[Doug G]

The thunderchickens planetary CCT inspired us (701) to build a simplified version of one this year and from the little testing we have done it seems to work very well. I absolutely credit Team 217 for inspiring our design - but it is different from theirs. Our planetary transmission is not really a CVT, just as the thunderchickens transmission isn't a true CVT either, it's closer to being a two speed transmission that doesn't require any mechanical shifter. Basically, we use the CIM as our sun and the drill drives an external ring gear which is connected to an internal ring gear. The planetaries (output) rotate between the sun and internal ring gear. Thunderchickens (as explained in their white paper by Paul C.) use the drill and FP motor driving a worm gear on their external gear. This was to prevent backdriving of the motors when the output is stalled. We are able to overcome the backdriving effect by gearing down both the CIM and the Drill motor to the almost the same output torque. We thought this would be much simpler than incorporating a worm gear system. Since it is next to impossible to perfectly match them up we compensate for backdriving by using the current sensor to monitor the CIM current. As it begins to spike, we reduce the power to the Drill motor. Important Note: we are a small outfit that had to machine many of the parts ourselves on a mill / lathe that we got just after kickoff - thus we didn't finish it until Feb. 20!! There is so much more testing we need to do - but we did test it briefly and it supplied a high torque and low speed when the sun and external gear were moving opposite of each other and low torque and high speed when moving in the same direction (an effect the Thunderchickens CCT doesn't provide according to Paul C. - I'm still confused as to why...). We were able to manually adjust the backdiving effect and sure enough were able to stall both motors together. The one part of the system that was never finished was the programming of the current sensors - we'll give it a shot at competition and see what happens - but we are very pleased with the results so far. And it required very little machining (housing is probably the hardest part!). We'll provide more info after the Sacto Regional. Regarding the Thunderchickens patent pending design.... If we are presented an award solely on the planetary design - we would not except it. If we are presented an award for the overall drive / control system, we would graciously except it. I would very much like some feedback on this sensitive issue from the CD community.