RE: Frequency for SSRs using PWM

["Flier" <flier-at-sbcglobal.net>]

Hey Joe,

1Khz seems to work good.  Since the SSR max off time is 1ms, 1khz is about
all I could do anyway.

I went a little bit different tact and am using linear equations to generate
the duty cycle based off the RC pulse width from neutral.  I count the PPM
pulses at 10us intervals so there are ~50 intervals from center to either
end (for ~1ms PPM pulse width) so you could say I have 30-40 different duty
cycles.  The down side is for radios that provide significantly greater or
less than ~1ms pulsewidth the PWM calibration (the linear equations) would
have to be tweaked (even though I have built a cal routine to establish end
and midpoints).  Anyway, it seems to work using some 12v motors I have
laying around and as long as it works with my radios the rest is gravy.

I wish I'd have known sooner on the SSRs!  I'm afraid I sold two to pay for
the rest and have promised the other two to a friend who's building a tank
here.  I'll holler if I run across some more.

Regards,

Ted



-----Original Message-----
From: tanks-admin-at-rctankcombat.com
[mailto:tanks-admin-at-rctankcombat.com]On Behalf Of Joe Sommer
Sent: Tuesday, March 16, 2004 9:02 PM
To: tanks-at-rctankcombat.com
Subject: Re: Frequency for SSRs using PWM



Ted,

At 07:54 PM 3/16/2004 -0500, "flier" <FLIER-at-sbcglobal.net> wrote:
>What PWM frequency (or period) are you guys using
>with the SSRs for your motor speed control?

I use 1 KHz.  You can actually hear the motors whine at
1 KHz when they stall.

For Makita 6216 motors driving Intralox track with
no load on the Hetzer, the lowest usable duty cycle
to overcome friction in the drill gearhead and track is 40%.
The Hetzer SSR mixer uses 5 discrete speeds
approximating an exponential PWM-to-speed mapping
with duty cycles of 40%, 50%, 60%, 70%, 100%.

The new Anvilus hybrid relay/SSR mixer uses 7
discrete forward and reverse speeds for EV Warrior
motors with chain or belt speed reducers.  I have
not yet experimented to find the best PWM frequency
or PWM-to-speed mapping for the EV Warriors.
However most motors are quite happy at 1 KHz.
I expect my chain drive to have lower friction than
the planetary gear trains in my drill motor gearheads
so the lowest usable duty cycle may be 20% to
30%.

I just received two bare PCBs for the new Anvilus
hybrid mixer but I have not had time to solder them.
I have the PIC 16F876 code almost ready but I still
need to tweak it on new board.  The board carries
four on-board VF4 SPDT relays for forward /off/reverse
mixing and has TTL output connecters to drive two
off-board SSRs for PWM speed control.

Can you view Gerber files?  If yes, I can send them
and a parts list to give you an idea how simple the new
board is.  You can use my Gerbers directly or lay out
your own PCB using mine as a model.

I hope to tune the PIC code this weekend and can send
you a copy if you wish.  It looks very much like my old
SSR mixer code that I sent previously.

In that you have six big SSRs and only need two for
your Panther, would you be interested in selling two
to me?  I will need two for my new M1A1.

Best wishes,
Joe


**********************************************
Joe Sommer
2378 Nantucket Circle, State College, PA 16803
814.234.4773     anvilus9-at-adelphia.net
http://www.anvilus.com