[NLRS] Elevation rotators for small stuff

[Dr. Gerald N. Johnson]

On 9/4/2013 6:08 PM, Doug Reed wrote:
> I agree with Jerry that a motor driven screw actuator of some sort is
> likely to be the best option. It certainly will have enough guts to
> move and hold the dish. I was considering something like a C-band dish
> actuator to lift a dish assembly from the "stowed" position to
> "operating" position for a mobile dish system. If it can lift the dish
> 90 degrees in a reasonable time, you can also use pulse-width
> modulation to make small adjustments to elevation at a slower rate.

Pulse width on a DC motor is very good at giving low speed with lots 
more torque than simple low voltage gives. I set up one to demonstrate 
on a HO locomotive long ago. With a short pulse of the full throttle 12 
volts DC I hitched a rubber band to the rear coupler and anchored it. 
The locomotive didn't have enough traction to stop the drive wheels 
(steam model) when it stretched the rubber band. I think if commercial 
model train controllers got to a good full amplitude pulse modulated 
drive the have only done that in recent years. In early years of pulse 
it was simply an SCR delaying the start of each half cycle turn on, not 
a square wave at all but very simple to make with AC available though it 
didn't work as good.
>
> I hadn't considered the old U100 rotor, but it might work for
> elevation if you can
> slow it down enough for final positioning. Even an old CDR-22 could do
> it with different mounting. But the rotors are designed to shed water
> when vertical so you'd have to add a cover to protect it from water
> when horizontal. Driving the motor with 24VAC might be a bit of
> a trick in the car, but not impossible. I seem to remember the
> original motor is a bit of a pancake shape which might be hard to
> replace unless you can find a suitable stepper from an old 8" hard
> drive.

More than a few U100s have been used for satellite elevation rotors 
without modifications for weather proofing. In the one I'm using now for 
azimuth on the roof tripod the direction rheostat is unreliable. But its 
a direct worm drive on the hollow tube so has small backlash, unlike the 
CD45 and HAM-x series. A Ham-M with the pot and rotation stops removed 
then hooked to a dish with a significant (like 1:5 or 1:10) chain or 
gear drive would move a pretty big dish.
>
> At one point I considered using a video camera motor driven pan-tilt
> pedestal for turning a dish. But the one example I have is too loose
> to hold a dish steady enough for our needs. It probably has 5 degrees
> or more play in the mechanism and it really isn't rock stable.... Most
> old ham rotors are about as bad.

There are commercial dish mounts remote controlled for RVs. And some 
military units have shown up in surplus. The documentation for 
controlling them has been difficult to find and the new RV automatic 
dish mounts are high priced.
>
> I really tend to prefer a screw-lead motor and crank-arm to do the
> lifting. You're trying to lift 5-10 pounds at the end of a 3' to 5'
> lever arm so it needs to be powerful. But that extra 3' on top of the
> car roof will get you over most of the corn.  :-)
>
> If you reduce the range of motion to +-20 degrees with a manual link
> to raise the dish and do gross positioning, you could probably use a
> lot simpler mechanism for fine positioning. If you want to try doing a
> full horizontal rotation, it will be a lot more complex. The real
> trick is to have something solid with minimum backlash so it can hold
> a sub-degree bearing. Although maybe I'm over complicating things and
> holding 1 degree would be enough.
>
> Most of the DSS dishes have a tilt adjust joint on the mount. I'd look
> for a small screw assembly to use that joint to make small adjusts to
> elevation. Just use a manual mechanism to lift the dish to the
> operating position. An old electric screwdriver coupled to a
> lead-screw and nut? A similar lead screw and swing arm and screwdriver
> to make small horizontal adjustments?
>
> It would be very nice to have the system computer controlled for
> adjusting the dish position so it automatically points based on your
> GPS position and the target site. A small electronic compass and
> inclinometer on the dish will give you the info needed for automatic
> positioning although the accuracy might not be entirely adequate.....
> But pointing the dish near the target is usually enough to simplify
> manual final positioning.
>
> If you have real good connections for surplus, the motor lift assembly
> from a fishing boat will have a sealed motor that runs on 12 volts DC
> and can lift and tilt a 100-200 pound motor.
>
> Don't forget to put a small video camera on the dish so you can
> describe the correct pointing direction for everyone else. :-)
>
> 73, Doug Reed, N0NAS.
>
Driving home from 2012 CSVHF in Cedar Rapids driving from hardware
store to hardware store I worked out an alternative design for a
roof top dish that I've not yet built. Fundamental is an azimuth 
arrangement using a heavy duty lazy susan ball bearing. They can be had 
rated at 900 pounds for under $20, a litte more at Rockler but better in 
some hardware stores. I figured on a 4' square of 3/4 plywood on the 
roof rack, and the rotation part a 4' disk of 3/4 plywood. Hand turning 
the edge of that plywood disk gives some leverage meaning small motions 
at the edge are smaller at the dish. I figured on carrying wood blocks 
to fill the space at the edge between the two plywood sheets and 
clamping with a quick acting hardware clamp, like the ones I picked up 
at Rhinelander WI Menard's on my way home from the UP last year. For 
elevation I figured on using a hand crank on a 50:1 work gear box 
available inexpensively from Burden's Surplus Center 
(www.surpluscenter.com). I figured a spring loaded claw clutch could 
allow rapidly raising from flat to the operating position. I figured 
using LM400UF to the rig inside car or truck would limit the feed line 
losses. Then only the dish and feed would be out in the weather while 
roving and setup would take seconds. I have the clamps and the bearing. 
I've not done anything else with the idea.

Arlis had a tilt over tower mounted in the back of his pickup carrying a 
30" or 1 meter dish last month. Without gear drives to move it slowly 
and to hold it he was frustrated trying to make contacts and went home 
early.

73, Jerry, K0CQ