Servo always buzzing


 
I just loaded the snapshot, mid cook, working ok for me.

The servo moves into position and then shuts off.... If I manually rotate the servo when it is off it moves back to the proper position about every 5 seconds. That seems good, a servo energized less should last longer, less chatter, win win so far.

I will let you know if I spot any negatives....
 
Very nice. I just got up and did read the good news. But now I have to go work :-(
I will test today in the evening , once I return from "work work".
 
Is anyone noticing any reduced range of motion at all with the new code? Because HeaterMeter doesn't know if the servo ever made it to position, it just has to assume the move completed. Because it is stepped 50 times in that second before it turns off, I would think it has 50 chances to either get it right or go wrong. It looked fine on my test bench (with my newly printed RD3 damper, thanks Ralph!) but my perception is always skewed toward the "Works for me!" result.
 
You know, my cooking graph was a bit more wavy the other night after I flashed the new servo motion firmware, but I was not paying much attention to the cook and how it was executed so I fluffed it off... I am going to do a long low and slow sometime this weekend and will be testing the new ramp and hold feature. I will keep an eye on the RD3 to see if it seems to be keeping up with what the HM is telling it to do.

From what I saw after I flashed the new firmware the servo seemed to move back to position within a few seconds of being moved out of position, so I assume if some steps were missed on a move it would be corrected within a few seconds?

I did notice when at 0% and 100% if you move the servo it will not move back to position, as you explained when you released the snapshot. This worried me a bit when I read it here, I feared the servo could become out of calibration and perhaps peg itself on the next move. However, in practice this is not a problem because the servo moves to the exact proper position the next time the HM tells it to move regardless of where you have manually moved it.

I hope this ends up to work properly, because I like how it turns the servo off when it's not moving. I had actually added a switch to disconnect the servo on one of my older HM's, so after I shut the RD down to 0% I could turn it off and save some life on the servo. It seems like a waste to have the servo sit there energized and not be moving....

Though a thought just occurred to me. Thinking of the original RD and some of the rigs I've seen with super large blowers. If the RD was not sitting straight up and down when the servo de-energizes the off center weight of the blower might make the RD slip from it's position. So the RD might end up looking like someone nodding off and waking up every couple seconds... lol This wouldn't be a problem with the RD3 because the blower doesn't move and the damper disc is completely symmetrical.

On the new Ramp & Hold function... Am I correct in assuming it is completely independant from the individual alarms on the probes? Meaning, if I tell the ramp & hold to monitor a food probe I don't have to set the alarm on that food probe to trigger it?
 
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RalphTrimble said:
From what I saw after I flashed the new firmware the servo seemed to move back to position within a few seconds of being moved out of position, so I assume if some steps were missed on a move it would be corrected within a few seconds?
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Nope. What you're seeing there is a delayed move probably. The damper moved to a position, there was another move but it wasn't large enough to fire up the servo for so it started the "servo holdoff timer". When the timer expired it committed the new position and appeared to return to the proper place, but really it was moving to a new place really close to where it was. If the PID output switches back and the servo is supposed to return to the position it is in already, the holdoff timer is effectively canceled and the servo is never energized at all.

Though a thought just occurred to me. Thinking of the original RD and some of the rigs I've seen with super large blowers. If the RD was not sitting straight up and down when the servo de-energizes the off center weight of the blower might make the RD slip from it's position. So the RD might end up looking like someone nodding off and waking up every couple seconds... lol
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I've thought of this too. Yup, there's no "holding torque" any more so if a design is relying on the servo to hold some sort of weight, then it will slip. However, because the PID output is usually changing constantly, it will be pulled back to position every 10 seconds or if it really needs to move so maybe it won't be a problem. I don't think anyone has a servodamper design that the de-energized position opens up the damper, which would create a problem as the PID output hits 0% and never energizes the servo again. If it does end up being a problem I could make this an option, but I like to err on the side of not adding a million options that will never be disabled.
On the new Ramp & Hold function... Am I correct in assuming it is completely independant from the individual alarms on the probes? Meaning, if I tell the ramp & hold to monitor a food probe I don't have to set the alarm on that food probe to trigger it?
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Yeah the ramp is completely independent of the alarms. The only think it has to do with them is that it is on the same configuration page. However, if you have a "Setpoint" action for your alarm, when that alarm triggers it will turn off ramp mode (unless the setpoint is the exact same temperature as the ramp is currently at).
 
