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Old 05-13-2008, 11:31 PM   #1
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Exclamation Effect in gearing size?

What is the effect in performance between using a bigger spur with smaller pinon Vs smaller spur with big pinon if both is having the same gear ratio & rollout?
Example - 80 spur with 23 pinon (Ratio of 3.47)
Vs 125 spur with 36 pinon (Ratio of 3.47)

In particular to 1/12th, how do we gauge the correct combination to use? What will be a good combination for use in MOD & 23T class?

Any expert out there can help?
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Old 05-13-2008, 11:51 PM   #2
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In terms of mechanical efficiency there is very little difference. Drag from the teeth meshing together on this size of gear is minimal, weight of gears is negligible... The biggest (only) difference would be weight distribution. On a 1/12 there is a solid 1/2" that the motor can move... that's a lot to move something as heavy as the motor.
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Old 05-17-2008, 08:40 AM   #3
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It has got a big difference as it'll distribute the weight differently making your car faster or slower but every cars differs on the setting if youoverdo it it'll be hard to handle qas it's too slow or hard to handle as it's too fast.Same engine on different gear ratio will show different results try it out and you'll know what i mean.
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Old 05-17-2008, 08:26 PM   #4
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the bigger spur will smooth out the motor's powerband and make it smoother obviously
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Old 05-18-2008, 07:45 AM   #5
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mostly it only relation to your chassis's fitment and layout. unless you want to use the heavier metal one as pinion and spur gears, so they can be use as flywheel weight.
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Old 05-18-2008, 03:00 PM   #6
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I wouldn't want you to think that there is too much merit in these comments from a mechanical engineering viewpoint, except Gubbs3's one about the weight distribution. Because mechanical gears are very efficient at transferring power, you'll not notice any difference that can be measured on the clock.

Power transmission gear designers (and we're talking gears that are used for power generation, pipeline pumping and seawater injection - 5 to 30MW) will go to great lengths to get their gearboxes from 98.4% to 98.6% efficiency, because that's worth a whole lot of fuel over a 15 year life! Usually though, it's the bearings that absorb the power more than the gears themselves.

The only benefit we get that can be felt is that the larger the pinion, the more tooth 'flank' is in contact, and therefore the less likely you are to strip a spur. So, given your choice, I'd go for the 125/37 as being the least likely to suffer damage in an accident, on a bumpy track, or, for Off-Road, landing from a jump. HTH

(As an aside, if you have a choice, the best involute tooth forms I've measured are on Kimbrough spurs and RW pinions. These will give you the best efficiency. HTH too! )
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Old 05-20-2008, 03:20 PM   #7
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I'm going to side with SlowerOne.

I've been told from the old time oval racers that keeping the roll out the same, go the largest spur/pinon combo you can cram in there. Most oval cars are pan cars so using a larger pinion/spur move the motor closer to the pivot point making the reducing the unsprung weight for better reaction to bumps.
I was also told that gears under 13 teeth get very inefficient at transfering power compared to larger gears. What SlowerOne pointed out that the "flank" or face in contract. This is critical for transfering torque. Since motors produce power in phases, the lower tooth count gears may stall a little bit before turning if the torque is needed between a motor's phase. The higher tooth count helps reducing the cogging that can happen and help the gear "ratchet" each degree forward more easily. Yes inertia does keep the wheels spinning duning the dead band in the power phases.
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Old 05-22-2008, 09:12 AM   #8
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you can also try switching from 48p gear set to 64p gear set, it may give you the same effect.
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