Hybrid Human-Electric Bicycle Testbed

This is one of test setups I used to test the efficiency of the Motor and Generator that I'm planning to use on my Hybrid Human-Electric Bicycle.
I built a driveshaft coupler out of a piece of clear plastic tubing and a couple hoseclamps. This worked ok at 36volts, however when I tried going to 60 volts the unbalanced coupler caused so much vibration that it tore apart. :-(
The 55000 mfd Capacitor smooths out the pulsating DC created by the generator. The 10 ohm wirewound resistor provides a load for the generator.

These are the results from the test:

This indicates an overall efficiency of about 64% or somewhere around 80% efficiency each.
note: both the drive motor and the generator were operating at far below their power rating. When run at peak power the efficiency should improve.

Latest Update
I built a driveshaft coupler using some Automotive type rubber tubing, the real thick stuff that's reenforced. I also used four hose clamps, arranged so that they are ballanced, this reduced the vibrations considerably.
It was able to hold together when I ran the drive motor at 60 volts. I'll post more details later but the good news is that efficiency increased to 68% (total). Assuming both motors have the same efficiency (they probably don't)this would indicate that the motors are running at approximately 83% efficiency.