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Is a warm RA motor normal. I have never noticed this before. I have a 10 month old G11G.

On Sun, Feb 25, 2024 at 01:10 PM, @VictoryPete wrote:

Is a warm RA motor normal. I have never noticed this before. I have a 10 month old G11G.

?

It is a DC Servo motor. They get warm under use. This is typical of all DC servo motors.

Generally speaking a servo motor will not be damaged unless internal temperature is higher than 130C and outer temperature should be below 90C. You are not likely to encounter these temperatures with sidereal loads, even with the occasional slew… but yes it will get warm. No need to worry about it.?

Apparently, it was tracking with intermittent RA Stalling. I thought an RA Stall stops the motors. I had adjusted the worm gear a few days ago so I am surprised it tightened up so soon.

VictoryPete:

With the greatest respect, most people overtighten their worm mesh in my experience in an attempt to totally eliminate backlash.
This happens even more often with DEC.

In addition, worm mesh very, very, slightly varies around the circumference of the worm wheel. So to do it right you really need to (tedious, I know) turn the worm wheel thru 360 degrees to find the high spot.
Otherwise, you'll risk setting the lash at a lower spot and then, after hours of operation, the high (tightest) spot will rotate into position and things will be too tight.

But to make a possibly useful suggestion, what voltage are you running at? Stalls are more likely at lower voltage.
Also, get a non-contact thermometer that has both a personal and house (aka Object) mode and measure the temperature numerically.

Best regards,

Mark Christensen

Hi Mark, thanks for the thoughtful response. I understand all that you have said. I am an electrician with a degree in electronics, so I understand quite a bit about the subject. I have read here that the Gemini should work just fine with 12V. Right now, I have 12.7v from my Primalucelab Eagle 5 Pro. I do have the 15v power supply from Losmandy. I don't use it anymore to eliminate one extra cord and plug to power my system. I have wondered about switching back to the higher voltage. I am waiting for it to do the intermittent stall warming again and I will then change to the Losmandy power supply. I was surprised that the motors did not stop with the Stall warning, isn't that what is supposed to happen?

FWIW, I would caution against increasing voltage to solve a stall that is accompanied by a warm motor. A higher voltage may help the motor overpower excessive friction or imbalance, but will also put more current through the motor, resulting in more heat and a potential burn-out. Both, a? warm motor and stall messages indicate the worm/gear mesh being too tight, or mount not being balanced. I'd solve these mechanical problems, first, before increasing supply voltage.

Regards,

? -Paul

On Mon, Feb 26, 2024 at 11:14 AM, Paul Kanevsky wrote:

FWIW, I would caution against increasing voltage to solve a stall that is accompanied by a warm motor. A higher voltage may help the motor overpower excessive friction or imbalance, but will also put more current through the motor, resulting in more heat and a potential burn-out. Both, a? warm motor and stall messages indicate the worm/gear mesh being too tight, or mount not being balanced. I'd solve these mechanical problems, first, before increasing supply voltage.

Regards,

? -Paul

I understand this, but there is a gray area I am in here, a cause and effect inversion of sorts. I was surprised this happened because I adjust my spring frequently, just for practice's sake. I even have some Jet Lube MP-50 on the way. If the extra voltage could prevent it from stalling in the first place, the motor may not get a chance to overheat. On the other hand, I don't really want to have the extra power supply connected if I don't have to. Isn't the motor supposed to get shut off when there is stalling??

On Mon, Feb 26, 2024 at 02:36 PM, @VictoryPete wrote:

I understand this, but there is a gray area I am in here, a cause and effect inversion of sorts. I was surprised this happened because I adjust my spring frequently, just for practice's sake. I even have some Jet Lube MP-50 on the way. If the extra voltage could prevent it from stalling in the first place, the motor may not get a chance to overheat. On the other hand, I don't really want to have the extra power supply connected if I don't have to. Isn't the motor supposed to get shut off when there is stalling??

I would rather have the motor stall than risk overheating, but that's just me.

On Mon, Feb 26, 2024 at 02:45 PM, Paul Kanevsky wrote:

I would rather have the motor stall than risk overheating, but that's just me.

So would I, why did it continue to run? It said Stall on both the Web Page Server HC and the actual HC.

