Good Final Crawl Ratio & Wheel Spin Combo??

[RevoRacer]

I am planning to build a crawler with a 72T spur, 9T or 12T pinion, Twin Force tranny and Revo diffs. I am trying to decide what kind of motor I should use (55T or faster turning motor) and if I should use a GD600 or not. I'm inexperienced in deciding what is a good final crawl ratio and wheel spin combination. :?

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If I use a 72T / 9T combination that ratio = 8:1

I believe a stock Twin Force ratio is 2.35:1 X 8:1 = 18.8:1

Revo diffs (like Maxx) are 2.8:1 X 18.8:1 = 52.64:1

Now if I add a GD600 with a 13T pinion 3.5:1 X 52.64:1 = 184.24:1 Final ratio.

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Basically I want to make sure I have good torque and good wheel spin at the same time.

I guess what I need to know from you more experienced crawlers is:

1.) Is this a good final crawl ratio. I know I can use different spur and pinion combos to tweak the final ratio.

2.) And what motor should I use to get good wheel spin? Also I know faster turning motors (less turns) use up batteries faster. Is this much of a concern? We all want long run times!! :-P

Lets hear those expert opinions!! And as always, THANKS GUYS !!!!!

[TwistedCreations]

I personally found 90:1- 110:1 to be a good ratio. It gives the slow crawling, plus has wheelspeed. I run a GD600 though witha 22t motor.. It seems to go with a faster motor with a reduction unit. If you go with only a 55t lathe motor and no reduction, you may have a crawl ratio of 80:1, but with the slower turning motor, it will actually be a lower ratio than that.


My last truck ran around 160:1 and had no wheelspeed to bump up stuff.. If you run a GD600, stick with the stock 18t pinion that comes with it

[RevoRacer]

Thanks for the advice TC...

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Okay so if I use a 72t / 12t combo I would get: 6:1

6:1 X trans ratio (2.35:1) I get: 14.1:1

14.1:1 X diff ratio (2.8:1) I get: 39.48:1

39.48:1 X GD600 ratio (standard 2.5) I get: 98.7:1 Final crawl ratio.

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Right in the middle of your suggested ratio!


I have a 25t double motor to use with this combo. Does that sound good??

[mazdaparts]

Another thing to consider is the tires you will be using. A tire that is 7" tall will have more wheel speed that a tire that is 5.75" tall using the same gear ratio. Personally I have found that my final ratio of 113:1 is a little fast using 6.8" tall tires. I plan on going to a 129:1 as soon as I am done cutting my tires. Forgot to mention I am using a Johnson 550 can motor with 15200 rpms on 7.2 volts. I also have a johnson 550 that does 10300 on 7.2 volts.

[RevoRacer]

Yeah, that's right. I forgot about that. I will be runnung Moab XL's, so that's a pretty tall tire. I'll keep that in mind. -- Thanks!