Electric Recumbent? Is That Really Possible?
Introduction: Electric Recumbent? Is That Really Possible?
I love cycling, but the hills around my town are punitive. Electric bikes are getting more popular and I became motivated to add some electrical power to my recumbent bike.
Researching the possibilities, I mostly found kits for regular bikes. Not much out there for recumbents. But I settled on a motor and controller kit that, although designed for regular bikes, seemed well reviewed and could be flexible enough to be mounted on my frame.
This Instructable is not a step by step instruction, but rather details some of the challenges I faced. I hope it may provide a useful reference for anyone trying a similar conversion. At the end of this Instructable is a list of links to the parts I bought.
Step 1: ORIGINAL BIKE
My recumbent was manufactured by BikeE, a company which built a lot of these bikes, then failed in the early 2000’s. The drive train is unusual. It has a single drive sprocket at the crank, with an 8 sprocket rear cluster, and a three speed internal hub in the rear axle. This gives it 24 speeds. The bike is very comfortable to ride, like sitting in a lawn chair. But even with 24 speeds, climbing hills is hard, as you can not stand up and put your weight into the pedals.
The frame is a rectangular aluminum tube. It's reasonably rigid for riding, but if you try to clamp onto it tightly it compresses and threatens to collapse. This presented a more of a challenge than expected.
Step 2: THE KIT
The ebike conversion kit I bought is designed to be mounted at the rear axle of a single speed bike, next to the chain sprocket. 668
This requires an overrunning clutch (sometimes called a freeewheel) to allow both the peddler and the motor to drive the rear wheel without interfering with each other.
Definition: An overrunning clutch transmits torque in one direction only and permits the driven shaft of a machine to freewheel, or keep on rotating when the driver is stopped. On bicycles, such clutches permit the rider to coast without moving the pedals.
The first problem I discovered when the kit arrived was that the chain and clutch/sprocket provided were something other than standard 3/32” bicycle chain. This sent me to the web to buy the correct parts. I needed an overrunning clutch with sprocket for 3/32" chain, and a length of that chain.
Step 3: MOUNTING THE MOTOR
Here I try to explain how I managed to mount the motor onto the aluminum frame without squashing it. The main rail looks sturdy, but it is actually thin folded aluminum. The first picture shows my plan for clamping tightly on the frame.
I started with two steel fence “L” brackets from Home Depot. I drilled some holes to attach the motor to one and cut off the “L” on the other. Then using 4 ¼-20 bolts in new holes, I clamped the main bike rail between the plates. To prevent collapsing the rail, I inserted spacers onto the bolts through oversize holes on the left side of the rail, then clamped the left plate against those spacers. The spacers were cut so they are just under sized for the width of the rail. When it is all assembled, the mounting plates are tight against the spacers on both sides, and the main rail is only slightly compressed. Since the holes in the right side of the rail are still ¼”, the spacers and bracket on the right side also clamps the right side of the rail between them.
Here are the steps I took to ensure all the holes in the brackets and in the rails were aligned correctly:
* Clamped the two brackets together off the bike and drilled four ¼ inch holes through both plates.
* Temporarily clamped the plate with the motor onto the bike rail and adjusted its position so the chain was not too tight or loose. Then marked that position on the rail.
* Without motor, clamped both plates to the rail, adjusting them by eye to be aligned.
* Drilled the 4 holes in each plate using the ¼ inch holes as guides.
* Removed the plates, and enlarged the holes only on the left side of the rail so the spacers could slide in.
* I bolted it all together using 1/4x20 bolts and Nyloc nuts so that they wouldn’t rattle loose over time.
Step 4: THE DRIVE SYSTEM
As shown in the images, the motor is mounted near the front sprocket, forming a mid-drive solution. This has the significant advantage that by driving the crank arm, the motor and the rider both have use of all 24 gears. 226