Drum speed rpm's

This evening I was testing my new Bullet’s drum speeds from D-9 to D-1. Reason for doing so is that I read on Scott Rao’s blog about proper drum speeds to correlating roaster sizes.
He recommends about 70-80 RPM’s for 1-2kg machines and less RPM’s the bigger the roaster is. He mentioned that it primarily depends on the drum diameter, in which case there can be a narrow and long 1kg drum, or a wide and short 1kg drum. This made me want to check my roaster’s rpm.
So I went ahead and marked the shaft from midpoint to perimeter and marked the outer bearing race as it’s stationary. Then I proceeded to turn on a 1 minute timer and counted revolutions in 1 minute on all drum speeds(roaster was empty, I don’t know if coffee beans in the drum would make a difference) Here is what I found:
D-9= 80rpm
D-8= 80rpm
D-7= 80rpm
D-6= 80rpm
D-5= 75rpm
D-4= 70rpm
D-3= 67rpm
D-2= 62rpm
D-1= 60rpm

My take on this is, that the rpm is in the correct range as far as I can tell.
However if I had not manually checked the rpm, then I could have potentially thought that I was changing my drum speed going from D-9 to lets say D-6, but that wouldn’t have been the case at all.
Just be aware of this and perhaps check your roaster as it could be different than mine.
I have taken note for myself what my settings correlate to in actual rpm’s.
Happy Roasting!


This is good information that is as helpful to know as the recent “Fan RPM” data that Jacob shared with us for the Firmware ver 5.0.7 change. It is odd that there would be no change in drum-speed above D6. :thinking:

Jacob, do you have any RPM data to share with us on the drum speeds?

Useful information ! Thanks. Aren’t you dizzy right now of all the rotations :grin: ?

Thanks @luisens for doing this. Your objective test confirms what I thought I was seeing/hearing when I initially got the Bullet in Jan 2019. It was f/w 475 at that time. Seemed like no discernible change between D9 and the rest of the top end of the range. However I should have been able to detect a difference between D1 and D9, but I thought they were all the same at that time. Perhaps there’s been a change in the firmware since 475 that corrected a drum speed issue… ?? I gave up fiddling with drum speed as a wasted effort when I got no response to that comment here.

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