Hi all,
I was wondering if anyone had used one of these SW electric focusers before. I installed it on my SW ED80 refractor the other day as per the very good instructions on youtube but soon ran into difficulties.
At several points along the drawtube's travel the motor strains and struggles and simply can't move the drawtube. I tried loosening the focuser screws slightly to reduce the tension on the focuser pin but in order to get the motor to move the drawtube past the point of resistance the drawtube can virtually be pushed in by my finger.
I have tried gently wiggling the drawtube from side to side as I tighten the focuser screws to ensure that the flat section of the drawtube is well seated on the focuser.
I also tried a very light dry lube but that seems to make no difference. I was hesitant to try a stickier slide oil until it was absolutely necessary.
Given that the motor always struggles at the same points on the drawtube, I had considered that perhaps the drawtube is not entirely flat and hence was sticking. I have a straight aluminium block with adhesive abrasive paper that I use for levelling frets on my guitars, I had considered trying to gently level the flat section of the drawtube to see if that helps. Good idea or no?
These SW electric focus motors have been around for quite a while, and I
have heard no complaints about them, other than the early ones chewed
up batteries in no time , even when switched off, necessitating fitting an
on/off switch to break the circuit. They are very strong, and will turn
the focuser wheels and shaft even if you forget to unlock the focuser
after an imaging run.[assuming that a Crayford style focuser is being used, not a rack and pinion].
Assuming that you are using the Crayford style focuser, when you say it strains and struggles, does the motor actually stall, or keep turning, but not move the draw tube? As I said, the motor is strong, so loosening the tension on the shaft will just cause it to slip. If the motor keeps turning but the draw tube doesn't move I suspect that the tension needs increasing not
decreasing. When the tension is right it should be quite hard to move the
focuser in or out by hand by pushing or pulling on it. It's a pity that the
electric system doesn't have a quick release so that large focus adjustments can be done manually. I just push or pull on my focuser to
do large adjustments.
raymo
Hi Raymo,
Yes it's a Crayford style.
When the focuser is fully screwed in the motor actually stalls and doesn't spin. I can manually turn the fine focus knob on the other side and help it along, but I can definitely feel some resistance there. Once it gets past the 2-3mm zone of resistance in the travel it frees up again and the motor works under it's own power.
Possibly the bearings under the drawtube? When I take the focuser off though the drawtube slides very easily, so that leads me to think it's not that.....
When the focuser reaches the fully in/out position the focuser knob should
barely slow down, let alone stop, so only two likely possibilities:
Battery low, if yours suffers from the problem I mentioned before, even
leaving the battery installed overnight is enough to partially or completely
flatten it, so worth checking the battery, or trying another one that you know
is good.
Motor, or motor controller circuitry is faulty.
If the motor is freed from driving anything, does it go through the changes
in speed seamlessly when you rotate the speed control knob, and it should
feel powerful if you try to stop it turning by hand when running at high speed.
If you can easily take the focuser through its range of movement using the knobs when the motor is not attached to it, you can forget the focuser as being the cause of your problem.
The battery should last for ages, so if it turns out that your new battery
is already seriously low, it looks like you have the problem I mentioned
before, and will have to put an on/off switch into it, like I did, or remove
the battery between each viewing session, or return it for a refund.
raymo
Last edited by raymo; 30-04-2016 at 03:57 PM.
Reason: correction
Howdy, I had the same issue when I fitted one to my ed80.
I turned out that the coupling was rubbing on the hole. It was a tight fit.
I had to losen off the other end and pull the spindle through a little bit,
So when I attached the motor and coupling it would not rub.
Hope this makes sense.
I will add a photo later if needed.
Thanks
Thanks for the tips. It's definitely not the motor itself, when the focuser is removed from the telescope it revolves happily with no obstruction. It's something to do with the motor's interaction with the telescope.
I think VP might be onto something here, the silver bracket of the motor that grips the spindle might be rubbing on the telescope, though I swear it completes more than a full revolution before binding (you'd think it would jam at the same point on every revolution).
I'll check it out tonight and let you know if that resolves it.
Thanks again!
