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Homeroasters - Home Roasting Coffee Community » BUILDING A ROASTER » Turbo Oven Roasters

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Baby George Foreman Roaster
renatoa	#61 Posted on 11/05/2017 3:18 AM
Administrator Posts: 2497 Joined: September 30, 2016	In this video I see the drum speed is close to the motor speed, one rotation is about 20 seconds, from 1:30 to 1:50 https://www.youtu...P0tHdsYd00 This means the gear ratio is 1:1 or very close. If the gear is plastic, should be easy to enlarge the hole to 3-4 mm as you can find other motors on eBay. Much easier than mod direct drive the drum shaft. About speed rotation, from my experience 10 RPM is the minimum acceptable, IF adding a lot of vanes inside drum, like Behmor. Else, without additional agitators 30 RPM is a minimum, 60 RPM is desirable. Gene roaster turns also by 10 RPM, but it has inside a big paddle ! You can also have a look at a Dieckmann Roestmesister drum, to have an idea about the movement of 300 grams at 20 RPM in a drum without any vanes. Speed control for this design is a gimmick, not waste your time and resources, this is not a real drum roaster, to worry about drum speed, or hope you see any effect from only 20% change. Roasters: DIY: TO based IR 640g Moded commercial: Dieckmann RoestMeister, Nesco, popper(s). Electrics: TC4ESP, MS6514, USB/Artisan/Apps, PID controllers Grinders: Arco, Xeoleo ghost burrs, Krinder, vintage PeDe Dienes, MBK Feldgrind Brew: Flair, Kompresso, Rota Aeropress, Hario Cafeor dripper, Gaggia Mini


coffeeismagick	#62 Posted on 11/06/2017 11:17 AM
Newbie Posts: 34 Joined: September 14, 2017	Quote renatoa wrote: In this video I see the drum speed is close to the motor speed, one rotation is about 20 seconds, from 1:30 to 1:50 https://www.youtu...P0tHdsYd00 This means the gear ratio is 1:1 or very close. If the gear is plastic, should be easy to enlarge the hole to 3-4 mm as you can find other motors on eBay. Much easier than mod direct drive the drum shaft. About speed rotation, from my experience 10 RPM is the minimum acceptable, IF adding a lot of vanes inside drum, like Behmor. Else, without additional agitators 30 RPM is a minimum, 60 RPM is desirable. Gene roaster turns also by 10 RPM, but it has inside a big paddle ! You can also have a look at a Dieckmann Roestmesister drum, to have an idea about the movement of 300 grams at 20 RPM in a drum without any vanes. Speed control for this design is a gimmick, not waste your time and resources, this is not a real drum roaster, to worry about drum speed, or hope you see any effect from only 20% change. Thanks for the suggestions. I had completely dissembled the gearbox and took out the motor and the gears for examination. The motor shaft is driving a planetary gear that rotates at 11 RPM based on the gear ratio calculation. The driver gear has 12 teeth, the driven gear has 44 teeth, the ratio is 1:3.666, so with the drum speed at 3 RPM, the motor speed is exactly 11RPM, which is very common for this type of motor. If my above observation and calculation is correct, all that I need to do to increase the drum speed to 10-16 RPM is to replace the motor with one that runs at 35-60 RPM, this is better than what I originally thought that I would need a 300 RPM motor based on the assumption that that the existing motor speed is 60 RPM. I was not able to find a 300RPM motor at this size, but 60RPM motors at this size (5CM D x 2CM H) is much easier to get on ebay.


renatoa	#63 Posted on 11/06/2017 2:34 PM
Administrator Posts: 2497 Joined: September 30, 2016	A crazy idea... is there any chance to mechanically swap the wheels, turning the 1:3.67 reduction ratio into the same ratio but reversed=multiplication ! Will result 33.673.67 = 40 RPM, a nice speed, but beware, proportionally less torque... worth a try though :) Roasters: DIY: TO based IR 640g Moded commercial: Dieckmann RoestMeister, Nesco, popper(s). Electrics: TC4ESP, MS6514, USB/Artisan/Apps, PID controllers Grinders: Arco, Xeoleo ghost burrs, Krinder, vintage PeDe Dienes, MBK Feldgrind Brew: Flair, Kompresso, Rota Aeropress, Hario Cafeor dripper, Gaggia Mini


coffeeismagick	#64 Posted on 11/06/2017 5:44 PM
Newbie Posts: 34 Joined: September 14, 2017	In theory I can replace gears and get whatever ratios I want; in practice, it is almost impossible to to find the gears that would fit the existing holes and the gearbox layout. Changing the motor appears to be the easiest option, but I was still unable to find a motor that is the same size as the existing one and with the centered shaft layout, most gear motors have the shaft off center. The hardest part is to find a 12 teeth pinion gear that would fit the motor shaft, I had not been able to find one.


coffeeismagick	#65 Posted on 12/12/2018 9:01 PM
Newbie Posts: 34 Joined: September 14, 2017	One year after my last post. I was not able to find a suitable motor to replace the original motor, nor was I able to figure out how to modify the gearbox, therefore I have been using this roaster at 3 RPM drum rotation speed, beans have been consistently evenly roasted, so 3 RPM drum rotation speed is actually perfectly acceptable for this type of steel mesh drum roaster. I have not performed any additional modification to this roaster since my last post, because it works exactly as it is expected to: I can roast 230g in under 11 minutes or 250g under 15 minutes, FC occurs at around 7 - 9 minutes depends on the load size (230g to 250g). I am using the roasting time as my main roasting control, while I also use cracking sounds and smoke as confirmation to terminate the roasting. Right before the 1st crack, I remove the vent cover, which immediately causes a slight environment temperature drop, to lengthen the development time, since I don't have means to control the temperature of the heating element. I could also open the glass door slightly to let some cool air in, but so far I have not had the need for doing so. All that has been accomplished with a $53 roaster without any major mod except for adding tin foil to cover the glass door and some insulation tape to cover up some holes and gaps. This has been a great learning experience, turning a cheap rotisserie oven into a perfectly functioning "drum" roaster with just two little tricks (that cost less than $5)! Would my coffee tastes better if I had spent thousands of dollars on a 500g or 1-kilo real drum roaster that I can run automated profiles using Artisan? Perhaps so, but I think I am perfectly happy with this cheap, simple but very capable "drum" roaster. If I ever need to roast a 500g or larger batch, I can always add that spare heating element that I purchased for $15 last year, it serves as a spare heating element for the peace of mind as well. Edited by coffeeismagick on 12/12/2018 10:58 PM

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