Thread: CHIPS
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Unread 19-05-2004, 00:38
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Tristan Lall Tristan Lall is offline
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Re: CHIPS

Quote:
Originally Posted by roboteer49
wow ok, the reason for this post was because i want to keep the gearbox very simple adn achieve a speed of 9 ft/sec. also torque. This is the first time im designing a drive train and i want it to run smoothly. Im also scared of dual motors because theree is like a .5 mm shaft on the drill and i don't want it to crap out and its too complex for my first time. The reason i thought the chips would be better because they seem like they never break, and they have almost 5 time the rpm of a drill. From what im hearing is that the chip is only slightly less powerful, speed can be adjusted in gears but torque cannot, right? So, here's my question, if two robots were identical and one had chips and the other drills with gearbox(high and low) who would win in a pushing match? thanks
Hang on a second--speed and torque can be adjusted by gears; it's (mechanical) power that is constant. Once again, rotational speed × torque = power. Since power is constant, speed and torque are varied by the gear ratios.

Also, that little shaft on the drill has a steel pinion (i.e. small gear) pressed onto it. Some teams have managed to get it off, and replaced it with something more suitable to their needs, others elected to use the pinion as supplied. In any case, provided you're comfortable with assembling gears, the drills are only marginally harder to work with than the CIMs. (Finding a matching 0.7 module, 20° pressure angle gear is, however, quite annoying--try PIC Design, and order very early!)

(Or are you referring to the threaded shaft on the gearbox? That's another issue entirely.)

As for the CIMs never breaking, that's a little extravagant, I think! (We had a slightly defective one in the kit this year--it was replaced with a good one.) But you're absolutely right that they can stand much more abuse than the drills.

I've noticed that you seem to be thinking of the drills as the entire drill motor + transmission assembly. We've (or at the very least, I've) largely been thinking of the motor alone. If you don't feel like separating them, remember that they have high and low gears by default and therefore their torque and speed will differ in each gear. (In other words, you need to specify either high or low gear, or no gearbox, if you want to describe speed and torque for the drill motors.)

As for the actual question, I have to modify the wording a little:
Q. If the robots were identical, and they were geared to run at the same final drive speed when identically loaded, etc.
A. Theoretically, the drill-powered robot would win, since it is capable of outputting more torque (i.e. more power for a given speed). But that's not the whole story! Many drivetrains are traction-limited, so that the robot will actually spin its wheels at maximum torque, rather than doing any further useful work. If that's the case, and both robots are otherwise identical, it could well be that both robots spin their wheels and don't do anything productive. At this point, it comes down to which robot can sustain this condition the longest--and here's where it gets interesting. You'd need to look at the graphs and examine the electrical system (including efficiency), and determine which robot will run out of (electrical) power first. (I would tend to favour the drill, even under these circumstances, but that's an educated guess, since I haven't done this analysis of which I speak.)

9 ft/s is an average-to-high speed, depending on the year and the game. Without running the calculations through, I would tend to say that this sort of configuration would produce low-to-average torque--which isn't quite what you had in mind.

Edit: Beaten to it, not once, but twice--but they're saying the same sort of thing!

Last edited by Tristan Lall : 19-05-2004 at 00:51.