Automated Corretto Questions

[greencardigan]

Hi there,

I havent posted here for ages but am now after some advice on a new DIY roaster.

My current roaster is a tricked up crazy popper with PID temp control and separate fan speed control. It can do up to 180 grams per batch which isnt quite enough. I usually do at least 2 batches each roasting session.

So, Im considering building a corretto roaster with all the features that my popper roaster has.
- customizable roast profiles with PID temperature control
- in roaster cooling
- temperature logging

Essentially I like to be able to set the roast going and come back tomfind the beans roasted and cooled.

Theres 2 things Id like some thoughts on.

1. How to cool the bean IN the bread maker? Would the fan
In the heat gun be able to cool the beans quick enough or would the metal tin hold too much heat?

2. Should I pulse the power to the heat gun? Or should I separate the heating element and pulse it separately (this is what I do with the popper)?

3. What about automated temp control by automatically adjusting heat gun height? Or diverting a variable proportion of the heat gun output away from the bread maker?

Sorry Ive asked so many questions. Any advice welcomed.

Thanks, GC

[Dimal]

Re: Automated Corretto Questions

Essentially I like to be able to set the roast going and come back tomfind the beans roasted and cooled.

Gday GC....

BIG ask in my opinion mate. There are probably Industrial Scale Roasters that do this but the end product wouldnt be as good as you could achieve with a more hands-on roaster....

1. How to cool the bean IN the bread maker? Would the fan
In the heat gun be able to cool the beans quick enough or would the metal tin hold too much heat?

Ive used about five different makes and models of Heatguns over the years and none of them are capable of producing enough unheated air to provide adequate cooling rates. Youd be better off coming up with a separate device to do this for you.

2. Should I pulse the power to the heat gun? Or should I separate the heating element and pulse it separately (this is what I do with the popper)?

Pulsing the power to heatgun has been tried by quite a few other CSers over the years and has proved to be most unsatisfactory. Almost impossible to arrive at anything like a controlled thermal gradient.

You end up with the same sorts of problems associated with Popper Roasters in that the Fan is usually supplied from the voltage drop across a section of the Heating Element. You would therefore, have to separately supply both the Heating Elements AND the Fan - A lot of mucking around in my opinion.

If youre thinking of controlling the Heatgun Output, youd really need to use a Proportional Output PID Controller to the input of a PWM Thyristor Drive (lots of schematics and parts lists for these to be found on the Web) that ultimately drives the Heating Elements. Forced Air, Fine Wire Elements do not lend themselves to pulsed output control unless youre talking about high frequency pulses in the order of several KHz. The volume of air involved cools the elements down too quickly with the result that bean mass temperature will fluctuate excessively and produce less than optimum roast quality results. The pulsed output from most PID Controllers operates at a frequency usually less than 5Hz and most often 2-3Hz.

3. What about automated temp control by automatically adjusting heat gun height? Or diverting a variable proportion of the heat gun output away from the bread maker?

Anything is possible of course. It just comes down to practicalities in the end when striving to design a reliable and controllable system. The former would be fraught with too many variables to be overcome, in my opinion and the second may be possible but probably intricate.

Sorry Ive asked so many questions. Any advice welcomed.

You can never ask too many questions mate; its the questions you dont ask that can cause you problems...

All the best,
Mal.

[russellb]

Re: Automated Corretto Questions

Hi GC

Have you seen http://coffeesnobs.com.au/YaBB.pl?num=1259627839/16

Needs 240v electrical expertise, but it sounds as though you may have that.

Ive not used it, but it looks a possible.

Russell

[Dimal]

Re: Automated Corretto Questions

Yes Russell,

This and variations of it work well and is more or less what Ive explained above. Plain store-bought PID Controllers wont work anywhere near as well unless youre prepared to spend a lot more money for Ramp/Soak Proportional Output units - Probably overkill for this sort of application.

If you have the skills or are prepared to learn, it would be possible to implement an Arduino style PID MicroController design (Australian Source), which would be capable of doing everything you want in a single but compact package. It all comes down to how much effort you want to put into it all, I guess.

Anyway. Yes, all is possible but one needs to properly research the underlying physical constraints and then put together a system that addresses them adequately. Im not sure if Tridges controller powers the Heatgun element direct - the much preferred option - or the entire Heatgun as a whole. It would be worth the effort in my opinion, to do a full implementation of this sort of control rather than a partial one. But, thats just me....

Mal.

[bassway]

Re: Automated Corretto Questions

I have PIDed up a corretto.

I agree with everything that Mal has said but will add more.

