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Re: Cleaning and lubing the worm and worm gear

 

Hi Bill,

I get "Motor Lags" from time to time...you can look for imbalance in the scope load.? The lags messages are a minor concern...the mount will still work ok.??

However, "Motor Stalled" means a severe imbalance or jammed worm gear.? ?A jammed worm gear can be caused of course by getting too aggressive in worm adjustment pushing it too firmly into the ring gear.? You can get a cable snag too, like a dew heater cable ... lots can go wrong in the dark.

?I suppose with the severely cold weather of winter, lubricants can also freeze up.? That's why folks recommend the SuperLube product, that stays slippery to very low temperatures.

You can have a motor go bad over time too.? Apparently they can lose their strength with age.? Today, Losmandy sells a newer HiTorque motor for ~$225.??

Yet, there is a way to get more torque from any DC motor: use a Gemini supply voltage of 17-18 volts, not 12 volts.? The drive servo motors are DC motors, and their torque is directly proportional to the motor voltage.? If you are home, you could just get a 17 volt DC power source and help your motors get 42% higher torque.

If you are using a 12V car battery, say in the field, you need a way to boost the voltage up.??

For that reason, I make a nice 12V in to 17 V out unit with ammeter and voltmeter to show you how much current the Gemini and it's motors are taking.? That allows you to use the motor current reading to balance the load ...you out the counterweight bar horizontal, then do a fast slew in opposing directions.? The current draw should be the same? if the load is mechanically balanced.? I'll send a photo of the power booster unit on this email.??

Always a lot of details to discuss!

Best of luck,
Michael?








On Fri, Dec 4, 2020, 8:37 PM Bill Tschumy <bill@...> wrote:
Michael,

Thanks again for the helpful information.? Can the bad diode cause the ¡°motor stalled¡° messages?? Last week I also got a ¡°tracking stopped¡± message when I was observing the Sun and didn¡¯t do any GoTos.? In both cases there was noticeable play in the RA axis.

This mount has been a bit of an albatross ever since I got it.? It wasn¡¯t my primary mount so I didn¡¯t obsess over it.? But now it has become totally unusable.? Possibly I had a marginal board from the very beginning.

If you are pretty sure it is the board, I can send it to you for repairs.? What do you charge for this service?

--?
Bill Tschumy
Otherwise

On Dec 4, 2020, at 9:12 PM, Michael Herman <mherman346@...> wrote:

?
Dear Bill,

I repair Gemini-1 units.? Let me know if you want yours evaluated and repaired.

Now some details:

Once the Gemini-1 boots up and reads data from the SRAM, the 3V battery is not used. The system runs off of a 5V power supply that is inside the Gemini-1.? So the faulty behavior of your Gemini-1 is not the battery (unless the SRAM data is corrupted).

The problems can be caused most often by:
? ?damaged SRAM chip? ?You get corrupted data.
? ?damaged CPU chip? ? ?You get corrupted behavior.
? ?damaged serial port chip... if it won't talk to the PC properly, or won't autoguide properly.?

The problem is not really the 3V battery, per se.? If the battery measures 3V while it is in the Gemini-1 then it should work perfectly fine.? But a degraded D1 chip causes the SRAM to become damaged and damage the CPU.?

Why do the SRAM and the CPU chip ever fail?? The Gemini-1 is only on briefly during its life of operation.??

The problem in Gemini-1 is a part labelled D1 on the board.
That part is a dual diode in the battery path.? The diode has (as all diodes do) a diode "drop".?
The diode drop is causing trouble to the SRAM when that D1 wears out.

And when D1 wears out, it causes the CPU chip to fight with the SRAM chip, wearing both of them out.

I revitalize the Gemini-1 units by
? ?replacing D1
? ?installing a transistor circuit that bypasses D1

There is another?small chip that regulates the bootup of the unit, and when the units start to spontaneously reboot, that chip is likely the problem.? I fix those too.

Stay well,
Michael





On Fri, Dec 4, 2020 at 7:13 PM Bill Tschumy <bill@...> wrote:
Decided to go ahead and measure the battery while the mount was still cold.? It read 3V, which is somewhat lower than the nominal voltage of a 3V battery.? Any thoughts if that could be low enough to cause problems?



On Dec 4, 2020, at 7:39 PM, Bill Tschumy <bill@...> wrote:

Just came in from another failed session. ? I¡¯m now suspecting an electrical problem rather than mechanical.? I may be that the battery in the Gemini 1 unit has gotten too low.? I think I replaced it around 2.5-3 years ago but have not used the mount much since then.? I will check it in the morning.

I successfully slewed to 6 different stars (3 on each side) for alignment.? That all went perfectly.? Then I went to an object near the first alignment star.? Partway there I got a "Motor Stalled R¡± message.? I didn¡¯t see an A after the R. ? I tried to GoTo a couple more times and got the same message.? I checked the play in the RA axis and the counterweight bar wiggled with maybe 1/8th inch of play.? Shouldn¡¯t be getting a stall.

I power cycled the mount and did another cold start.? This time when I did a GoTo, rather than saying ¡°Slewing¡­¡± it kept scrolling the mount info on the screen that you see after a cold start.? Power cycled again and saw more weirdness on the hand controller display.

What is the symptom when you have a low battery?? I thought it displayed a low battery message, but maybe I¡¯m misremembering.

It was around 30?F when I was using it.? Like my last session, it worked fine for 15-20 minutes and then problems started.? That¡¯s why I thought it might be a low battery.? The cold and initial use may have drawn it down too low.

The mount has been stored in a dry location at all times so I doubt it is water incursion or anything like that.

Bill


--?
Bill Tschumy
Otherwise -- Longmont, CO





--
Michael Herman
mobile: 408 421-1239
email: mherman346@...
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