Actuator Counts Per Inch

[Lone Gunman]

As some of you know I recently embarked on a mission to fix a worn out VonWeise acme nut. That endeavor was successful as was the near zero clearance on the thrust bearing that holds the acme screw to the gear housing. That first one I rebuilt has been on my 10ft Winegard dish now for a couple of weeks and is doing fine.

So my next project while rebuilding the second VonWeise I have was to increase the counts per inch since one of the two actuators only has 4 magnets in the counter wheel. Being the "I can make it better" kind of guy that I am, I decided that rather than getting another 8 magnet wheel like the one on my other VonWeise, I was going to make one and use 10 magnets instead of 8. Got that 10 magnet wheel made and installed it on that actuator a couple of weeks back. This morning the postman delivered my new Vbox X so I've been playing most of the day. Connected that VonWeise with the 10 magnets to the new Vbox X and believe it or not it works!! Set the count on the Vbox then traveled a measured inch and got my 60 counts! For those of you that are interested, here is a picture of that wheel and also a picture of a weather seal I made out of a piece of 1 3/4 inch radiator hose.

 

[Lak7]

Set the count on the Vbox then traveled a measured inch and got my 60 counts!

Hows does that equate to degrees of travel?

 

[Lone Gunman]

Hows does that equate to degrees of travel?

Won't really know the answer to that one until it's mounted on a dish and I've zeroed in on two satellites but I've upped the counts available on one of these actuators from 48 to 60 per inch, which is like a 20% increase. Probably going to put this one on that 6 ft Janeil Junior solid prime focus I got laying on the ground right now and it will be Ku only when it goes on the post. Speaking of which, I just acquired another post the other day to so now I gots to dig another hole, which is the one part of this hobby I don't like.

 

[crackt]

what size magnets did you use ?

crackt out,.

 

[Lone Gunman]

what size magnets did you use ?

crackt out,.

The magnets are 1/4 inch x 1/4 inch but I think you could use smaller 3/16 or 1/8 inch ones and they are available from DigiKey ($.30 each). Mine are just pressed into a 1/4 inch hole. The material is hifax and is 2 inches in diameter and 1/2 inch long with a 1/4 inch step cut on the back side to make it look similar to the factory piece. If your VonWeise has the 5 screw terminal strip then you'll have to modify the one closest to the wheel by removing the screws and filing the plastic separators down for clearance. Right now I have 1/16 inch clearance between the switch and the magnets.

Keep in mind that the polarity of the magnets has to alternate, ie, north and south polls so there has to be an even number of magnets to make that happen. Notice also that I drilled another 1/8 inch hole in the reed switch mount to move it away from the wheel. Used a larger wheel so that distance between magnets could be increased. Of course, you "might" be able to use smaller magnets and the factory diameter and possibly do the same thing but keep in mind that what I have DOES work as I've tested it on the bench.

I believe the real critical part is that the center hole and all the machining operations must be concentric to eliminate run out at the switch and also I reamed that mounting hole with a .249 diameter reamer to make sure it was a press fit on the output shaft. Positioning of the magnet holes isn't "that" critical but try to keep the spacing as equal as you can. I laid mine out with a magic marker and a pair of dividers. Put a bolt thru the center hole and ran it in an electric drill to scribe a line 3/16 inch from the outer edge then used the dividers to mark hole locations across that scribed line. Center punched their locations then drilled them on my Bridgeport, holding them in place with a 1/4x20 bolt and nut clamped up in the vise. Drilling by hand might make those holes too large so I'd do them in a machine (drill press or mill) if at all possible.

As it stands right now I have 3 more of these VonWeise movers that were given to me along with two 12ft dishes so I'll likely modify a couple of those for future use also. Ya just can't have too much "stuff"! ;-)

 

[truckracer]

on my 36" venture arms, 13 pulses gets me 2 degrees of arc. not sure how many inches or distance that is. i know if try to use a diseqc positioner, it gets out of sync pretty quickly. my analog boxes stay spot on for quite a while.

