PDA

View Full Version here: : Rowan EQ6 belt mod tuning by ammeter


StuTodd
10-03-2018, 08:35 PM
I'm just about finished with putting my EQ6 together again after installing the excellent belt mod. I was intrigued by a site I found in which the author claimed to get PE of 5 arcsec peak to peak and an RMS PE of 1".

http://www.myastroscience.com/rowan-astronomy-eq6-belt

He uses an ammeter on the motor which I guess is simple but how would I do that? Simply use a multimeter on the + and -ve wires from the PCB to the motor?

In fact, the chap has a lot of good mods on his pages..

Stu

luka
10-03-2018, 09:17 PM
For measuring currents you have to disconnect one of the wires that carries the current and connect it to the multimeter. Then a different wire connects the multimeter to where the first wire was disconnected to close the loop. Also make sure you use the right connectors on the multimeter and not the standard voltage connectors.

If I was to do this on the EQ6 I would probably measure current in between the power supply and the EQ6. The wiring would, for example, go like this:
1. +ve from the power supply goes to one of the multimeter current connectors
2. The other multimeter current connector goes to the +ve input on the mount.
3. The ground (-ve) goes like it did before.

The more accurate way would be to tap directly into the motor wiring but that is way more difficult. The above method would measure the total current used by the mount, which is basically the motors. You should use only one motor at the time during the measurement, otherwise the total current won't tell you which motor is using what.

StuTodd
10-03-2018, 09:24 PM
Thanks Luka, that makes sense. Electronics = Voodoo to me but that is good.
I see you did the mod too, did you do the feel method? Do you reckon you can get an improvement using this electronic method? Be really good to find out eh......?

billdan
11-03-2018, 12:28 AM
What's the purpose of measuring the motor current?

The EQ6 uses stepper motors with 6 wires connected to two field coils. The steppers are fed pulses from the on board micro-processor, measuring its current achieves nothing.

A different story if they were DC servo motors with only two wires, then you can adjust the balance of the scope by minimising the servo current draw..

Confused
Bill

EDIT: I just had a look at the link. He is using the ammeter to measure the total current draw the mount consumes as an indication of correct worm mesh. That might work, unconventional though??

luka
11-03-2018, 01:43 AM
Bill, your comment got me thinking about something else. Measuring the total current of the mount would make sense if the EQ6 was using DC motors but it does not, it uses stepper motors.

The current through a stepper motor is set by the driver and it is constant, no matter if the stepper is rotating or not. More importantly, the current does not depend on the load, unlike in the DC motors.

So... even if there is an extra load on the worm or even if the worm binds there should be no change in the total current drawn by the stepper motors. Again, these are not DC motors.

:shrug:

StuTodd
11-03-2018, 08:33 AM
Yes,
I may try his method after doing the usual tightening as the author seemed to rate the idea...:shrug:

Perhaps he just got lucky though?

billdan
11-03-2018, 10:36 AM
Good on ya Luka, you expressed what I was trying to say.

Stu, if his ammeter method doesn't work for you, here is Astro Baby's link to the conventional way of adjusting the worm.

http://www.astro-baby.com/EQ6%20rebuild%20guide/EQ6%20worm%20alignment.htm

Cheers
Bill

StuTodd
11-03-2018, 11:22 AM
Thanks Bill.

I've been following AstroBaby and I'll continue to do so now.
So there's absolutely no way this would work really? Again, electric = magic to me. When people state the EQ6 draws 2 amps whilst slewing, what are they measuring, and could that be a way to determine the worm gear set up?

billdan
11-03-2018, 11:43 AM
When the EQ6 is slewing to a target both RA and DEC motors are turning, so I would say each motor is drawing approx 1A each, plus whatever the electronics inside draw as well.

A typical Nema14 motor draws 0.75A and the bigger Nema17 motor draws 1.5A. but I don't know what brand the EQ6 uses.

Merlin66
11-03-2018, 11:59 AM
I have a TURNIGY power meter permanently connected to the main 12v power supply to my NEQ6 and all the usb hub and cameras.

iborg
11-03-2018, 05:08 PM
Hi All

I wouldn't bet on this "A typical Nema14 motor draws 0.75A and the bigger Nema17 motor draws 1.5A."

MEMA 14 and NEMA 17 indicate the defined size of the faceplate. It does not even indicate how long the motor is, much less the current draw.

"It is perfectly possible for a NEMA 14 to 'out pull' a NEMA 17 or a NEMA 23."

From http://reprap.org/wiki/Stepper_motor

Take a look at these two NEMA 14 stepper motors.

https://www.omc-stepperonline.com/hybrid-stepper-motor/nema-14-bipolar-18deg-125ncm-177ozin-1a-35v-35x35x28mm-4-wires-14hs11-1004s.html

https://www.omc-stepperonline.com/hybrid-stepper-motor/nema-14-bipolar-18deg-40ncm-567ozin-15a-42v-35x35x52mm-4-wires-14hs20-1504s.html

Philip

StuTodd
12-03-2018, 11:15 PM
But that's my question, I'm only interested in the RA axis, 1 of the 2 amps usually quoted (which is guided most as Dec should be doing minimal with a good alignment).

When folks quote the draw of the EQ6 as 2 amps slewing, 1 amp in either axis yes. But where do they draw that figure from? How to measure it.

I think this is the part I'm needing an answer to. To set the RA draw as 1.10 to get the worm "just so"...or perhaps I'm grasping at smoke...

luka
12-03-2018, 11:29 PM
The answer is that few of us believe that the method described in the article does not work.

The stepper motors always draw the same current, no matter if they are turning or just holding the load. The current won't go from 1A to 1.1A when the worm starts to "bite" and it will not go even higher when the worm binds. It will just stay 1A.

But if you want to try, do like I described above. You need to measure the current at the power connector which will include both motors. Disconnect, say, +ve wire, pass it through the multimeter (in current measuring mode) and then pass it back to where you disconnected it. You want to close the loop so that the current can flow and power the mount.

StuTodd
12-03-2018, 11:36 PM
Thanks, Luka.

I contacted the guy with no response as yet. I will give it a go using your method and report back.

I'm expecting an "I told you so" so nothing lost :thumbsup:

StuTodd
18-03-2018, 08:30 PM
So I tried the ammeter tuning method.

The mount was drawing 0.4 amps at idle with just the synscan handset on.
This figure rose to 0.82 and peaked at 0.84 as I turned the mount in R.A on rate 9. There is a fine line between there being no play in the axis and the worm being too tight and binding and making the belt slip. This figure didn't change noticeably as the gear tightened though...

I think the test would be to see if the PE changes with slight changes in amp draw but I'm doubting it. :)