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Unread 04-01-2016, 15:46
aldaeron aldaeron is offline
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AKA: -matto-
FRC #1410 (Kraken)
Team Role: Mentor
 
Join Date: Jan 2010
Rookie Year: 2010
Location: Denver
Posts: 224
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Re: Sonic Shifter - recent feedback?

Quote:
Originally Posted by BoilerMentor View Post
Gear ratios were 18.75:1 and 7.08:1. Gearboxes were lubricated with moly grease containing Teflon. The gearbox direct drove a 6" x 2" wheel at the center of the robot which was chained to the other two wheel in the drive train side, also 6" x 2" wheels. All wheels were treaded with blue nitrile. Center direct drive shaft was supported with a bearing in the outer plate. Two other axles were dead shafts with bearings in the wheel.
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.

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.

I am assuming the output of the gearbox was direct driving your center wheel in a tank drive. How do you think a 2 stage 3-CIM shifter would work if offset from the wheel axles and with a #35 chain reduction between the gearbox and wheel axles in lieu of the Vex 3rd stage?

Quote:
Originally Posted by BoilerMentor View Post
The high load situation I believe created the problem was encountered when the driver returned the control stick to a neutral position with the robot at a high speed. The auto shifting code would have immediately tried to shift the robot to low gear with all three cim motors braking.
Was there a particular reason for adding this "stop on a dime" feature? Did it work as you had hoped? Would you recommend it? It does seem like a recipe for gear teeth shearing.

Quote:
Originally Posted by BoilerMentor View Post
I've spent a fair amount of time "behind the glass" as it were. I'd challenge you to find a driver who pushed their robot harder and drove more aggressively.
Based on photos and gearing - I agree - you win!

-matto-

Last edited by aldaeron : 04-01-2016 at 15:47. Reason: Clarity