Quote:
Originally Posted by J57ltr
1. I never said that it was a fact in fact I asked if it could make a problem worse.
2. Data? No I don't I was asking a question. And giving my thoughts on what could happen. I also didn't say it was the problem I only said that with subpar batteries that maybe this could possibly be a problem.
3. I never said there were any gear changes. It was an analogy to show that a difference in gear ratio from the same speed causes the motor spins faster at the same given speed. Which could cause more back EMF.
4. You said according to your "math says the opposite" leads me to believe that you calculated something. It will take me some time to get some accurate calculations but when I get back I'll bone up on my ME books and see what I come up with and post how much power it takes to stop from different speeds. I don't think you have calculated anything because you still don't see that going from accel to decel changes the mechanical advantage on the motor.
5. I am not sure what a shim is (other than a thin piece of material). Not to be smart, but I can't tell if it is a spelling error or what.
6. a 5 tooth difference gives me this:
the only difference between these 2 setups is the body EVERYTHING else is the same same number of cells even charged on the same charger. We usually do top speed runs but my setup always changes from a 3.3Kv all the way to a 10.5K motor and I run everything from .8 to 1.0 to 48 pitch gears depending on what I am doing at the time. I run anywhere from 2S A123 to 4S A123.
To TexasSP: Yes to stop in the same distance it takes much more power, but I'll have to get back to you on that for an approximate value
To lydiasdad
What is the typical internal resistance of a lipo? I know my 4S1P A123's come in at .032 ohms. Or about .008 ohms each and that's with the connections. I don't know off the top of my head of the 2P packs.
Jeff
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1. - You did not say it was fact. But...you won't accept that it is not true, either. I have tried to explain through various analogies, which you are reluctant to accept. You revert back to a similar vehicle speed with a smaller pinion, which requires an input voltage change along with the gearing change - this is not the topic being discussed, or did I miss something? I thought we were discussing a simple gear change and its likelihood of being the cause of failure on an esc.
2. - subpar batteries IS the problem - not a smaller pinion
3. - you suggested gearing down as an example, which indicates a gear change. Without the gear change, if the vehicle is going the same speed with shorter gearing, the motor HAS TO BE spinning faster to begin with(higher input voltage), which is not apples to apples here. The discussion was regarding a simple gearing change. This gearing change will also change vehicle speed, and therefore required braking force. I don't need an example to show that a different gear ratio results in different motor speed at a given vehicle speed - this is not only obvious, but has been my point all along. At a given vehicle speed, a shorter gearing requires higher motor rpm. However, if driving a vehicle at a given voltage, a gearing change ALSO changes vehicle speed. I am not disputing the fact that higher motor rpms yields higher back voltage. I am simply disputing the higher rpms to begin with(unless you change input voltage, output rpms won't change with a given Kv motor).
4. - When you do your calculations, you will plainly see that the motor's mechanical advantage DOES NOT CHANGE from acceleration to deceleration (accept in your car scenario when you physically change the advantage through a gear shift). Without a mechanical change, the mechanical advantage does not change. I look forward to any data that refutes this.
5. Shim is a spelling error. Sorry for the confusion. I meant to say run the vehicle into your SHIN at 8.62 mph to see the energy that must be disippated. Then try it at 0 mph and let us know if there is a difference in force applied to your shin. :)
6. - your data verifies my statement - The A123 cells are subpar for the task at hand AND the ratio is extreme. And it is a speed run. That is exactly what I said(subpar batterries, extreme gearing etc.). In 1p configuration, the A123 cells drop voltage significantly, as has been well discussed. If you want to go 75mph in the Rustler, you need more than 2s1p A123 packs(unless the rustler is in the back seat of your real car). Still, lower gearing in all cases results in less load on the electronics.