10/12/16

This week, I spent time looking at gearing as well as the motor in general. The original idea for the motor was to use one that was 24volts and  200watts. Under the assumptions that the amount of power that could be delivered to the motor was 75 watts, divided up as 24 volts and 3.3amps. The motor could produce a torque of .275Nm. Considering the assumption that the bogies and pod weights 600lbs, the amount of torque needed to turn the 6 inch wheels would have been 35Nm. Meaning that the motor would have to be gear 1:125 just to turn the wheels. The 35Nm doesn't even include the gearing losses, rolling resistance, and bearing frictions, which would bump up the 35Nm to 42Nm.
At this point, there were only two options that could be taken, try and gear down the motor to the point it could turn, or use a larger motor with more power applied. Looking at gearing, there were a few different possibilities, worm gears, planetary gears, and simple gear chains. Worm gears were considered for a time considering the amount of torque they can convert given a limited space. Yet, the problem was that once the motor stopped turning, the wheels would completely lock in place due to the nature of worm gears, which would make braking difficult to do slowly. Using planetary gears would have the benefits of efficient motion conversion. Yet, due to the complex design, and need for specialty gears, it was not an option worth seeking. Finally, with conventional gears, the design is easy enough to create, but using this method to gear down a ratio of over 100:1 wound result in a large gear chain with similarly large gears.
Due to gearing being a rather difficult to produce, I started to look at using a different motor, possibly one that is 48 Volts instead of 24 volts and at a higher amperage, say 9 amps. Under those conditions a 400 watt motor can increase the stall torque to something more reasonable for this project.