It would be kinda nice to be able to select the hold off time, how long the servo is energized and what is considered a significant enough move to energize the servo, but in reality I think those parameters will be fine hard wired into the program. Perhaps after some experiments and feedback you may alter them a bit but there's a lot of slack in this adjustment so one set of parameters should be good enough I think...

The HM does adjust the servo like crazy, way more than required to regulate the cook, so an averaging out of the movements should be just fine.
 
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I wonder if this new servo code would allow the adapter board to remove the extra ground connection for the thermocouple amp and probes. Since there would be less noise on the ground connection with the servo turning off when it's not moving.

If this does reduce the noise then one could have all 3 probes on an adapter board and thermocouple, using just the cat5 connections.
 
I wouldn't expect this to cure any noise issues, because the servo still moves and the fan still blows, the noise might not be as constant but it will still be there.
 
Bryan Mayland said:
Is anyone noticing any reduced range of motion at all with the new code? Because HeaterMeter doesn't know if the servo ever made it to position, it just has to assume the move completed. Because it is stepped 50 times in that second before it turns off, I would think it has 50 chances to either get it right or go wrong. It looked fine on my test bench (with my newly printed RD3 damper, thanks Ralph!) but my perception is always skewed toward the "Works for me!" result.
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First real use of this new code on a 16 hour butt cook. I noticed during the cook that the temp was holding 10 degrees high with fan/damper at zero on heatermeter. The temp wasn't dropping which is strange for my egg. Went out and saw damper maybe 10% open when should be closed. Thought damper jammed but went to manual mode and back to auto fan and damper closed. For some reason the servo didn't get the closed command and since temp high, heatermeter never tried to move it again. My vote is to go back to chatter mode again as this has never happened before or resend signal every so often even if no changes. Thanks again for all your work.
 
Dan, being a new function it will most likely need some tweaking before it is perfect. Though my servo never really chatters at all even with the old software I do like the new servo motion scheme. I think the 10 sec delay is a bit long and should probably be shortened a bit, and perhaps there may be more tweaks required to make SURE the servo is doing what it is supposed to...

I too have noticed sometimes when I have shut down my grill the servo stayed open a tiny crack rather than closing fully, but not always. You are right, with the old motion it ALWAYS closed down exactly right and locked there with holding torque, so there is more confidence in that... but I think the new scheme just needs a few bumps ironed out and it will work just as reliably. This is probably the first report Bryan has seen about this odd behavior, not closing fully, give him a chance to work things out before you throw the baby out with the bath water....
 
Yeah this is the first I've heard of this. It always worked perfectly in my testing. I'll keep an eye on it.

The 10 seconds is plenty short already. If you need to move more than ~5% it will move immediately, so waiting on average 5 seconds to move 4% is really nothing. There's no way to tell if the servo has moved into position so we just have to assume it didn't get stuck on the way. Pulsing it will just make it chatter again, and still doesn't guarantee that it went were it was supposed to when you ask it a second time.
 
Can you make the servo hold for a brief period after each movement? This might help assure the servo is seated in the proper position before it turns off...
 
I considered that too, but there's still no guarantee it gets to where it was going. It already had a few chances to get there, why isn't it there? Go, you little servo, go!
 
I've had more than a few of the tower pro servo's through my hands in the past year, and man oh man does the quality, size, strength, calibration, lettering, pretty much everything varies from supplier to supplier. Quite a lot in some cases, sometimes I wonder if ANY of them are genuine products or if a genuine Tower Pro MG90s even exists! LOL

So I'd tend to place the blame on the servo for not following marching orders efficiently rather than the HM giving lax marching orders, but with the old always powered servo scheme it did land in the right spot reliably while I've seen it fall short a time or two with the new configuration.

How long does the servo stay powered after a move right now? Or does it just make the move and power down instantly? Could it be programmed to move and hold power for a sec or two after each move before it powers down?

THE most important position to get right is the closed position. Is there any way you could make the servo energize every 10 seconds even if it is in the OFF position? It would seem that would assure the servo valve is being reliably closed.
 
Had the same thing happen this weekend with the servo ---- should have been closed but was at 20% --- unplugged heatermeter and plugged back in and it went to 0%. I thought it was stuck also.
 
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