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nel33

calculating gear ratios on brushed motors

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how do you calculate the ratios on brushed motors? i see guides for brushless motors but cant find one for brushed motor. im going to install a highspeed gear set on the manta with 22t pinion and would like to see how it will agree with the HW1080. the HW1080 is most likely all good as im running nimh 15t brushed motor and the esc can handle 540,550, 775 series 2s lipo or 30k rpm at 7.4v. the DYN1172 15tmotor doesnt have a RPM limit listed so i need to calculate that. to see where i land with the highspeed gear set and 22T pinion.

ive figured out the Spur Gear / Pinion Gear = Gear Ratio easily enough but get stuck trying to figure out the rpm so the FDR is unclear to me.

the stock manta gear set is 74T and the highspeed set is 69T and the smaller gear attached to it looks like it has 16 teeth.

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1 hour ago, nel33 said:

how do you calculate the ratios on brushed motors? i see guides for brushless motors but cant find one for brushed motor. im going to install a highspeed gear set on the manta with 22t pinion and would like to see how it will agree with the HW1080. the HW1080 is most likely all good as im running nimh 15t brushed motor and the esc can handle 540,550, 775 series 2s lipo or 30k rpm at 7.4v. the DYN1172 15tmotor doesnt have a RPM limit listed so i need to calculate that. to see where i land with the highspeed gear set and 22T pinion.

ive figured out the Spur Gear / Pinion Gear = Gear Ratio easily enough but get stuck trying to figure out the rpm so the FDR is unclear to me.

the stock manta gear set is 74T and the highspeed set is 69T and the smaller gear attached to it looks like it has 16 teeth.

The formula to calculate FDR is spur / pinion x internal ratio

Internal ratio is set by the gearboxes. FDR stands for final drive ratio and doesn't take wheel size into account, which is why a 17.5T touring car will run FDR around 4 but a buggy is around 5.5

The manual will show the internal ratio, and also have a table with the FDR for the available pinions with the stock spur.

You only really need the high speed gearset for brushless motors. A 15T brushed will probably need the biggest spur (which is the kit one I think) and one of the smaller pinions. Use motor temperature to check. Run a couple of minutes then check the motor temp. If its cool go up a pinion, if its too hot go down.

To give you an idea I have the high speed gearset for my Top Force but ended up with the kit spur gear for the kit silvercan and Super Stock 23T

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1 hour ago, Jonathon Gillham said:

The formula to calculate FDR is spur / pinion x internal ratio

Internal ratio is set by the gearboxes. FDR stands for final drive ratio and doesn't take wheel size into account, which is why a 17.5T touring car will run FDR around 4 but a buggy is around 5.5

The manual will show the internal ratio, and also have a table with the FDR for the available pinions with the stock spur.

You only really need the high speed gearset for brushless motors. A 15T brushed will probably need the biggest spur (which is the kit one I think) and one of the smaller pinions. Use motor temperature to check. Run a couple of minutes then check the motor temp. If its cool go up a pinion, if its too hot go down.

To give you an idea I have the high speed gearset for my Top Force but ended up with the kit spur gear for the kit silvercan and Super Stock 23T

thank you for the reply. the gearing stuff is still new to me. im just trying to see if i should worry about burning the motor or not. the esc should handle it fine but the motor is more of a vague answer. a burning esc is a fairly big worry should it happen but a burnt motor is less serious as i could order one easily enough. a melted tub is more serious. im hoping to get somewhere in 35-40KMh at the most and have it to be easily handled. a vid with top force and 2s had speeds closer to 58kmh which is too much for my liking to say the least. that setup was brushless and lipo so its not the easiest comparison. im not ready for that speed limit. 

i didnt build this car from a kit which is how i came across the current motor/pinion as i wanted something faster than sport tuned. i dont particularly see an internal ratio on the online manual, maybe i missed that part but i can only count the teeth at this point. if the motor is cool enough with 22tpinion and im happy with the speed then it should be optional to go to a higher pinion? the manual has 16-21 pinion options. i will be speed testing the manta in both gear sets to see what difference there is.

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I just had a look at a manual online and page 5 showed the optional pinions and the FDR was shown under each. In the manuals for older cars its often on the page where you fit the pinion.  I'm pretty sure the high speed gearset comes with a little instruction sheet and that includes the table showing the FDR.

The ESC should be fine but the motor will cook. It will keep going but deteriorate ove time (may get so hot solder melts, the leads fall off etc). It could melt the plastic too.

If you don't get there with this setup brushless would be the way to go for a reliable 40kmh. Go for 4000kv or 10.5T - 13.5T and that should comfortably do it without stressing the electronics. 

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1 hour ago, Jonathon Gillham said:

I just had a look at a manual online and page 5 showed the optional pinions and the FDR was shown under each. In the manuals for older cars its often on the page where you fit the pinion.  I'm pretty sure the high speed gearset comes with a little instruction sheet and that includes the table showing the FDR.

The ESC should be fine but the motor will cook. It will keep going but deteriorate ove time (may get so hot solder melts, the leads fall off etc). It could melt the plastic too.

If you don't get there with this setup brushless would be the way to go for a reliable 40kmh. Go for 4000kv or 10.5T - 13.5T and that should comfortably do it without stressing the electronics. 

thank you for the reply,  i was worried i might scrap the motor. im not going to risk scrapping this motor this fast on purpose. so those are the ratios under the pinion, how do you interpret the numbers by component? the motor mount is aluminum but the chassis is plastic. im guessing a 21T pinion and high speed gear would be near or past the limit of the current motor?

im not a big fan of brushless but it if gets the desired speed then that might be worth the investment. i got enough money sunk into this build so a bit extra isnt strange at this point. its already raining so a bigger downpour doesnt change how wet your clothes get... its Lipo that im not willing to get into, brushless motors arent a deal breaker for me. i was first considering 13.5T motor but wasnt able to find one locally, online has enough choices but the 15T motor was easily ordered locally. i guess a better esc would also be needed to go brushless, the 1080 is brushed motor only.

i can easily hit close to 45-48kmh with the slash if i bother to swap the gears out but will do that should i ever need to take it apart for some reason. atleast thats what is advertised.

on a side note, why does tamiyaUSA say the highspeed gear set isnt compatible with Manta/Top Force when they say its for TA02 chassis? its a bit weird but im guessing the FDRs might not be compatible??

the LHS has an ESC and 13.5T brushless combo available: HWI38020240 XR10 Justock ESC Justock 3650 SD G2.1 Motor 13.5T - Combo. not sure if thats the best price available on the market but i wont have any shipping costs as in-store pick up is free.

i reckon if i go brushless in the manta, i could possibly transfer the 1080 15Tmotor and put a 17T pinion on the td and put the sport tuned on the super sabre... no use in letting the 15t motor and ESC sit in a bag when i could be used elsewhere. i dont trust TBLE 02 escs so freeing a 1060 that would be used on a kit would be useful if the lunchbox esc goes haywire.

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