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I'm still learning to use my new-to-me? GM-8 with Gemini-2 system.
Last night I had a scary incident.? I was manipulating the hand controller to slew about one hour into my session.? All of a sudden one of the motors started driving immediately at top speed? (without the "slow start") and quickly jerked the telescope past its limit while screeching.? ? I don't know what happened but I knew something was very very wrong and I hit the power switch as fast as I could.? Upon restart, nothing seemed wrong and I returned to using the mount normally.??
I had previously updated the main firmware (via the webpage).? But the HC was still 2014-era firmware.? (I have since used the GFU utility to update everything).
I've read that bad cables can cause this?? What else should I look for?
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?papagordygrapes:
This high speed run away happened to me a few times several weeks ago. Some of the things I tried were reseating the RA and Dec cables, bad connection?
Also I changed the slew speed in the Hand Controller menu from 800 to 600. And after startup, I immediately change the speed on the HC screen from Slew to Guide or Center before touching any of the directional buttons. After I did these steps it seemed to have solved the problem. Can't speak to the exact cause, but the aforementioned may help.
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I did also hit an RA Stall during slewing, so I slowed down to 600 and didn't see it again.? But previously I had seen a DEC stall during guiding (also not reproduced yet).
Something seems a bit flakey in my system.??
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papagordygrapes
Please contact us at techsupport at losmandy dot com
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On Mon, Mar 29, 2021 at 12:50 PM John Kmetz < jjkmetz54@...> wrote: ?papagordygrapes:
This high speed run away happened to me a few times several weeks ago. Some of the things I tried were reseating the RA and Dec cables, bad connection?
Also I changed the slew speed in the Hand Controller menu from 800 to 600. And after startup, I immediately change the speed on the HC screen from Slew to Guide or Center before touching any of the directional buttons. After I did these steps it seemed to have solved the problem. Can't speak to the exact cause, but the aforementioned may help.
-- Brian?
Brian Valente portfolio
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Ok, contacted and was sent troubleshooting tips.? Either cable, connectors, or motor.??
The challenge is that I haven't reproduced yet.? Last night I did many many slews while giving the cables some slight tugs and did not reproduce.
My guess?? The encoder in one of the motors might be going flakey.? Lose the encoder signal and I imagine the Gemini-2 cranks the current on the motor.??
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That is true....if the Gemini does not sense the motor optical encoder wheel move it will keep sending motor power to see if it can move it...and the motor will appear to run away.? ?It could have been programmed to stop and report a stalled motor or motor signal not received...but c'est la vie.??
Ok, contacted and was sent troubleshooting tips.? Either cable, connectors, or motor.??
The challenge is that I haven't reproduced yet.? Last night I did many many slews while giving the cables some slight tugs and did not reproduce.
My guess?? The encoder in one of the motors might be going flakey.? Lose the encoder signal and I imagine the Gemini-2 cranks the current on the motor.??
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I think it's more likely a loose connection
if an encoder was bad, it would happen every time. The encoders won't "lose signal", but rather than encoder disk is marred in some way
Ok, contacted and was sent troubleshooting tips.? Either cable, connectors, or motor.??
The challenge is that I haven't reproduced yet.? Last night I did many many slews while giving the cables some slight tugs and did not reproduce.
My guess?? The encoder in one of the motors might be going flakey.? Lose the encoder signal and I imagine the Gemini-2 cranks the current on the motor.??
-- Brian?
Brian Valente portfolio
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Yes, though the lose connection could be on the circuit board in the motor assembly (or the connector or the cable or the circuit board of the Gemini-2).??
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Yes, that is why we have the troubleshooting diagram, to determine where that may be
FYI it does happen in the Gemini, but that's pretty rare?
Yes, though the lose connection could be on the circuit board in the motor assembly (or the connector or the cable or the circuit board of the Gemini-2).??
-- Brian?
Brian Valente portfolio
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Well, not just a diagram, but that process (as shown in the diagram) to isolate where is the root cause :)
On Tue, Mar 30, 2021 at 10:49 AM Brian Valente via <bvalente= [email protected]> wrote: Yes, that is why we have the troubleshooting diagram, to determine where that may be
FYI it does happen in the Gemini, but that's pretty rare?
Yes, though the lose connection could be on the circuit board in the motor assembly (or the connector or the cable or the circuit board of the Gemini-2).??
--
Brian?
Brian Valente portfolio
-- Brian?
Brian Valente portfolio
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On Tue, Mar 30, 2021 at 11:09 AM, Michael Herman wrote:
That is true....if the Gemini does not sense the motor optical encoder wheel move it will keep sending motor power to see if it can move it...and the motor will appear to run away.? ?It could have been programmed to stop and report a stalled motor or motor signal not received...but c'est la vie.??
