Bubba Grills smoker / custom controller

[jbruce]

I bought a Bubba Grills reverse flow offset smoker a few months ago. I had Lonnie add a custom exhaust to the top of the firebox [surely he thinks I'm crazy]. I built a custom raspberry pi PID controller for it that controls a tractor flap on top of that exhaust. There are no fans, no choking off the fire etc. It keeps the temps within a few degrees F of the set point. The tractor flap changes angle every ten seconds to maintain the set point. It was a fun build [and frustrating at times], but works well.

I've cooked brisket, ribs, and pulled pork with it so far. Next is more challenging, trying to make jerky. The temps are lower and the schedule changes over time.

Here's a 30 minute graph [updated every 10s] where I was smoking a few pork butts. It was windy that day, but the controller handled it fine.

If you want more detail, see https://github.com/jbruce12000/smoker-controller

 

[jbruce]

The average error over the 9 hour cook for the pork butts was 9.8F. This includes:

• doors being opened 8 times to move, cover and jab meat with thermometers
• rainy / windy day
• changing the pid parameters every hour or so to tune it (once it's tuned, it does not change). this causes oscillation around the setpoint which might be fast or slow. so it causes significant error when it's not tuned.
• adding a red oak split or two every 30 mins to 45 mins, no charcoal
• near the end of the cook I added two splits early and raised the temperature too high for the controller to compensate. this system has about 75F to 90F window of control. if you go outside that, the controller wont help. fire mgmt is still important, but this design gives you leeway to make small mistakes.

Here is what that error looks like over the 9 hours. Those spikes are the doors being opened...

You can see the tuning got much better there at the end. Since the pid is now well tuned, I think the average error will between 2 or 3 degrees F average for my next cook.

 

[jbruce]

Has anyone propped one of their doors partially open to maintain a low temperature in their smoker? I'm wondering if this is an option for making jerky. Based on my experience to get temps around 160 in a small stick burner is tough and will require some techniques I don't yet know about. You can see above that I can maintain a temp, but I can only make a fire so small.

 

[motocrash]

Pretty slick.
Did you get a rebate for the advertising on top of the smoker?

 

[jbruce]

Pretty slick.
Did you get a rebate for the advertising on top of the smoker?

Lonnie Smith is bold and he wants you to know his support line.

 

[Cajun Smokes]

I like

 

[jbruce]

I made jerky in the freezing cold yesterday. I dried about 5lbs at 150F for about 5 hours. It was a challenge managing such a small fire. The temperatures were just above freezing and the winds were gusting to 30mph. One of the doors was cracked open using a stick to help lower the temps. I rotated the meat and moved things around six times (that's the spikes). The average error over the whole 5 hours was 2.68F using the controller described above. Seemed like the fire got tougher to control after the sun went down.

 

[DonP]

So it maintains temperature by letting heat escape the firebox?

 

[jbruce]

So it maintains temperature by letting heat escape the firebox?

Yes. If the flap is all the way open, the maximum amount of heat is lost and does not go to the meat. If the flap is closed, all the heat goes to the meat.