Suggestions on gearing

[Cr00zah]

I am using the LNC axles, suspension, and other bits in a hybrid build. I am dead set on staying brushed & 2S (since I have a bunch of this stuff and don't want to buy new batteries etc).

For the axles, I have some HD worms on the way, so they'll be 21:1 reduction.

My goal is to make this build for rocks, and general trail work. Ideally, I'd like it to be able to move a bit faster than I normally walk.

I am thinking to couple the motor directly to the transmission - which much to my surprise is just a straight shaft, no gears - and do away with all of the external gears. Then, mount a transfer case to the tranny output.

What I am stuck on is what turn motor; and whether I should go for additional reduction in the transfer case. Again, staying brushed and 2S! and obviously I'd prefer this not melt down/go up in flames.

TIA for any suggestions.

[Olle P]

Why not just use the stock LNC tranny? It's light and it's good!
Coupled with a Traxxas Titan 27T 550 motor it will provide some more speed without overheating.

You need to know why worm drive crawlers are (inherently) slow.

[Cr00zah]

Hi Olle, I was hoping you'd chime in. I have read your in-depth technical threads and feel comfortable with what I'm facing when using the LNC axles.

When you say the LNC tranny - do you mean the external gears? Because when I say tranny, I am talking about the plastic case with the straight-through shaft (no gears inside). I'm thinking I might like to have this case inline with the motor, and do away with the external gears altogether. Might that allow me to run a higher-turn motor w/o burning it up?

[Olle P]

Originally Posted by Cr00zah

When you say the LNC tranny - do you mean the external gears? Because when I say tranny, I am talking about the plastic case with the straight-through shaft (no gears inside).

I mean principally everything stuck to the motor plate (part LOSB3015).
You need some way to transfer movement to that shaft anyway.

Originally Posted by Cr00zah

I'm thinking I might like to have this case inline with the motor, and do away with the external gears altogether.

How then do you transfer the rotation from the motor axle to the outgoing shaft?

Originally Posted by Cr00zah

Might that allow me to run a higher-turn motor w/o burning it up?

The motor to drive shaft gear ratio is the way to adjust the load on the motor. A 1:1 ratio forces the motor to provide three times more torque than a 3:1 ratio. More torque = more heat (for a given motor).

A higher turn motor (as in "slower rotating with more windings") will provide more torque with less heat than a low turn motor... BUT it will also provide less maximum power than a low turn motor with the same voltage feed.

Thus a low turn 540 size motor won't be able to deliver the power you need to go as fast as you want, if you stick to 2S LiPo.

You need a much bigger motor (800 size or so) to get that combination of torque and power from 2S, and those motors are typically designed for higher voltages. That bigger motor will add weight and thus need for even more power...

The key for you is to first decide on a motor able to deliver more power than the stock motor, while not overheating. That means BIGGER and possibly with less turns. (So I recommend the Titan as a cheap alternative that will deliver some more power.)
Then you can adjust the gearing to suit the motor.

I've seen one very elegant solution for running Losi axles without a tranny.
That's a Norwegian guy using a brushless outrunner with the motor axle sticking out at both ends, and have the drive shafts attached directly to the motor axle.

[Cr00zah]

Thanks again Olle. When I suggested removing all of the external gears, I mentioned using a transfer case off the tranny shaft to get power to both axles. But after considering your advice, I will follow it - stick w/ stock gears for now, get an entirely different motor and adjust from there. Thank you again for your wisdom!

[Olle P]

I see a made a small mistake in my previous posts.
The Traxxas motor recommended (#3975) is 21 turns, not 27 turns (and, very important, not to be confused with the now common 12T motor!)
The 21T motor might need a little adjustment to the gearing, using a smaller pinion.

[Cr00zah]

Cool, thanks! I have a bunch of pinions to play with, I am sure I'll find the sweet spot for my needs w/o any trouble.

[GiJoe]

Originally Posted by Olle P

I've seen one very elegant solution for running Losi axles without a tranny.
That's a Norwegian guy using a brushless outrunner with the motor axle sticking out at both ends, and have the drive shafts attached directly to the motor axle.

Olle P, are you referring to JENS? I have also seen the DAHU with a direct drive set-up. Both those vehicles using the Turnigy G15 710KV motor.


I just ordered one of those motors today! I want to try this in a scale crawler. Do you see any harm in running this on 4 or 6S (other than potential breakages! )

I was hoping the higher voltage would help alleviate some cogging from the unsensored motor, but not sure...

[Olle P]

Originally Posted by GiJoe

Olle P, are you referring to JENS? ...

Probably. I don't remember the name...

Originally Posted by GiJoe

Do you see any harm in running this on 4 or 6S ...
I was hoping the higher voltage would help alleviate some cogging from the unsensored motor, but not sure...

4S no problem. 6S can possibly (but not surely) damage the motor.
Higher voltage doesn't help against cogging.

The multi-pole nature of this motor makes cogging less problematic than for a similar two-pole though.