Quote:
Originally Posted by J57ltr
No it doesn't but it does change the way braking works The amount of power delievered back into the system is the same, but with the smaller pinion it will be delievered faster (Force over time) with the samller pinion. braking will be quicker than it would be with a larger pinion. After all we are only talking about an 8.62 mph difference.
This question I have posed was answered by Patrick is:
Now on the large pinion smaller pinion issue is it safe to say that having a numerically higher gear ratio will cause more back emf which could exacerbate the problem if the batteries are sub par?:'
and his answer was:
In 99% of the cases, that is exactly true.
Yes the motors are spinning at the same speed given everything but the pinion, but the amount of energy dissipated (mechanical to electrical) is higher during braking with the one with smaller pinion will get rid of it’s energy more quickly than the one with the larger pinion.
And with the low KV motors you guys use (under 3K) the generated voltage is higher. I switch between motors all the time and depending on what I am running I may have to take the braking force to 30% but on a high KV motor I might have to have it at 100%, even though the gear ratio changed to correspond to the motor and batteries being used.
So unless the batteries have a low resistance then the voltage will start to rise to a dangerous level. If Regen is occurring, then it must be a higher voltage than the power source. And since 6 S is just about at the limit anyway so the back EMF is going to be higher (but for a shorter period of time) than it would be with the larger pinion.
So unless someone has some voltage numbers on the decel rates at these differing gear ratios we aren’t getting anywhere.
Jeff
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Patrick's statement was further clarified by saying that a smaller pinion causes less ESC Stress in 99% of all cases - indicating the opposite of what you said(and your "numerically higher" gear ratio comment was likely misconstrued - which was also discussed).
Why(how) does the vehicle with the smaller pinion get rid of more energy more quickly? My math says the opposite. In this example, force is actually NOT the same - the vehicle with the larger pinion would be moving faster and would therefore require more force to stop itself(same mass at higher velocity has more inertia and requires more force to stop). In the vehicle with the smaller pinion, the vehicle speed is lower and the motor has more leverage at a given rpm. If anything, the faster vehicle with the larger pinion will
have to generate more force stopping itself. I don't see how it could be any other way.