HEQ5 Replacing motor - how easy is this ?

[Kev M]

Typically after waiting for what seemed like months for clear skies my HEQ5 has thrown a wobbler...

It makes a horrendous screeching noise as though some gears are stuck on the DEC drive.

After taking the side plate off, the gears appear to be free.....I can easily turn them using my fingers ( I cant easily move the RA gears ? ).

When trying to turn it using the handset it screeches like mad and none of the gears move....I assume therefore its the motor itself.....dont know what else it could be ?

How easy is it to replace these motors ?

Kev  😭

 

[Merlin66]

Kev,

Sounds like the grub screws which hold the gears to the shaft may have come loose?????

I'd double check that before panic sets in..............

 

[Kev M]

Just checked that.....when I turn the gears by hand the shaft revolves as well.

When I try to turn it using the motor the shaft doesnt move.

Panic setting in.....

[Merlin66]

Bumma!

 

[Kev M]

Ok tried the obvious just to check, swapped RA & Dec motors, fault follows the motor.

Removed motor...very easy.

Motor is very stiff & grindy to turn by hand as though something is catching inside.

Don't suppose anyone has a pinion extractor tool lying about I could borrow/buy/steal ?

🐼

 

Kev

 

 

 

[Kev M]

Done some further investigation.

It is a NEMA 14 bipolar motor 34mm long

Assumed Step Angle 1.8deg

Assumed 12v ?

Holding Torque ?

Current ?

It appears from my multimeter that one of the windings has a short circuit ( one pair is 7 ohms, the other pair is zero ohms ! ).

There are lots of equivalent stepper motors as cheap as chips that would probably work fine.....

However the biggest issue is the reduced shaft size at the end from 5mm down to 4mm ( approx. )

Does anyone know if these are the same motors in the EQ6 ?

[Kev M]

OK got in touch with Optical Vision to see if they could source a replacement....they came back quite quickly.

They said they would need my address to quote a price.....but delivery would be approx. 4 months.....yep .....4 months 😱

I haven't got back to them yet.....no rush.

 

The spindles on the EQ6 steppers appear to be different have a flat on them as opposed to reduced, dont know if the length is the same either.

This is not looking good.....😭

[JamesF]

Isn't the shaft size part of the spec?  So all NEMA14 motors should have a 5mm shaft?

James

[1parsec]

The motor shafts are 5mm, but the end of the shafts are machined down to either 3mm or 4mm diameter depending on the pinion gear bore size !
The reason for this is a 9 tooth gear is too small to have a 5mm hole through the centre.

I've even seen a mount with a 3mm bore pinion on the Dec motor and a 4mm on the RA .
Unfortunately a standard off the shelf NEMA 14 motor wouldn't have the shoulder to fit the pinion.

 

[Kev M]

50 minutes ago, JamesF said:

Isn't the shaft size part of the spec?  So all NEMA14 motors should have a 5mm shaft?

James

The HEQ5 motor appears to have been reduced to 4mm to allow the smaller cog to fit.

Picture shamelessly stolen from rowanastronomy.com ( they wont mind the plug ).

 

 

 

 

[Kev M]

1 minute ago, 1parsec said:

The motor shafts are 5mm, but the end of the shafts are machined down to either 3mm or 4mm diameter depending on the pinion gear bore size !
The reason for this is a 9 tooth gear is too small to have a 5mm hole through the centre.

I've even seen a mount with a 3mm bore pinion on the Dec motor and a 4mm on the RA .
Unfortunately a standard off the shelf NEMA 14 motor wouldn't have the shoulder to fit the pinion.

 

What he said....

[JamesF]

If you could source the appropriate motor I'm not even sure how you'd go about turning it down.  Perhaps mount the motor on a plate and lock the shaft so it won't turn somehow.  Sounds like a major pain in the neck.

I wonder if a belt drive conversion might offer a way out?

Waiting for four months for a motor to arrive would certainly be a bit sickening.  We could have had at least two clear nights by then.

James

[Kev M]

52 minutes ago, JamesF said:

If you could source the appropriate motor I'm not even sure how you'd go about turning it down.  Perhaps mount the motor on a plate and lock the shaft so it won't turn somehow.  Sounds like a major pain in the neck.

I wonder if a belt drive conversion might offer a way out?

Waiting for four months for a motor to arrive would certainly be a bit sickening.  We could have had at least two clear nights by then.

James

I would still need to source a motor of the right voltage, current, size etc etc.

However am thinking along the line of how standard these motors are....could the core of the motor be swapped....it appears to be the external windings that are faulty.

Also I don't think it would be that difficult to turn the shaft down....possibly could use the motor itself as a lathe..?

Still wondering about the EQ6 motors if they are the same size and shaft length.

Or I may just stay hidden in a corner and cry.....😪

[JamesF]

I'm amazed it's a NEMA14, I have to admit.  I was expecting at least a NEMA17.  You're certain on that?

James

[Kev M]

16 hours ago, JamesF said:

I'm amazed it's a NEMA14, I have to admit.  I was expecting at least a NEMA17.  You're certain on that?

James

Its 1.4 inches square …..

[JamesF]

Well, that's a disappointment then.  Earlier today I even managed this rather useful post that appears to apply to a completely different HEQ5 from yours :(

http://www.astronomyforum.net/telescope-mounts-forum/95029-stepper-motor-replacement-parts-eq5-heq5-eq6-pro-atlas-sirius-telescope-mounts.html#post1057150503

Makes me wonder which is in my own HEQ5 now.  Not that I'm desperate to open it up and find out just yet.

James

[Owmuchonomy]

I know you quote Rowan above but have you asked them if they can help you out?

[Kev M]

No, not yet, been to busy crying....

I suppose I should start pinging a few emails to Rowan, FLO and other suppliers.

 

[Kev M]

Another reply back from a retailer....4 months lead time from supplier......😫

[JamesF]

There has to be a better solution :(

James

[Kev M]

Came accross these ( on a well known auction site )

 

 

5mm to 5mm shaft coupling......

Theoretically I could cut the shaft of the old motor and attach it to the shaft of a new motor, hence getting rid of the issue with the reduced shaft size !

Might have to fiddle about to get the length correct , but I reckon if I deliberately went "long" it would be easy enough to pack the motor back a bit on its mounting to get the cogs to line up exactly

Maybe......

Back to finding the correct NEMA 14 motor ( any 5mm shaft length , as its going to be cut ) with the correct voltage/current/torque etc

 

[Kev M]

Possibly this motor

 

https://www.amazon.co.uk/STEPPERONLINE-Bipolar-1-8deg-35x34mm-Printer/dp/B07LBH93X4

Typically out of stock

 

[JamesF]

I reckon they'll be 12V motors.  The torque figure you might be able to guesstimate from the length of the motor.

James

[Kev M]

Will try and borrow oscilloscope to check voltage/current levels into existing motors to be sure.

Going to get one and give it a go.......cant wait 4 months....😱

 

 

[Kev M]

I think I may have found one......waiting for the supplier to come back...🙏