Quote:
Originally Posted by JVN
Don,
Do you have any of the data from the tests you've done, or any more info on how you take dynamic friction into account?
-John
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I'm going to throw an idea out there and I hope people will respond with why it would or would not work. As a starting point for explanation this stems from the spreadsheet for the cell "Drivetrain Efficiency", where I propose kinetic friction = %100 - "Drivetrain Effiency". What I've observed in my real and simulated tests is that kinetic friction will reduce the overall top speed that would have happened, and this is easy to measure by use of encoders. So perhaps it could work like this:
In reference to this (assuming you use CIM)
http://www2.usfirst.org/2005comp/Specs/CIM.pdf
1. Try to use the peak efficiency voltage to measure 19.8 amps by setting victors to a constant speed percentage. Measure with amp meter what you have.
2. Read back the rps from the encoder
3. Using the stall torque of 45 Oz-In converted to newtons use spread sheet equations to determine the max speed for the encoder
4. Similar to linearization of victors, get robot running at a steady state of the known speed in step 1... you may record each iteration of the encoders for later analyses
It should fall short of the optimal speed just as the drive train efficiency also lowers the max speed in the spread sheet. This would be because some of the 45 Oz-in torque is used to fight the friction.
My studies also show that Cof impact a delay in acceleration but a quicker response in deceleration (assuming victors are in coast). So far these timings are very small probably 5ms worst case when robot has light payload. I need to do further research for heavy payload.
In regards to dynamic friction and the stribeck curve... I think the steady state should have the most valuable coefficient, and it should be possible to conduct same test at different velocities.
I do not quite yet understand the link between kinetic and dynamic, so for now I propose the kinetic is the overall average one-number that represents the friction but only for one given velocity... just as it is for drive train efficiency cell in the spread sheet.
It should be noted that I believe a similar test to these steps are being done here:
http://www.chiefdelphi.com/forums/sh...hreadid=107889