PID tuning


 
R

Rob.Wainwright

New member
Guys I run a UDS (55G steel drum) cooker. I just got my HM4.2 built and I am running Ralph's Rotodamper and a 5cfm blower (same size output opening as the standard HM blower just less cfm). I ran a couple of "meatless" test cooks and am not getting anywhere close to where I need to be in controlling the temps. I think I have read every post here looking for other folks who run HM on a UDS and found several. I have tuned the BPIDs to where I can achieve +/-5*F but using both Rotodamper and blower I would expect to be able to get much closer to +/-1*F.

My UDS is extremely efficient and stable when setting everything manually and not using the HM at all so I really need to find some PID settings that make minimal adjustments i think.

I started with default BPID and then went from there.

I have tried using the blower set to 10%-50% and on at 100% only trying to let the damper do most of the work (0,2,.005,20) and playing with fan min/max output.

Just looking for a good starting point. I have a single 3/4" intake and I typically leave my exhaust 3/4 open (about 2.5" total area output").

So, any other UDS, HM4.2, Rotodamper/blower users willing to share their BPID settings?

Thanks
Rob
 
hmm.....I might have stumbled across part of my issue. I just started thinking about the output size of the damper. When I tuned my rotodamper (for range of motion) I tuned it to open the crescent full at 100% and close the crescent fully at 0%. But since the damper opening is much bigger than my UDS input (3/4"). I think I need to tune the rotodamper to only open to x% when the output needs to be 100% (to match the max opening area of my 3/4" air intake) If not, when the rotodamper reaches about 50% open, that would be the equivalent of 100% of my intake) so any adjustments the rotodamper makes at that point are having no affect (since the input is already wide open on the UDS). I guess this is all just theory until I get the exact rotodamper output area from Ralph.

I realize that the limiting factor on airflow is the size of the UDS air intake, not the size of the damper output BUT in theory the damper output and the smoker input should be of the exact equal volume (otherwise the damper will be making all kind of adjustments without affecting anything because the adjustments are being made after the UDS is fully open.

I did some quick math and the area of my 3/4" intake is .44" and the area of my crescent damper shaped opening is ~1.57". So I have adjusted the pulse rates of the servo to where it is open less than halfway when its at 100% and still fully closed at 0%. I think I should se much better results now. About to test again.
 
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I would like to know what you find out. I also have a UDS with a 3/4" intake but use a servo driven damper made out of PVC pipe as posted here by another member.
 
I have a Rotodamper and have 3/4 inch intake, with a ball valve. I also use a 28cfm or so blower at a max of 30%, anything higher I get a cooling effect and anything lower I cant get good control.

PID settings
1
15
0.00002
1
 
@David I am doing a ton of experimenting so I will let you know what all I try. @John, so 28cfm @30% would mean about 8cfm at 100% (that sounds like a lot) my blower is only 5cfm and I have it all the way down to 50% max. Your PID setting look interesting. Can you clarify what HM ver you are running. I thought I had read somewhere that the B setting really did nothing. But I will give yours a try.
 
The one thing I feel certain about is that the range of motion of the servo should be tweaked to create an opening at 100% that is very close to your maximum air intake. After my first few failed attempts, I realized that my damper opening is MUCH larger than the volume of my 3/4" air intake. So when my damper was only 40-50% open, I was already at 100% on my air intake. So now I have my servo set so that my damper is only about halfway open when at 100%.
 
When you are running empty for your tuning, do you have anything in the smoker? I've found that it maintains a better temperature when it has meat in it, or a pan of water. Something to act like a thermal damper. You want to tune the settings as close to your cooking ideal as possible. By placing a pan of water/sand in the smoker during tuning I think you will get better results.

I agree you do want your damper tuned such that 100% is 100% of your intake size for best control.

david
 
im running the 4.2.4 version with a thermocouple. I have had used a smaller blower probably about 4 years ago when I made the first version of the heatermeter and could not get it to control it very well. I have been using the same 28cfm blower on every version there after and has worked great.
 
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@David great point, I have done most all of my testing with an empty grate. I will definitely add some mass and play some more. I noticed last night that if I completely removed the damper and just used the fan, that I actually had very good control. Maybe the damper is just overkill, but its too cool to give up so I am going to keep trying.

@John, yeah I had been wondering about my 5cfm blower. I already had it on hand from a previous project so I wanted to give it a shot but I may move to a bigger blower if I can't better results.
 
Hi Rob,
Interesting on the servo opening to match air intake on the UDS. I'm trying that now on a cook and will share my experience tomorrow.

I've been having issues with PID tuning, I'm spoiled though - my old PID was self learning and had a different blower (~15CFM). I'm on the stock HM one now along with rotodamper, going to go to back to the bigger blower soon. The issues I have are all with my impatience and uselessness though, nothing to do with HM, I love HM :)
 
Sorry I haven't replied back recently, but I did finally get things dialed in on my UDS. I will list the steps here just in case it may help someone else.

This method may or may not work for other setups but for me using a rotodamper (Ralph’s model) and a 5cfm blower, this is how I set it up. After spending several days and several bags of lump testing diffent BPIDs, I finally figured out that I was wasting my time trying to tune my BPID until I got my damper opening and my air intake size to match 100% and got my UDS 100% dialed in properly without the rotodamper.

Step 1.

With nothing plugged into the HM, and the rotodamper unassembled (or disassembled if you have it already put together) I powered up the HM and set the fan to manual mode. I then went into the HM configuration page and set the servo up initially at a range of 800-2400 with inverted output. Then using the HM joystick push the fan output up to 100% and connect the servo to the HM. Now line up your rotodamper parts so that the opening (crescent shape if using Ralph’s version) is 100% open and then assemble the rotodamper. Then using the joystick take the fan output down to 0% and make sure the servo closes the damper 100%. If not, then gradually adjust your servo settings on the configuration page until the damper is completely open at 100% and completed closed at 0%, for me that was 950-2300.

Step 2.

Setup your UDS to hold 225F (or whatever temp you smoke at most often). Once I had the intake/exhaust set to hold 225 (I let it got for a full 45-60min at 225) I then made a mark with a sharpie on my ball valve to indicate the proper setting to hold 225 (for me that was about 65% open on my 3/4” ball valve). I then attached the rotodamper (without the fan (I just left the fan hanging off the rotodamper for this step). Then I opened the ball valve up to 100% and made manual adjustments to the servo setting until I could hold 225 again. This step lets you match the damper opening exactly to the opening of the ball valve. For me this was a servo setting of 1200-2200. At this point I moved the ball valve back to my mark and attached the blower to the rotodamper.

You should only have to do this setup one time (although you may need a couple of different setups for different temp ranges) for example I am sure I would have to ret-weak my UDS if I wanted to smoke at high heat like 275-300

Step 3.

Now just set your BPID and go. Once I had my rotodamper and UDS setup correctly I found that most any of the PBIDs other users are using work just fine. I seem to get my best results using 1,15,.00002,5 but I have also gotten great results just using the default BPID so I think the moral of the story is that if you get your cooker and your servo setup properly everything else works as advertised.

SmokeSignal-BBQ-Control.png
 
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Thanks Rob. I like your line of thinking.. the last cook, my servo settings also ended up similar. My ball valve settings pre-pid were also in the neighborhood of what you have. Luckily with UDS, they are so similar, so this information is very useful to the whole community - thank you.

Finally got a bigger fan like my old PID used (15CFM I think), just going to go on a test run to see how that works along with the latest info in this thread.
 
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