Hi Dave,

considering the particular design of the TMFR pump (magnetically coupled) I'd say that coupling it with a DC motor would be hard and probably expensive. Using a normal pump and a DC motor would be easier, but still you'd have to get an adapter to mount the pump, the motor it self would probably be quite big and noisy and on top of that there might be maintenance issues (on brushed DC motors, sure you can get a brushless one, but I'm guessing it costs a lot). Before I got the TMFR I was looking for something like that, but in the end decided to buy the TMFR and probably saved myself from spending more than it's cost.

Regards,
dsc.

Hi All,
Just thought I would add a few comments. The TMFR is a great solution but a bit expensive. Take a look at Gear Pumps. Fluid-o-tech makes a few with brushed DC motors. This makes the control as simple as putting a pot as the controller. There are also some great PWM Controllers at Criticalvelocity.com. Fluid-o-tech will be coming out with a new gear pump with brushless DC motor soon that will be a bit cheaper.

For those familiar with programming C for Atmel ATMega chips you will be happy to know that the GS3 uses a ATMega 32. It also has a few extra outputs that are available for use. You can get a 0-5 V PWM signal from this output as well. (it is not quite as easy as it sounds but works). In a few months I will explain another way of pressure/temperature profiling for home users that is quite a bit less expensive.

Bill C

Hi Bill,

do you perhaps know if the Strada uses a gear pump coupled with a DC motor? I heard that LM isn't using TMFRs and I'm curious what else is being used. If it is indeed a simple DC motor that would explain the pots on the paddles in the Strada.

Wasn't aware that GS3 uses ATmegas, still if you haven't got the original ASM/C code it's probably not very useful as you won't be able to simply modify it.

Regards,
dsc.

I am not totally sure if the Strada will use the gear pumps. The prototype did and I assume they will continue with this method.

Yes you are correct about the original ASM Code. This is why it is not as easy as it looks. You essentially have to rewrite the entire code and then mod as you see fit. It is not too bad if you are experienced enough. Most of the pinouts are known and the operating parameters are simple enough. The only hard part really is getting the PID code to work exactly the same. I have recreated this and is essentially working the same. If you, or you know someone interested in completing this task let me know and I could help.


Bill

Hi Bill,

I'm actually planning to use a PIC16f877 which is quite similar to the ATmega 32, but at the moment I'm programming it in ASM which as you are probably aware is a bit of a pain when it comes to PID control. It's not that the algorithm is hard, it's just quite hard to handle floats and bigger numbers with ASM. I might switch to C though or mix C/ASM.

One thing that's I've noticed about the gear pumps is that they have very different characteristics compared to normal rotaries. I'm talking flow vs pressure specs, if you look at the gear pumps there's a rather large flow drop with pressure changes and normal rotaries keep the flow pretty much constant in a wide range of pressures. This is actually one of the reasons I have not decided to buy a gear pump.

I haven't got a GS3, but I'm sure Nicholas would be interested in something like this.

Regards,
dsc.

You are exactly correct about the pressure drops. However this is really not important at all concerning espresso as long as you do not have the autofill activating during the brew process. Gear pumps have high flow low presure and low pressure high flow (generalization). After the PF Basket fills with water the coffee is such a big restrictor that the flow rate is very small. The amount of variation after this occurs is negligible compared to the capabilities of the gear pump. Unless of course something else wants water from the same pump. Also, one cool thing about gear pumps is that they are pretty accurate compared the the revolutions of the motor. hence they can also be used as flow meters. They are just as accurate as the current flowmeters used in this industry.

Hi Bill,

what's the price of those gear pumps by the way?

I guess the high-flow/low pressure might not be so good during the end of the shot when you really want to have less flow through the already mostly extracted puck. With a standard rotary you should be able to drop the pressure and keep the flow pretty much the same, with a gear pump you drop the pressure you and get more water running through the puck. Or am I mistaken?

Regards,
dsc.

Sorry I was not completely clear. I was referring to the maximum case like in the spec charts. If you run the pump full out with no back pressure the flow rate is greater than if you run the pump full out with coffee puck resistance. Now if you reduce the speed of the pump with the same end boundary condition i.e. the coffee puck, you reduce the pressure, and consequently you reduce the flow rate since the coffee puck is the restrictor and flow rate is dependent upon pressure. So in either case of rotary or vibe or gear pump, if you reduce pressure you reduce flow rate through the coffee puck.


Bill

Whoops, I forgot the price. From the manufacturer they ae about $95. Not sure what the street price is. I see them on EBAY for about $80 every once in a while. here is a link to the Fluid-o-tech website for the gear pump.

http://www.fluid-o-tech.com/files/MGC4-11.pdf

Hi Bill,

curious how it works and it would be nice to get just to try it out. Well perhaps it will happen someday when I'm finished with this one.

You mentioned something about in-expensive temperature profiling as well, care to share some details?

Regards,
dsc.