On Mon, Feb 26, 2024 at 03:02 PM, @VictoryPete wrote:

So would I, why did it continue to run? It said Stall on both the Web Page Server HC and the actual HC.

Can't say. Maybe after the motor slowed down, it was able to overcome the friction, and continued despite the stall? Just guessing.

I have the latest version. I was not aware you could tweak the motor steps. There seems to be no wiggle room (pun intended) in the adjustment of the screw. What is further confusing is the springs screw gets adjusted first, then the other screw. There seems to be some randomness to setting the spring's screw. "Tighten all the way, then loosen 1/2 to 3/4 of a turn". I go to about 2/3. Then the 2nd screw is extremely sensitive, Scott says 1/50th of a turn in one video and 1/16th in another.

The spring screw is tightened all the way down and then backed off 1/2 to 3/4 of a turn to allow maximum spring pressure while also allowing for some spring travel. If you just tightened the spring screw all the way down, there would be no travel and you might as well have no spring. This also allows some play for the second screw to have some adjustment room. You can back it off a full turn if you want.

The second set screw sets what I call the base pressure on the worm gear block. If the set screw is not making contact with the surface then the worm gear/ring gear interface gets the full force of pressure from the adjustment spring. This will undoubtedly cause too much friction and will result in a stall on the affected axis. By screwing that set screw clockwise, you (very slightly) space the worm gear block away from the ring gear to the point where they can interface freely. Back it off too much and you induce room for backlash... don't back it off enough and you induce stalls... hence the very very small window for the "sweet spot" when Scott is referring to 1/50th of a turn to 1/16th of a turn. Too little and the gears won't turn... too much and there isn't enough spring pressure left... just right gets you a bowl of perfect porridge and a comfy bed.

That sweet spot will vary from mount to mount, and from one temperature to another. Once you adjust it you will need to slew the axis from stop to stop to ensure you didn't make it too tight and allowed enough play to avoid a stall...?

Also consider that a stall is not what you want to be pushing up against. There are plastic gears in the gearbox that can be affected over time if you are constantly pushing up against stalls. I made the mistake of erring on the side of too much tension and ended up replacing my gearbox.

Remember, RA backlash is not really a big deal. Your RA spins in one direction and if you are guiding at 0.5 sidereal than your RA axis is always moving in the same direction between 0.5x and 1.5x sidereal rate... it isn't reversing... and as long as your rig is balanced it should not impact performance excessively.

Dec backlash is more critical, but this is lessened with proper balancing and is still only reducible to a point as you do not want to induce stalls/excessive wear and tear.

I may be mistaken but I thought there was at least a delrin gear in the reduction gearbox.. I'm sure Paul or someone else can correct me. One of these days I'll pop open an old damaged one and know for sure.

Nothing wrong at all with plastic or delrin gears. ?You can replace your GB with a Mckennan 25:1 GB that has all metal gears but the question is why?

You also need to do some fiddling an change the motor pinion gear (comes withKit)

But why is this all of a sudden an issue? ?You wouldn’t want to do such a change with out baselining PE a few times first, as you could end up worse! ?

Michael Herman (and others) have done write ups on this but Michaels is very comprehensive. ?I’ve thought of doing it but without a base line it could lead to a disaster. ?Plus if you get bad enough stall or mechanical crash the plastic gears in the GB Should strip ? Buy in reality the stall detection routine stop this in the G2 ?

Not that I have heard of that happening (stripped gears). ?Many plastic gears are used in situations like this as they tend to “flow” during mesh. ?I had one apart the other day and there was very little backlash in my GB gears, over 14 yrs old now. ? Be just doing my own “rivet mod” to them. ?Because I can.?

But all this needs a seperate thread as off topic diversions like this disrupt thread continuity. ?

it’s just everything heads in a tangent so forum members using search function can end up Miles from what they are looking for.?

Oh motors to get warm especially if out of balance and giving stall warning. The warnings are just part of new stall detection routine in the servos telling users there is something NQR but it’s still working. ? Motors get very hot on axes crash! ?This I know! ? But luckily I had my clutches set just right and the motor survived ?

Use the HC servos balance feature yo fix this.?

