EZM Powered Trailer with Electronic Brake

[bodged bikes]

Here is my latest project: an EZM powered trailer with an electronically controlled, servo operated brake. The primary goal of this build was to motorize one of my road bikes with minimal modification to the bike. This trailer can be disconnected from the bike in less than a minute; leaving only the control box and a portion of the throttle cable behind.

Trailer Details:
The trailer frame is made from 16ga, 3/4", square tubing. The 1" square tubes that connect to the bike pivot at the trailer end on 3/8" bearings and at the bike with 10mm rod ends. The bike's rear hub quick release axle was replaced with a longer length of 10x1 threaded rod that holds a washer, nut, rod end, and lock nut on each side.

The rear wheel is a 20" BMX rim laced to a Shimano disc hub. A King's 39 tooth sprocket is bolted directly to the hub. The tire is a 1-1/2" wide high pressure type normally used on recumbent bikes.

Control Details:
The throttle is made from a Shimano front shifter with the release lever cut off and the ratchet pawl removed. To increase the amount of cable pulled by the modified shifter, a road lever-to-direct pull brake adapter is used (see the pulley on the side of the control box in the photo). I made a quick disconnect for the throttle cable from a 2 part key ring. The tight bend in the throttle cable at the carburetor is made with a brake noodle.

The control box for the brake is attached to the bottle mounts on the down tube. The box contains the servo controller, battery, switch, and an adjustment knob to set the resting position of the servo. The maximum braking force applied by the servo is set low enough to ensure the wheel will not skid.


Some pictures of the trailer:

 

[bodged bikes]

Some pictures of the controls:

 

[srdavo]

Mighty crafty design!!!

I like it.

 

[MotoMagz]

Nice and clean...very cool

 

[KilroyCD]

It's a nice looking design that looks well executed. Please let us know how it drives. However, I have a question regarding the rear sprocket. I'm basing this question on my experiences with the same drive on a 26" bike, not driving a 20" wheel like yours. Have you tested it with that sprocket? I'm just wondering if the 39-tooth sprocket might be too small. The drive has tall gearing to begin with. On my bike I originally started out with a 48-tooth rear sprocket, and I had virtually no accelleration to speak of. In fact, I went almost nowhere. It was just geared too high with that size sprocket and a 26" wheel. I'm running a 64-tooth sprocket now that allows me to cruise easily at 30mph, plus a friend (who weighs much less than I) took the bike to 40mph. With that drive, usually bigger is better. What are your findings?

 

[bodged bikes]

I'm just wondering if the 39-tooth sprocket might be too small. The drive has tall gearing to begin with.

The drive kit came with a 56 tooth sprocket. Scaling the sprocket down from a 26" wheel to a 20" wheel works out to be 43 teeth. I chose to start with 39 teeth because I pedal assist most of the time. As it is, the maximum speed is 30mph under engine power alone on a flat road. However, I do plan to increase the sprocket size to allow the engine to rev a little higher. I will probably try 43 teeth next. That will add about 500 rpm at 30mph.

 

[Quenton Guenther]

Fantastic design!

Really clean looking.


Have fun,