Quote:
Originally Posted by nathannfm
I am thinking about designing a gearbox that would have a CIM, a Mini CIM, and a larger pulley belted together and I had a few questions.
Are there any problems with belting the 3 together considering the ~15% difference in free speed between the CIM and the Mini CIM?
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We did not have any problems with the mismatched free speeds. CIMs and MiniCIMs were designed to be interchangeable; Additionally the free speeds of both motors have a huge tolerance range so you really have no idea how mismatched they are.
CIM Free Speed: 5,310 rpm (+/- 10%)
MiniCIM Free Speed: 6,200 rpm (+/- 10%)
Quote:
Originally Posted by nathannfm
Is 20T the smallest you can get away with this type of belt, and why was it chosen over 9mm wide, 5mm pitch HTD belts?
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Firstly, no; you can put a smaller pulley on the CIMs. GRT has used 16 tooth pulleys in the past and you might be able to go smaller, we haven’t tried.
However, there are a lot of considerations that you have to be aware of when designing belt/pulley system. (here are just a few)
1) To get the full strength from a Gates Powergrip series belt you need at least 6 teeth in mesh and at least 60 degrees of wrap. When you use a smaller pulley this becomes harder to do.
2) When you use a smaller pulley you put the belt through a tighter radius, which can lead to a decreased belt life.
3) The width of a belt (IIRC) linearly correlates with it’s maximum power transfer
HTD vs GT2: HTD belts have substantially lower max power ratings so switching to HTD would have put the belt far out of spec.
5mm vs 3mm Pitch: using 5mm pitch components would have been safer due to their increased load ratings, however the pulleys required to get the reduction (with correct wrap, ect.) I wanted would have been a lot bigger and did not fit with the rest of the design.
Quote:
Originally Posted by nathannfm
Did you have any problems with this gearbox over the season and did you end up needing to use the tension adjustment CIM mount holes?
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We never removed the gearboxes from the robot over the course of the season and they never need any repairs. The holes are to account for the manufacturing tolerance in the belt length; once installed, the belts should not need to be retensioned.