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Unread 09-02-2009, 17:27
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dtengineering dtengineering is offline
Teaching Teachers to Teach Tech
AKA: Jason Brett
no team (British Columbia FRC teams)
Team Role: Mentor
 
Join Date: Jan 2005
Rookie Year: 2004
Location: Vancouver, BC
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Re: pic: Ungreased toughboxes!!!!

Quote:
Originally Posted by kajeevan View Post
Well to answer a few questions, the gearboxes ran for about 10 hours each on the playing surface using the rover wheels. ...
I have to admit I was intially quite reluctant to believe that a lack of grease alone would cause such catastrophic failure in a Toughbox... after all, we just dab a bit of white lithium grease on there and have never had a problem. But I doubt that even our last year's gearboxes have seen ten hours of continuous driving.

I find that even with the wheels up and off the ground and just the drag of the gearbox and chains, the CIM draws just under three amps and needs to be cooled after 20 minutes or so of continuous use. With the robot on the ground and driving, I wouldn't rate the CIMs at even a 50% duty cycle. This means that based on my experience, ten hours of continuous practice driving is going to require somewhere in the neighbourhood of 20 hours at a practice facility at a minimum. I doubt we have ever had more than an hour or two of actual driving time on our toughboxes before we ship, including a 20 or 30 minute "break in" period that we give each gearbox. (Yeah, I know the gearboxes shouldn't "need" to be broken in, but we find that the drive system as a whole seems to run smoother and at a lower current draw after it has been spun around a few thousand times.)

Given that a regional involves, say, 12 two and a half minute matches (admittedly some teams have a slightly higher average...), and assuming an equal time spent practicing on the practice fields, it would be unlikely for a toughbox to see much more than an hour's use at any given competition.

So I guess what I'm getting at is that 10 hours of actual driving under load is actually a pretty good lifetime for a Toughbox, particularly one without grease. With grease, it would be reasonable to assume a lifetime greatly in excess of ten hours, making them, for all practical FRC purposes, eternal.

Thanks for posting that crucial piece of information about time to failure... I had been assuming this was a new gearbox, freshly assembled, that had failed in less than an hour of use and that just didn't seem to make sense, grease or not.

Jason
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