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SPEC class brushless controller timing.

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SPEC class brushless controller timing.

Old 05-03-2020, 08:56 PM
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Default SPEC class brushless controller timing.

I'm looking to buy a brushless controller, and I'm deciding whether to buy the SPEC version or full-house optioned version which will cost more money.
For my purpose I am not racing, so I don't mind if it IFMAR / ROAR compliant or not. My plan is to use a 17.5 turn motor with mechanically adjustable timing.

My questions:
1) If I end up choosing the less expensive Spec controller, is there much advantage to have a motor with mechanical adjustable timing for tuning the KV and efficiency?
2) Does the spec controller run a lot of advance timing by default to maximise the power and RPMs?
3) What is the typical no-load RPM (or KV value) for a 17.5 turn Spec complaint motor with Spec controller?
4) How much additional RPM could be gained by using mechanical advanced timing on the motor? (I'm thinking to tune for better top-end with short gearing.)

Obviously I'm a newbie when it comes to brushless motors. Basically I'm a tech-head who wants to buy the good stuff. Thanks in Advance++
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Old 05-03-2020, 10:21 PM
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17.5 class runs the ESC in blinky mode. That means no timing with the ESC. All the timing is done on the motor can. Typically you run between 40 and 50 degrees of advance on the motor can. If it were me, I'd just get the Hobbywing Justock ESC. It only runs in the blinky mode and will work great for what you want.
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Old 05-04-2020, 11:07 AM
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Anything to do with motor sports comes at a cost. Budget or value items will rarely be at the same level of performance as "the good stuff". But it isn't unreasonable to want to buy reliable products at a decent price that have good performance. Having said that here are my non-expert responses to your questions:

1) Why limit yourself to a less expensive Spec Electronic Speed Control (ESC) if you aren't planning on racing. The difference in price to a blinky/zero timing and unlimited timing speed control is very small. The more expensive speed controls can usually be set in blinky/zero timing mode. Also the unlimited speed controls usually offer external programming options that make adjusting them easier than less expensive options.

2) Spec Electronic Speed Controls are typically set at zero degrees of advanced timing if they are IMFAR/ROAR compliant.

3) I have edited this for clarity. Sensored brushless motors that are used for r/c racing are built to meet the specific guidelines of racing organizations such as ROAR or IFMAR. As such the measurable differences between multiple manufacturer's motors are usually very similar. For example all ROAR legal 17.5 motors should all perform very similar while being raced. However as rules change and manufacturers improve the quality of their motors, the performance of earlier generations of motors can be different than the latest generation. There are also tuning options available for brushless motors such as different stators that affect the performance - RPM rotors vs Torque rotors. In organized spec racing, the rules have evolved to specify that the motor cannot be altered from the specification of how it was approved.

So the short answer is that when setting a baseline for a specific turn of motor, you need to know what specifications the motor was built under or if it was non ROAR/IFMAR approved. In other words, a 17.5 ROAR approved motor built in 2015 will perform differently than one built in 2019. A spec motor 17.5 motor will also perform differently to any "outlaw" motors.

Rules organizations and racing bodies have a vested interest to keep the perception that r/c racing is fair. Realistically there ARE minor differences between legal motors, but usually it is not enough to affect the on track racing. If you are interested in reading about a real world motor that didn't perform the same as other motors, just search for all of the controversy surrounding the Trinity D3.5 17.5 motors. Thankfully rules organizations used that experience to improve the specifications and testing of the spec motors that are being used currently.

If you want to read about some of organizing bodies rules, the following links should provide you with more information.
ROAR Racing
https://www.ifmar.org/approval-lists/

I would like to add that it is not recommended to run brushless motors under no load as it is possible to damage the motor. However many people will tell you that the numbers that they see in testing DO NOT always related to real world performance. Spec motors from different manufacturers will often show different test results but perform very similar under racing conditions. In other words, bench racing and real world racing often produce very different results.

4) You can use timing to adjust how a motor performs, but it is one of many variables that affect the speed of the vehicle. Proper gearing in combination with a motor that is set at optimal timing often results in better overall real world performance. Also using the proper setup and tires will always get the power to the ground better than if you are spinning your wheels or sliding around the racing surface because you have a "fast" motor. Using timing alone CAN give the motor more RPM, but often at the expense of causing extra heat in the motor (possible damage to magnets) and drawing more/too much power away from the motor and/or receiver. It is possible to draw too much power from the battery that some receiver have been know to lose communication to the transmitter (brown out).

----------

If I'm reading between the lines, it sounds like you may have something specific in mind that you want to do in this hobby. If that is the case, please feel free to share this information. There are plenty of people on this forum/online that are happy to help. At a minimum, we may be able to direct you to a better resource to answer your specific questions.
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Last edited by IndyRC_Racer; 05-06-2020 at 11:27 AM.
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Old 05-04-2020, 08:06 PM
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Spec motors have reverse disabled (dont take this literally its to get you asking around what i mean). You should look into that and consider it.

here is a story with fake numbers to help you understand the difference between manual timing and end bell timing.

