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 Acuter Merlin (etc.) + MX2 - Speed Setting Advice? 
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Joined: Mon Jan 25, 2010 6:04 pm
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Location: Culver City, CA
Post Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
Hey All.
I'm really amazed at what this Acuter head can do out of the box. As others have commented, this thing is dead silent and an impressive piece of gear to watch over a period of time. I really hope it lasts in the field for a long long time.
Since the head is sold under so many names (mine was a SkyWatcher Backpacker system $149.95 with a telescope!) I'll just assume everyone is using the same thing.

I'm running the Dynamic Perception MX2. Since it's such a numeric system, does anyone have stats or information on good settings or data for different speeds? With a long lens, or a wider lens over a longer time period, even "0.01" on the MX2 seems too fast.
Is there a way to slow down the Merlin head?

Would be cool if we could create an MX2 / Merlin speed over time matrix for easy reference in the field.

Ideas?

Thanks! -Bob


Thu Feb 17, 2011 9:53 am
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Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
It's definitely got the low end speeds for super wides in MSM and Can go even slower in pulse (continious) mode... Telephoto lenses are tough for any motion control system. That said, without too much wind you can get away with a little more.

It's always the same old problem. The matrix is pretty complex when you add focal lengths and distances from objects. Then cross all that with intervals. I'd love to see an app though... :-)


Thu Feb 17, 2011 1:14 pm

Joined: Mon Jan 25, 2010 6:04 pm
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Location: Culver City, CA
Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
First off, thank you for persevering through the effort of developing a piece of hardware and putting it out to a niche market at an affordable price. Truly excellent.

As for the speeds, I'm shooting MSM (interleaved) and the speed still seems a bit quick at the lowest setting. Can you set axis speeds on the Merlin through the MX2? Thought that wasn't an option.

Man, the learning curve sure is fun, though!

Thanks again,

Bob


Fri Feb 18, 2011 5:10 pm
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Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
bereshr1 wrote:
First off, thank you for persevering through the effort of developing a piece of hardware and putting it out to a niche market at an affordable price. Truly excellent.

As for the speeds, I'm shooting MSM (interleaved) and the speed still seems a bit quick at the lowest setting. Can you set axis speeds on the Merlin through the MX2? Thought that wasn't an option.

Man, the learning curve sure is fun, though!

Thanks again,

Bob


Check out the Dynamic Perceptions web page relating to scope heads http://dynamicperception.com/?main_page ... age_id=334

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Sat Feb 19, 2011 1:13 am
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Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
bereshr1 wrote:
First off, thank you for persevering through the effort of developing a piece of hardware and putting it out to a niche market at an affordable price. Truly excellent.

As for the speeds, I'm shooting MSM (interleaved) and the speed still seems a bit quick at the lowest setting. Can you set axis speeds on the Merlin through the MX2? Thought that wasn't an option.

Man, the learning curve sure is fun, though!

Thanks again,

Bob


Bob, to get a much slower speed, set the motion type to "pulse", and now your inputs are in degrees per minute, instead of degrees per shot. If you shoot 1 shot every six seconds, this means 0.1' is 10x slower than in "interleaved" mode.

It's worth noting that the limitation here is really the Merlin, not the MX2. The reasoning is as follows:

"Interleaved" (aka MSM) mode, is designed for two purposes: accuracy and reducing blur in shots. To fulfill the first purpose, I have to make sure that the Merlin doesn't deviate too heavily from the entered distance. At low distances of travel, the built-in GOTO function in the Merlin firmware cannot accurately do 0.1' of motion - it typically overshoots from 50-150%. Thus, I re-wrote the control to instead move at an extremely slow speed while I read back the position. It takes time to query the head, get a response, and then process the result - in fact, so much time that 100% accuracy is impossible. So, I build in an "acceptable inaccuracy range" of around 20 pulses. (How many pulses per degree depends on the specific head - each variation of the Merlin is slightly different, but on average it should work out to around 10% deviation). The problem here, is that on the average Merlin head, < 0.01' is on the range of about 1x the "acceptable inaccuracy range" - meaning, I have mere milliseconds in which to achieve the control, reading, and stop code - except that the Merlin's baud rate is 9600 bps giving me only a few hundred possible cycles per second, assuming that I didn't have to actually get a response back... Now, add in that we have to support querying the merlin while interrupts are firing for other control activities in the MX2, and we end up missing distances < 0.1' by a LOT more than the original 150% slew of the built-in GOTO function.

