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Unread 16-05-2011, 23:12
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JesseK JesseK is offline
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Re: Mecanum Einstein this year

Quote:
Originally Posted by AdamHeard View Post
Not to pick on you, but there are quite a few flawed assumptions here.

I can only speak for us, but I would assume 254 has the same reasoning.

We don't gear for top speed, but for a "sprint distance".

Low gear is well past traction limited. 254 was likely pushed in fm1 due to being underweight. There was no lack of torque. 99% of robots would not have been able to do that to them, 469 was really an edge case with their drivetrain.

Using the same geometry, you can easily gear to get a top speed in a smaller range (in 2010 we were 13.5 fps with LARGER wheels...). We're not stuck with 18fps.
I get that 'sprint distance' concept; it's why I made my "gearing vs time" charts in my recent calculator. Other than that, a couple of things --

I was under the impression, from talking to kids on all 3 teams, that the drive train gearing between 254, 973, & 1868 were identical. Due to the collaborative nature of the machine shop setup (which is great, imo) I presumed many discussions and similar conclusions were made.

I'm having difficulty getting the geometry for less than 18ft/s correct by using 3.5" wheels, the 15:48 & 28:35 combos for the shifting stage, and 11:40 for the first stage; this is why the presumptions were made. It's easy to get less than 18ft/s after adding a 3rd stage, but that's extra weight/inefficiency. Increasing the 40T gear on the first stage interferes with the dog gear; decreasing the 11T pinion further to a 10T pinion without increasing the 40T gear causes the CIMs to touch (at least). For anyone wishing to use the COTS solutions from AndyMark without extra milling on the gears for the dog gear setup (such as my team), this is what we'd have to use.

So really, I have difficulty in understanding how you get the dimensions needed for 13.5 ft/s in the same geometry (2 stages of reduction); it doesn't work out for me.
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Last edited by JesseK : 16-05-2011 at 23:15.
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