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Need a couple of brushless questions answered

Need a couple of brushless questions answered

Old 05-15-2012, 08:15 AM
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Default Need a couple of brushless questions answered

1) Whats the part that "wears" or "breaks" in brushless motors?
2) What can/should you upgrade in brushless motors? Rotors? Bigger = better?
3) What is the relationship between temperature and gear? I have heard the both under gearing and over gearing will raise temps?
4) Timing. I have seen both timing done on the motor or programmed in the esc.
5) What should i look for in a 13.5 motor for racing in stock/super stock?

6) It seems like almost everyone wants to use the Tekin RS Pro. Why is that?

7) Why would you ever want sensorless over sensored?


I quit RC racing a few years ago, just as brushless was really taking off. Now, I need to learn all about 2.4Ghz radios, Lipo's and new brushless motors. The main thing that has changed is costs. The hobby seems to cost a lot more than it has in the past.
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Old 05-15-2012, 09:40 AM
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I with you but my layoff has been longer...like 20 years....my last good car was the Losi JRX-2. I know NOTHING about brushless.

Do you have any resources to share? I have questions about sensored vs sensor-less as well.

I'm loving the new battery and brushless technologies I just don't know what the heck I'm doing or looking at. I bought a RC10T4.1 brushless RTR and compared to the Evader EXT brushed I had it was faster and ran longer on a charge. So I upgraded the Evader to brushless but I wish I had done some more research before buying the ESC/motor combo I purchased (Duratrax Element by Castle).
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Old 05-15-2012, 09:49 AM
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1)i don't know for sure what wears out exactly but its usually the rotor and/or the stator, the magnets get weak and wear out

2) you dont have to ugrade rotors its just about tracks and preference mostly i never have and im fine with it cause my motor runs great

3) and yes this is true both under gearing and over gearing can cause heat

4) timing on the esc can be done manually or through a program card or PC if esc allows, on the motor its adjusted from the endbell usually by loosening 3 screws on the back, but remember more timing= more heat from both esc and motor

5) Pretty much all 13.5 motors out there will do u good i use the dualsky z5 in my cars check em out here ckhobby.com i also run the xc550tf-mj esc and with the usb this esc is a dream

6) the rs pro would not be needed unless you are running motors like 5.5 turn and down but people just like them because of the better fets and such and it does run a little cooler but for 13.5 it wont be needed youll just be paying extra for nothing really

7) sensorless is generally used for rtr's (they usually come with it) and bashing, sensored is the way to go for racing

hope this helps
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Old 05-15-2012, 09:59 AM
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Originally Posted by rcduder
1)7) sensorless is generally used for rtr's (they usually come with it) and bashing, sensored is the way to go for racing

hope this helps
Why? What do you get when you go sensored? Serious question here.
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Old 05-15-2012, 10:07 AM
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Originally Posted by Grasschopper
Why? What do you get when you go sensored? Serious question here.
sensored gives no cogging at low end and has better throttle and brake responses and generally runs smoother sensorless can be used for club racing (i know i did when i bought my first t4.1 rtr brushless and cogging would just make me mad so i went to sensored and havent had any problems with it yet) but i wouldn't recommend using it in competitions due to like i said cogging is a big issue, and also on every sensorless motor ive seen they can't be rebuilt if something goes wrong inside vs sensored motors are totally rebuild-able
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Old 05-15-2012, 10:12 AM
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Originally Posted by rcduder
sensored gives no cogging at low end and has better throttle and brake responses and generally runs smoother sensorless can be used for club racing (i know i did when i bought my first t4.1 rtr brushless and cogging would just make me mad so i went to sensored and havent had any problems with it yet) but i wouldn't recommend using it in competitions due to like i said cogging is a big issue, and also on every sensorless motor ive seen they can't be rebuilt if something goes wrong inside vs sensored motors are totally rebuild-able
Sorry...again total brushless rookie here and just getting back in after 20 years out.

What is cogging?
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Old 05-15-2012, 10:18 AM
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Originally Posted by Grasschopper
Sorry...again total brushless rookie here and just getting back in after 20 years out.

What is cogging?
its totally cool man im glad to help any time

cogging is basically what u could call glitching in a brushless motor and since you cant solder any capacitors on a brushless motor there not much you can do about it which is why sensored is the better way to go for racing because glitching like this is bad for racing, what happens is the motor at low end will stutter until u let off the throttle and get back on it again. what causes this is the esc trying to find the position of the rotor to keep it going when you hit the throttle which is what the sensor on a sensored motor helps with which = no cogging

hope this helps
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Old 05-15-2012, 10:23 AM
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Originally Posted by rcduder
its totally cool man im glad to help any time

cogging is basically what u could call glitching in a brushless motor and since you cant solder any capacitors on a brushless motor there not much you can do about it which is why sensored is the better way to go for racing because glitching like this is bad for racing, what happens is the motor at low end will stutter until u let off the throttle and get back on it again. what causes this is the esc trying to find the position of the rotor to keep it going when you hit the throttle which is what the sensor on a sensored motor helps with which = no cogging

hope this helps
Hmm interesting...I haven't seen that yet in forward. I TOTALLY see it in reverse on my RC10T4.1.

Thanks for the tutorial.
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Old 05-15-2012, 10:26 AM
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Originally Posted by Grasschopper
Hmm interesting...I haven't seen that yet in forward. I TOTALLY see it in reverse on my RC10T4.1.