Now, as to why continuous can go so much slower? I don't have to read back the position and ask where it is so that I know when to stop it =)

HTH,

!c


Fri Feb 25, 2011 6:23 pm

Joined: Wed May 12, 2010 7:29 pm
Posts: 43
Location: South Dakota, Wisconsin
Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
shutterdrone wrote:
bereshr1 wrote:
First off, thank you for persevering through the effort of developing a piece of hardware and putting it out to a niche market at an affordable price. Truly excellent.

As for the speeds, I'm shooting MSM (interleaved) and the speed still seems a bit quick at the lowest setting. Can you set axis speeds on the Merlin through the MX2? Thought that wasn't an option.

Man, the learning curve sure is fun, though!

Thanks again,

Bob


Bob, to get a much slower speed, set the motion type to "pulse", and now your inputs are in degrees per minute, instead of degrees per shot. If you shoot 1 shot every six seconds, this means 0.1' is 10x slower than in "interleaved" mode.

It's worth noting that the limitation here is really the Merlin, not the MX2. The reasoning is as follows:

"Interleaved" (aka MSM) mode, is designed for two purposes: accuracy and reducing blur in shots. To fulfill the first purpose, I have to make sure that the Merlin doesn't deviate too heavily from the entered distance. At low distances of travel, the built-in GOTO function in the Merlin firmware cannot accurately do 0.1' of motion - it typically overshoots from 50-150%. Thus, I re-wrote the control to instead move at an extremely slow speed while I read back the position. It takes time to query the head, get a response, and then process the result - in fact, so much time that 100% accuracy is impossible. So, I build in an "acceptable inaccuracy range" of around 20 pulses. (How many pulses per degree depends on the specific head - each variation of the Merlin is slightly different, but on average it should work out to around 10% deviation). The problem here, is that on the average Merlin head, < 0.01' is on the range of about 1x the "acceptable inaccuracy range" - meaning, I have mere milliseconds in which to achieve the control, reading, and stop code - except that the Merlin's baud rate is 9600 bps giving me only a few hundred possible cycles per second, assuming that I didn't have to actually get a response back... Now, add in that we have to support querying the merlin while interrupts are firing for other control activities in the MX2, and we end up missing distances < 0.1' by a LOT more than the original 150% slew of the built-in GOTO function.

Now, as to why continuous can go so much slower? I don't have to read back the position and ask where it is so that I know when to stop it =)

HTH,

!c


I set my MX2 to pulse and the scope settings to 0.1 for both pan and tilt. Is that the slowest it can be set at? I haven't shot anything with it yet, but it looks like it may be a little to fast yet for 30 second shots, if I want it to run for 3 hours or so.

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Fri Mar 11, 2011 8:46 am
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Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
Hi Randy,

hope your System is running well...

I will get my MX2 and the Dolly Zero System by this week and the cable to connect everything to the Merlin a week later. I want to use the Dolly/MX2/Merlin mainly in Pulse mode and set to the slowest sideral speed - for Astro/Landscape TimeLapse. I'll post the results as soon as I have some.

Cheers
Chris

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Sat Mar 12, 2011 6:12 pm
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Joined: Wed May 12, 2010 7:29 pm
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Location: South Dakota, Wisconsin
Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
deepspace wrote:
Hi Randy,

hope your System is running well...

