MT2/MT4 motor for Vixen GPDX

[Ludd]

One of the motors on my recently-acquired GPDX sounds quite ill and, on top of its unhappy noises, it does have some irregular movement. Does anyone know if there are any equivalents to the old Tsukasa stepper motors that Vixen used in their MT2 or MT4 motor units? Or are there any sitting around in anyone's shed?

For the time being I've swapped the motors round so that the smooth-running motor is on the RA axis - does anyone see any problems with this? The motors look identical to each other.

[pete_gamby]

The motors are indeed identical and therefore interchangeable.

Cheers, Pete

[Ludd]

Thanks for confirming that Pete, I'm reassured.

Now for the hunt for a replacement!

[grchif]

If you do find any, please do post - they're very hard to get hold of by all accounts, so it would be a very useful thing to know.

(If your noises are squeaks or squeals, try taking off the rear encoder outer cover and cleaning and re-greasing the little spring-loaded ball-bearing behind it. This seems to be a common cause: three people I know have had that fault!)

Colin

[grchif]

Incidentally, I thought these were dc servos, not steppers?

[rowan46]

E321Keith is somebody I have always found to have a great knowledge of vixen (amongst other things) maybe you should drop him a pm if he doesn't see this

[rowan46]

Sorry terrible at numbers I mean E621Keith

[Ludd]

I think you may be right about these being servo motors - am I right in thinking that stepper motors don't need optical encoders?

[E621Keith]

I'm pretty sure the MT4 is servo, but I don't know anything about the MT2 motors.

I think your best bet is to put a wanted Ad on ABS. The SS2K controllers are starting to die as their internal battery depletes. There may be some people with dead controllers but functional MT4 motors.

[Ludd]

Thanks Keith. In fact the really helpful former owner has said that, despite the bargainousness of the price he agreed with me, he would be able to provide a replacement motor if I cannot get this one to behave properly. I may try a bit more tinkering this evening though.

[grchif]

MT2 and MT4 are I believe identical. Vixen increased the encoder resolution when they went from MT2 to the MT3 motors but had significant problems with missed counts, so reverted back to the old encoder; to avoid confusion (hnn) by having MT2 being 'later' than MT3, they re-named the MT2 to MT4.

Now double the confusion...

Colin

[bthoven]

Mt4 is servo motor.

Regarding the internal battery died down, I can easily find a replacement battery.

[kenpo154]

Glad to hear I can get a replacement battery for my hand controller! Have not neede one yet, here a some pics of my set up. When I first got the ss2k my motors were acting crazy so I had them replaced by vixen.

[Ibbo!]

Just reviving this thread

you say the ball bearing and spring at the rear encoder

I have just taken the motor out of the housing and removed the "adjuster "   shouls the ball and the spring be between the ali top and the shaft

if so i do not have the bearing and spring

if it is further in I need some smaller allen keys

Steve

[grchif]

From memory, yes - the encoder is mounted on the rear of the motor under the ally cover, the shaft of the motor protrudes through the encoder, and the end of the shaft presses against the ball bearing in the centre of the ally cover. The screw and spring are on the outside of the cover. The BB is very small; the screw is threadlocked in - in my case, I simply pushed the BB in a little with a small screwdriver and washed out with thin oil, then added some thicker stuff.

Can you post a pic?

Colin

[skybadger]

The motors are replaceable from vendors like reliance and trident using the Tsukas spec sheet. The thing to remember is the internal 36:1 gearbox and the encoder resolution of 400 counts/rev, the rest is gears. Expect motors to cost £90 or more new.

As has been mentioned, the battery is replaceable using the thionyl battery from RS or Farnell and is fairly easy to replace if you can handle a soldering iron.

IU have two hand controllers and I'm on the lookout for some more motors to motorise a third mount. I can't stand the ioptron hand controller once I have used the SS2K and the Meade handset isn't any better.

The biggest weak link in this setup is the cabling. Its very easy to get a bad contact and the power polarity is pure japanese

Cheers

Mike

[GraemeC]

Hi, this is my first post . I have a Vixen GPDX and I replaced the internal battery without any issues. I took photos of the circuit board and components before I dismantled it. There are instructions on the Internet if you do a search. I had to replace the battery because the handset was forgetting the time and location data.

The single improvement I have made is to the cabling - my GPDX connector is permanently attached in order to avoid flexure and stress at the connector. I keep the plug in, and the cable loops around to the side where it is attached with a cable tie and also (further down) with a stick on pad and another cable tie. I did this because I was worried that the cable connector looked a bit weak and I wouldn't want to pull out accidentally and cause damage. For me, I always pick up the controller and cable as a single unit now and it doesn't cause any problems.

I use the GPDX as a portable mounting for wide angle imaging.

Graeme

[Ibbo!]

Look like I need to find a ball bearing and spring then.

My cabling is also playing up and needs replacing

Thanks

Steve

[Ludd]

I probably ought to report back on my motors, having been out using them briefly last night.  In short, I can hardly believe the performance of this set-up.  A while ago I replaced the battery (not without its adventures - i'm not good at soldering, particularly with that lead free stuff, and ended up shorting the battery, but not for long enough to do any damage, thank goodness!) and so it now remembers where it is and what time it is, which saves a lot of time.  And although the motors still make their chattery noise, the vibration seems not to come through to the eyepiece.

Last night I did a rough polar alignment using the polar scope with its reticle (not illuminated, as I must have left it switched on and the battery seems to be dead) and then a two star alignment on Aldebaran and Capella.  I asked it to go to Jupiter, which it did, placing it off-centre in my 18mm eyepiece on my C8.  I centred Jupiter and aligned again, but it decided to ditch Aldebaran and just confirmed a two-star alignment.  I watched Jupiter for a bit, but the scope needed to cool down a bit more, and food was nearly ready, so I went in, leaving the mount tracking.  An hour and a half later I'd finished eating, washed up and had a game of scrabble.  I went outside and Jupiter was still in the centre of the FOV.

[GraemeC]

Yes, that's very satisfying . The more care you take with the alignments, the better it's performance gets. I have taken a bit of a leap of faith with mine on a couple of occasions with good results. for example.... after setting it up with a two or even three star alignment, I've told it go to go a convenient nearby faint fuzzy object of some sort (eg a random DSO). Not seeing anything in the field of view doesn't put me off.... I've then set my piggy backed DSLR for a few minutes exposure. When the exposure is finished I've looked at the image in the camera, and hey presto, the faint fuzzy object is there. . Cool, huh.....

These early images of mine of DSOs don't rank very highly if you compare them with some of the images in this forum but it's great to know that you've found the object you were looking for.

Graeme