Motor & Gearing for Axial 3 gear trans with TRX-4 Portals

[volumeknob]

Guys,

Looking for some advice on a build. Using the VP VS410 chassis kit with the Axial 3 gear trans running TRX-4 portals for my UMG10 build. Whats the best brushed motor for this application? Was thinking HH 13T 5 slot Crawlmaster Sport on a HW 1080.

The spur and pinion gearing is where I'm getting snagged, I'd like to stay with the stock 56T spur but don't know the largest pinion I can run with this trans to speed the truck back up due to the reduction in the axles. Is it wise to run a 18-20T pinion on a "fast" motor to get the wheel speed back up?

[svt923]

Do you have an idea of your preferred gearing range or how much top end speed you want?

An Axial 3 gear with TRX4 axles and a 56T spur would need to run a 27T pinion to get to the same ratio as a SCXII RTR (42:1). Unfortunately, the SCXII manual lists a 18T pinion as the largest that will fit on a 3 gear setup which would give the truck a gear ratio of about 64:1. That ratio would mean a 13T Crawlmaster on 3S would top out at 4-5 MPH. To get more wheelspeed from there, changing the spur to something smaller so larger pinions fit is probably the most cost effective option.

[volumeknob]

Originally Posted by svt923

Do you have an idea of your preferred gearing range or how much top end speed you want?

An Axial 3 gear with TRX4 axles and a 56T spur would need to run a 27T pinion to get to the same ratio as a SCXII RTR (42:1). Unfortunately, the SCXII manual lists a 18T pinion as the largest that will fit on a 3 gear setup which would give the truck a gear ratio of about 64:1. That ratio would mean a 13T Crawlmaster on 3S would top out at 4-5 MPH. To get more wheelspeed from there, changing the spur to something smaller so larger pinions fit is probably the most cost effective option.

I don't know but the RTR SCX10 ii is too fast for my tastes out of the box in the past.

I was thinking 18T pinion on the 56T spur which is 3.11:1, the trans is 2.6:1 and axles are 7.11:1, so isn't that 3.11 x 2.6 x 7.11=57.49:1? I have a Crawlmaster 16T that's slightly faster I believe, so that should help too.

[Voodoobrew]

My signature has a gearing chart you can play with.

Sent from my SM-N950U using Tapatalk

[boldfin]

I took a similar route to that suggested by Harley in his video on my VS4-10 chassis with a 3-gear trans and TRX-4 axles. I went with a 50T spur and 21T pinion. Harley went with a 20T pinion, I think. But I'm also running Underdrive in my rear TRX-4 axle, so that put me right where I wanted to be:

2.30 (Portal ratio) X 3.09 (Stock Front Axle) X 2.60 (3 Gear Trans) X 2.38 (21T Pinion / 50T Spur) = 44.01 on the front.

2.30 (Portal ratio) X 3.50 (Underdrive Rear Axle) X 2.60 (3 Gear Trans) X 2.38 (21T Pinion / 50T Spur) = 49.83 on the rear.

12.41% Overdrive.

I am running the AXE 2300Kv system, and going for moderate to slow crawling / occasional trailing. I can always drop a tooth or two on the pinion if I want to, but so far I am liking this setup. It's definitely slower than a stock SCX10-II.

[zane!]

Important question here: are you planning to run 3S Lipos? That alone will bump up your wheelspeed by close to 50% compared to 2S and needs to be accounted for. Is your baseline/preferred speed based on 2S or 3S?

For reference, I dropped to 9/60 on my truck for slow crawling with the AR44 axles and now with 3S packs I have a bit more wheelspeed than stock on 2S packs which was my baseline.