I will get my MX2 and the Dolly Zero System by this week and the cable to connect everything to the Merlin a week later. I want to use the Dolly/MX2/Merlin mainly in Pulse mode and set to the slowest sideral speed - for Astro/Landscape TimeLapse. I'll post the results as soon as I have some.

Cheers
Chris


It seems to really vary each time for me. On one test run the pan moved about 90 degrees in about 3 hours with the MX2 set at .1 on pulse mode, the tilt also moved about 90 degrees at .1. Some times the pan will move at what looks like 4x with it set at .1 on the MX2, way too fast. Sometimes rebooting the MX2 will get it back to the .1 speed above, but it may takes several times. Not really sure what I'm doing wrong. It would be great if it had a little slower speed, especially for the tilt for long exposure night time stuff. I think I have it at the slowest speed.

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Sat Mar 12, 2011 7:36 pm
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Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
randyh wrote:
It seems to really vary each time for me. On one test run the pan moved about 90 degrees in about 3 hours with the MX2 set at .1 on pulse mode, the tilt also moved about 90 degrees at .1. Some times the pan will move at what looks like 4x with it set at .1 on the MX2, way too fast. Sometimes rebooting the MX2 will get it back to the .1 speed above, but it may takes several times. Not really sure what I'm doing wrong. It would be great if it had a little slower speed, especially for the tilt for long exposure night time stuff. I think I have it at the slowest speed.


Randy,

That seems odd - as the speed is set to what the Merlin head thinks is 0.1'/minute. That is, the speed is calculated by asking the merlin head how many counts it has per revolution, and then instructing it to move at a specified speed that maps to that many counts per minute. There may be an issue where the merlin is getting confused, especially if it works ok after a re-start (and, to be honest, you should re-start both the head and the mx2, not just the mx2 - the only reason to re-start the MX2 is so that it will re-initialize the head). There are known issues like that using the GOTO function of the head, and for that reason I avoided using it at all.

I'm wondering if there's some command that's being issued in the process of using it that causes the problem. Try this:

* Set the merlin manual control speed for both axis ([enter], [down] to scope, [enter], then edit the values) to the maximum speed
* Go into manual control for the merlin head, and then move each axis a bit
* Go back to the main merlin menu, and then set the speeds to 0.1

See if this remedies the problem (especially after you've noticed it happening). If so, I may be able to put in a software fix for you.

!c


Mon Mar 14, 2011 6:27 pm

Joined: Wed May 12, 2010 7:29 pm
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Location: South Dakota, Wisconsin
Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
shutterdrone wrote:
randyh wrote:
It seems to really vary each time for me. On one test run the pan moved about 90 degrees in about 3 hours with the MX2 set at .1 on pulse mode, the tilt also moved about 90 degrees at .1. Some times the pan will move at what looks like 4x with it set at .1 on the MX2, way too fast. Sometimes rebooting the MX2 will get it back to the .1 speed above, but it may takes several times. Not really sure what I'm doing wrong. It would be great if it had a little slower speed, especially for the tilt for long exposure night time stuff. I think I have it at the slowest speed.


Randy,

That seems odd - as the speed is set to what the Merlin head thinks is 0.1'/minute. That is, the speed is calculated by asking the merlin head how many counts it has per revolution, and then instructing it to move at a specified speed that maps to that many counts per minute. There may be an issue where the merlin is getting confused, especially if it works ok after a re-start (and, to be honest, you should re-start both the head and the mx2, not just the mx2 - the only reason to re-start the MX2 is so that it will re-initialize the head). There are known issues like that using the GOTO function of the head, and for that reason I avoided using it at all.

I'm wondering if there's some command that's being issued in the process of using it that causes the problem. Try this:

* Set the merlin manual control speed for both axis ([enter], [down] to scope, [enter], then edit the values) to the maximum speed
* Go into manual control for the merlin head, and then move each axis a bit
* Go back to the main merlin menu, and then set the speeds to 0.1

See if this remedies the problem (especially after you've noticed it happening). If so, I may be able to put in a software fix for you.

