Ok thanks, that solved it!

I'm curious, though.

Why is it that water too high leads to spill over when not pulling a shot but does when I do pull a shot? I mean, I get that there's no where for the pressure to go downwards through the spouts when they're blocked off but I was barely even letting the arms fall and water started spilling over the sides. Even when I've choked the robot because I've ground too fine I've never had anything spill out of the top of the basket.

It is the piston pushing the water out. With the arm's fully up, the piston is out of the way so this does not happen.
https://en.wikipedia.org/wiki/Archimedes%27_principle

But I think what is confusing you is the difference between attaching the portafilter with or without the basket in place. With the basket in, the tightness of the seal on the piston against the basket prevents water from getting pushed up and out. (That is the seal's purpose: to force the water down.)

Well, what's confusing me is that all I did was put the silicone disc in the bottom of the spout part of the portafilter and kept everything else the same. So, the filter basket etc. is the same. The only thing I didn't put in was the shower screen. But other than that, I was doing everything else I do when I pull a shot but using only water, no shower screen, and the spout attachment on the bottom of the portafilter.

You're also adding more water.

Hi all

Curious if anyone else has crossed this rubicon.

I bought a robot a few months ago and I haven't really enjoyed it. Please take that with a grain of salt though as I've only made about half a dozen shots with it...my sample size is very small. While I have frustrations with my 9barista, in comparison I find I do really enjoy the shots it produces. (As an aside I have also had not so great experiences with the 9barista depending on the stovetop used).

I'm sure I will come to enjoy the robot as I spend more time with it. In the meantime, I purchased a few dc heaters from aliexpress in an attempt to heat the group.

I got a bevy of pads, but the 50mm by 100mm seem like the way to go. To my surprise the supplier actually sent different pads depending on whether I selected 12v or 24v. The 12v has 9ohm resistance. The 24v heater had 30ohm resistance.

I can't recall if this is the exact supplier, but it seems like the same products.
https://m.aliexpress.com/item/4000454364722.html

With great difficulty I placed the pad inside the piston. I looped it underneath the axel supports, I wiggled it for about half an hour...removing the pressure plug and nudging it through gently from underneath trying not to puncture it. It fits pretty nicely after all is said and done. Next time I open it up I'll take a picture.

I bought a cheap 3v-24v dc power supply rated at 2amps. I wish now I had just splurged for a proper dc power supply, but I didn't know how this was going to unfold.

The aliexpress page suggests running the pads at 0.4w/cm^2. At first I tried 12v and 2 amps, which is close to 0.5w/cm^2. The pad was hot, the piston got warm, but I found myself wanting more.

I settled at 18v and at 2 amps, and that means I'm closer to 0.7w/cm^2. The pad gets very hot, almost too hot to touch. The piston does get very warm now, I don't yet have a probe to measure. The sides of the piston are noticeably hotter than the bottom, this because of how the pad is oriented inside. There is a bit of a plasticy smell...I'm guessing because: it's a new pad, and I expect there is also some melting going on inside the pad.

After a few trial runs I opened the piston back up and didn't notice anything alarming, so I put it back as it was before. Id wager it takes 4-5min to hit max temp at the settings above.

I haven't pulled any shots yet. Not sure I am knowledgable enough with the robot to give any valuable comparisons of no heat vs preheat.

Curious if anyone else has any similar experiences, or can offer any insights, or has any questions.

Edit - May 25th. Adding pics.

I experimented with flexible fabric heating pads (also here). They were 12V and got quite hot (they actually partially melted / self-destructed in the confines of the inner piston). But the total power was only 30W. While it would get the piston hot it wasn't fast enough for me.

I thought about making something more powerful (I didn't want to use 120VAC) but ultimately I discovered that a passive solution was nearly as effective and much more practical. So even though I liked the notion of a powered Robot I shelved the idea and planned instead to make a durable, food safe, non-metal piston.

That said, some Korean guy used 24V Kapton thin flexible heaters and claimed to get very fast heating. I did not see any specifics as to the temperature he achieved but I recall calculating the wattage and figuring he had gotten it right. He made a number of other very cool modifications to his Robot.

https://m-blog-naver-com.translate.goog ... r_pto=wapp

Thanks for the reply John.

I definitely recall seeing your post. Thanks for linking it specifically. I had seen the video of the walnut robot, but I had not been able to find the blog post about it. Thanks for that. Are the Kapton heaters supposed to be superior? I had read yes, but they seem a little fragile. The walnut robot has the wires cleaned up nicely. I also did not want to use an AC heat pad with the robot.

Do you recall if the thunders / thermal underwear yielded better results than the heat pad?


Was the non metal position you settled on the one cited by Charles here:
Cafelat Robot Temperature Tests

Thanks for the help.

Brian Quan's Thundies is basically just a fitted version of the "cup of boiling water propped up with something" method. That's the standard I used for testing: a plastic cup of about 300ml actively boiling water straight from the microwave, propped up by something else, and left with the piston soaking in it for two minutes. There are a number of variations on the same theme. It works. It's just sort of an annoyance. I also have a suspicion that soaking the piston in boiling water affects the longevity of the seal. I could be wrong.

Charles is the person who gave me the idea for the plastic version. I would have never imagined that standard PVC pipe fittings from the hardware store were a perfect fit. I added a piece of silicone to shield the end of the PVC from the water since it gets soft when hot. I also slathered the whole thing in FDA food safe silicone adhesive to make it safer. PVC is fine for cold water but what happens when you heat it?




My piston worked great but the adhesive wasn't very durable. After using it daily for a few weeks there were signs of it starting to peel and I retired my plastic piston. That was about two years ago and I still haven't made an improved one despite plans to do so. Partly this is because I'm lazy. But it's also in part because I started drinking a lot of Neapolitan coffee which does not require any preheating.

Thanks.

Out of curiosity, is it that you just aren't using the robot at the moment, or you are using it with the stock metal piston again and no heat pad?

Stock metal. The temperature decline is desirable for the coffee I'm using. I've wondered if/when I make a plastic piston if it will force me to use colder starting water with this coffee.

With lighter roasts I still preheat the piston and do a double pour or something like that.