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Old 06-25-2014, 09:57 AM   #1
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Default Brushless spec motor tuning?

So, last night at the track I ran a buddy's 17.5t touring car and it was a rocket, an unbelievably fast rocket. Some of you may remember the "Motor Black Book" that was around back in the day for brushed motors; is there a modern equivalent? If not lets share the tips, tricks and secrets that will get more speed out of our brushless stock spec motors.

The first thing I'm going to try is shimming the rotor to keep the magnet in the optimum position.

Questions I have:

How does motor timing effect the powerband and peak power output of the motor?

How do different rotors effect the powerband and peak power output of the motor?

How does the drive frequency effect the power of the motor?
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Old 06-25-2014, 10:26 AM   #2
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The optimal FDR varies, depending on the motor, the rotor, the amount of end bell timing and most importantly, the size and flow of the track.

You would want the lowest resistance stator. For TC you generally want the strongest rotor in the largest legal diameter. There is a reason companies sell "top 5%" cherry picked motors for $150+. They are definitely a bit faster than the average off the shelf motor.

For a 1s pan car you wouldn't want some crazy high torque rotor. They don't tend to work very well with a motor that might be insanely quick in a TC.

Having a very free drivetrain is extremely important in stock classes. Also having a very powerful cooling fan makes a big difference in the amount of performance you can extract from a motor.

Some motors simply suck for stock TC classes and there is very little you can do to make them more competitive.
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Old 06-25-2014, 12:06 PM   #3
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Originally Posted by WheelNut View Post
How does the drive frequency effect the power of the motor?
If you are referring to maximum power output of the motor, this is a non-question, since the motor drive is not pulsed at full throttle.

Otherwise, during partial-throttle operation, the drive frequency affects the throttle "feel", with higher frequencies giving a more progressive response curve, similar to using exponential curves on the transmitter.
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Old 06-25-2014, 12:28 PM   #4
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If you are referring to maximum power output of the motor, this is a non-question, since the motor drive is not pulsed at full throttle.

Otherwise, during partial-throttle operation, the drive frequency affects the throttle "feel", with higher frequencies giving a more progressive response curve, similar to using exponential curves on the transmitter.
That's what I thought. This local guy was insisting that he found the drive frequency had a big effect on the power of the motor. Maybe he was just trying to throw me off, as he is a bit secretive about his setups.
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Old 06-25-2014, 06:54 PM   #5
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Quote:
Originally Posted by howardcano View Post
If you are referring to maximum power output of the motor, this is a non-question, since the motor drive is not pulsed at full throttle.

Otherwise, during partial-throttle operation, the drive frequency affects the throttle "feel", with higher frequencies giving a more progressive response curve, similar to using exponential curves on the transmitter.
That was true with brushed motors, but not brushless. The field rotates by the ESC firing the coils in the stator at the right time, so the motor is always pulsed.
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Old 06-26-2014, 03:27 AM   #6
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That was true with brushed motors, but not brushless. The field rotates by the ESC firing the coils in the stator at the right time, so the motor is always pulsed.
That is correct. But I was referring to PWM of the coils, as was the OP. My apologies if I was unclear.
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Old 06-26-2014, 04:24 AM   #7
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In my testing of brushless motors I found that each stator/rotor combination has a definite sweet spot on timing. Finding that correct spot and matching the gearing for the car type and the track is the science behind being fast. Small tight tracks with a lot of grip you want a torque setup. On big (outdoor) lower grip tracks lighten up on the torque and go for the rpm motor.
Turning up the timing beyond what I call the sweet spot produces more rpm and usually power but at the cost of efficiency. On our beloved D3.5 (cough) that is about 20 degrees on the end bell, a Novak Ballistic it is 44.
All of this comes from testing on a Fantom Dyno and shows up well on the track.
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Old 06-30-2014, 01:06 AM   #8
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Originally Posted by old_dude View Post
In my testing of brushless motors I found that each stator/rotor combination has a definite sweet spot on timing. Finding that correct spot and matching the gearing for the car type and the track is the science behind being fast. Small tight tracks with a lot of grip you want a torque setup. On big (outdoor) lower grip tracks lighten up on the torque and go for the rpm motor.
Turning up the timing beyond what I call the sweet spot produces more rpm and usually power but at the cost of efficiency. On our beloved D3.5 (cough) that is about 20 degrees on the end bell, a Novak Ballistic it is 44.
All of this comes from testing on a Fantom Dyno and shows up well on the track.
Only problem with the ballistic (25.5 at least) is knowing if the timing label is affixed correctly and there are big differences in where that timing label is placed from motor to motor (as much at 10%).