 

[SatScanner]

I was inspired by this thread to attempt to modify the linear actuator on my own 10' dish.

Here is the original encoder wheel.





I made a measurement pointer out of scrap wood to indicate when the actuator had moved one inch.



Here is a closeup of the pointer. I measured out one inch from a measuring tape you can see two black lines on either side of the yellow indicator.



Moving the dish one inch one inch yielded about a count of 40 on my GBox V3000. I had read that the V3000 has a count doubler? If that is the case then my counts per inch is only about 20.


I reverse engineered the original and had a new one machined out of nylon but with 10 magnets instead of 4.



I pressed in a stack of six 3mm x 1mm magnets because just one turned out to not be even be close enough to being powerful enough.



Even with six magnets per hole I had to move the reed sensor so close it was practically touching. I then attached 5mm x 2.5 magnets to the 3mm magnets which helped a lot. The computer froze while I was transferring the pictures, unfortunately the pictures with the 5mm x 2.5 magnets were lost or corrupted. I'll try to take the pictures again the next time I work on the dish, I still have to try to align the dish to the satellite arc.

Here is the actuator with the new encoder wheel installed before I added the 5mm x 2.5mm magnets.



With the 3mm magnets I only got 48 counts per inch, divided by two, that was 24 counts per inch, not much of an improvement, it must not have been detecting all of the magnets as it turned. After I added the 5mm x 2.5mm magnets on top of the 3mm and adjusted the sensor for the added height I got 100 counts per inch, divided was 50 counts, much better! I wanted 60 counts per inch. I tried slightly bigger magnets and adjusting the sensor but the most I could get was 50. Is 60 counts what is expected with a 10 magnet sensor? Does anyone have any thoughts on the 10 counts per inch difference?

Thanks

 

[gabshere]

my plan which has been on hold for some time now was to add a second sensor in effect doubling the count

like i said my play time is on hold for now but if someone is wanting to try adding a second sensor i have some basic sensors (switches) just let me know .... i bought i think 10 for like $4 several years ago. these are just the switches and not the full sensor itself .

 

[SatScanner]

How would you go about adding a second sensor?

 

[gabshere]

of course my wheel is different than yours but exact opposite side offset a bit so it wouldn't count a the same times as the first sensor.

this is a magnet wheel form a Super Jack Pro Brand International it has a marking where its ( i took it ) magnetized and goes by the sensor the gear that turns this magnet rotates several times ( i took it to be either 32 or 48 ) to move the actuator arm 1 inch

additional pictures are of a reed sensor that sets sideways awaiting the wheel to rotate

by my guesswork you could add a 2nd 3rd or even 4th sensor so the counts would go up on the v-box and the actuator arm would move in smaller increments.

this was just me guessing i didn't get to try it out

 

[gabshere]

the way your sensor & wheel are located you probably couldn't add another sensor

attached is an old Superjack motor with magnet wheel it has a slot for the sensor on the left but there is still room to attach several more sensors that the wheel would come in contact with .

that was my theory anyway.

your way works .. mine is just a different way with a different type wheel & sensor no way to add more magnets to mine sensors maybe.

 

[Lone Gunman]

RE: Extra counts? Well, after using that mover for a while now, I really can't say that it's THAT much better than the SuperJack that's on my other dish that has half the counts per inch than what this one has. Mind you there is probably "some" difference but it's difficult to tell if it's any better than the other one. In other words, I probably won't do any more like this. ;-)

 

[Lone Cloud]

Basically, depending upon the size and weight of a dish, you have a certain amount of momentum when it moves. I am just guessing, but the whole thing isn't going to stop immediately when the count is reached. Wind will also affect it. When you are dealing with single degrees or two, even small amounts of momentum will cause the dish to travel past the peak.

These experiments are worth trying, but I think there is a certain number of clicks that will be optimum, and adding more won't make much difference.

Maybe if your screw rod were fine threaded it might work, but that might make the wait when switching satellites unbearably long.

I don't know though. All a guess