Augusto Yipmantin wrote:

>Thank you for the reply to all.
>The motor schematic is as follows:
>
>         +--00000000----+
>A 0------!              !
>         +--00000000--+ !
>                      ! !
>                +-----+ !
>                !     ! !
>    150uF50V   =3D=3D=3D    ! !
>                !     ! !
>                +-------+
>                      ! !
>B o-------------------+ !
>                        !
>C o---------------------+  =20
>=20
>48VAC to A-B the movement is CW
>48VAC to A-C the movement is CCW
>
>The motor speed gives me one turn of the antenna each two minutes.
>What I need is one turn in 5 minutes.
>This will give me more precision pointing the antenna, the reduction of
>the velocity never can be variable, it must be fixed.
>
>The rotor is a CDE Ham IV, and has some gears to reduce the motor=B4s
>velocity.
>
>Regards,
>
>Augusto
>
> =20
>

Augusto:

One way to reduce the speed is to "cycle steal" the AC power to the=20
motor. Use a PIC, for example, and a triac to interrupt the current to=20
the motor so that, for example, it receives only every other AC cycle.=20
This will produce the same effect as if you manually pulsed the control=20
switch but at a rate of 60 times per second. However, this may not be=20
very good for the long term life of the motor. Plus, since the motor=20
rotor has inertia, the amount of speed reduction will be limited and the=20
more reduction you try to get, the less the torque the motor will develop.

I think that perhaps you are approaching this in the wrong direction.=20

Is your real problem overshoot--you find it hard to release the control=20
switch so that the rotor stops in the desired position? Either you=20
release it too early and the final position falls short or you release=20
it too late and the rotor stops beyond the target position?

If so, you might be better off looking at changing the control system.=20
You might do this by replacing the current manual control box with a PIC=20
controlled one that would let you pre-enter the desired azimuth. the=20
controller would then use an algorithm that then automatically cuts the=20
motor off at a pre-determined lead angle so that the stopping point will=20
be at the desired azimuth.

One complicating factor is the way CDE rotors read the rotor angle. The=20
position potentiometer at the rotor top shares a ground connection with=20
the motor and brake solenoid so that the position display meter has a=20
large AC component when the rotor is turning. I've done some work trying=20
to read the potentiometer with a PIC and found it necessary to use a=20
very low frequency (5 or 6 Hz cutoff) low pass filter to remove the AC=20
ripple from the potentiometer circuit. The display meter, of course,=20
ignores the superimposed AC and reads only the DC current through the=20
rotor's position potentiometer.

There is a pre-made electronic digital control box for the CDE rotors=20
that does this, but the box is rather expensive as I recall.

Finally, there is a limit as to how accurately you can read the azimuth=20
due to potentiometer linearity error. I would not be surprised to find=20
this is a few degrees. And, also the brake mechanism uses a solenoid=20
wedge that forces the position into one of a finite number of positions=20
if I recall the construction of the Ham IV correctly.

73 de Jack K8ZOA






--=20
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