So using the Fantom dyno, how do you go about determining where the sweat spot is?

Last edited by John Wallace2; 06-30-2014 at 01:18 AM.
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Old 06-30-2014, 04:02 AM   #9
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Only problem with the ballistic (25.5 at least) is knowing if the timing label is affixed correctly and there are big differences in where that timing label is placed from motor to motor (as much at 10%).

So using the Fantom dyno, how do you go about determining where the sweat spot is?
Just below where the free rev amp draw jumps. I had two and on both it was right around the 43-45 degree mark. I ran those two motors for a year and a half. I sold them and someone asked me how I made them so fast. I told them I took them out of the box, put them on the dyno, adjusted the timing to my quesstemated (new word) sweet spot. I then bolted them in the car a geared them to come off at 145 degrees (in VTA). I told the racers that bought them to gear them in there cars like that. Pretty simple but a few people still felt that I had somehow messed with those motors.
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Old 06-30-2014, 04:52 AM   #10
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I was taught by a top level driver how you can kind of feel / hear the sweet spot for any motor without a dyno if you do not have one. Just move the timing whilst revving the motor on full throttle, you can hear the motor purr when its revving optimally. Once its there you just gear around it and never change the physical timing.

As to drive frequency, it does give you an advantage if you use the above method. I can use it to make the car feel more torquey if I need it, or also more smooth and Revvy. As mentioned it will not affect the top speed (Just need gearing etc) but if you are stuck with the one motor it does help it feel more versatile.
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Old 06-30-2014, 09:38 AM   #11
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How does the drive frequency effect the power of the motor?

Drive frequency does not affect anything at full throttle, so drive frequency cannot affect max power or max RPM of the motor. Drive frequency only affects how a motor feels at part throttle.
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Old 07-08-2014, 05:53 AM   #12
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When shimming the rotor, is it best to get it as close to the sensor board as possible or are you looking for the magnetic center (is that what its called?) like brushed motors like?
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Old 07-08-2014, 06:15 AM   #13
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Quote:
Originally Posted by Qatmix View Post
I was taught by a top level driver how you can kind of feel / hear the sweet spot for any motor without a dyno if you do not have one. Just move the timing whilst revving the motor on full throttle, you can hear the motor purr when its revving optimally. Once its there you just gear around it and never change the physical timing.

As to drive frequency, it does give you an advantage if you use the above method. I can use it to make the car feel more torquey if I need it, or also more smooth and Revvy. As mentioned it will not affect the top speed (Just need gearing etc) but if you are stuck with the one motor it does help it feel more versatile.
Is this done without the pinion on?

I just started using the hobbywing xerun v10 21.5t, from a quick run in the parking lot I can say it feels pretty fast, though I don't have much to compare it to.
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Old 07-11-2014, 02:46 PM   #14
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Originally Posted by old_dude View Post
Just below where the free rev amp draw jumps. I had two and on both it was right around the 43-45 degree mark. I ran those two motors for a year and a half. I sold them and someone asked me how I made them so fast. I told them I took them out of the box, put them on the dyno, adjusted the timing to my quesstemated (new word) sweet spot. I then bolted them in the car a geared them to come off at 145 degrees (in VTA). I told the racers that bought them to gear them in there cars like that. Pretty simple but a few people still felt that I had somehow messed with those motors.
Thanks sort of what I thought.
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Old 07-12-2014, 11:38 AM   #15
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I too would like to know more about shimming the rotor. Also what about polishing the rotor? Is it worth the time and if so what do I use for polish?
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