Quote:
Originally Posted by aldaeron
I want to point out for folks who don't spend a lot of time looking at gearboxes that this is a very aggressive gearing with one of the highest CoF wheel tread materials. My quick calcs say this generates ~747 pounds of force at the wheel patch with 6 CIMs, well over the traction limit of 185 for a maximum weight robot in 2014. Meaning it is an extreme case and may not be the best one to guide the decision of an average team.
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I second this.
Though that said, we used the same gearbox in 2014 with a 26.04:1 low gear and a 7.08:1 high gear on 4" wheels with the same tread.
Quote:
Originally Posted by aldaeron
Overall this is great feedback. I have been wondering how the 3rd stage on the 3 CIM works at high loads. I always thought the sheet metal with standoffs 3rd stage looked a bit rickety. I am curious if you ever subbed out the 7075 aluminum gears for 4140 steel gears in the third stage of the 3-CIM shifter? Sounds like it was a misalignment issue more than a material strength issue. Did you ever try stacking on a second Vex third-stage plate to add stiffness to the third stage bearing? This would pickup more of the bearing race and possibly prevent angular deflection.
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I don't think the issue is the plate stiffness, but the fact that the small output gear (the one with the missing teeth in the photo on the last page) is on a cantilevered shaft. If one was to modify the plate so that another bearing could be used on this shaft, there likely would not be any problem.
On a related note, our team actually did this recently with a pair of VexPro 2 CIM Ball Shifters that we had inadvertently ordered without the 3rd stage (and apparently the output shafts on the 2nd stage are longer when order it like this). So we made a pair of
replacement plates so that the smaller 3rd stage gear could be retained by an additional bearing instead of having to remove the shaft and lathe a snap ring channel into it.