Gear question to a new build E-Maxx

I´m building a new E-Maxx Brushless (MMM) with a lot of option parts.

At the moment I´m not sure if I choose the right parts for the gear.

I use the Traxxas transmission, motor 17T/68T and would like to use the HB Diffs C8178 with the pinion C9009.

Do I have to change the motor gear or will it these parts fit?

The Maxx should not be a high speed racer, more a basher. I will use 4S lipos and 6S aswell.

Thanks for your comments

[suicideneil]

No need to change the main spur/pinion gearing- using 1/8 buggy diffs lowers your overall gearing slightly, it has the same effect of using ~1 less tooth on the pinion or 2-3 teeth less on the spur, but the overall effect is minimal.

Originally Posted by suicideneil

No need to change the main spur/pinion gearing- using 1/8 buggy diffs lowers your overall gearing slightly, it has the same effect of using ~1 less tooth on the pinion or 2-3 teeth less on the spur, but the overall effect is minimal.

Hi suicideneil,

that´s not correct. I read a lot of it meanwhile. If you chosse the 43/10 ratio, a standard E-Maxx will run with 4 S batt a max. speed (calculated with R/C calculator) of 36,61 km/h. With a 43/13 it goes up to nearly 48 km/h.
The axle torque at 43/10 is 30% higher, than with the 43/13....so the gear with some tooth up and down as a great influence i think.

[Overdriven]

The standard emaxx uses a 37/13 diff ratio, and neil is correct. If you went with the standard buggy gearing of 43/13, it would be the same as using a 15T pinion with the stock emaxx diffs. Also, your axle torque does not depend on the diff ratio. It depends on the motor and the overall final drive ratio. I don't know what motor you're using or what you're speed goals are, but I'd recommend the 43/13 buggy ratio.

Overdriven,

I use this one

http://www.scriptasylum.com/rc_speed/_gear_calc.html

and here the top speed estimator:



The upper is the standard E-Maxx andtop speed is 34mph, torque 10
The lower has a top speed 26mph, torque 13
changes in the second: from 37/13 to 43/13 and from 17T to 15T.

Don´t know from which experience you took your advice, but this says it´s different...

[suicideneil]

You need to use a BIGGER pinion gear when using the 1/8 scale diffs, not a smaller one:

bigger pinion and/or smaller spur = gearing up

smaller pinion and/or bigger spur = gearing down.

Thats why your speed is greatly reduced when using the lst diffs in the example above, becuase lst diffs have a lower ratio than the emaxx ones- you introduced a 2-folder gear reduction

I happen to use 43/13 diffs in my GorillaMaxx with 70/24 gearing on 5s lipo for ~40mph topspeed; redo your sums with an 18-19t pinion & the lst diffs and you will find it comes out about the same as the standard emaxx example

[Overdriven]

I used 15t with 37/13 and 17t with 43/13 since that's what you said you wanted to run. With 37/13 + 15/68 you get 48km/h, 23.65:1 fdr (final drive ratio), and 11.36 axle torque. With 43/13 you get 47km/h, 24.25:1 fdr, and 11.65 axle torque. So my point about axle torque being dependant on fdr is correct, and changing to the 43/13 diff ratio requires changing the pinion by 2 teeth to maintain the same speed and axle torque. Although I think there is a language barrier thing or lack of explaination going on contributing to the confusion.

I say go with 43/13 over the 43/10 because of gearing options. With 43/10 you'd need 54/22 gearing and 6s to get to 45mph (70km/h). With 43/10 diffs and the 17/68 gearing you said you wanted to run, top speed was around 20mph. But maybe you're okay with that. Either way I hope our answers have helped in your descision making process.

agreed thanks

at the moment I only have the C8178, which is 43/10 (I ordered some parts to build up a 43/13 ratio out of them). So until I got the parts (I hope they will fit) The HB C80841(43/13) is not available and I need some diffs which fit into FLM hybrid´s.

I decide to go with 65T /22T, axle torque is at 11,19 and top speed at 4s nearly 51km/h.
With the standard 68T / 17T axle torque inceases to nearly 15 and I don´t know if that´s too much, and it´s too slow