap around the rack. Perhaps a better solution would be to use a small ratchet strap. Just make sure the batteries are very firmly attached to the rack. Otherwise mounting and removing the drive unit from the bike is very cumbersome.










Spend however much time is necessary to get a solid concentric fit between the skateboard wheel and the motor shaft. If the skateboard wheel wobbles at all it causes extreme wear on the motor bearings.


I put grip tape around the wheel to help it maintain a solid grip on the back tire. I got the stuff sold by Home Depot intended for outdoor use on steps and ladder treads.

It is still sticking tight after several miles.


The rear tire of my bike had a row of knobs down the center that would have caused a problem with the drive wheel bouncing and loosing contact with the tire.

Rather than buying a hybrid tire with a smooth strip down the center, I just sliced off the center knobs with a razor knife. It didn't hurt the tire a bit, and actually helped smooth out the ride when I'm not using the motor.

I never ride off-road anyway.




The rack came with a variety of spacers to provide a tight fit to the seat post. I only kept the largest one, and the only reason for it is to prevent metal to metal contact and scratching. It's important to allow the rack to have some freedom of movement up and down so the weight of the motor and batteries help the skateboard wheel keep pressure on the bike tire. Also, it makes it very easy to remove the whole unit from the bike.






Another idea I had before going with the plywood brace was bolting a pair of pipes to the frame just below the seat post that would extend up at an angle.

I didn't do that because I didn't want to drill additional holes through my frame. Also, I already had had some plywood on hand.


Make sure this brace has good stability side to side. It is important to keep the rack lined up solidly with the rear tire.


My brace is held in place by a single quarter inch bolt, so removing it only takes a minute.


I think something similar should work on most bikes. I had a perfectly positioned hole through a brace on my frame to fasten it down. Lacking that, it would pretty easy to install the same arrangement with a couple of small u bolts.














There are probably better things  than a trailer light connector for the purpose of connecting the throttle wires, but I had one in my junk pile.










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