Our team is considering using a servo-switched 2-speed drill motor assembly coupled to a geared-down Chiaphua shaft via a direct sprocket/chain tie. We do not want to build an external transmission.
We would gear the Chiaphua down to about 440 rpm to match the drill rpm in low gear, in hopes of nearly doubling our low gear torque. In high gear the Chia motor would then be spinning at about 14000 rpm (2.4x its free load rpm) and so inhibiting locamotion to some extent. We’re thinking back-current is not a problem, and that the drill motor probably has more than enough power for our high-speed tasks plus spinning the Chia at these high rpms.
What do you guys think? Is this dangerous? Do we need to bench test to see what kinds of resistance the Chia develops? Thanks for your insights! J#
Are you saying gear up the Chiaphua motor? If so, that is a bad idea. Could you explain your question further? You can have only the drills and shift it or you can have the chias and drills and not shift. You may want to check out this thread http://www.chiefdelphi.com/forums/showthread.php?s=&threadid=16100&highlight=matching+drill+chiaphua
The thought was to use the power of the Chiaphua to suppliment the drill motor/gear assembly in low gear only. To do this we would gear the Chia down about 10:1 and direct link it’s output shaft to the output shaft of the drill assembly (probably via sprocket gears and a chain).
The rub comes when we switch the drill motor into high gear without changing the gear ratios to the Chia. Now the Chia is spinning well above its free load rpm. We are assuming we don’t need any contribution from the Chia in the high speed mode, but are wondering if anyone has experience with the resistance we might expect from the Chia in this mode, and if there is some other, obvious or other, reason not to use this configuration.
I’m afraid the 2-way operation of the motors would make difficult a racheted gear or one-way slip clutch. We’re on a very limited budget and without a decent machine shop and so are, at this point at least, trying to torque-up in low speed mode w/out building an external shifting mechanism (other than the servo swiching of the drill gearbox).
I also just saw the previous thread. Thanks for the link!
As long as you cut power to the “chalupa” you probably wont damage anything. If you built some sort of clutch (or way to disengage the chalupa from the drill motor) you would be even better.
As far as i know if you have the chalupa and drill coupled running at different speeds (after reduction) they will fight, get very hot, trip breakers, and release their magic smoke rendering them useless. I believe a electic motor is similar to, say, the engine in your car. You can shift into first going down a hill and the motor will provide braking force (though this is just an analogy, as a gas engine does this because of internal compression and a electic motor does this because of… well im not entierly sure, my guess would be timeing on the commutator).
I’m by no means an expert and wouldn’t be suprised if someone told me im totally wrong, but to the best of my knowledge what I said is correct 
I suggest doing some research yourself.
Greg
You’ve hit the root of my question. Why cut the power to the Chalupa? The drill and Chalupa would both operate in their strongest rpm window during low gear mode- no fighting. In high-gear the Chalupa would be spun at 2.4xs its free load rpm as the drill motor would be doing all the work (all we’ve changed is the drill assembly output speed by shifting its gear from low to high). The voltage would still be applied to the Chalupa so it’s turning resistance should be less. Also back current shouldn’t be able to over power the 12v applied? J#
Well just a rough calculation shows that if the atwood was turning 2.4x its rated speed it would generate around 24 VOLTS… also the bearings in that motor are probally not designed to do that kind of speed… it would be WELL worth your time to design a way of takeing it out of the gear train. have a servo push its spur gear on the shaft with one huge keystock in it when it shifts the drill… also when you do this it is going to take alot of power to keep that atwood spinning that fast… and that power is going to be robbed from your wheels. and one way sleeve clutches arent very expensive at all… if you can afford the gears to do this then you can easily afford a clutch for it.
I would only evean attempt this if I had lots of spares of the motors, speed controllers, relay modules, and the RC.
It seems to me that it would be easier to gear the Drill and Atwood motors to the same RPM and connect them through a geartrain. Then mount the drill gear shift to the output shaft of the first geartrain. That way you’d be shifting both of them.
Thanks!
If you shift the drill transmissions, and reduce 3 or 4 to 1 on the final drive to 6 " diameter wheels there should be no need for ganging drive motors. The 2 to 1 reduction worm gears coupled with the big wheels in the kit is way to much speed and too little torque. It was nice of FIRST to try to give the rookies some good stuff, but if that is used directly with no further reduction they are going to get pushed all over court. The FIRST people may not have realized how much pushing power a lot of teams had las year.
Hint 1: The kit wheels may not be the best grip out there.
Hint 2: Learn what wheels give good traction on all 3 surfaces.
Hint 3: Max power output form the motors is when they are loaded down to about 1/2 of free speed rpm when powered to full voltage. Look at the current draw if you have 4 big motors at max power and if they are stalled?
Hint 4: Shifting is not hard, but you need to learn how to make sure the shift is complete before putting the pedal to the metal, a little programing and limit switches can make this happen.
Enjoy,
Rob at Rage
The Chiaphua motors are not meant for too much resistance and the drill motors can not reach the rpm of the chaphua, so as mentioned it will fry your circuits and the gear ratio wont be balanced. What you could do is keep the drill motors at its highest speed and try to balance the rpms of the chia with them for maximum speed. If you want torque then keep the drill motors at low speed and reduce the gear ratio even further.[email protected]