I'd like to run something crazy by you guys.

Who would like to design their own grinder?

It will would have no hopper and only enough coffee beans for a triple would fit at one time. The grounds would drop straight down into a portafilter.

I'd like a grinder that used a nice DC motor (no start capacitor issues) with big cool running burrs. (Mind you conicals would also be nice). The first system produced would be more of a test of the motor and electronics and would not be expected to produce anything that useful.

Ideally all parts could be designed by CAD and produced via http://www.emachineshop.com as I do not have a machine shop.

1. Procure a grinder head assembly (San Marco's appear to nicely detach the grinder head from the motor mount). A thread in the wanted area of CoffeeGeeks is seeking one out. Alternatively find suitable machinable brass carriers.
2. Motor control unit. A custom AVR microprocessor controlled system with an LCD display and a DC motor. This will run the motor at the speed we desire. (I'm an Electrical Engineer that does software programming so this part should be one of the easier parts for me to get done). Electronic start/stop/timing with built-in micro-switch inputs for control. BTW: This is a relatively inexpensive compared to the burrs and carrier.
3. Sweepers that cleanup
4. Gears driven instead of belt driven (hate slippage in pulley system).
5. Other ideas?

Your thoughts? Pictures of assemblies/ideas that people think are important would be most helpful to me.

Mark

mhoy wrote:
2. Motor control unit. A custom AVR microprocessor controlled system with an LCD display and a DC motor. This will run the motor at the speed we desire. (I'm an Electrical Engineer that does software programming so this part should be one of the easier parts for me to get done). Electronic start/stop/timing with built-in micro-switch inputs for control. BTW: This is a relatively inexpensive compared to the burrs and carrier.

Pretty much been done for years - lots of direct drive DC motors on turntables with incredibly accurate
speed controls. Techinics SL-1200 is the most well known, thoroughly researched DC motor design.

Would there be enough torque? Well, then how about a big DC motor - Staber industries makes a
Washing machine with a speed control DC motor.

Guess ,what I'm saying is there are lots of existing designs that may fit without a ton of specialized
one-off work. Some time should be spent investigating off-the-shelf assemblies, once the requirements
for torque and speed have been determined.

mhoy wrote:3. Sweepers that cleanup

So there's a doser?

mhoy wrote:4. Gears driven instead of belt driven (hate slippage in pulley system).

Don't several of the high end grinders use gears? Like to Robur and big Compak? And one could
use a toothed belt, which wouldn't slip.

Bob

mhoy wrote:4. Gears driven instead of belt driven (hate slippage in pulley system).

Why not chain drive? Seems simpler than gear drive. If you use bike chain & cogs you could cheaply & easily change out drive parts.

BobS wrote:Some time should be spent investigating off-the-shelf assemblies, once the requirements
for torque and speed have been determined.
Bob

True enough, something smaller than a washing machine motor and heftier than my Technic turn table would work. I don't work in the DC motor field so unless someone can suggest something that is cost effective in smaller volumes...

BobS wrote:So there's a doser?
Bob

I may have used the wrong terminology, the grinding assembly should sweep itself clean.

BobS wrote:Don't several of the high end grinders use gears? Like to Robur and big Compak? And one could
use a toothed belt, which wouldn't slip.
Bob

A toothed belt would also fine. Just nothing that slips.

A sufficiently geared down DC motor may be able to directly drive the grinder, but that places the motor above the grind head if I want it to fall into a portafilter without a chute.

As to the development time for a custom controller, it's quite inexpensive from a one-off point of view.
An AVR micro controller with LCD, temperature sensor, flash, sram, timers, and 512K EEPROM is $20. Drivers for DC motors (or steppers) can easily be interfaced. Development of the 'C' code is just my time, so it could be considered free.

Mark

Mark, this package ought to get you the parts you need! There is even a La San Marco in the bunch.

http://cgi.ebay.com/SRE-MEGA-GRIN...rdZ1QQcmdZViewItem

Yeah, I noticed that. However it's openning bid is above the current budget.

Mark

mhoy wrote:A sufficiently geared down DC motor may be able to directly drive the grinder, but that places the motor above the grind head if I want it to fall into a portafilter without a chute.

How about the grinder motor below the counter? No heat, super quiet, clean look. Mount the burrs vertically on a minimalist body. It would pair nicely with the Jet-Stream Ai-1 (OK, I'm half joking about the last part).

I wonder if our wives would be up for another hole in the granite counter? For now I had better not chance it.

I'll be leaving the super conducting motor, mass flow meter and the real time laser particle size analyser for later upgrades.

mark

To save design time a motor with gear box would work. How about a something like: 70 oz-in torque, 250 watt motor, 200-2500 rpm for 64 mm burrs? Not sure of the torque required to start a SJ grinder with duranium burrs with beans in it. Hmm a Super Jolly has a 350 watt motor but it's an AC motor (less starting torque), so a 250 watt DC motor should be very close. Over driving the motor for intermittent use (grinding) should be fine.

This motor does not match these specs, but the mounting is VERY interesting.


The coupling to the grinder needs to allow for adjusting the grind. Perhaps move the carrier up and down and keep the burrs fixed in place.
=-=-
Mark

HB wrote:How about the grinder motor below the counter? No heat, super quiet, clean look. Mount the burrs vertically on a minimalist body. It would pair nicely with the Jet-Stream Ai-1 (OK, I'm half joking about the last part).

The jet-stream is a pretty slick affair, it's more like a piece of art! I hope they make a go of it since they are being very innovative.

Anyone have comments on the various burr assemblies? The little window that the coffee shoots out of in most of the grinders is really an area that needs frequent cleaning, how could this be fixed? The mechanics of driving the burr set from the top seems at odds with a clean path out the bottom since there needs to be a bottom thrust bearing for support. Having not seen the insides of a Versalab grinder, I've no idea how they do this.

The KitchenAid Proline type of assembly with SHARP vertical burrs vs more standard horizontal burrs assembly is one way. The Versalab and the very interesting La Marzocca "S" Grinder from http://flickr.com/photos/82921813@N00/330542934 is another way.


AndyS has some interesting comments on grinders too.
See http://www.portafilter.net/archiv...08_01_archive.html

Anyone for a PID controlled Thermo-electric Peltier module actively cooled grinding chamber?

Mark