Servo Config / Testing


 
C

Chris Statton

New member
Hi all,

I'm in the final stages of completing my Heatermeter / Rotodamper v3 setup for my Ugly Drum Smoker and have a few quick questions on servos.....

I purchased a Turnigy TGY-90S (apparently identical to the Tower Pro MG90S). In the Heatermeter software, I entered the appropriate settings from the servo data (1000us to 2000us), saved the settings and then tried to confirm correct operation on the damper. The servo was not rotating at all when using the joystick on the HM to manually adjust the damper opening. Have I missed some kind of setting somewhere? Fan operation is fine, so I assume the wiring side has no issues.

I also noticed in a video online, when hooked up to a "servo tester", the MG90S was only rotating a total of approx 120°. Is this correct, or will it operate the full 180° when connected to the HM with the full timing entered (1000us - 2000us).

Thanks in advance for any help
 
The servo you linked is a digital servo, the Tower Pro MG90s is an analog servo, so not identical... but from what I read digital and analog servos should work on the same controllers so I think it should be fine, though I have never used a digital servo with the HM.
You can use a multimeter to measure the voltage from the gnd and +5V pin on your CAT5 jack (pin 4 & 3) to verify that is present, they should connect to the brown and red wires on your servo respectively. Then the orange (or is it yellow?) wire goes to SERVO (PIN 6) on the CAT5 jack.
All the Tower Pro MG90s I have had rotate just a bit more than 180 degrees, but SPD numbers of 1000-2000 seem like would make the servo move about 120 degrees in my estimation, so perhaps that's what you saw in the video? My RD3 SPD numbers are usually about 700-2100 to rotate the valve the required distance, which is a bit shy of 180 degrees....
 
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Well, don't I feel stupid.....

They always say you should check the obvious things first. Turns out that it was a dodgy ethernet cable brand new out of the packet. Changed it over and the servo worked!

Now, I noticed there was a LOT of chatter, like basically all the time when the servo wasn't moving. I purchased this HM pre-made by John Bostwick, a unit he made for someone else who didn't really "get it" and was lost in all the config. Not sure when it was made, so I updated the AVR image anyway to the latest on the repo, and the chatter has completely gone!

Now on to sorting out my connection to the drum and away I go!
 
Some servo's chatter when holding position, I had thought the digital type might be better in that area but I guess not. The new servo movement scheme has the servo move into position and then turns off the servo, it never really "holds" a position, so by-by to chatter. I've found the chatter varies a LOT from servo to servo though, the Tower Pro MG90s I am running right now is really great, it never chatters even when holding, I have other that chatter really bad... luck of the draw I guess....
 
What are you running for your blower settings? The pit seems to be reacting very sharply to the HM changes, perhaps a bit too much fan blowing? What kind of grill again?
 
It's an UDS with a 1" inlet and two (closed) 5/8" inlets. Weber lid with vent all the way open.

I have changed the D setting now, but was running standard PID settings.

Settings currently:

YIVxKaj.jpg


Any suggestions greatly appreciated
 
With max set to 100% you will get a LOT of air flow when the HM hits 100% and the fan comes on at full blast. I would back that way down or make sure you manually trigger lid mode before you lift the lid... Otherwise the blower is gonna stoke your fire up and give you a nudge into overshoot right away when you lift the lid.
 
I was wondering about that... There are the lid mode settings for how far the temp dips before lid mode activates, you might want to increase that number.

I was confused and thought you were running a kamado rather than a UDS... I've never run a UDS, but being large and non insulated would seem to make them need more air. John Bostwick has done a lot of experiments with the UDS and he seems to indicate they need a fair amount of air flow. So you might be better off with the blower on all the time rather than max only with a UDS.

I see the blower is on right now and running about 50%, so I assume you made that change already?
 
Not being on site it's tough to diagnose, but what I see on your graph is your blower set to run at 50% speed and max only not selected (as I see the blower indicator ramp up half the scale when the HM is at 100%). It appears that as the blower speed ramps up there is a rapid cooling of your pit, which eventually goes low enough to trigger lid mode. When lid mode triggers the blower turns off and the temp ramps up right quick, then the blower kicks on and the cycle starts over again. This suggests to me that too much air is being pushed into the pit and driving down the temp rather than stoking your fire. So suggestions would be to reduce the fan speed by a LOT, like down to 10% and see how that works, then scale it up from there if the HM keeps running at a high %. Another thought is perhaps the way you are putting the air into the pit is allowing it to bypass the fire and go directly into the food area... So you might look at your air inlet and how the flow coming from it relates to where your fire is...

Finally, I have always had better luck with the older default PID settings than the newer ones, so you might try
b:4
p:3
i:.005
d:5

Perhaps John Bostwick or another UDS user will chime in to share more customized UDS settings....
 
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Sorry I didn't see Page 2, so wasn't aware you had replied.

I've set the old PID defaults to see how they go.

I'm confused about the fan speed. Are you suggesting having it on all the time at 10%?
 
I was just watching your pit and something really strange is going on. Looking at the output bar I see at times just the darker blue indicating the servo only, then I see the lighter blue pop on at 50% of the output value.... The (lighter blue) blower portion keeps popping on and off seeming at random, following neither the Max Only setting or the always on setting??? Really strange, I have never seen that before... It seems your HM is having some odd behavior there that I can not explain... Unless that is from the long distance viewing perhaps???

You should note the display, the light blue and dark blue, see if your fan is actually coming on seemingly at random as it looks from over here? It would seem from what I see on the graph the blower is coming on and off at 50% which would be pushing blasts of air through the pit....

So I am really wondering what is going on with your HM, perhaps try installing the latest release version of the AVR firmware and see if the behavior normalizes? I believe there was a firmware version released recently that had a problem where it did not remember hitting the setpoint and kept resetting to the Startup Max rather than Max setting. This is not that exact behavior, but it is really odd...
 
Whatever you just did seemed to level out the response quite a bit, was that the PID change?

And yes, I was suggesting to let the fan run all the time at MAX=10% as an alternate method, and since you are moving to constant forced air mode you might need to keep the top vent pretty tight as well. Although that comment was based on the response I was seeing when you reported running Max Only mode... since I am seeing the fan indicator pop on and off that would seem you are not running the blower at Max Only for whatever reason (perhaps malfunction?)... so I am really at a loss, you need to investigate what is really going on with your blower.....
 
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Yes I changed to the PID settings you suggested. Fan is currently set to 10% and NOT at max only. Does that explain the blower behaviour?

Also of note I pulled the set temp back to 225°F as the meat temp was climbing too quick for estimated eating time.

HmCJGKV.jpg
 
the behavior I was seeing did not match the settings you posted previously nor the settings posted above.
What You have there
Min 10
Max 10
SU Max 100

This should run the servo damper the full range of motion and will deliver air in puffs at 10%, since both Min and Max are set to 10%. I wouldn't go with Min=10% unless you are running a blower that will not spin below 10%... The stock blower can be run with a Min=0%, with Min=0 and Max=10 your blower should smoothly ramp up in speed from 0-10% as the HM Output goes from 0-100%.
 
When hovering over any point in the graph and looking at fan speed, am I right in assuming that the % shown there is the % of MAX fan speed, not % of fan speed? ie 90% would mean 9% if MAX is set to 10%?
 
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