Extend the actuator for more accuracy

[linuxman]

This is a spin-off of the VBox III and accuracy thread and deals with making an extension for the mounting ring to allow for more pulses/counts and better accuracy.

The nasty weather held off long enough for me to get on the roof this afternoon and take a couple of pictures. I have added real measurements for Anole so we can make some predictions about how many counts extending the actuator will produce.

I have also included a picture of the mount with the dish pointing at 43W just to see the break-over point a little more accurately.

I also included a picture of a 10' Perfect 10 mount to show the off-set way they do their mounts. SAMI mounts are the same way.

Here are the pictures to start the discussion:





As you can see when the dish is over to the East, extending the arm out very far might produce problems trying to bring the dish back West.

That's a question that will have to be answered by testing.

 

[gpat]

they do make high pulse count actuators but Im sure you know that already

 

[linuxman]

Hi Gpat,

Yes, but most of us who have found dishes have taken what was on them and are trying to get the most we can out of them at a minimal cost.

 

[Hermitman]

I agree that if you add an extention to the dish ring mounting bracket, you'll get better accuracy positioning with the actuator. You'll have more actuator motor counts/pulses per degree of dish movement. However, the down side is that your dish movement will be limited. You'll get less satellites because the dish won't be able to rotate as far east and west. If you use some simple geometry, you should be able to figure out how many degrees of total movement you'll get if you extend the bracket by x inches. Although I read the VBox thread, I've never had problems with accuracy and pulse counts unless there was a sensor problem or a wiring problem where the receiver was receiving bad data from the actuator. Maybe I've just been lucky.

 

[Anole]

Interesting pictures. Thanks for posting them.
Some of the geometry or placement of pivot points must be for a reason.
I wish I understood those reasons better.

But one thing that's pretty easy to see, is this.
If you move the attach-point for the end of the motor out one inch from the ring, then at full east, the motor will need to extend one more inch.
Same for the west side - it'd need to retract one more inch.
Assuming the motor can do that, then you'd get about 100 extra counts (roughly 48 + 48) since that motor does 48 clicks per inch.
Two inches would get ya close to 200 more counts.
Three inches would get nearly 300 more counts.

At some point you run out of motor extension, and a new problem arises with the dish all the way west.
But within reason, you should be able to get a few more hundred, if that's a useful goal.

See how the motor attach-point past the ring's edge sticks back (north) in a one inch tab?
Thats for clearance when the dish is all the way east, and you might need to do something similar, so keep that in mind.
That also helps a little if your dish flops all the way left, I think.
I'd stay out of the far-east zone.

So, just based on seat-of-the-pants observation, I'd think you might get two more inches and 200 counts, but doubt you'd get the three inch extension to work.
Feel free to prove me wrong! - :up

If I recall from previous discussions, we're talking about 600 basic counts across the arc, so 200 more would probably be useful.
edit: Oh, it's not 600 from lock-to-lock, so...
...you'd get less than the hundreds of counts predicted ...
... by some percentage, but still . . . more counts is good.

I'm sure there are some clever mechanical people reading along.
What have we missed in this discussion, and what could be done better?

 

[linuxman]

So, just based on seat-of-the-pants observation, I'd think you might get two more inches and 200 counts, but doubt you'd get the three inch extension to work.

I would agree, two inches would be feasible and possibly three.

In the picture above, the entire actuator assembly can be slid in and out through the clamp to allow for more retraction or extension than the motor itself will do.

If I recall from previous discussions, we're talking about 600 basic counts across the arc, so 200 more would probably be useful.
edit: Oh, it's not 600 from lock-to-lock, so...
...you'd get less than the hundreds of counts predicted ...

The counts are not lock to lock. They are from where I have set the East and West limits. Basically all the viewable satellites in my arc. So three inches of extra travel would net 150 counts spread across the arc.

That all depends on how much I can slide the actuator into the clamp and where the dish ends up sitting on the West side in relation to the blocks on the mount.

From Hermitman:

However, the down side is that your dish movement will be limited. You'll get less satellites because the dish won't be able to rotate as far east and west.

Just looking at it, as long as you don't get carried away (not go over 2 or 3 inches), and with the proper adjustment on the clamp, you should still be able to view all the satellites I currently view.

Only implementing the proposed extension will prove that.

As Anole suggested, it may be necessary to put a tab on the extension to keep out of trouble on the far East.

Even if it is just 100 counts across the arc, that would give in improvement. If you have 50 positions, that is an extra 2 counts per position. Might be just enough.

 

[linuxman]

Well I gave it a shot today.

I made a piece out of 2-1/2" angle steel, got my holes all drilled like I wanted them, warmed up a little, so took it to the roof, and it won't fit.

I need a piece of steel 1-1/4" wide and about 1/4" thick, then I can drill holes in it, and I think it will fit. I'll try and find a piece tomorrow, and hopefully can get it on before it gets real cold again.