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Unread 10-22-2003, 09:13 PM
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Need some help

Is there a relationship between gears I need to know while makeing a drive train on paper?

with circumferences of gears or with teath sizes?
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Unread 10-22-2003, 10:42 PM
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its spelled *ya'll*, not *y'all*
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[(# teeth on gear 1)/(# teeth gear 2)]*[input speed]=[output torque]

[input torque]/[(# teeth on gear 1)/(# teeth gear 2)]=[output speed]

...unless i have them mixed up (kinda tired right now...)
a good place to look would be in the CD white papers
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Unread 10-22-2003, 10:59 PM
sanddrag sanddrag is offline
back to school ;-)
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This subject alone is responsible for burning out a majority of FIRST participants. I can't even count how many times I and others have answered questions such as this. I'm a really helpful type of person and I don't usually make posts like this but go check the white papers or something -- I am tired.
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Unread 10-22-2003, 11:41 PM
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I'm bettin that you can find your formula here in this file. Now I have no idea what the formula is -- I've never really felt a need to calculate ratios exactly for our robots -- but this paper sounds pretty fly so check that out.
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Unread 10-22-2003, 11:56 PM
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It seems like you're going to be taking a shot at designing your team's next drivetrain. If so, or even if it's only a casual interest, I'd suggest taking a look at these:
Boston Gear "Gearology" (Only chapters 1 to 5 are relevant, and if you're busy, just 1 and 2 would suffice for most applications.)
PIC Design Technical Information (Formulae, calculators and reference, in a web-based form.)
They are relatively heavy reading, but they'll give an excellent overview of how gears themselves work. (It's more complex than one might imagine.)
If you're interested in a book, take a look at:
South, David W. (ed.) & Mancuso, Jon R. (ed.); Mechanical Power Transmission Components; 1994; Marcel Dekker; New York
It's got a rather comprehensive section on gearing (not to mention all sorts of other information). Once again, it's heavy reading, and will be too much to read cover to cover (901 pages!), but if you can get it from the library (mine's borrowed from the University of Waterloo library), chapter 7, "Gear Drives" is worth a look.

Those sources I've quoted will go a very long way in designing an effective geartrain, but you don't need to absorb anywhere near all of it at once. (Though you're encouraged to try... )
As a matter of fact, most teams fly by the seats of their pants in designing a drivetrain--and it usually works well enough. But a little additional knowledge of the basic operation of gearing might just stave off trouble in the long run.
If that leaves you discouraged, you've got the wrong idea. The best way to learn about this stuff is to try it, and give it your best shot: maybe it won't turn out perfectly the first time, but that's fine, you can adapt and improve. (As a matter of fact, my first shot at designing and building a gearbox didn't go completely according to plan...but it did turn out quite nicely in the end.)
-Tristan Lall
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Woburn Robotics
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Unread 10-23-2003, 12:06 AM
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Quote:
Originally posted by Dan 550
I'm bettin that you can find your formula here in this file. Now I have no idea what the formula is -- I've never really felt a need to calculate ratios exactly for our robots -- but this paper sounds pretty fly so check that out.
Incidentally, this paper deals mostly with the characteristics of the robot's wheels as they turn and slide on the ground, especially as that relates to turning ability. The paper doesn't go into selecting the correct ratios between individual gears, rather, it advises you that you'll want to make a few calculations to ensure that whatever you do, you make sure that your gearboxes can put out enough force to allow the robot to tank-steer. Choosing individual gears is an entire subject unto itself. You'll have to take into account everything from size and weight to cost and availability of parts (and many other factors).
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Unread 10-23-2003, 06:51 AM
Andy Brockway Andy Brockway is offline
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One thing that is very important is that meshing gears are the same Diametral Pitch (DP) and Pressure Angle. Mating different DP and Angle will cause gears to self-distruct over time. Of course this has been made to work in this competition due to the short duty cycles and ususally only with the drill motors due to their 0.7M metric DP.

I discuss gear ratios and how to choose center distances in Team 716's Dual Shifter white paper (sorry, haven'y learned how to insert the link) posted here 10/7/03. It also discusses how to choose gears so that adjacent gears that should not mesh can be selected.
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