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EPEC - did you try it?

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sleepwalker:
Hi Tobi,
ich denke, das war ich  ;)
CS, Dennis

Tobias:
Hallo Dennis,
ja das warst du! Da ja die PNs nicht mehr aufrufbar sind... war ich mir nicht mehr sicher - sorry. Schön, dass du hier nun auch aktiv bist, so können wir da evt weiter machen - falls sich etwas ergibt.

Cs Tobias

PS Gut, dass du die Encoder noch nicht gekauft hast, da ja scheinbar der Epec nicht funktioniert… wäre schon schön gewesen.

Armando:
Hi Dennis and Tobias,

if EPEC doesn't work then a TDM style solution could be used: I think ST4 is the only way to properly manage the encoder feedback.
Anyway, even if more versatile and not limited to LFEP, a TDM style board is difficult to be realized. It will also oblige to guide by ST-4.
During the autoguiding exposure it should send its own ST4 corrections; while receiving ST4 corrections the board should use encoder feedback to keep a different speed (e.g. 1x+0.33x or 1x-0.33x) : this way it will effectively track also the correction.

I think enabling autoguiding is a requirement, also in case of an ideal polar alignment: it should solve possible integral errors caused by oscillator frequency issues and by the same encoder limited accuracy.
Orlando Andico published on CloudyNights his attempts to make a feedback by a sine rotary encoder useful to reduce the tracking error (with no autoguiding). But some troubles occurred because of possible PE due to the encoder itself!

We could prefer the EPEC by converting sine outputs to TTL ones. In case it won't work we will be obliged to switch to a TDM style solution.

I think currently it's not priority to take into account possible encoder feedback issues while the mount is slewing or because of a movement by hand. In the worst case a quick solution will be to provide a command to toggle EPEC off/on by ASCOM driver (and automatically for GoTo commands).

If LFEP is able to track 20000 ticks/s I see no encoder reading issues at all at sidereal speed.
What I'm not sure is EPEC. As a 5000cpr encoder is not cheap at all, do you think it's worth it?

AFAIK EPEC option is enabled by an appropriate firmware update.
I bought my LFEP unit with all options enabled; afterwards Rajiva announced the end of the LFEP support.

CS
Armando Beneduce

Armando:
According to the noise coming from RA motor (by assuming that EPEC works by moving RA motor at 1x+0.33x or 1x-0.33x) I found that simulated high (resp. low) speed forces LFEP to decrease (resp. increase) tracking speed.I see no troubles while switching between sidereal and lower speed. But as soon as the higher speed is activated the controller remains locked at that speed. :(
I've no way at home to check by a telescope.

CS
Armando

sleepwalker:
Hi Armando,
The encoder error is not unimportant. My encoder has a maximum error of 60% per tick. This is a half arc second. I think that is tolerable. Also should not be used as a gearbox in order to increase the resolution. It makes no sense to try error of gears with other gears to fix.

It is not only the polar alignment. The stiffness of the mount against wind and vibration as well as the bending of the telescope itself must be minimized.
The bearings should have no gap and have to run very precisely.
(1 arc second are only 1mm at 200 meters)
These are very high demands on a payable mount.
My mount is a self made with 60mm diameter axis and handles very precisely.

My encoder is an optical non-contact encoder ring. Thermal expansion is not a problem.
If only I could somehow get the EPEC option for testing.
Is there really no more updates? :'(

I think that there should be a way to improve the EPEC.
It can not be so difficult to influence the speed of a stepper motor controller.

5000 tpr are not quite enough. With quadrature you have a resolution of 65 arcsec.
(1296000 "/ (5000tpr x 4 (quadrature)) = 64.8")
And then comes the potential errors in the Enoders ...

What annoys me with the LFEP: an encoder that allows EPEC, makes no GOTO by hand.
No matter if TDM or LFEP, I need currently 2 encoder on the RA axis to have both.

Perhaps there is a way (with additional box) to save the tick and leave in a specific maximum speed to the LFEP. GOTO by hand is then slower but doable.

CS, Dennis

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