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gearing quesiton

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gearing quesiton

Old 04-08-2020, 05:30 AM
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Default gearing quesiton

I recently purchased a Traxxas Bandit. It had been set up for drag. It had a 6 cell setup in it, I replaced the ESC with a Traxxas 5xl HV out of my TRX4 and it had a stock 12t Traxxas motor ( I bought and quickly smoked a second 12t). I only ran it on 2 cell and quickly burnt the motors up. The gearing is 25/83. The tires on it are 4.75 inches in diameter. Tires were from a TRX4 Mercedes. I am pretty sure that gearing / tire size combo lead to the destruction of that motor. Those tires suck on a crawler but do pretty good on the basher.

Question?
What should the prober gearing be? I know this is a subjective question but the basher is for fun, not any competition, so longevity of the motor is the goal. I a sure I will end up with a brushless system at some point, Would a brushless motor be destroyed with the gearing I mentioned above?

Last edited by MOguy; 04-08-2020 at 05:53 AM.
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Old 04-08-2020, 09:29 AM
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With the larger tires, you probably have the motor way over-geared. Try a much smaller pinion gear, around 20 or less. You can also try a larger spur. Also check the motor every few minutes, to see how hot it gets.
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Old 04-08-2020, 09:43 AM
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Calculate the roll out of the original car where the motor is from and recaclulate it to the tires and gears of the Bandit.

how to calculate rollout
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Old 04-08-2020, 10:06 AM
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stock gearing for the trx4 was 11 pinion w 45 t spur..came with 21 t 550 ..so now ur try to run a 12 t titan with 25/85 w the tires your trying to run way less gearing will need to happen..Id start w a 10t p with the 85.. run it for less that 45 seconds. check temps.then increase run time at 2 minutes check temps..unlikely rollout of trx will help you in the bandit..2 different drive train setup..
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Old 04-08-2020, 10:38 AM
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Originally Posted by Roelof View Post
Calculate the roll out of the original car where the motor is from and recaclulate it to the tires and gears of the Bandit.

how to calculate rollout
Thanks,

do you know if they are using inches?

If so stock roll out would be 4.01 mine would be 4.49.

If I want my engine to last longer do I want a lower roll out number? Would this apply to brushed and brushless?

Does the motor need to be taken into account when figuring this?

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Old 04-08-2020, 08:25 PM
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You can gear the car to balance motor heat against speed by measuring temperatures and adjusting the gear ratio.

you can also build the car around the motor. Ask the MFG what is the rpm of peak power and peak efficiency. Gear the car so the average rpm is at 1 of these peaks or between the two. It still comes down to temperature.

So once you build the car around the motor you can refine it further by understanding what is meant by average rpm. If you need to travel 24 feet in 3 seconds what is the average speed you need? Its 8 feet per second. But if the car accelerates for 1 second, constant speed for 1 second and decelerates for 1 second for a total of 3 seconds over 24 feet how fast does it have to go in that 1 second between acceleration and deceleration. If you average speed needs to be 24 feet per second then the speed between acceleration and deceleration has to be allot more than 8 feet per second.

None of it is hard but running it safely and measuring temperature and then adjusting gearing to drop temperature is good enough. Ask the mfg and dont get hung up on all the different ways to get a motor running great cuz just when you do there will be another concept that just might take the fun out of racing or bashing.
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Old 04-13-2020, 12:39 AM
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try getting a heat temperature gun or dongle to check the temps of your car after either bashing or doing a couple speed runs.

You want to usually check the heat of your battery , esc and motor from time to time after either a couple runs or bashing for a few mins this will let you know if something isn't going right or if you are over working your car which in this case you did.

Brushless is the way to go but it is no different than brushed when it comes to heat killing it.
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Old 04-14-2020, 08:55 PM
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Originally Posted by ReMiXeDg View Post
try getting a heat temperature gun or dongle to check the temps of your car after either bashing or doing a couple speed runs.

You want to usually check the heat of your battery , esc and motor from time to time after either a couple runs or bashing for a few mins this will let you know if something isn't going right or if you are over working your car which in this case you did.

Brushless is the way to go but it is no different than brushed when it comes to heat killing it.
this really is the answer if you want to bash or have the fastest brushless chassis out there. Speed come from mechanical power and how milking every scrap of power the motor has. The byproduct of power is heat without exception and if you arent on the edge of over heating you arent using all the power of a brushless motor. The only problem is that you can create a bunch of heat with very little power if you dont understand how to tune the motor to the track by modifying everything between the motor and the lap time.
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