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New to RC motor gets hot. Losi mini 8ight T

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Old 05-13-2017, 01:53 PM
  #1
thadarknight
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Default New to RC motor gets hot. Losi mini 8ight T

Hello everyone I'm Edwin and pretty new to the RC world. I picked up a highly upgraded Losi mini 8ight T but I'm having heating issues with my motor.

​​​​​the guy I got this from changed the stock spur to a from a 62 to a 60 steel using a Robinson racing 14t pinion.

He also upgraded the stock 4500kv motor to a 5200kv 18t motor from hobbywing and matching 25a esc.

​​​​​he gave me 2 brand new venom 1300mah 3s 20c lipos as well.

My problem is my motor after 5 mins or less gets so hot you can't touch it but the ESC stays cool.

I was reading the manual for the losi and it states if using any lipo on stock gearing of 62/14 you must drop the pinion to 12 making it 62/12.

My issue is my spur gear is a 60 and pinion is 14 so is my gearing the issue here? I'm new to gearing.

Should I keep the 60 spur and drop to a 12 pinion?


P.s. I still have the stock 4500kv motor and esc.

​​

Last edited by thadarknight; 05-13-2017 at 02:14 PM.
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Old 05-14-2017, 04:58 PM
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If you got only the 60T spur gear, then by all means drop down to the 12T pinion gear (if you got room). Don't forget to consider you are using a 3S LiPo pack as well. You may need to go even lower in tooth count on the pinion gear.
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Old 05-14-2017, 06:05 PM
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If you have the 62T spur gear, I'd install it. If you are using 3S LiPo packs,and the 5200kv motor, you definitely want a higher gear ratio to compensate a little for the motor's higher RPMs. I think it's always better starting with a very conservative higher gear ratio using a smaller pinion and working your way up. For a situation like yours, and having components that are not stock, some type of IR thermometer might be a good idea.

Lots of articles out there on gearing. This is just one:

R/C Car Gear Ratios

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R/C Car Gear Ratios

The gears of a car follow a simple concept but can have an enormous effect on the performance of the vehicle. The diameter of the gears should be adjusted to match the specific application in which the vehicle will be used for. This means that a different gearing will be used for a large track with sweeping turns than for a small track with tight turns. A simple explanation of gearing is necessary. Basically, a large pinion gear (the little gear attached to the motor) will offer increased top speed and decreased acceleration and a smaller pinion gear will offer decreased top speed and increased acceleration. The opposite is true for spur gears (the large gear attached to the tranny that the pinion gears runs against), a smaller spur gear will increase top speed and decrease acceleration while a larger spur gear will decrease top speed and increase acceleration. A standard way of comparing gear sizes between cars is to use Gear Ratios.

There are 2 basic types of gear ratios for your RC car, the pinion to spur ratio and the overall drive train ratio. To equate the pinion to spur ratio, a simple formula is used:

Pinion to Spur gear ratio = # of teeth on spur gear / # of teeth on pinion gear

To give an example, assume you have a 25 tooth pinion gear and a 100 tooth spur gear installed on your car. The pinion to spur ratio is 100/25 = 4. Therefore; your pinion to spur gear ratio is 4 to1. This means that the motor must rotate 4 times to rotate the spur gear once.

The other basic gear ratio is the overall drive train ratio. To equate this, the following formula is used:

Overall Drive Train Ratio = (# teeth on spur gear / # teeth on pinion gear) x Tranny Gear Ratio

Here is an example. Assume you have a 25 tooth pinion gear and a 100 tooth spur gear installed on your car. Your transmission gear ratio is 2.25 to 1 (the transmission gear ratio is complicated to equate but it is usually given to you in the transmission instructions). The overall drive train ratio is (100 / 25) x 2.25 = 9. Therefore; your overall drive train ratio is 9 to 1. This means that the motor must turn 9 times to fully rotate the wheels of the car once.

Sometimes people refer to the gear ratio of the car instead of the number of teeth on the pinion and spur gears. A low gear ratio number will offer increased speed and decreased acceleration and a high gear ratio number will offer decreased top speed and increased acceleration. For example, a 3 to 1 ratio will give your car more speed and less acceleration than a 5 to 1 ratio.

It is important to understand that there are limitations to what an electric motor can handle when it comes to gearing your car. This means that a larger pinion and a smaller spur will increase your vehicles top speed up to the point in which the motor is overloaded. When the gear ratio is too low, the motor will not have enough output to benefit, and reduced performance can be expected. The key here is that a proper gear ratio is very important. Don't just put on the largest pinion gear and smallest spur gear that you can find and expect to go fast.

Another issue regarding gear ratios is tire size. The size of the cars tire will have an effect on the speed a vehicle reaches. A larger tire is like running a lower gear ratio and a smaller tire is like running a higher gear ratio. The formula used to calculate gear ratios that take tire size into consideration are very complex and aren't necessary for most applications. Just remember that a larger tire will increase top speed and decrease acceleration and a smaller tire will decrease top speed but increase acceleration.

There is no strict rule for setting up gear ratios in your vehicle. Different cars, tracks, motors, batteries, driving style and many more variables all affect the size of the gears to be used. The best method of setting up your own ratios is to start with manufacturer recommendations and then experiment on your own. Use a stop watch to see if changes you make are for the better. The proper gear ratio selection can make the difference between an A main finish and no finish at all.


POSTED BY AZMIZI MUKHLIS
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Old 05-14-2017, 11:10 PM
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I read the manual as 62/12 for 2S , 62/10 for 3S . Thats with the 4500kv motor .
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Old 05-15-2017, 03:19 AM
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Quote:
Originally Posted by seedygreenute View Post
I read the manual as 62/12 for 2S , 62/10 for 3S . Thats with the 4500kv motor .
In that case, I'd start with an 8 tooth pinion gear. Is that even possible? Are they even made? I don't know.
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Old 05-15-2017, 03:56 AM
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Quote:
Originally Posted by thadarknight View Post
Hello everyone I'm Edwin and pretty new to the RC world. I picked up a highly upgraded Losi mini 8ight T but I'm having heating issues with my motor...​​
What type of RCing are you doing...speed runs, or normal everyday bashing? How and where you do your RCing will play a big role on one's gearing needs.

Food for thought: I have sensitive fingers. I've done the two, three ....whatever second method of motor temperature guessing for years. Prices have dropped. After finally giving in to getting a thermometer, I found what I thought was super-hot was actually within safe levels for brushless motors temps . I'm always swapping motors in and out of RCs; up and down the gear ratio scale, and running in varying ambient temps. $13 for an IR temp "gun" was some of the best money I've spent in this hobby.
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Old 05-16-2017, 01:24 AM
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I ended up selling both 3s lipos and keeping the 60/14 gearing and picked up a floureon 2200mah 35c 2s lipo and it has made a drastic difference especially with heat
​​​​​​
​​​​motor and esc are staying nice and cool to the touch.

I took out the 5200kv motor and replaced the stock fuze 4500kv motor as well. I will be picking up a temp gun.

So far 2 packs through it and it's running great.
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