On Wed, 28 Oct 1998, Andy Kunz wrote:

> >Why didn't you say so ;) Is it going to be wet ? If so, a twin plastic
>
> Not while I'm balancing it.  It's for a dynamic balancer along the lines of
> what is used in full-size cars.  I'm sure some heli guys will like it.

What do you use for accelerometers and do you index it or what ? Because
if you index the axis position to determine which way the inbalance vector
pulls then you already have a speed-related signal that you can tap into.

> >2 or 3 blades). If the LED is pulsed with 1 Amp pulses at 30 kHz as for IR
> >remote applications it should work ok.
>
> 1A in an LED - what a concept!  What kind of duty cycle do you propose, the
> standard 30%?

IR remote control leds run at that power level with a duty cycle of 10%
(3us on in 30us or so). They are quite happy with it. A PIC can easily do
that by flipping an output bit with a nop or two between the on and off
commands. And where did you get the standard 30% from ? Is it an American
standard ?

> >tone and the one where a tone is to be displayed as speed. The 1st method
>
> I want digital RPM display based upon frequency the boat is putting out.
>
> >frequency to a counter. If the amplifier has some AGC, it will lock on the
> >loudest frequency around (such as, a nitro engine running full throttle
> >near it).  This last method works very well as I can confirm ;)
>
> These are electric, but the idea is the same.  We are much quieter!
>
> Do you have a schematic for an audio AGC which will give me the pulsing I
> need?  That's the real hangup for me - converting it to RPM is just software.

I don't know what the sound level is, that you start out with. By the way,
did you say ELECTRIC ? Multi-pole electric motors with a switched
collector draw current in gobs as the collector switches coils, and there
is a way to build even electronic stabilizers like this. No, you don't
need a pickoff resistor, use the length of cable of the '+' wire from the
regulator f.ex. A LM358 wired 1/2 as x 100 AC amplifier with differential
input and 1/2 as pulse shaper (comparator) should do what you want. Try
this, with 2 crocodile clamps to attach to the engine wire and a scope as
output (before the shaper). Some tinkering may be required. The crocos
attach one to the regulator '+' output and one to the motor '+' input. The
wire between them acts as sense shunt. Some amount of low-passing the 358
will be required.

Another way to get at the frequency of a running DC motor is to put a
pickup coil on it. A phone suction cup coil should work and so should a
vrac-wound ferrite rod antenna. The amplifier is the same. This should
work through the boat body (fiberglass or carbon I presume). Magnetic
pickups do not like to be in the same room with variacs and other mains
operated large transformers and motors, so maybe try the shunt method
first.

hope this helps,

Peter