Thankfully, that really is how it is programmed. When Gemini doesn't sense movement after applying maximum power to the motor, it will stall pretty quickly. That's what the stall message from Gemini represents: it couldn't move the mount or at least, couldn't get feedback from the encoders that the mount has moved. What may get one into trouble is if there are intermittent or poor signals getting in from the encoders. In that case, Gemini may continue to try to move the mount, applying whatever power is needed to get it to the desired position. That's when runaway slews occur: when there is some feedback from the encoder, but it's either wrong or inaccurate. Regards, ? ?-Paul
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Thanks, Paul!
A you say: a missing cable (like disconnecting it) the gemini says "motor stalled".? And that is what I observe.
A runaway motor would have to be caused by these: 1.? bad optical encoder transmitter in the motor is damaged (HEDS unit), 2. the cable has a bad or noisy wire 3. the detector unit in the Gemini is bad 4. the cable connector has a weak or noisy?connection. ? I have seen that on damaged Gemini and damaged Motors too.??
If the motor did a runaway as reported, and then the system came back to normal behavior... you would have to rule out a bad motor, and a bad detector, and say? 1. either the cable is bad,? or? 2. a connector that the cable plugs into could have a weak connection.
This suggests the owner with this problem should buy a spare cable (might as well be a long DEC cable in case the problem cable is either RA or DEC).?
Best, Michael
On Tue, Mar 30, 2021 at 11:27 AM Paul Kanevsky < yh@...> wrote: On Tue, Mar 30, 2021 at 11:09 AM, Michael Herman wrote:
That is true....if the Gemini does not sense the motor optical encoder wheel move it will keep sending motor power to see if it can move it...and the motor will appear to run away.? ?It could have been programmed to stop and report a stalled motor or motor signal not received...but c'est la vie.??
Thankfully, that really is how it is programmed. When Gemini doesn't sense movement after applying maximum power to the motor, it will stall pretty quickly. That's what the stall message from Gemini represents: it couldn't move the mount or at least, couldn't get feedback from the encoders that the mount has moved.
What may get one into trouble is if there are intermittent or poor signals getting in from the encoders. In that case, Gemini may continue to try to move the mount, applying whatever power is needed to get it to the desired position. That's when runaway slews occur: when there is some feedback from the encoder, but it's either wrong or inaccurate.
Regards,
? ?-Paul
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>>>. That's when runaway slews occur: when there is some feedback from the encoder, but it's either wrong or inaccurate.
or missing i.e., "still waiting?for it to hit that encoder mark"
On Tue, Mar 30, 2021 at 11:27 AM Paul Kanevsky < yh@...> wrote: On Tue, Mar 30, 2021 at 11:09 AM, Michael Herman wrote:
That is true....if the Gemini does not sense the motor optical encoder wheel move it will keep sending motor power to see if it can move it...and the motor will appear to run away.? ?It could have been programmed to stop and report a stalled motor or motor signal not received...but c'est la vie.??
Thankfully, that really is how it is programmed. When Gemini doesn't sense movement after applying maximum power to the motor, it will stall pretty quickly. That's what the stall message from Gemini represents: it couldn't move the mount or at least, couldn't get feedback from the encoders that the mount has moved.
What may get one into trouble is if there are intermittent or poor signals getting in from the encoders. In that case, Gemini may continue to try to move the mount, applying whatever power is needed to get it to the desired position. That's when runaway slews occur: when there is some feedback from the encoder, but it's either wrong or inaccurate.
Regards,
? ?-Paul
-- Brian?
Brian Valente portfolio
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The encoder theory seems plausible to me. This problem started for me right after I had swapped the outer RA and Dec drive assemblies (outer plate with the two drive gears, gear box, motor, etc. and disconnected at the Oldham coupler disc). I was seeking better backlash in RA (that worked). But when I first touched the upper Dec control button on the HC, the Dec motor went into a wild spin at something like 2x Slew speed and would not stop unless I turned off the Gemini 2 power switch.
So in this case, perhaps the Gemini could not immediately read the encoders, since the RA and Dec motors were switched. I tried replacing the Dec cable with a spare and put some dielectric grease on the contact pins to no avail. I also switched the motors back to their original drives, keeping the plates were they were, but this did not alleviate. I also replaced the Gemini battery and reset to HGM defaults, again with no luck. Perhaps if someone unintentionally switches their RA and Dec cables, this could create the same fault?
But as I stated earlier, lowering the slew speed to 600, and selecting Guide or Center from the default Slew on the HC right after start up, then briefly pushing the up and down buttons, seems to have fixed this (for now).? Perhaps a slower initial speed allows the Gemini to better read the encoders and not send a errant motor pulse. I am not an engineer, so I will leave the potential electrical causes to the experts. But these steps seem to be keeping it in check for now. After these initial changes, the Gemini seems to run fine from the HC and from the SGP app for the rest of the night.