17.5 turn
40 degrees timing on end bell
you have all the torque and efficiecy the motor can possibly deliver below 8000 rpm at 10000 rpm the motor begins to fall on its face. Efficiency is bad above 10k and the motor heats rapidly at 10k.

50 degrees ebell timing
you are missing 10-20 percent of the low end torque and power but you can 10% more rpm. The entire rpm range creates more heat than 40 degrees timing.

Electronic timing-
ebell is set at 40 so you retain all efficiency and torque below 8k. At 8k you start metering timing in through boost. You continue to maintain high efficiency and the torque and rpm comes along for the ride. Minimal heat impact if you trickl timing in with rpm. You’ve extended you rpm further than you could have with 50 degrees of end bell timing. Then you add turbo on top at say 15000 to adjust the timing acceleration required as the neutral plane skews.

think about a merry go round. As it spins you push it to accelerate it faster. If you push early or later you still add some acceleration but not as much as if you push it at the exact right time every time while its accelerating. Electronic timing allows you to adjust the timing of the push in small enough increments to minimize over working and push it harder than otherwise.

ebell timing is pushing it late, a little late, on time, a little too soon, too soon, allot too soon as the motor accelerates so the manual timing you select is a compromise or an average of sorts.

up to about 40 degrees the timing changes make very small differences. Above 40 degrees would be for rpms where the magnetic field distortion has a different slope than it has below 40. Somewhere between 40 and your kv limit will be a third rate change in timing from field distortion.

If you arent racing and just want to have fun but can control your urge to add too much just to see what happens electronic timing will be safer, more efficiency and the motor and esc will last longer. Manual timing should be illegal in my book. Its like keeping a crank handle to start your brand new car just because people kind of understand how to use it to start their car.
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Last edited by Bry195; 05-05-2020 at 08:13 PM.
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Old 05-04-2020, 08:44 PM
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This thread has been really educational. Thanks so much to you guys that posted your knowledge. One thing I learned is that End-bell timing is not the same as electronic timing. The controller can do a smarter thing than simply a fixed angle advance. That is a good reason for me to choose a PRO grade controller. For the product I'm considering, the PRO version has lower electrical losses so it should run cooler at the same power level. That's reasonable if am paying for better engineering. I didn't want to pay a premium price for some feature I would never use.

At the moment I'll be running an older model with limitations on the gearing. In the future I will probably use it for something completely different. I don't mind a few more RPMs, like a old style brushed motor, but I like to keep the power level sensible and keep everything running cool. I never liked brushes and springs in the old motors, it was a continuous annoyance and only really good for generating sparks and excess heat, which sucked.

Now I assume that a 17.5 turn motor has a KV value between 2200 to 2300 at zero timing. I get the impression I could run the controller in a "High advance mode", and possibly get 10 or 15% more RPMs, like a KV rating of 2500. If I want more than that, I should probably get a motor with fewer winds.
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Old 05-05-2020, 05:29 AM
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Originally Posted by Bry195 View Post
Spec motors have reverse disabled. You should look into that and consider it.
I don't know what you're trying to say here but this seems wrong. There's nothing about a spec motor that prevents it from reversing, that's an ESC thing.

If you meant spec ESCs have reverse disabled, well every spec ESC I have is configurable in that regard. Including the venerable Hobbywing Justock.
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Old 05-05-2020, 05:32 AM
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Originally Posted by UniRacer View Post
Now I assume that a 17.5 turn motor has a KV value between 2200 to 2300 at zero timing. I get the impression I could run the controller in a "High advance mode", and possibly get 10 or 15% more RPMs, like a KV rating of 2500. If I want more than that, I should probably get a motor with fewer winds.
They never run at zero timing. The lowest I've seen a stock motor run timing wise is around 20 degrees, they're typically 30+ degrees. The 21.5 R1 motor we use as control motor comes in at 2400KV (sealed timing) so I'd expect a 17.5 to be a bit higher than that.
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Old 05-05-2020, 05:54 AM
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Originally Posted by UniRacer View Post
Now I assume that a 17.5 turn motor has a KV value between 2200 to 2300 at zero timing. I get the impression I could run the controller in a "High advance mode", and possibly get 10 or 15% more RPMs, like a KV rating of 2500. If I want more than that, I should probably get a motor with fewer winds.
Sounds like you are talking about sensor-less motors and speed controls as I have never heard anyone discuss KV ratings for a 17.5 stock brushless motor. Maybe some clarification would help.
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Old 05-05-2020, 03:12 PM
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I found that most of US companies don't state the KV rating for their stock motors.
I found some specs from hobbywing motor:
https://www.hobbywingdirect.com/prod...iant=753594053
They claim KV value of 2170 for the 17.5 motor. The timing is not clearly expressed but there is a note with the "specifications" that says:
"The maximum output power is the test value obtained when the voltage is 7.4V, and the ESC timing is set to 0 degrees"
From what I learned on this thread, now I assume the hobby wing motor would have some end-bell timing built in.
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Old 05-05-2020, 04:03 PM
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Originally Posted by UniRacer View Post
I found that most of US companies don't state the KV rating for their stock motors.
I found some specs from hobbywing motor:
https://www.hobbywingdirect.com/prod...iant=753594053
They claim KV value of 2170 for the 17.5 motor. The timing is not clearly expressed but there is a note with the "specifications" that says:
"The maximum output power is the test value obtained when the voltage is 7.4V, and the ESC timing is set to 0 degrees"
From what I learned on this thread, now I assume the hobby wing motor would have some end-bell timing built in.
The motors you are apparently looking at are sensor less types and I don't know anyone running any onroad car who uses these types of motors.
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Old 05-05-2020, 04:45 PM
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Originally Posted by Bry195 View Post
Spec motors have reverse disabled. You should look into that and consider it.

