The simplistic motor mount I made for my electric bicycle (which consisted mostly of me bolting a motor to my wire basket and holding the basket away from the axle with a piece of PVC pipe) had been working well for five months. Until, that is, I ran over a particularly large pothole and the chain fell off. I took the hint that the PVC pipe and wire basket were not exactly up to my exacting quality standards and decided it was time to make something better.
I decided that the main problem was that my wire basket was not rigid enough, so my construction material of choice remained 3/4″ schedule 40 PVC pipe. This time I used TWO upright supports, one on either side of the axle and some C shaped metal shelf brackets bolted to my motor mount. (I also used PVC elbows and pipe to join the top of the supports.) This picture gives a good view of how the whole thing fits together. I am still using a hose clamp connecting it to my wire basket for left-to-right stability, but this produces much less stress on the basket, and a little left-to-right wiggle is unlikely to allow the chain to come off the gears.
I basically cut wedges in the bottom of each upright so that I could bolt them to the outside of the axle, and then notches so that the C shaped pieces of metal would fit into the pipes (for greater support that the simple wood-screws that hold the metal into the notches).
The main stresses on the system is vertical tension on the two PVC support pipes when the motor is powered as it tries to pull itself towards the axle along the chain. The motor also pulls the whole mounting system back towards the basket of the bike due to the direction of rotation. I added a torque brace that connects the chain side upright to the front fork of the bike using more PVC pipe and a hose clamp. Although probably not strictly required, it does stiffen up the whole assembly.
The picture at the top of the page shows the whole assembly spray painted (black) with the vacuform motor cover installed. The mounting system is relatively light, only adding 1.4 lbs to my bike, but the motor itself clocks in at 4.6 lbs. At least it’s not adding rolling weight (with the exception of the extra sprocket and chain), so this is equivalent to around a 3lb hub motor. This new motor mount added $7.33 to the cost of my electric bike, but I still have 6 feet of 3/4″ schedule 40 PVC pipe for the next project. You can read more about my inexpensive solar charged ebike by clicking here.