Best Regards,?
John
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Hi John
>>>The encoder theory seems plausible to me.
they are all equally plausible, which is why you want to run the test i outlined to determine which?is at fault. I've read your thoughts about "keeping it at bay" but I really think you are living on borrowed time here. you should determine which part is faulty and replace it (hopefully it's just the cable)
FYI the encoder tends to be very repeatable, so based on your assessment that you can 'avoid it', i don't think that's the likely culprit.??
>>>Perhaps if someone unintentionally switches their RA and Dec cables, this could create the same fault?
I never say never, but that is very unlikely. we do this all the time at the shop and never have that issue.?
On Tue, Mar 30, 2021 at 5:58 PM John Kmetz < jjkmetz54@...> wrote: [Edited Message Follows]
The encoder theory seems plausible to me. This problem started for me right after I had swapped the outer RA and Dec drive assemblies (outer plate with the two drive gears, gear box, motor, etc. and disconnected at the Oldham coupler disc). I was seeking better backlash in RA (that worked). But when I first touched the upper Dec control button on the HC, the Dec motor went into a wild spin at something like 2x Slew speed and would not stop unless I turned off the Gemini 2 power switch.
So in this case, perhaps the Gemini could not immediately read the encoders, since the RA and Dec motors were switched. I tried replacing the Dec cable with a spare and put some dielectric grease on the contact pins to no avail. I also switched the motors back to their original drives, keeping the plates were they were, but this did not alleviate. I also replaced the Gemini battery and reset to HGM defaults, again with no luck. Perhaps if someone unintentionally switches their RA and Dec cables, this could create the same fault?
But as I stated earlier, lowering the slew speed to 600, and selecting Guide or Center from the default Slew on the HC right after start up, then briefly pushing the up and down buttons, seems to have fixed this (for now).? Perhaps a slower initial speed allows the Gemini to better read the encoders and not send a errant motor pulse. I am not an engineer, so I will leave the potential electrical causes to the experts. But these steps seem to be keeping it in check for now. After these initial changes, the Gemini seems to run fine from the HC and from the SGP app for the rest of the night.
Best Regards,?
John
-- Brian?
Brian Valente portfolio
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Hi Michael,
What exactly is the detector unit in the Gemini?? I've done work with rotary encoders before and afaik they just use digital GPIO pins.??
Unfortunately the troubleshooting diagram is only useful if the fault is repeatable.??
I do like the idea of buying a spare cable.??
So far I've seen three glitches:
? ?*? DEC stall message during guiding operation
? ?*? RA stall when initiating a slew? (I've since slowed down slew rate to 600 from 800).
? ?*? runaway slew.? Happened so fast that I don't recall whether it was DEC or RA....I think maybe DEC.??
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these all sound like power issues
what are you using to power your mount?
Hi Michael,
What exactly is the detector unit in the Gemini?? I've done work with rotary encoders before and afaik they just use digital GPIO pins.??
Unfortunately the troubleshooting diagram is only useful if the fault is repeatable.??
I do like the idea of buying a spare cable.??
So far I've seen three glitches:
? ?*? DEC stall message during guiding operation
? ?*? RA stall when initiating a slew? (I've since slowed down slew rate to 600 from 800).
? ?*? runaway slew.? Happened so fast that I don't recall whether it was DEC or RA....I think maybe DEC.??
-- Brian?
Brian Valente portfolio
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sorry now all, the first two
Hi Michael,
What exactly is the detector unit in the Gemini?? I've done work with rotary encoders before and afaik they just use digital GPIO pins.??
Unfortunately the troubleshooting diagram is only useful if the fault is repeatable.??
I do like the idea of buying a spare cable.??
So far I've seen three glitches:
? ?*? DEC stall message during guiding operation
? ?*? RA stall when initiating a slew? (I've since slowed down slew rate to 600 from 800).
? ?*? runaway slew.? Happened so fast that I don't recall whether it was DEC or RA....I think maybe DEC.??
-- Brian?
Brian Valente portfolio
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Pyle PSL92X regulated power supply.? 13.8V @ 5A constant (7A surge).
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On Tue, Mar 30, 2021 at 11:57 PM, Brian Valente wrote:
hey are all equally plausible, which is why you want to run the test i outlined to determine which?is at fault. I've read your thoughts about "keeping it at bay" but I really think you are living on borrowed time here. you should determine which part is faulty and replace it (hopefully it's just the cable)
Brian,? You mentioned a test and a diagram, but I am not seeing them attached anywhere. Could you repost or direct me to where this is? Thanks, John
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Michael Herman
Paul Kanevsky