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Re: pic: Modified super shifter gear box
A bevel gear set creates a thrust load on each of the shafts -- motor and driven gear. This load is opposed by bearings of some type, causing a component of friction that is not present with the original spur gears.
This extra friction increases current draw and therefore reduces power available at the wheels when current is limited, as it will be by circuit breakers and by motor heating. Current draw with no wheel loading (fully assembled drive train with wheels-up; i.e., chassis on jack stands) is a good indicator of how much friction has been added.
A CIM with nothing attached to its shaft will draw about 2.5 Ampere from a 12V source while spinning "freely" at about 5300 rev/min. A CIM back-driving a second CIM (with its terminals disconnected) will therefore draw about 5 Ampere. A well designed, correctly assembled, and properly lubricated 2-CIM single reduction gearbox adds about 2 Ampere to this "free" current draw. Extra stages add a bit more, but the adder is less because the extra stages are not moving as fast. So, as an initial health check, I like to see free current less than 8 Ampere when testing a new spur-gear drive train.
Do you have free current measurements for this set up?
__________________
Richard Wallace
Mentor since 2011 for FRC 3620 Average Joes (St. Joseph, Michigan)
Mentor 2002-10 for FRC 931 Perpetual Chaos (St. Louis, Missouri)
 since 2003
I believe in intuition and inspiration. Imagination is more important than knowledge. For knowledge is limited, whereas imagination embraces the entire world, stimulating progress, giving birth to evolution. It is, strictly speaking, a real factor in scientific research.
(Cosmic Religion : With Other Opinions and Aphorisms (1931) by Albert Einstein, p. 97)
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