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'RC Speed Control Source'
1997\05\16@092339 by Jason E. Brown

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I have gotten WAY to may e-mails requesting source code for the ESC..


I don't have time to e-mail it to everyone,  So I will post a URL

http://www.cdc.net/~othrwrld/speed1.asm

Let me know what you think.....



Jason E. Brown
Other Worlds
3801 Dayton Blvd
Chattanooga TN 37415
(423)870-1074

spam_OUTothrwrldTakeThisOuTspamcdc.net = business.
.....jebrownKILLspamspam@spam@cdc.net   = me.

1997\05\21@085103 by Malcolm Goris

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Jason E. Brown writes:
> Let me know what you think [about the ESC code].....

One thing I have noticed is that the PWM frequency will be about 20
Hz, with a 4 MHz oscillator. You count 100 timer0 timeouts for each
pulse cycle. There is a table of values that returns the length of the
high part of the cycle but instead of using 100 separate pulse high
times there are actually only about 30 returned by the table
lookup. This means that you could use 32 separate duty cycles and
count only 32 timer0 timeouts instead of 100 and it would give exactly
the same duty-cycle resolution but increase the PWM frequency by a
factor of 3.

Even still, I was under the impression that it would be desirable to
have a PWM frequency in the kiloHertz range and that only 16 or
perhaps 8 distinct duty cycles would be needed (at least for RC
cars). Can anyone comment on this? Does anyone know what the time
constant of an RC motor is?

Mal Goris
--
http://www.nfra.nl/~mgoris/

1997\05\21@090516 by Andy Kunz

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>One thing I have noticed is that the PWM frequency will be about 20
>Hz, with a 4 MHz oscillator. You count 100 timer0 timeouts for each
>pulse cycle. There is a table of values that returns the length of the
>high part of the cycle but instead of using 100 separate pulse high
>times there are actually only about 30 returned by the table
>lookup. This means that you could use 32 separate duty cycles and
>count only 32 timer0 timeouts instead of 100 and it would give exactly
>the same duty-cycle resolution but increase the PWM frequency by a
>factor of 3.
>
>Even still, I was under the impression that it would be desirable to
>have a PWM frequency in the kiloHertz range and that only 16 or
>perhaps 8 distinct duty cycles would be needed (at least for RC
>cars). Can anyone comment on this? Does anyone know what the time
>constant of an RC motor is?

Malcolm's comments ought to be noted.

The PWM should be 2KHz - 3KHz for these motors.

I have 100+ distinct speeds in my ESC (forward-only), and that's only using
partial range on the input to generate full-range on the output.  It is
wise to have this many, otherwise one can hear the car "shift" and this is
a problem when you are close to the boundary between two speeds.

Andy

======================================================================
Andy Kunz - Montana Design - 409 S 6th St - Phillipsburg, NJ 08865 USA
             Electronics for Industry & R/C Hobbyists
        "Go fast, turn right, and keep the wet side down!"
======================================================================

1997\05\21@103838 by Jason E. Brown

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At 02:47 PM 5/21/97 +0200, you wrote:
{Quote hidden}

yeah,  It was a bit too slow..   That (plus many other reasons) is why I
scrapped that approach..

I am now working on a single motor driver... Better resoulution and less
buggy.

Now instead of using TMR0 interrupts to update the motor,  (too many timing
problems)

I am using interrupt change on PORTB..  When the RC pulse comes in, tmr0 is
reset and a flag is set.  It then returns to the main loop, when pilse goes
low tmr0 is put in a timing varable then direction and speed are calculated
and updated to the motor..

So far this is working much better...

Thanks for your input...
Jason E. Brown
Other Worlds
3801 Dayton Blvd
Chattanooga TN 37415
(423)870-1074

othrwrldspamKILLspamcdc.net = business.
.....jebrownKILLspamspam.....cdc.net   = me.

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