EAF Abnormal: Page 2 - ZWO User Forum

EAF Abnormal

w7ay

Liquidtravel Askar FRA300,

My FRA300 moves about 2.9 µm per step.

The drawtube has a range of 22mm, this corresponds to about 7600 steps.

Chen

Liquidtravel

What is the math that gets you to 7600 steps? Also, when you get to 7600, does your EAF keep going even though the focuser stops, or do both stop?

w7ay

Liquidtravel What is the math that gets you to 7600 steps?

You mean the 22 mm (distance) divided by 2.9 µm (distance per step)? That gives 7586 steps.

You can measure the µm/step number quite accurately by moving the EAF by say, 1000 steps. Measure the distance the drawtube has travelled using good metal shop ruler or caliper. That will give you the drawtube movement per EAF step (how I got my 2.9µm number -- actually 2.91µm) and lets you set the EAF steps to a high degree of confidence of the amount of movement relative to the critical focus zone (CFZ) of your OTA. By using 1000 steps, you can easily get accuracy of the order of a small fraction of micrometers per step.

Don't use my (2.9µm) number. Given the impreciseness of hobby products, your FRA300 may have a different scale than mine.

By the way, if you are curious, I had one time measured the ZWO EAF and found that it takes EAF 5760 steps to complete 360º revolution. So you cn estimate the EAF scale also by turning the focuser knob by one revolution.

Chen

w7ay

Liquidtravel Also, when you get to 7600, does your EAF keep going even though the focuser stops, or do both stop?

The drawtube has a hard stop at the two ends of the 22mm travel!

The EAF will beep if you try to go beyond the drawtube's mechanical limits. Do that too many times, and you thare is a smalll chance that it might harm the flexible coupler, or even a sensitive mechanical focuser (the FRA300 focuser is pretty roughly manufactured though, so it probably won't be much harmed beyond what it already is).

If you are afraid that you might accidentally go over the drawtube limits, set the EAF step at one end of the drawtube to 0. Then set the max limit of the EAF to something like 7500.

Chen

w7ay

Liquidtravel W

Here is an example of how I measure EAF scale with a caliper:

This one using a digital micrometer; the plate on the right has an M48 hole that is wedged in between two M48 spacers:

And if there is no convenient surfaces, I simply Gaffer taped an aluminum angle bracket:

Chen

Liquidtravel

That is very odd. My EAF does not beep or stop. I guess I am stuck with setting the max limit to 7500.

w7ay

Liquidtravel My EAF does not beep or stop.

If your EAF shaft continues to turn (i.e., slipping) even after it has reached a hard mechanical stop of the OTA, you haven't locked the flexible coupler grub screws sufficiently. Remember that one of the grub screws need to be tightened against the flat part of a shaft. Thighten that screw (on the flat part of the shaft) first, before tighening the other grub screw.

Do the same with the focuser's shaft (unless you have a Takahashi, where there is no flat spot on the shaft -- the knob is held on with an axial screw that is tapped lengthwise into the end of the shaft).

Chen

Liquidtravel

w7ay

From what I can tell, the 4 grub screws are pretty tight so I am not sure where the issue is

w7ay

Liquidtravel From what I can tell, the 4 grub screws are pretty tight so I am not sure where the issue is

I am attaching the EAF to the FRA300 in purely stock configuration:

When the drawtube reaches the hard limit, the EAF is prevented from rotating, and emits a double beep in protest. (Just tested to make sure, using ASIStudio from a MacBook Pro.)

However, the EAF step count does change in spite of it not advancing the shaft rotation (just another of these bugs from ZWO, because they do not test their software).

If you watch the EAF, you can see it counter-rotating a little each time it hits the hard limit -- and at the same time emitting the double beep. When you ask it to advance yet again, the action will repeat -- hits the stop, then counter rotating slightly, and emits a double beep again.

See if the flexible coupler is still rotating after the hard limit. If it does, check the grub screws at the OTA end. If the flexible shaft is not rotating, but the EAF indicates it is still moving past the hard limit, check the grub scrws at the EAF end.

As I described earlier, one of the two grub screws must be seated on the flat part of the shaft, otherwise, there is enough torque for the stepper motor to keep rotating.

You didn't connect the EAF to the slow motion shaft (the red knob in the above picture, did you? I think that shaft has a slip clutch (part of a standard planetary gear) and can rotate when the main shaft is fixed.

The only other thing I can think of is that the gears in the EAF are stripped due to some earlier use.

Chen

Liquidtravel

If you watch the EAF, you can see it counter-rotating a little each time it hits the hard limit -- and at the same time emitting the double beep. When you ask it to advance yet again, the action will repeat -- hits the stop, then counter rotating slightly, and emits a double beep again.

See if the flexible coupler is still rotating after the hard limit. If it does, check the grub screws at the OTA end. If the flexible shaft is not rotating, but the EAF indicates it is still moving past the hard limit, check the grub scrws at the EAF end.

I do see the counter-rotating slower as it gets close to its limit and then stops when it reaches its limit, even if the numbers continue to move. Therefore, I don't think it is stripped. I can't see the flexible coupler moving but I do hear a noise inside of the EAF once it hits the manual focuser limit, even if it has not reached the Max Step limit.

I just never get the double beep unless it gets to the max step limit.

Aragorn

New here,
Installed a new ASIAIR on my Redcat 71. Took it our for a spin and got the same message as above Abnormal.........when attempting to Auto focus. Had no issues with the EAF on the previous ASIAIR. Made sure MAX was on 60000. Popped the EAF off and sent it to 0. The unit double beeped as expected both the current and move sections had 0 in them. Sent it up to 60000 with the same results. The expected double beep and both move and current read 60000. set the move to 30000 to be in the center. Again both move and current read 30000. While I was doing that I manually focused the Redcat. I hooked the motor back up and ran the focus well beyond the normal to see how much play I had in the manual focuser. There is plenty. Hooked her back up and had the same results. Changed Tablets to an Android. Same problem. Changed focus motor and cable and went through the same setup as above. Same results. Many moons ago I had an issue like this. It was the max was set to 0. Easy fix. Possible bug in the new ASIAIR?????????? I rely on the auto focus when running plans........... Not sure what the next step would be.

Tech@ZWO

Aragorn Update the EAF firmware to the latest version and reset the max steps first.
https://www.zwoastro.com/downloads/windows

Then remove the EAF from the telescope to see if it works fine without load.

Aragorn

BINGO! The EAF had too much load on it. Why I have no clue but the manual focuser on the Redcat 71 was extremely tight. Evidently at first it would allow the focus motor to go so far until it bound up. The second time through the focus motor would not even try before the double beeps. That is when it became obvious that the manual focuser was too tight. Just put it through its paces and all worked well!
Thanks!

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