servo stopped - servoing


 

Stuart-mdnuts

New member
My HM and adapt-a-damper worked awesome through the first couple of cooks, by the third I noticed i had to adjust the damper opening a bit, by the 5th cook it totally stopped moving. I assumed I just installed it incorrectly and did some damage to it. I couldn't find a SG92R on amazon so instead i figured I'd get a metal geared one and got the Lewansoul 9G (Same performance specs). It fit fine in the case.

And it also won't open (or close). I go back to the first servo and the casing gets hot. I'm a bit of a loss here. I tried a foot and half long cable without any difference. It seems to be punching down okay in the keystone.

Any thoughts on what I can do to get a damper working again? The fan operates without issue.
 

Stuart-mdnuts

New member
On the odd side of things. Thinking maybe I bought a bad servo I went and bought a 4 pack of SG90s. Tried two and those didn't work. I was having a hard time getting voltage readings off of the keystone (tried two new keystones also). I had tried all variations of stripped wires vs not stripped. punched down then took a knife and made sure they were jammed in there. Tried stripping more wire, doubling it over and punching that down too.

Figuring it was unlikely that 4 servo's were all bad. I was about ready to wrap it up and just tried to punch one of them down again and suddenly it worked. So I really haven't the slightest idea. Maybe it would have been better if I'd been able to tin the wires for added thickness... Dunno.
 

Stuart-mdnuts

New member
Alright, I could use some insight if anyone has an idea.

Before the initial servo died my UDS was like a rock, very steady temperature. After getting a servo to work, my cook yesterday was all over the place, huge oscilltations, trouble holding temp, etc. I got the oscillations somewhat under control by adjusting pid.

Even after adjusting it, the damper would overshoot it's open and close spots, and so on. Trying to tackle the damper situation, I took the adapt-a-damper apart again and tinned the wires of the more expensive servo. Made sure connections were correct and secure and.... Nothing (fan works). Redid it again.. same result.

Tried one of the sg90s I tried earlier and.. nothing.

Tried the earlier working servo and it worked. It seems implausible that these servos would have such a high failure rate, especially the $9.00 servo.
 

Gary V

TVWBB Fan
Check to make sure your RJ-45 jack that is mounted to HM board does not have a cold solder joint. I am assuming the cable you used was a manufactured one. Also my personnel experience with cables up to 5' did not cause any fan or servo problems. Make sure on the +5v and ground terminals you have a 100uf cap 10-25 vdc to help keep the 5+ supply to the servo from dropping in voltage. All servo manufactures recommend you have a cap across the +5v servo supply.
 

Bryan Mayland

TVWBB Hall of Fame
Is the servo just getting jammed up from the damper dial being too hard for it to move? If the servo is getting really hot it sounds like it can't move the dial. You can test this by running the servo with the dial on it outside the damper and run it up and down a bunch in manual mode to see if reacts properly.

The other option (as Gary suggested) is to add a capacitor to the damper end on the 5V/GND pins, but usually what happens when the power isn't clean is that it jumps around all over the place.
 

Gary V

TVWBB Fan
but usually what happens when the power isn't clean is that it jumps around all over the place.
This is why I use a battery to run my HM. Nothing but clean power versus a cheap switching power supply.
 

Stuart-mdnuts

New member
Thank you for the replies.

Mostly just nothing happens. The original servo got hot but the other 3 didn't. 2 of the other 3 had no movement at all. The third one does but it is certainly not steady in terms of oscillation.

Just seems out of place that it was steady as a rock and then issues.

Even on the one working servo. I started a new cook and it was very steady, not a lot of fan or servo movement, it seemed to find a good spot and held the temp really well. About an hour or so into the cook it started oscillating. Not wildly swinging but noticable.

I'm thinking of getting a new fan, see about another fan housing so I have a practice set. I can try the capacitor on it too.
 

Stuart-mdnuts

New member
I went and bought a new fan, SG92R Servo and a 100uf capacitor. i used a new keystone and punched down the fan, servo and I pigtailed the capacitor punching that down as well. At first I tried the more expensive servo I previously bought on amazon and - nothing. tried the SG92R and it - servo'd right away.

Put all that into the housing and no immediate issues. But that brought me to a situation when doing a 14 hr cook. Right off the bat it was steady as a rock at 225 with +-5 degrees. Even after opening the lid it returned to pretty rock solid until i hit about 8-10 hrs into the cook. Then it started fluctuating about +- 12 degrees. It wasn't that bad so i left it as it was, but clearly didn't run quite as smoothly as before as it caused more activity on the fan/servo to get temps back to where they belong.

I'm sure it's about PID tuning, however why would it be so solid for the majority of the cook - then start to go off?
 

Bryan Mayland

TVWBB Hall of Fame
I'm sure it's about PID tuning, however why would it be so solid for the majority of the cook - then start to go off?
The problem is that PID controllers are meant to work with a system that has a more or less consistent response and smokers have a response that changes over time. There's a different amount of fuel burning all the time, the meat in it warms up and buffers the response a bit, something could drip and create steam that changes the apparent temperature, etc. It is pretty easy to use a PID controller to heat water to an exact temperature with electricity since it has a fixed response, but there are so many variables that it is hard to tune the controller. Usually when it is close enough it works fine, but if the PID settings are too close to the edge or something changes dramatically in the pit, it starts to oscillate. Typically that means the gains are too high, but that's a pretty wide generalization and may just be one of the gains is too high, or one is too low.

I wish there was an easier way to tune it, and autotune doesn't really work at all for us because the tuning process changes the response as it is trying to tune. It also would take forever (perhaps hours) because changes take so long to actually take effect. A single step might take 15-30 minutes just to ramp up and back down again. That's why it is really just a manual-only process which can sometimes be aided by the peak detection logs.

Sounds like you were able to get your servo squared away, but yeah, aren't these servos really hit-or-miss? The "you get what you pay for" often doesn't pan out when the expensive servo doesn't work but a cheap one does or anywhere in between. I think it is because there are so many clones and even the real ones don't get great QC and can change components inside as well.
 

 

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