View Full Version : get my motor burnt

08-03-2003, 09:13 PM
After a few runs with my (home made) mini monster, I get my stock motor burnt. So I have to rewind for another touring X and I plan to put the new power train maybe with the 180 motor. Any other idea?

08-03-2003, 09:16 PM
I put 34T gear at the main power shaft. Any idea about the pinion? 10? 11? 12?
THank you.

Hooters Driver
08-04-2003, 01:18 AM
I'm not sure what gear ratio would be best for your monster truck since I don't know what size the tires are.

Here is how you can calculate the gear ratio to at least get you close. Using the original tires/gears this is the mini-x original final drive ratio.

The stock tire is approximately 28mm tall so in one revolution of the tires the car moves (28mm * 3.1416<pie> = ~88mm). So with the stock gear ratio (35/8 = 4.375) it takes 4.375 engine revolutions to travel 88 mm. Therefore, each revolution of the engine makes the car travel ~ 20.1 mm (88/4.375).

As a starting point you should try to achieve that same ratio ( 1 motor revolution equals 20.1 mm travel distance). Since I don't know the exact diameter of your new tires I will just give you an example and you'll have to plug the actual numbers in to figure out what gears you need. If your monster tires have a diameter of 75 mm then one revolution of the tires will move the car 236 mm. You are running through the stock differential plus a second differential which will multiply the ratio a second time. So here are the calculations:

s1 = original spur gear
p1 = original pinion gear
s2 = added spur gear
p2 = added pinion gear
td = tire diameter
dis = distance traveled per motor revolution
Pie = 3.1416

First we'll use a formula to calculate the original ratio:

dis = (td*Pie)/((s1/p1)

dis = (28*3.1416)/(35/8)
dis = 20.11 mm

Now to calculate the correct pinion gear for your new combo we'll use this formula:

p2 = s2/{[(td*Pie)/(s1/p1)]/dis}

p2 = 34/{[(75*3.1416)/(35/8)]/20.11}
p2 = 12.7 teeth

So, if your monster tires are 75 mm tall you will need roughly a 13 tooth pinion gear to maintain the same approximate overall gear ratio as the mini-x originally had. This would only be a starting point and you would probably want to experiment from there to get the best possible acceleration.

I'm sure there are easier ways to come up with the correct pinion gear but this was the best I can do. Hope it helps and was not too confusing.


08-04-2003, 03:06 AM
Wow...! It was a very detail answer. To be honest, I got surprise for the long formula but this is the best answer I've ever got. Very mechanically. Thank you very much and I let u know the result soon (as soon as I get the wallet filled back, hahahaa..). See U Mic..!

08-04-2003, 05:37 AM
Originally posted by Hooters Driver
I'm sure there are easier ways to come up with the correct pinion gear but this was the best I can do. Hope it helps and was not too confusing.


With 50mm diameter of tire I have to get 19T pinion.
Well I hope 19T available in the market/LHS. SOmebody could help?

Hooters Driver
08-04-2003, 05:50 AM
It might be easier to look for a smaller spur gear instead. If you can find a spur gear with between 18 and 20 teeth you can use a pinion between 10 and 12 teeth. With a 50 mm tire the key will be to maintain an approximate gear ratio of 1.79:1 for your second gear set.........and I'm glad I could help you.

08-04-2003, 06:11 AM
Yes. It was flashed on my mind to do so. I'll find that one. You're help me MUCH, Mic.
Thank you.

Hooters Driver
08-06-2003, 03:58 PM
I was in my LHS today and they do have pinion gears in the 19 - 22 teeth range but they appeared to be for a larger motor shaft diameter. They also had a wide variety of spur gears but I didn't see anything right off hand that looked like it would just slip on and work. I'm sure if you look hard enough you should eventually be able to find the right gear combination that will work without modifications. If you can't find anything else let me know and I can send you some gears from my LHS.


3series takumi
08-06-2003, 04:37 PM
shouldnt rs4 micro gears work, i think they are the same motor shaft size

Hooters Driver
08-06-2003, 04:55 PM
I'm not too familiar with micro rs4 parts. That may have been what the gears I saw were intended for. Do they offer micro rs4 gears in the 17 -23 tooth range?


3series takumi
08-06-2003, 05:00 PM
the tallest i have seen for a pinion is 15t at 48pitch

08-06-2003, 09:19 PM
Originally posted by 3series takumi
shouldnt rs4 micro gears work, i think they are the same motor shaft size

RS4 is not popular in Indonesia so it's difficult to find one. Anyway, I'm still search for any gears that available in Jakarta's LHS.
Thank you.

08-14-2003, 04:34 AM
AfterI rewound my anchor with 0.5mm wire, I found one of my FETs got hot now it's didn't wotk at all. I put the pic to tell u which FET (white circled) and my rewound anchor. What's the function of that FETs since I know the stackable FETs which could run the motor.
Oya, I ran with 6 cells. The same cells when I got my motor burnt.
Now I have to find the new FETs, finally.

08-14-2003, 04:39 AM
this is my 0.55 wire rewound motor. It eats the esc!