Pulsing the heatgun element does cool it down too much. You need to run air through the heatgun while the element is on otherwise you can burn out the element very easily. And yes, I needed another power supply for the fan as it ran off a voltage drop from the element.

The one thing that the cheap pulse PID is good for is controlling a large mass with pulses to get and stay at a certain point. So in my corretto I insulated it and put on a lid. Not that useful to first crack but very useful to the second. This is because the PID works more like a brake. That way I can hold out the roast as long as I want to second crack.

So in the end the PID in my corretto is more about roaster "assist" not automated control. I actually put more manual input into a roast with a PID than without.

I dump my bean into a separate cooler as the heat mass is far too high.

Now to reiterate what Mal said:
It sound like too much stuffing around. Putting too much effort into tricky electronic control rather than building a good physical system. I would love you to build it and prove me wrong!

I also think that you will always need some manual input to get an excellent roast.
How do you compensate for different beans? Some beans need to be roasted harder/softer/longer/shorter/pre dry/high drop temp/low drop temp etc....
I see the same bean hitting first and second crack at slightly different temps. This may only be 1 degree that could be caused by the beans or thermocouple but in an automated system where the operator walks away it may change the roast. All of this can also change with a different outside environment (temp, humidity).
What happens as your green bean ages?

You may get an ok to good roast but I dont think that you can get excellent results most of the time.
Probably could equate this to manual vs auto coffee machine. Automation might work well in a larger roaster with good flame and air control and with someone who knows their beans well.

All of this is just my opinion and as Mal said anything is possible. It just seems like a lot of time/money spent on a system that probably wont suit your needs.

[Thundergod]

Re: Automated Corretto Questions

How about starting with a stock standard manual corretto and re-evaluating after that?

For a start, the increased capacity will save you some time.

I started with a Crazy Popper and upsized to a corretto.
I liked the control I had by being able to move my heatgun closer or further from the beans.

I still think its more accurate than the built in temperature dial on my new gun.

There are a few variables that can affect trying to fully automate a corretto.
- Ambient temperature
- Humidity
- Wind
- Bean
- Batch size

I wouldnt trust a PID to roast as well as my manual intervention.

[Dimal]

Re: Automated Corretto Questions

I wouldnt trust a PID to roast as well as my manual intervention.

Exactly TG.... 8-)

And very well explained bassway.... [smiley=tekst-toppie.gif]

A PID Controller is just another tool to help you attain the ultimate that a bean has to offer. Besides, home roasting is a lot of fun and is the main motivator for me and heaps of other CSers. Andys CS Roast Monitor Software coupled with the CS Thermologging DMM provides the roaster with all the information needed to control a roast to the nth degree, and makes the entire process so much more visible too.

My background is in Process Control and SCADA so I spose if anyone would dive into fully automating the roasting process, youd think Id be at the head of the queue. I have no intention of doing this however. Just enjoy the tactility of home roasting, the fantastic assault upon the senses and then the wonderful results in the cup. Once you start, youre hooked and then all thought of automation will slip away....

Mal.

[greencardigan]

Re: Automated Corretto Questions

There are a few variables that can affect trying to fully automate a corretto.
- Ambient temperature
- Humidity
- Wind
- Bean
- Batch size

I wouldnt trust a PID to roast as well as my manual intervention.

But shouldnt the PID controller be able to deal with these changing variables? My PIDed crazy popper follows the same bean temp profile regardless of the ambient temp or humidity etc.

If its following your desired roast profile, how can it be worse than manual control?

[Dimal]

Re: Automated Corretto Questions

A PID Controller, on its own, can not create or maintain a batch profile. You need, in addition, a means of creating the "template" youve decided is the target and then a means of transferring that template to the bean mass.

If you want to be able to control the thermal gradient and modify this through the progression of the profile then you need to use a PID Controller with Ramp-Soak facility. In the end, I think you would be far better off learning about the "Arduino" micro-controller system and customising elements of this to do what you want. These can be easily interfaced with PCs to run templates on the fly as it were as well as being capable of complete stand-alone operation.

Time for some study I reckon.....

Mal.

[greencardigan]

Re: Automated Corretto Questions

Ah... Ive never used an off the shelf PID controller so I wasnt sure how they worked.

Im already up to speed with the picaxe microcontrollers. My popper uses a stand alone controller which uses some custom PID algorithms and can follow a preset template.

[Dimal]

Re: Automated Corretto Questions

Im already up to speed with the picaxe microcontrollers. My popper uses a stand alone controller which uses some custom PID algorithms and can follow a preset template.  

Much better way to go mate..... 8-)

Mal.