Thanks for the tutorial.
yup anytime when i had the t4.1 it wasn't as bad in forward as a lot of sensorless systems but it did happen at the track mostly because of varying from throttle to neutral to brake frequently is what causes cogging to start acting up

and like i said im here to help anytime so if u got any more questions feel free to ask or you can PM me, especially about the t4.1 if you need any setup help or advise on anything
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Old 05-15-2012, 12:16 PM
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Originally Posted by rcduder
yup anytime when i had the t4.1 it wasn't as bad in forward as a lot of sensorless systems but it did happen at the track mostly because of varying from throttle to neutral to brake frequently is what causes cogging to start acting up

and like i said im here to help anytime so if u got any more questions feel free to ask or you can PM me, especially about the t4.1 if you need any setup help or advise on anything

Yeah, I had issues in reverse with the Castle MMP. I went to a sensored 7.5 Reedy Sonic and burned out the sensor board in a 4 minute run of the main. I am trying to figure out what I need to do to get performance from the motor without frying it. When I got home, I saw my esc was running in SMART mode, sensored at low throttle and sensorless at higher throttle. I have no idea if that whats toasted the sensor board or if its because i was geared wrong. So like a gas motor I am tuning for a temp? What temperature range should i look for in 13.5? or even 7.5, since i plan to fix the motor. My battery or room temp after a 8 minute main, the esc is just warm and the motor takes the flesh from my fingers...Just kidding, but I cant hold my figure to it after I finish marshaling the race after mine.

Also, I am thinking of ditching the MMP for my LRP Sphere Competition V2 from 3 years ago. It just feels smoother to me, maybe its my imagination.
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Old 05-15-2012, 12:20 PM
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Grass,
Cogging is like sputtering or uneven acceleration. If you were used to smooth linear acceleration it would be more noticeable to you. But after 20 years, it probably seems fine, lol.

I had an old gold chassis RC10 that I raced a few years before the JRX2 came out with its revolutionary link rear suspension, lol.
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Old 05-17-2012, 02:58 AM
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1) Whats the part that "wears" or "breaks" in brushless motors?

The fastest way to ruin a bl motor is by overheating it. Heat cycles will reduce a magnet's strenght, which is inevitable but can be prolonged by keeping the motor as close to ambient temp as possible. The stator can also be shorted out if the motor is exposed to extreme internal heat which can melt the enamel around the wires. This would be an extreme worst case scenario with bad gearing/timing/load. Also, the rotors have an RPM limit, which if surpassed, can shatter the magnet due to vibration/centrifugal forces (I've had this happen with a non-sintered rotor).

2) What can/should you upgrade in brushless motors? Rotors? Bigger = better?

Standard bearings can be upgraded with ceramic, like all other bearings in the RC world, but can be much more important in a motor due to the much higher RPMs they are exposed to. Some bl motor manufacturers offer different size rotors for different applications. More of a fine tuning thing, but a bigger rotor yields more torque by increasing the diameter of the rotor ex:12mm vs 12.3mm (think of it as torquing down a bolt with a 11" ratchet vs a 16" ratchet) and by getting the magnetic fields of both the stator and rotor closer. By moving to a bigger rotor, keep in mind that the overall RPMs of the motor will also drop (ie the kv will be lower).

I don't necessarily see the need to change rotors, as it has a very similar effect as changing gearing to suit driving style/preference. I would sooner upgrade bearings than change rotors, especially on a mod motor. For a 13.5, I wouldn't worry about it unless the supplied ones fail.

3) What is the relationship between temperature and gear? I have heard the both under gearing and over gearing will raise temps?

Undergearing overheats the motor (whether it be brushed or brushless) by having it unload unnecessary RPMs, similar to trying to keep your daily car in low gear on the highway. Overgearing overheats the motor by creating a heavier load on the motor than what it can handle. I've found brushless motors to be quite more forgiving than the brushed motors I used to run, however, I've also seen a brushless motor cooked in both situations.

4) Timing. I have seen both timing done on the motor or programmed in the esc.

Most motor/esc combos offer timing adjustment to be made in one way or the other, but not both. ESC timing is regarded as a more sophisticated method than endbell timing, and is rightfully so when an ESC applies it in a variation system. Much like variable valve timing on gasoline engines have made it possible to have both low end torque + efficiency on low RPMs, and more horsepower on higher RPMs, some ESCs can give you an edge in performance. Such ESCs include the MMP with the CHEAT mode, and the Tekin RS Pro. I believe this method requires sensored motors; to be able to determine the RPM of the motor in which to kick-in the timing.

5) What should i look for in a 13.5 motor for racing in stock/super stock?

First thing I can say is that not all 13.5 motors will perform the same. Not all 13.5s have the same kv rating or torque output, despite the use of wind labels to categorize such ratings. I would first find out what other racers are using at the track you want to race on, and make a decision based on that.

6) It seems like almost everyone wants to use the Tekin RS Pro. Why is that?

(See above/#4), and as stated, because of the quality of the FETs, and also customer service. I'm not biased, and believe both the MMP and RS Pro are great ESCs from great companies.

7) Why would you ever want sensorless over sensored?

Sensorless is a lower priced route, due to the simpler manufacturing process, but is subject to low rpm 'cogging'. Sensored provides a smoother powerband, no 'cogging', but is subject to more parts failure. My rule of thumb = Sensorless for 'bashing' and budget racing, sensored for more serious racing (if you get serious with racing, get serious with the extra coin).
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