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#1
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Re: pic: 2011 "Nova" Swerve Drive (Front)
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Also, you didn't mean to include a differential, right? (I seem to recall a team having a design similar to this, but with differentials on all wheel pairs. Might have been 1140 around 2005.) |
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#2
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Re: pic: 2011 "Nova" Swerve Drive (Front)
Currently the gears are baseline steel.
As you probably know, selecting the Bevel Gears was by far the trickiest part of this design. If the mounting distances are too large, the wheel separation makes rotation of the module impossible. On that end, if you happen to know where I might find a hardened, spiral bevel gear set that fits near the specifications for under $120, I would greatly appreciate it.... Also, how exactly do you calculate gear strength anyways? |
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#3
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Re: pic: 2011 "Nova" Swerve Drive (Front)
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And by the way, if you need more clearance for the pinion (too wide), you might consider dishing out the wheels facing the centre of the gearbox (so that the pinion and gear sit in a depression in the wheel, sort of like a typical west-coast style wheel with the spokes on one face). Typically, in FRC applications, gears fail because the teeth are overstressed. (Other failure modes are possible.) The important characteristic is therefore the bending strength of the teeth. There are a few ways of evaluating this, with varying levels of complexity and accuracy. The Lewis-Barth method is traditional and conservative, and requires relatively few parameters. AGMA has another method that takes fatigue and contact stress (another failure mode) into account, as well as a whole slew of other design factors—but you probably won't know what values to assign to them without some sort of basis for comparison. Given that bevel gears are a bit of an unusual system for an FRC application, I'd avoid relying on rules of thumb alone (so don't just take my word for it). For an introductory reference, see this. Check out the literature provided by the manufacturer. Also, there's this: a whole book about gears, with a good explanation of the Lewis method. For more about the AGMA method, I recall that any recent edition of Shigley's Mechanical Engineering Design should include a chapter (written for upper-year mechanical engineering students). You might find this a convenient resource for equations and examples. Definitely search the Chief Delphi forums for other resources. Last edited by Tristan Lall : 11-08-2011 at 03:29. Reason: More content. |
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#4
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Re: pic: 2011 "Nova" Swerve Drive (Front)
I suggest looking into worm gears, they can get you a lot more reduction in that space, and I bet it will be easier to find a set that small. with a worm gear you may be able to remove the cimplebox entirely.
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#5
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Re: pic: 2011 "Nova" Swerve Drive (Front)
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#6
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Re: pic: 2011 "Nova" Swerve Drive (Front)
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#7
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Re: pic: 2011 "Nova" Swerve Drive (Front)
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According to the JVN mechanical design calculator; 7 feet per second after frictional losses. 196 LBS of pushing force with rough-top tread. |
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#8
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Re: pic: 2011 "Nova" Swerve Drive (Front)
Is it possible to reduce the CIMple box further, I was hoping to get right around 10 FPS
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#9
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Re: pic: 2011 "Nova" Swerve Drive (Front)
You mean reduce it less. And I would just decrease the reduction on the bevel gears.
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#10
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Re: pic: 2011 "Nova" Swerve Drive (Front)
With all due respect, if you can't figure out gear ratios, you really should not be designing a swerve drive.
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#11
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Re: pic: 2011 "Nova" Swerve Drive (Front)
With all due respect, I didn't post myself on this website, I posted my design. If you have a comment or criticism about that, I'd be happy to hear it. But if you only want to discourage me from experimenting and learning, I'd prefer if you kept that to yourself.
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#12
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Re: pic: 2011 "Nova" Swerve Drive (Front)
From looking at it, you have a fairly robust looking module with most of the issues attended too, aside from that bevel gear looking tiny.
What i'd be concerned with in this module is the amount of power necessary to steer those wheels (depends on the number of modules and what motors are steering). Also depending on your steering arrangement some method of angle adjustment between the steering sprocket and the module may be necessary. Do you have the machining capabilities to make that one piece bracket and securely mount it to the vertical support? It also looks rather huge, but i like small compact packages if you look at our recent swerves. Chris's statement has some merit, and I've learned to like when people are straight up blunt with me, as it makes things much easier to gauge and get a realistic evaluation of your current state. I would suggest listening to his advice and getting a firm grasp on gear ratios and the efficiency of various methods of power transmission, this will only help your design. Exercises like this are a chance to develop further, and as has been pointed out you could use some work in the gearing arena. Don't immediately think someone is attacking you when in reality they're just trying to bump you back to the path you've strayed from. He gains nothing from tearing you down. |
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