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Originally Posted by Salik Syed
i have some serious questions as i get into actually building a two speed tranny (contemplating building that is/ ordering parts)
anyways here the set up:
FP motor w/ a 20 th pinion goes to a 64 th gear
the Chiphuah motor links directly to the 64 th gear...
now this should couple the motors for 4050 RPM right? but how about the motor curves and what not will they match for the most part?
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Which F-P motor? The more recent ones have had 19 tooth pinions, while the 2002 edition had a 20 tooth pinion.
For the 2003 and 2004 Woburn robots, I've tended to use 54:19 as the reduction between these motors. That's based (approximately) on the statistics for free speed, maximum efficiency, and maximum power. (
See here for some more information.) At the 2004 F-P's free speed is approximately equivalent (with this reduction) to the 2003/2004 CIM's free speed: 15 700 * 19 / 54 = 5524 ≈ 5342. Similarly, at maximum efficiency: 14 200 * 19 / 54 = 4996 ≈ 4649. And at maximum power: 7900 * 19 / 54 = 2779 ≈ 2671. Those are close enough.
So it begs the question,
how good is your scenario? Using last year's motors, at maximum efficiency (your number, 4050 rpm was closest to the CIM's max. efficiency point--so I
assume that you're trying to base the calculations on this speed), 14 200 * 20 / 64 = 4437 ≈ 4649. Which isn't as good as the ratios that I used. But more importantly, unless you're using some factor for efficiency losses, I don't see how you came up with 4050, because that number isn't on any applicable spec. sheet, nor is it easily derived from those sheets (as far as I can tell).
As it stands, I don't think you're correctly matching those motor curves.
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Originally Posted by Salik Syed
second major question :
this tranny will have some major loads on it....
the 40 AMP RPM is about 2000+ (the shifting stage comes after the first stage( which is 4050 RPM) then the shifter reduces either 2:1 or 3:1.... )
will some of the nicer BRONZE bearings hold up to thise load.... (i'm talking about the 841 type not 660) . then after this we'll put a chain reduction of 4:1 to 6" wheels....
will it work? will i burn bearings / create a heater....
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For basic sleeve bearing (a.k.a. bushing) calculations, refer
here for explanation of terms, and
here for information on specific materials (SAE 660 and SAE 841 among them). That information comes from
McMaster-Carr, who sell these things.
SAE 841 is good for higher speeds, at the penalty of reduced resistance to static loading--so it's not always a superior material. You haven't given shaft diameters and bearing sizes, so I couldn't say for sure whether your application is feasible--but realistically, you should be
easily within the capabilities of these bearings, if your design is remotely typical for a FIRST gearbox. As for efficiency, if your design can accommodate it, and you can afford them, use ball or roller bearings--their efficiency is better under almost all circumstances. Indeed, the only reason you would likely overheat those bearings is if you misaligned your shaft very severely--but then, it's probable that the bearings would disintegrate first.
Gracious professionalism... otherwise, the program has failed. - Yan Wang [more] 
31-10-2004, 13:43
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