FWIW

CHeers?
--
Brendan

On 2/26/2024 9:10 PM, Ryan Noonan via groups.io wrote:

The spring screw is tightened all the way down and then backed off 1/2 to 3/4 of a turn to allow maximum spring pressure while also allowing for some spring travel. If you just tightened the spring screw all the way down, there would be no travel and you might as well have no spring. This also allows some play for the second screw to have some adjustment room. You can back it off a full turn if you want.

Don't forget that the spring screw also functions as an out travel limit because when screwed all the way in until it stops, it bottoms on the right hand worm block post inside the base plate.? When you then back it out a small amount, you are making sure that the block is free to move a small amount as you adjust the backoff screw BUT the worm cannot be forced completely out of mesh (ie., able to skip a tooth) when you push the scope by hand with the clutch engaged. If the worm is ever forced out of mesh to the point where it skips a tooth, it will damage the worm teeth..... and don't ask me how I know this ;)? Cost me a $100 worm.? But on the up side, the replacement is absolutely perfect with no measurable 240s periodic error ;)

IMO, the actual spring pressure is not critical because as designed, it is always sufficient to hold the worm backoff screw firmly against the baseplate.? In my experience, motor will likely have stalled by the time the mesh gets tight enough to actually move the worm block outwards and lift the backoff screw off the base plate.

Paul

--
Paul Goelz
Rochester Hills, MI USA
pgoelz@...
www.pgoelz.com

I thought I read here that the older mounts had the plastic gear boxes, but new ones are metal.

A moving motor, even at higher voltage, is better than a stalled motor at lower voltage.? This group is full of stories concerning people experiencing stalls at 12V.
Losmandy provides a 15V supply for a reason.

If it was me I'd get a DC-to-DC converter to step up the 12V (actually 13.8 with lead-acid) to something like 15-16V.
Not a great fan of running AC power outside, esp if the telescope is in the grass. But even with an observatory I'd have isolated low voltage to the equipment.
Most of the power bricks sold have a little house icon on them, meaning they are intended for in house use only.

Where I live the temps get down to -10 to -20 on clear winter nights. So I use the Superlube low temperature grease.

The meaning of a stall warning (full stop vs unexpected demand for more current vs who know what criteria) depends on the software ---- "Computers simulate determinism. Only Tao is Perfect." Geoffrey James.

Mark C.

Hi Mark,

> A moving motor, even at higher voltage, is better than a stalled motor at lower voltage.?

A corollary is that a working stalled motor is better than a cooked motor that was forced to overcome a stall :)

Higher voltage helps overcome rotational inertia at the start of a slew or at the end by providing more torque. If the same high torque is required for the whole duration of the slew, you are going to heat up and possibly overheat the motor. This is when it's important to heed the stall warning and try to make mechanical adjustments to reduce it.? Stalls are a safety mechanism, don't try to overcome the symptom -- a stall warning -- unless you're really sure there's no mechanical issue.

>??This group is full of stories concerning people experiencing stalls at 12V.

As it is full of stories about burnt out motors or motors with uncontrolled slews because the servos were overloaded. Personally, I'd rather get a stall warning than have to replace a motor.

> The meaning of a stall warning (full stop vs unexpected demand for more current vs who know what criteria) depends on the software?

Amazingly, we have the designers of this software to tell us what the algorithm is. Maybe they can provide better insight into current stall detection (David Partridge, Rene)?

My understanding is that it's based on counting encoder pulses while ramping up the duty cycle to near 100%. If the mount doesn't move for a short period of time, despite a large duty cycle, the mount will signal a stall. On the other hand, if the increased duty cycle is able to power through the friction or imbalance, there will be no stall, and the mount will continue to labor for the rest of the selw at a very high duty cycle. This is when the motors overheat and can burn out. (Don't know if this is handled better in L6, but certainly in L4 and L5 this was a common failure mode).

I've been using a 16v supply for 20+ years. But larger voltage is not the solution to mechanical problems, it's a solution for carrying heavy loads on a well-adjusted, well-balanced mount.?

My recommendation is to first make sure your mount has no tight spots, is balanced well, mesh adjusted not too tight. Only then try raising voltage or change Gemini servo configuration, assuming you still see stall messages after a mechanical adjustment.

Regards,

? -Paul