I got a new trike a week ago and decided to motorize it with a 500w 24v electric wheelchair motor i had in the shed. Top speed is about 15mph and range is about 20 miles on a charge.
Step 1: Parts and Tools.
A trike! I got mine at the local wally world for around 250 USD.
Electric wheelchair motor with gearbox.
I like wheelchair motors because they usually have a gearbox on the motor that turns the output shaft 90 degrees. The gearbox also reduces the shaft speed down from 2500RPM to around 200RPM. This matches the speed of a bicyclist peddling so you can use the original bike gearing.
I used a rear sprocket off of a kids bike. Removing the sprocket from the coaster brake assembly was really easy. If you use a large sprocket you get more speed. I used a smaller sprocket so i can get massive torque to climb hills.
The motor i have is 24 volt. I used two 12v 50ah batteries for this project. Since the batteries are wired in a 24v configuration i have a 24v pack with 50ah of storage. The batteries i use are heavy but cheap lead acid batteries. Look for a local place that remanufactures batteries, it will cost much less.
Speed controller PWM.
I used this controller from Amazon. Speed controller link
It can provide a 1440w @ 24v and since the motor only pulls 500w it should hold up to the abuse i will put it through.
Circuit breaker or fuses.
FOR SAFETY! With this much storage capacity and amperage you want to be as safe as possible. I use a 50amp breaker placed between the battery packs.
Some 5 or 7 strand thermostat wire.
Use this to extend the wires on the speed control switch to make it reach the handlebars.
Wire and connectors.
You will need some thick wire to run the battery leads to the controller. Use wire connectors to hook everything up and make it look clean.
To keep wires in place and you can never have too many zip ties.
The tools required for this project will vary. If you have a cordless drill and a basic set of tools you should be good.
The only part that may be tricky for some people is welding the sprocket to the wheelchair motor hub. If you have a local mechanic, muffler shop, high school metal shop, or somewhere that has a welder just offer an employee 10 or 20 bucks to weld it. The job will take 10 minutes and they get some lunch money.
Step 2: Mounting the Motor
Figuring out how and where to mount the motor is always the hardest part. This new trike has a very wide rear fork. I managed to slip the motor right in and it lines up with the rear gear perfectly. The plates i used were the original mounting brackets from the wheelchair the motor came from. They are basically flat bits of aluminum with holes in them. The plates are bolted to the gearbox and then bolted to the bike frame.
Step 3: Making the Drive Sprocket and Connecting the Drive Chain.
The wheelchair motor i have came with a hub to mount to the original wheelchair wheel. On the end of the hub i welded a sprocket from a kids bicycle.
When you make this hub you need to make sure the sprocket is on straight so it does not wobble around when the motor is running or the chain will fall off. Take your time and do it right. Make sure the welds are strong.
Try putting the hub on the motor and powering the motor with a small battery. This will help position the sprocket before welding.
This setup deletes the front pedals from the drive chain. I have ordered a front sprocket with a freewheel clutch inside it so the pedals do not spin when the motor is running. I originally tried the setup with the front connected but it led to me getting my shins whacked every time i stopped peddling with the motor on.
This bike is a 7 speed and all the gears work. 1st gear only goes 5mph but will climb very steep hills. 7th gear tops out around 15 to 17mph. The multiple gears helps control speed, torque, and motor load/temp.
Step 4: Wiring Up the Electrics.
This is simple. the + and - from the battery pack go to the B+ and B- on the controller. Make sure + from the battery goes to B+ and the - from the battery goes to B- . If you reverse the polarity of the B+ and B- on the controller it will short out immediately and you will be placing another amazon order.
The speed control knob that comes with the board needs the wires lengthened so you can place it on the handlebars. Use the thermostat wire to lengthen the wire.
Connect the motor to the M+ and M- on the controller. The way my motor is placed in the bike i need to run the motor backwards. So i flipped the M+ and M- and it spins the correct direction.
Step 5: Battery Basket.
The two batteries i used fit perfectly in the basket only taking up the front half. I cut some plywood boards to place in the bottom of the basket and lined the basket with rag rugs from the dollar store. A little upholstery foam makes good padding for the sides of the batteries so they don't rattle around. All the battery weight is placed directly on the rear axle which helps with balance.
To cover the back half of the basket i got a board, drilled holes in the end of it, and zip tied it to the basket using the zip ties as the hinge.
Step 6: Stuff You Should Carry With You.
Trial and error goes hand in hand with building your own stuff. It is a good idea to keep some tools with you to fix the bike if you break down.
Most useful tool.
For undoing just about every nut and bolt on the bike.
Needle nose pliers.
For small stuff
Handy but not essential
For the motor mounting plate bolts.
Large adjustable pliers.
For rounding off nuts and bolts in fits of rage.
For cutting wires and zip tie tails.
Its tape! It fixes most things for 5 or so minutes.
Because tape cant fix everything.
Bike lock, Battery charger, Extension Cord.
To secure the bike and also recharge the battery where an outlet can be had.
Step 7: Accessories and a Ride.
You should always have lights on your bike. A bright headlight for the front and a blinking red light for the rear.
I have also added a short distance light to my handlebars because the streets in my area are really bad. The short range light helps me see bumps and holes.
Phone holder. This is great for installing an old phone for speed/mileage tracking and maps/navigation. I have an old S3 that i run Goodle maps on (download offline maps) and DigiHUD speedometer. They both use GPS to get location so no cell service is required. Maps are downloaded and updated on wifi.