Benefits of Gearing Down

[swerv512]

I have a TRX4 Sport Kit. It has an 36.25 FDR out the box (39/17). My rig is currently at 9lbs. I have a HW 1080 ESc and a HH Crawlmaster Sport 12T motor. I run it on 3S with 4300mah LiPo. I get insane runtimes right now. My typical run is maybe 10 minutes of "trailing" to get to the rocks and then i can usually get an additional 60 minutes out of the pack (slow crawling- not dirt rooster tailing wheel spinning up the rocks). When the terrain requires more wheel speed than finesse my motor heats up after a bit (140-160 degrees) after a series of non-stop mixed crawling. I am never above walking speed except for the occasional "speed run" when trailing.



Sorry - now the question...


What's the difference between using my finger for throttle control with my current setup versus gearing down for SLOW CRAWLING (I have a 45T spur and a few pinions to get me in the 47 to 79 FDR range) besides slower top end = lower wheel speed ( i dont mind losing a bit off the top end on the trail but sometimes i think a bit of UMPF helps me get up obstacles). If electric motors have 100% available torque all the time, is gearing down just a finer motor control than i can do with my finger?

 

[Steve g]

36 FDR seems high, especially for the weight.. Gearing it down will increase low speed control (like you suspected), increase drag brake, decrease motor temps, and increase run time( during crawling). I can get the same run time as you with a 1600mah battery on a 2.2 rig with about a 70 FDR. (But that's with a brushless motor, so more efficient than brushed).
So I'd recommend gearing down. And if you can, try out a 4s battery to gain back the lost wheel speed. (You would need a different esc though, as I'm sure you are aware).

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[DRED805]

The only con to gearing down is the extra noise coming from the drivetrain.

My truck with 76:1 / 110:1 (front/rear) final drive ratio is loud as ****. Crawls nice and slow with a 1600kv motor on 6s, though.

https://youtu.be/YoXsIsADpLY

 

[swerv512]

36 FDR seems high, especially for the weight.. Gearing it down will increase low speed control (like you suspected), increase drag brake, decrease motor temps, and increase run time( during crawling). I can get the same run time as you with a 1600mah battery on a 2.2 rig with about a 70 FDR. (But that's with a brushless motor, so more efficient than brushed).
So I'd recommend gearing down. And if you can, try out a 4s battery to gain back the lost wheel speed. (You would need a different esc though, as I'm sure you are aware).

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The only con to gearing down is the extra noise coming from the drivetrain.

My truck with 76:1 / 110:1 (front/rear) final drive ratio is loud as ****. Crawls nice and slow with a 1600kv motor on 6s, though.

https://youtu.be/YoXsIsADpLY

+1 to you both. I threw in the 45t spur with the 13t pinion before I went out crawling tonight and I really enjoyed the experience better- minus the extra noise (I need to re-shim my clicking Transmission. For some reason the clicking noise returned with this lower FDR 57 vs 36. I know the TRX4 is built like a tank but mine sounds like one!

Anyways low speed control was much improved. I could lay into the trigger a little more and crawl in the meaty throttle zone a bit more if that makes sense. And true again- my motor ran much cooler after an hour and 40 minute session. My 4300mah pack was at 3.8v per cell when I finished.

I still have an 11t pinion and a 9t pinion. Going to try to re-shim the shafts and slap jn the 11t pinion next.

 

[swerv512]

The only con to gearing down is the extra noise coming from the drivetrain.



My truck with 76:1 / 110:1 (front/rear) final drive ratio is loud as ****. Crawls nice and slow with a 1600kv motor on 6s, though.



https://youtu.be/YoXsIsADpLY

One side note, how do you calculate the FDR with over/under drive? Thanks

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[DRED805]

One side note, how do you calculate the FDR with over/under drive? Thanks

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https://scriptasylum.com/rc_speed/top_speed.html

 

[swerv512]

https://scriptasylum.com/rc_speed/top_speed.html

Thanks for the link.
I installed the 11t pinion last night and went out for a shakedown run. Modulation is even better with the 11t pinion but this is as high a gear ratio I'll go- no 9t pinion for me. Any slower top end and I won't be able to correct front flips when descending steep stuff. The motor after 1.5 hrs last night of mixed crawling the usual lines was at 98 degrees. It was a little cold out last night but that's a huge drop from the 160 degree I was at just a few nights ago with the stock 17/32.

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