here is a story with fake numbers to help you understand the difference between manual timing and end bell timing.

17.5 turn
40 degrees timing on end bell
you have all the torque and efficiecy the motor can possibly deliver below 8000 rpm at 10000 rpm the motor begins to fall on its face. Efficiency is bad above 10k and the motor heats rapidly at 10k.

50 degrees ebell timing
you are missing 10-20 percent of the low end torque and power but you can 10% more rpm. The entire rpm range creates more heat than 40 degrees timing.

Electronic timing-
ebell is set at 40 so you retain all efficiency and torque below 8k. At 8k you start metering timing in through boost. You continue to maintain high efficiency and the torque and rpm comes along for the ride. Minimal heat impact if you trickl timing in with rpm. You’ve extended you rpm further than you could have with 50 degrees of end bell timing. Then you add turbo on top at say 15000 to adjust the timing acceleration required as the neutral plane skews.

think about a merry go round. As it spins you push it to accelerate it faster. If you push early or later you still add some acceleration but not as much as if you push it at the exact right time every time while its accelerating. Electronic timing allows you to adjust the timing of the push in small enough increments to minimize over working and push it harder than otherwise.

ebell timing is pushing it late, a little late, on time, a little too soon, too soon, allot too soon as the motor accelerates so the manual timing you select is a compromise or an average of sorts.

up to about 40 degrees the timing changes make very small differences. Above 40 degrees would be for rpms where the magnetic field distortion has a different slope than it has below 40. Somewhere between 40 and your kv limit will be a third rate change in timing from field distortion.

If you arent racing and just want to have fun but can control your urge to add too much just to see what happens electronic timing will be safer, more efficiency and the motor and esc will last longer. Manual timing should be illegal in my book. Its like keeping a crank handle to start your brand new car just because people kind of understand how to use it to start their car.
Very interested read. I really like the detail. The only thing I would like you explain on here or on our text group is this. " Spec motors have reverse disabled. You should look into that and consider it."
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Old 05-05-2020, 07:15 PM
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I texted you. I was being lazy with my language.
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Old 05-05-2020, 08:32 PM
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There is a chart out there that breaks down the turns of a motor to the kv. Ive taken an unloaded 17.5 up to 32000 rpm but it not very useable. Power is rpm and torque. You can get allot of one and not have the other which results in less power. It almost always comes at the expense of allot more heat. If you use the manual method and the end bell is the only place to make timing adjustments either give it 40 degrees to retain all the torque and efficiency and gear the car around it or do something you have seen others do successfully.

at 40 degrees you can get 70% efficiency in the conversion from electrical to mechanical power but that efficiency is maybe 10% of the curve. The idea if going out to say 50 lowers that peak efficiency to maybe mid 50 to low 60 efficiency. Its a wider power band that is easier to drive because its not peaky. 70% is peaky and harder to drive. Somewhere in between 40 and 50 is easy to drive with enough power under the curve to be pretty close.

If you run a chassis on a track with gearing that keeps the motor at 70% efficiency it will beat cars that are at 55%. The reasoning is you will have gearing that still pushes the motor close to the thermal limit but its 15% more efficient.

electronic timing widens the power and retains the peak. Its the best of both worlds. You can take a motor that at best is 125 watts to over 300. Permanent magnet motors can generate allot of efficient power if timing is synchronized to rpm. A 17.5 is 125 watts with ebell timing. If I had my choice for blinky classes I would prefer to drop a winding and allow auto timing. An esc can calculate the right timing angle for a given motor at every rpm if they are programmed to do it. So a 21.5 with auto timing would be better than a 17.5 with manual timing. The benefit would be that nobody would need to place with motolyzers and timing anymore. One less thing to overthink.
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