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picking the correct pinion gear for electric on road

picking the correct pinion gear for electric on road

Old 04-19-2015, 05:30 PM
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Default picking the correct pinion gear for electric on road

I purchased a Yokomo BD7 2014 edition .I bought a LRP Flow works esc and am going to buy a Reds 8.5 or LRP 10.5 motor .How do I calculate what pinion gear to buy for the motor.Car will not be raced at events ,just to run with my nitro cars .I would like it to be as fast or faster.Thanks for any help .Buying a 2 s lipo to power it.Main gear on car is 94 tooth ,do I need to go up.Im am new to electric so go easy on me
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Old 04-19-2015, 06:41 PM
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Originally Posted by martind1318 View Post
I purchased a Yokomo BD7 2014 edition .I bought a LRP Flow works esc and am going to buy a Reds 8.5 or LRP 10.5 motor .How do I calculate what pinion gear to buy for the motor.Car will not be raced at events ,just to run with my nitro cars .I would like it to be as fast or faster.Thanks for any help .Buying a 2 s lipo to power it.Main gear on car is 94 tooth ,do I need to go up.Im am new to electric so go easy on me


In case nobody has the same car and can tell you what they use...

You can calculate the gear ratio. But you need to have a better idea of your ideal top speed than "as fast as my other car". If you have a max mph and motor KV, you can figure it out with a little math.


It goes a little like this:


(desired MPH) * 5280 * 12
------------------------------- = rpm of wheels
60 * (tire circumference)


(rpm of wheels) * (internal gear ration) * (spur gear tooth count)
---------------------------------------------------------------------------- = Motor KV
(pinion gear) * (battery voltage)


You will have guess a pinion size and see what KV you get. Keep changing the pinion (and spur?) until you get a KV that roughly matches whatever motor you plan on running.

An example--my dest210 has an internal gear ratio of 2.6:1. With a spur/pinon ratio of 9, and a 6,200 KV motor, I could theoretically go 25mph!

This formula only gives the theoretical top speed. Actual results will depend on the actual rpm of the motor under load, and also the strength of the motor. And no guarantee that your motor/esc combo can actually handle the gearing required for whatever top speed you decide you want.
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Old 04-19-2015, 07:49 PM
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Get a RC FDR Calculator.
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Old 04-19-2015, 10:46 PM
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Most brands have a chart of how much turns with what default FDR, just look them up.
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Old 04-20-2015, 04:57 AM
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Internal ratio of the BD7 is 2.0

What ratio you run depends on your motor *and* if you plan to run blinky or boosted.

If you're not racing, best to run it mildly boosted to as it is lower stress than blinky (with heaps of timing to chase speed)

For a 10.5, this means a FDR in the 7's or so - you can do that with a 96spur, but you're better off getting something larger.

96 spur and 25 pinion will give 7.6
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Old 04-20-2015, 06:06 AM
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Thanks for all the help guys,now I can get some stuff ordered and experiment .
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Old 04-20-2015, 07:06 AM
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http://www.petitrc.com/reglages/yoko..._GearChart.pdf

I don't run mod but 94 is more of a blinky 17.5 sized spur gear. Mods usually run around 116. Also make sure you get Panaracer or kawanda spurs. Lots of other brands won't fit right.
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Old 04-22-2015, 02:11 PM
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Thank you sir ,will do
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Old 04-22-2015, 03:09 PM
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The main thing you want to concern yourself with when it comes to gearing an electric car is the temp of your motor. If you have an infrared temp gun for your nitros, use it on your electric motor after a few minutes of hard running. In general, you don't want your motor temp to get above 160 degrees. If you're still running cool, you have room to gear up. If you're getting too hot and want to save your motor, gear down.

My only experience is with racing 17.5+ stock motors in blinky mode, so some mod/boost guys may want to chime in, but I'm assuming the idea is roughly the same.
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Old 04-22-2015, 03:54 PM
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Thanks,getting very good usable info .I do have a temp gun to use.Thanks
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Old 04-22-2015, 03:56 PM
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The difference in mod is you won't get anywhere near that sort of temperature - unless something is very wrong typically.

But unlike blinky, in mod you have more things than just the gear ratio and can timing to balance out. But gear ratio is (and can timing) no where near as critical either. Look at most of the pro setup sheets for mod and you will notice they all run pretty similar FDR no matter what motor they have or what track they are on.

You run low can timing, gear for the motor wind, then add boost/turbo to suit the layout (ie: too much turbo at the wrong part of the track is trouble, but you want it "all in" on the straight)
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Old 04-23-2015, 10:20 AM
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Thanks for the info cplus. I don't want to hijack the thread, but I think this is along the same lines as the OP: What sort of temps are expected for mod motors after a solid run? Is there a certain temp you generally don't want to go over?
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