# Motor braking power

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**1****Motor braking power**

This question is simply for personal curiosity. Using 2 identical esc's having identical programming. Does a 3.5t motor have the same, weaker, or stronger brakes then a 25.5t motor?

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**2**
esc determines braking power as in amps drawn. but a 3.5T will take long in micro seconds to brake due to turn # over a 25,5T which will be instantly ..so a 25.5T will look like it has more brakes due to its slower Kv rating .

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**3**Tech Rookie

If they had exactly the same gearing the 3.5 would have stronger brakes at higher speed and the 25.5 at lower speed.

However if you geared them for a similar top speed the 3.5 would have stronger brakes everywhere.

However if you geared them for a similar top speed the 3.5 would have stronger brakes everywhere.

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**5**Tech Regular

iTrader: (1)

And tc4 with a rsx and a 17.5 both equal settings just the 17.5 has 10*

And braking is 10000x harder and responsive on the 2.5

Not everything on the interweb is accurate or true.

Oh and my tc6 mmp Tekin 5.5 brakes harder than my sprint2 Tekin rs pro/lrp 5.5

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**7**
how the brake frecuency (PWM) can be adjusted o n the ESC to get more brake?

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**9**Tech Champion

iTrader: (159)

If the motors were out of the car and spinning at the same RPM, the 25.5 turn would provide more braking force.

If both motors are in a car and geared for the same top speed, the 3.5 would have a much larger mechanical advantage due to the gear reduction would provide more braking force at the same speed.

If both motors are in a car and geared for the same top speed, the 3.5 would have a much larger mechanical advantage due to the gear reduction would provide more braking force at the same speed.

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**10**
These are interesting responses and I appreciate everyone taking the time to answer.

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**11**Tech Elite

iTrader: (37)

Correct. I have edited my previous post to match your observation.

*Last edited by howardcano; 02-28-2018 at 04:36 PM.*

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**12**Tech Champion

iTrader: (159)

Correct. I have edited my previous post to match your observation.

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**13**Tech Elite

iTrader: (37)

You are assuming the voltage created in the motor is the same between a 25.5 turn motor and a 3.5 turn motor at the same rpm. This isn't the case. Let's say the 25.5 motor is rated as 1,500kv and the 3.5 is 9,000. This rating also tells you (roughly, not accounting for losses/inefficiencies) the voltage created by the motor when you spin it. At 3,000 rpm, the 25.5 is creating 2 volts. The 3.5 would only be creating 0.33 volts.

*The back-EMF of the motor is proportional to the magnetic field strength, enclosed flux (rotor and stator size), speed, and the number of turns.*

At the same speed, stator and rotor sizes, and rotor field strength, the back-EMF of the 3.5T is (3.5/25.5) = 0.137 times that of the 25.5T.

*The resistance of the motor is proportional to the square of the number of turns*(if the stator is completely filled with wire).

The 3.5 has (3.5^2/25.5^2) = 0.0188 times the resistance of the 25.5T.

*Torque is proportional to the current, the magnetic field strength, enclosed flux (rotor and stator size), and the number of turns.*

At the same speed, stator and rotor sizes, and rotor field strength, current through the 3.5T is V/R = (0.137/0.0188) = (25.5/3.5) =7.29 times that of the 25.5T.

Finally, the torque of the 3.5T = 7.29*(3.5/25.5)=1 times the torque of the 25.5. The torque is the same.

*Last edited by howardcano; 03-02-2018 at 04:56 AM. Reason: Italicized general rules for motor parameters. Corrected "1/(3.5^2/25.5^2)" to "(3.5^2/25.5^2)"*

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**14**Tech Champion

iTrader: (159)

I did not assume that.

At the same speed, stator and rotor sizes, and rotor field strength, the back-EMF of the 3.5T is (3.5/25.5) = 0.137 times that of the 25.5T.

The 3.5 has 1/(3.5^2/25.5^2) = 0.0188 times the resistance of the 25.5T.

At the same speed, stator and rotor sizes, and rotor field strength, current through the 3.5T is V/R = (0.137/0.0188) = (25.5/3.5) =7.29 times that of the 25.5T.

Finally, the torque of the 3.5T = 7.29*(3.5/25.5)=1 times the torque of the 25.5. The torque is the same.

*The back-EMF of the motor is proportional to the magnetic field strength, enclosed flux (rotor and stator size), speed, and the number of turns.*

At the same speed, stator and rotor sizes, and rotor field strength, the back-EMF of the 3.5T is (3.5/25.5) = 0.137 times that of the 25.5T.

*The resistance of the motor is proportional to the square of the number of turns*(if the stator is completely filled with wire).The 3.5 has 1/(3.5^2/25.5^2) = 0.0188 times the resistance of the 25.5T.

*Torque is proportional to the current, the magnetic field strength, enclosed flux (rotor and stator size), and the number of turns.*At the same speed, stator and rotor sizes, and rotor field strength, current through the 3.5T is V/R = (0.137/0.0188) = (25.5/3.5) =7.29 times that of the 25.5T.

Finally, the torque of the 3.5T = 7.29*(3.5/25.5)=1 times the torque of the 25.5. The torque is the same.

I won't disagree on the calculations for an ideal motor as, yes, they should be the same. My answer was based on including inefficiencies is all in addition to the data I have come across through work. I didn't mean to imply that the 25.5 turn has 10 times the braking force due to the voltage difference in my previous post, but I wasn't sure where to start with my reasoning.

I just realized that the 25.5 in question is probably ROAR spec'd to a certain wire diameter, so my assumption that the 25.5 turn would have more fill was incorrect. In the end, I meant that the 25.5 will have maybe 5% more braking power at the same rpm if the wire size was optimal for each motor.

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**15**Tech Elite

iTrader: (37)

Speaking of calculations, we both missed my error in the calculation for resistance. Somehow a "1/" snuck in there! I've fixed it.