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Re: Climber help: thermal breakers.

Quote:
Originally Posted by Munchskull View Post
Part of my teams strategy has been to have a fast climber. When I say fast I am talking sub 5 seconds. Our biggest factor on that is the thermal breakers.

We plan to use a two 775 pros, each with a 33.33:1 reduction. Using the tall robot size means that it would travel a little over 2ft to reach the top. On the 1.25in roller we are playing to use that ends up giving us a solid climb speed of about 7.5 seconds. CAD suggest that our worst case would be a 100lb robot. Across each breaker that would be 40.48amps assuming a gearbox efficiency of 90%.

I got 90% efficiency from some read I did on planetary gear systems and spur gears. I will admit that I choose that based on some hunch math. I was lead to understand that you would get roughly a 3% efficiency loss from every planetary stage. Using two per side that would equate to 94%. Then from there I plan to reduce using spur gears at a 2.1:1 ratio. It is my understanding standing from my reading that spur gears have a loss of 2-6% so I choose 4% loss for my happy medium. Putting that in to JVN got me my number of 40.48 amps.

Now I might be crazy but I would love a sub 5 seconds climb without adding motors. With a 20:1 gear ratio I would draw 67amps for for seconds, could the thermal breakers handel a spike of the current for that long. Also what would the main breaker risk be?
Check your math. I don't know what you've done wrong, but you've done something wrong with your math. If I punch in 2 775 pros, 30:1, 154lbs, 24 in, and 1.25 diameter pulley into JVN, I get 35A motor load, and a 0.82s lift. Which sounds much more like a 2 775pro lift.

Your numbers aren't even consistent assuming you got the motor load right. 40A = 30% FLA = 70% free speed = 12600RPM / 60 / 33 * 1.25 * pi = 25 in/s.
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