!c


I tried that but the MX2 doesn't seem to be storing the value, I press enter after I change it. I got up to over 5000 and it was still going up, how high does it go? I can't seem to get it to move on manual mode now, I was before but it was intermittent. For some reason it doesn't seem to move at all in Pulse mode now either.
I can get it to work about 1/3 of the time in interleave mode, but it seems to require several reboots of both the MX2 and merlin. I haven't found any certain step that I'm doing different. The merlin seems to work ok with the controller it came with though. So not really sure what the deal is.

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Wed Mar 16, 2011 5:59 am
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Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
randyh wrote:

I tried that but the MX2 doesn't seem to be storing the value, I press enter after I change it. I got up to over 5000 and it was still going up, how high does it go? I can't seem to get it to move on manual mode now, I was before but it was intermittent. For some reason it doesn't seem to move at all in Pulse mode now either.
I can get it to work about 1/3 of the time in interleave mode, but it seems to require several reboots of both the MX2 and merlin. I haven't found any certain step that I'm doing different. The merlin seems to work ok with the controller it came with though. So not really sure what the deal is.


Well, the maximum value is 360 or so. I guess I should have specified that... It doesn't matter how high you go, when you save it, it will automatically limit it to the maximum value (if it doesn.t that could be a big part of the problem =)

We have one other person so far experiencing the same issue, and I fear it may have to do with differences in the firmware on the Merlin heads. Each branded version is actually unique in its internals, even if they run the same firmware - and some vendors have been upgrading, or not upgrading, the merlins they sell.

The other person having the issue seemed to have much better luck with 0.81, but I don't recommend 0.81 firmware due to major issues in a lot of areas - including Merlin control.

Let's rule one thing out first: reset the mx2 to factory defaults ('Settings' -> Reset Mem -> 'on' -> save -> power cycle mx2). There may be a stored value in memory that has gotten corrupted somehow, causing issues in odd areas. But, I highly doubt that is the source (it wouldn't be the first time it fixed a difficult to nail-down problem, surprisingly)

I'm thinking the issue may be that the difference in firmware is resulting in ratio differences, which would mean there is little visible difference in two speeds shown on the screen, because the speeds are calculated given a particular ratio, and that the firmware on the Merlin you have is getting goofed on the ratio somewhere in the communications/

Ultimately, this means getting the following back into the firmware: merlin.setRatio(1,1); merlin.setRatio(2,1); at the right place. Colin L. is currently working on seeing if he can try changing it with his head which is having a similar issue, and if it fixes it, I can introduce a patch.

!c


Tue Mar 22, 2011 4:50 pm
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Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
shutterdrone wrote:
Ultimately, this means getting the following back into the firmware: merlin.setRatio(1,1); merlin.setRatio(2,1); at the right place. Colin L. is currently working on seeing if he can try changing it with his head which is having a similar issue, and if it fixes it, I can introduce a patch.

It worked Chris. I added the ratio command before the direction function and the head now operates correctly. Thanks for your help.

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Thu Mar 24, 2011 6:03 pm
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Post Re: Acuter Merlin (etc.) + MX2 - Speed Setting Advice?
colinmlegg wrote:
shutterdrone wrote:
Ultimately, this means getting the following back into the firmware: merlin.setRatio(1,1); merlin.setRatio(2,1); at the right place. Colin L. is currently working on seeing if he can try changing it with his head which is having a similar issue, and if it fixes it, I can introduce a patch.

It worked Chris. I added the ratio command before the direction function and the head now operates correctly. Thanks for your help.


Awesome Colin, I'll get a new dev build of the firmware up on the dev page w/ the changes in the next couple of days.

!c


Fri Mar 25, 2011 7:21 am
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