Quote:
Originally Posted by Andrew Lawrence
I've always read about how y'all prefer to gear more conservatively with your 6 CIM drives to abuse the acceleration boost, yet whenever I play around with acceleration and time to distance calculators I find that the extra motors become decreasingly more useful the closer you get to the "sweet spot" you have determined. At higher speeds - regardless of target distance - my calculators show that the extra motors can save a tenth of a second or so (nothing significant), and at lower speeds (especially around your sweet spot) the calculator shows improvements of a few hundredths of a second at best. Could you go into detail as to how you determine how much time you save with the extra motors to travel a set distance, and what tools you use? I feel I'm doing something wrong with the calculators I have due to the disagreements my data is showing compared to yours, but I cannot figure out what it is.
|
You are correct that the difference between 4 CIMs and 6 CIMs is not huge when geared lower. To be honest, we didn't compare the performance of different numbers of motors in great detail. The kids wanted 6 CIMs, so they got them
We use a spreadsheet that was originally written by Andrew Keisic on team 294. It should be here on CD, but I looked the other day and wasn't able to find it. Anyway, the spreadsheet allows you to input various drivetrain parameters, and outputs time to target distance as well as distance vs time graphs. Based on the assumption that we were using 6 CIMs, and choosing an average distance we think we would be driving during the game, we adjust the gear ratio until the time to drive that distance is minimized.
In answer to your question, if we pick a distance of 20 ft, the spreadsheet predicts it would take our robot (geared for 11 fps) 3.2 seconds to get there. Dropping down to 4 CIMs, the time increases to 4 seconds. As you said, it's not a huge difference, but perhaps more than you are seeing with your calculator.
A spreadsheet provides a method for relative comparison between drivetrain setups, but it's never going to be perfect. We also like to compare current designs with past robots. We were pretty happy with the drivetrain on our 2013 robot, so ultimately chose a gear ratio last year that would give us similar performance, even though the construction was completely different (gear drive vs chain drive). This is easy to see on the distance vs. time graphs.
One thing I would like to do is gather some real data from past robots to see how accurate the spreadsheet results are.