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GETTING STARTED

Electric Drive Basics (A/B/X Class)


In Energy Reality Check, the finite amount of energy available during the BikeRayce is discussed. Because you have a very limited amount of energy available, if you want to complete your 100 km in a short amount of time, it is important to efficiently transmit the energy from your solar panel and battery to the wheel. In this section, we'll look at some methods of delivering this energy.

OPTIONS FOR CONNECTING MOTOR AND WHEEL
The energy from the battery and solar panel will travel to your motor on its way to the wheel. The motor will convert the electrical energy into kinetic energy.

There are three basic options for connecting motor and wheel:

  • Direct or Geared Drive;
  • Chain or Belt;
  • Friction Drive to the tire.

Direct or Geared Drive
This option is a hub motor or extensive wheel hub modification. Hub drives consist of special low-speed motors built right into the wheel. In the last few years, new hub motors have become available that are sized and priced within the range of many solar bike teams. Because a hub motor turns the wheel directly and has no transmission, it can be a very efficient system.

Chain or Belt
Several motors are available that spin at a much faster rate than the bike wheel. Motor speeds are in the range of 3000 rpm to 12000 rpm while a 26" bike wheel turns at 323 rpm at 25 mph. In order to use one of these motors, you will need a transmission system to "gear down" the motor speed.

The largest ratio possible using standard bike chain components is on the order of 6:1 - too little to be of use by itself. A primary reduction of 3:1 to 4:1 would be required to provide the additional reduction needed. A second flat cogged belt or chain to the wheel can complete the drive system. Stay away from "v" belts like those used in automobiles - they're very inefficient. If you decide to try this drive option, you'll need to connect a sprocket or pulley to the bike wheel. Both front and rear wheel hubs are available with brackets to attach a disk brake. This would be a good place to mount a sprocket. You also need to consider what would happen if your battery runs low - you don't want your rider to have to turn a dead motor! A freewheel could be used to accomplish this function. See your friendly local bike dealer for more information.

Friction Drive
The tire friction drive units gear the motor down to a small metal roller. The roller presses against the top of the front or rear tire to turn the wheel and give the desired over-all gearing. This was the most common system used by early electric bike conversion kits. Most kits are geared for under 20 mph (too slow for raycing) but they can be adjusted by increasing the diameter of the -------------------.


MOTORS AND MOTOR CONTROLLERS
Finally, consider the motor and controller. Conversion kits use tiny motors to keep weight down (a very important consideration). In raycing, though, you may be using more power than these motors can handle, so check with the manufacturers to see if their units should be modified.

Good rules of thumb are that you should be using a 1/3 to 1/2 horsepower continuous-duty motor, and the higher the voltage of the motor, the smaller and more efficient it will be. Surprisingly, motors of this power range are available for model airplanes.

Controllers allow you to adjust the power and speed of the motor. Most kits provide a simple on/off switch, and this may be sufficient for raycing. More sophisticated controllers are available from Aerovironment, Astroflight, and AERL.

Finding the right drive train is a bit like a treasure hunt: the best system will result from careful design and asking lots of questions. Get on the Internet and the phone and happy hunting!




 
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