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Old Jul 27, 2011, 01:04 PM
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Guelph, ON
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Marine Viper 15 ESC whining...

At slow speeds I am getting loud whining from my motor. I know this more or less normal, and is caused by the waveform the motor is getting from the ESC, but is there any way of reducing the volume?

Right now you hear more sound from the motor than the speaker at low speeds.
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Old Jul 27, 2011, 01:26 PM
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Run the boat farther out in the lake, sound diminishes quickly, with the square of the distance.

I keep meaning to test a theory, never get around to it... Put a flywheel on the shaft, and see if that does anything. This could work IF the sound is coming from torsional excitation.
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Old Jul 27, 2011, 01:38 PM
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Originally Posted by patmat2350 View Post
Run the boat farther out in the lake, sound diminishes quickly, with the square of the distance.
Sort of like turning up the car stereo so that annoying engine noise doesn't bother you anymore

I don't have room in the Springer for a flywheel, but I have an identical motor that I will try this with.

Would a pair of biggish capacitors across the leads help, or would they interfere with the motor feedback the ESC "listens" for?
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Old Jul 27, 2011, 02:05 PM
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Nope, changing the capacitors won't help. There are two ways to eliminate the whine:

1- Try another ESC with a different chopping rate.
2- Try a different motor. Windings and armature are acting like a speaker.
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Old Jul 27, 2011, 02:13 PM
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Actually, some big honkin' capacitors might help, would smooth out the wave form. No idea how big... electrolytics wouldn't do though, they're polarity-sensitive.

Brushed motor ESCs don't listen to anything but the throttle signal from the receiver. The ESC is like a guy at a switch for a light in another room. Someone tells him to turn the light on and off (real quickly), but he doesn't know how bright or dim it is in the other room.
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Old Jul 27, 2011, 02:25 PM
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Originally Posted by green-boat View Post
Nope, changing the capacitors won't help. There are two ways to eliminate the whine:

1- Try another ESC with a different chopping rate.
2- Try a different motor. Windings and armature are acting like a speaker.
That's not the answer I wanted to hear! The motor is very well suited to scale operation, and I don't really want to invest in another ESC without knowing that it will solve the issue for sure...

Pat's solution (larger lake) is sounding better!

Hmm... I wonder if adding shock mounts to the motor would offset the "speaker effect". Right now it is mounted to a large aluminum plate... That can't be helping matters.
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Old Jul 27, 2011, 02:29 PM
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Pat,

I was thinking of using a pair of electrolytics, each connected with a diode between the negative lead and the motor lead... (pics in a minute..)
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Old Jul 27, 2011, 02:44 PM
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Quote:
Originally Posted by patmat2350 View Post
Brushed motor ESCs don't listen to anything but the throttle signal from the receiver. The ESC is like a guy at a switch for a light in another room. Someone tells him to turn the light on and off (real quickly), but he doesn't know how bright or dim it is in the other room.
I'm sure you are correct. The "back EMF" idea came from looking at servo driver circuits when I was using a servo as a speed controller for my Lindberg Diesel tug the first time around.
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Old Jul 27, 2011, 03:35 PM
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Motor Whine

Quote:
Originally Posted by RGinCanada View Post
At slow speeds I am getting loud whining from my motor. I know this more or less normal, and is caused by the waveform the motor is getting from the ESC, but is there any way of reducing the volume?
Big capacitors across the motor leads will just draw more peak current out of the Electronic Speed Control, possibly letting the magic smoke out. Diodes for the caps won't help either the caps will just charge up.

Try putting a "Bifilar wound Toroidal Inductor" in between the ESC and the motor. This will reduce the rate at which current will build in the motor windings. This happens naturally in the motor anyway as the RPM of the motor increases. All the inductor does is get it started a little sooner.

Take one of the wires from the ESC that goes to the motor and wind it around the inductor in what would appear to you to be clockwise direction. Wind for example ten turns closely spaced filling up about half of the available space on the core. Take the other wire Start right next to the first one and wind the same number of turns on the core, but wound counterclockwise. Reconnect the wires to their original locations. Ideally the inductor will be right next to the motor. As close as you can reasonably get it.

Please observe my crude drawing.

Do you know what gauge these wires are?
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Old Jul 27, 2011, 04:14 PM
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Thanks for the suggestion and diagram. Is the inductor a simple iron core?

I think the wiring is 18 gauge... quite light, but the motor only draws 2A at a dead stall. The ESC is rated for 15A, and I have a 10A fuse between the battery and the main power bus.

I don't know that 24V / 2200uf capacitors would really cause an amperage spike. The diodes are intended to prevent reverse biasing the capacitors. In my mind (not bearing any resemblance to reality, you understand) they would have this effect on the voltage waveform:
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Old Jul 27, 2011, 07:00 PM
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No Capacitors

Hey RG,
Large electrolytics will not work. The leading edge of the PWM will no longer be square as it charges the cap, trailing edge the same on discharge. Your motor response will be "muddy" at best.

I took an old Astro 207D (forward only) ESC , 12V with a switching rate of about 3 kHz (the ringing you are hearing) and set it up on my bench with a lab power supply and a 500 series can motor, with an scope on the motor positive lead. With a 100uF electrolytic, the motor was still controllable, with very distorted PWM. A 470uF distorted the waveform as described above such that the motor had essentially three speeds, off, inbetween, and on.
No diode was used, as the 207 is not a reversing H-Bridge type ESC.

Tomorrow I will try the suggested toroid. My initial feeling is that the ringing will persist, the inductor is only changing the phase of the current delivered to the load.

This is why the modern brushed ESC employ much higher switch rates, like 20kHz ! Ya can't hear that unless you're a real junior (age wise) R/C'er!

JOhn
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Old Jul 27, 2011, 07:16 PM
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Ringing Followup

RG,

I tried four motors, ranging from a 500 can upto the American Bosch man killer.
They ALL rang with the 3 kHz 207D ESC. I had always noted this with the Astro brushed controllers, but it never really bothered me.

I developed a two channel, 80A, H-Bridge controller, which is based on a PIC micro switching at 20 kHz - no ringing! This was in response to the price of the Astro 208d single channel reversing ESC - about $90 several years ago when they were available! I used them in my Darby, but resolved never again!

Let us know if you beat the problem.

John
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Old Jul 27, 2011, 08:17 PM
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Waukesha, WI
Joined Dec 2006
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Sound is produced by motor being switched at freq in range of hearing.
Rubber mounts and soundproofing around motor will dampen sound. Your
boat may be resonating like a swiss music box at same frequency making the sound louder.
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Old Jul 28, 2011, 12:50 AM
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Quote:
Originally Posted by RGinCanada View Post
Thanks for the suggestion and diagram. Is the inductor a simple iron core?
No it's not an Iron core, it's usually some ferrite blend. Much better high frequency response.

It will be interesting to see what WA3ETD finds out with his experiment.
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Old Jul 28, 2011, 12:58 AM
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Quote:
Originally Posted by WA3ETD View Post
switching at 20 kHz - no ringing!
The higher the switching rate, the greater the heating effect on the motor.
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