ESC frequency & efficiency?

Archiver

I'm using a BS2 to intercept servo signals in my RC tank (yee haa!
see http://members.aol.com/patmat2350/Tiger/PatsTiger2.htm), and to
command a home made twin ESC (input speed and steer commands,
calculate different tread speeds to steer and go [noparse][[/noparse]for more realistic
operation- real tank has steer wheel, not 2 sticks]).

I can PWM the motors at any frequency; I'm using an Intersil
CDP68HC68 serial-in/PWM-out chip. Currently, it's about 1300 Hz, and
makes a lot of motor whine at "part throttle".
Q's:
1) Are there any (reasonable) techniques for reducing the whine at
any given PWM frequency?
2) Commercial RC ESC's brag about operating at "high frequency" (2-3
kHz). Are there any fundamental reasons not to operate at lower (<1
kHz) or higher (> 10 kHz) frequencies? Power efficiency? Other?

thanks, patmat

Archiver

Thera are some considerations for your questions:

1) Higher (ultrasonic) PWM frequencies can eliminate the whine BUT the
MOSFETS and circuit may not support because limited bandwidht of rise
and fall timings! Be careful. Vantec (a manufacturer of commercial and
industrial ESCs) says that increasing freq from normal 330 Hz to 21KHz
may increase 30% or more in derated amperage. Also may be there are a
substantial increase in RFI.

2) Efficiency may decrease at higher frequencies. The inconvenient
of lower frequencies may be the "vibration". I have used industrial ESCs
with low frequencies 170Hz ~ 340Hz that are not so audible as the
"screaming" 1~ 4 KHz with very good efficiency.

ACJacques


patmat2350@a... wrote:
>
> I'm using a BS2 to intercept servo signals in my RC tank (yee haa!
> see http://members.aol.com/patmat2350/Tiger/PatsTiger2.htm), and to
> command a home made twin ESC (input speed and steer commands,
> calculate different tread speeds to steer and go [noparse][[/noparse]for more realistic
> operation- real tank has steer wheel, not 2 sticks]).
>
> I can PWM the motors at any frequency; I'm using an Intersil
> CDP68HC68 serial-in/PWM-out chip. Currently, it's about 1300 Hz, and
> makes a lot of motor whine at "part throttle".
> Q's:
> 1) Are there any (reasonable) techniques for reducing the whine at
> any given PWM frequency?
> 2) Commercial RC ESC's brag about operating at "high frequency" (2-3
> kHz). Are there any fundamental reasons not to operate at lower (<1
> kHz) or higher (> 10 kHz) frequencies? Power efficiency? Other?
>
> thanks, patmat
>
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Archiver

In playing around with a MOSFET H bridge I made, I found that if the PWM
frequency is too low, the motors will be very jerky. At too high a
frequency, the motor lacks power. This is with a couple of gearhead
motors -- other ones may work better.

What I use on the sumo bot is a single number from 0 to 16 to represent the
speed ratios of two servos. ie 0 = stop, 4 = hard right, 8 = reverse, 12 =
hard left, and 16 = forward. The steps inbetween are ratios between forward,
right, left and reverse.

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Original Message

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> I'm using a BS2 to intercept servo signals in my RC tank (yee haa!
> see http://members.aol.com/patmat2350/Tiger/PatsTiger2.htm), and to
> command a home made twin ESC (input speed and steer commands,
> calculate different tread speeds to steer and go [noparse][[/noparse]for more realistic
> operation- real tank has steer wheel, not 2 sticks]).
>
> I can PWM the motors at any frequency; I'm using an Intersil
> CDP68HC68 serial-in/PWM-out chip. Currently, it's about 1300 Hz, and
> makes a lot of motor whine at "part throttle".
> Q's:
> 1) Are there any (reasonable) techniques for reducing the whine at
> any given PWM frequency?
> 2) Commercial RC ESC's brag about operating at "high frequency" (2-3
> kHz). Are there any fundamental reasons not to operate at lower (<1
> kHz) or higher (> 10 kHz) frequencies? Power efficiency? Other?