I made a pair of these pumps to test out an idea I was playing with regarding inline mixing, but also to just get some experience designing/building peristaltic pumps.
I designed it to be printed from resin, but I think the main challenge if trying to make it FDM would be getting the bearing races smooth.
Once the parts are assembled, you just load your tubing by feeding it in as you rotate the rotor. And you’re good to go! You should now be able to turn the rotor and pump fluid in either direction through the pump! The one struggle (with this and every other peristaltic pump I’ve worked with) is with keeping the pump from drawing in the tubing do to friction with the roller. As long as you keep it tied up or restrained somehow, you should be fine.
More to come — I’ve currently got 3 follow-up designs building dosing pumps for hydroponics test systems that I’ll be adding when I get around to them :)
In my seemingly-endless tinkering with Peristaltic pumps, it occurred to me that the same concept used in a peristaltic pump to move fluid, could also be used to create a valve mechanism. So I decided to give it a shot, and it actually works pretty well!
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There are three main elements to the design:
One of the frames will have four, M3 heat sets inserted for attaching the frames together. These should be inserted from the inside (the smaller diameter).
Both frames will get four, M3 heat sets inserted around the perimeter, for attaching the shoes.
If you are going to insert the M4s into the frames, be careful when inserting the M3s to not obstruct the one M4 hole that intersects. You may want to use a shorter M3 for these holes.
The final M3s go into the Rotor_Upper. I was wanting to test using the expansion of the post when inserting the heat set to make an interference fit with the bearing, but I was too conservative on my post diameter. So no need to have the bearings in place when inserting the heat sets.
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This design is for a digitally-controlled, four ‘channel’ valve assembly. I designed this specifically for the application shown in the picture above, where I wanted to be able to controllably dose from individual reservoirs to individual target plants. By combining a couple of these valves with a peristaltic pump, I could supply four plants from up to three reservoirs.
The valve works by the camshaft pushing steel balls against the tubing passing through the valve. The channels are closed except when the cam rotates such that the ‘pocket’ for that channel is rotated such that the ball can lift and release the tube. The video below shows one in action.
A good friend (and far better engineer than I) was kind enough to record a full Design Review video for this…but technical difficulties (aka I’m still new to OBS Studio) meant none of his audio was captured…oops…I am curious if people would actually be interested in these sorts of Design Review videos, any opinions or suggestions would be much appreciated!
I’ve now made a handful of these valves, and I’ve made all of them from Overture PETG. I generally like working with PETG, and it holds up well for these. The only downside is that PETG does wear a bit at the contact between the drum and the steel balls. I haven’t experienced any problems, but I anticipate it will lead to progressively worse sealing over time. I didn’t want to use PLA because I expect mine to see a fair bit of UV exposure, but I’d be quite curious to hear what else folks try and what works well.
Please note, I sliced/printed these prior to the release of organic supports in Prusa Slicer, of which I am a very big fan. If I were printing these today I would use organic supports…and actually, I just realized that for the build I did in the images below, I did indeed slice it with them. But the screenshot I saved, is the screenshot I saved!
This project is part of a collection of AgTech projects that I am working on putting together as an open source hardware project, JFS Agri. I am excited by the intersection of growing my own food and playing with tech toys :) if you’d like to see a summary of the projects along the way, I’ve started an overview page here. I’d love to find like-minded folks with a similar interest that are interested in collaborating, generating data, or just chatting about AgTech!
Like the bucket of assorted fasteners on that bottom shelf, this category is for stuff that I didn't know how to group...oh, and speaking of those fasteners, check out the little sortin fella!
2020 Aluminum Extrusion Hardware |
Quick Bolt Sorter |
During the good financial decision-making times of Covid lockdowns, etc. I decided it was a good idea to buy a license for the Fusion360 Generative Design extension...Good news, I did finally pay that off :) I had worked around, and been somewhat involved in a handful of Topology Optimization/Generative Design projects through my work, and I've found the tech super interesting for some time. So after the free trial, and feeling like I was just starting to gain some level of competence in Fusion360's tool....I done did it, and bought the year. Ok, now that I'm done justifying that to myself...I mean you...
<engineering/design> What I really like about Generative Design is that it forces the designer to think about the thing they are trying to design from it's core requirements: Forces, Interfaces, and Keep Outs. I think it's far from perfect, especially given the still very primitive Design For Manufacture capabilities these tools have (among other shortcomings, but this one is certainly a big one to me.)
<precision engineering> One last also (for now), but ALSO, what I find exciting about these tools from a precision engineering perspective, is that the above-mentioned focus on forces and interfaces, these tools are extremely well-suited to kinematic/exact constraint designs! I think every one of the Generative Design projects below features at least some aspects of kinematic constraint (I say, "I think" because I may or may not be writing this before I go through my files and remind myself what all I actually made vs what I just thought about making ¯\_(ツ)_/¯ )
A lot of projects I work on/have worked on seem to involve the controlled movement of fluids. Below is a bit of a history of my builds involving attempts at obtaining this controlled movement for incompressible fluids. I haven’t done much myself with making custom solutions for the compressible stuff, but if you’re interested in such things, I thoroughly enjoy Major Hardware’s “Fan Showdown” series :)
This article/section is by no means intended as a thorough overview on the design and operation of pumps. While I will try to give some overview on operating principles and design considerations as I go, this is mainly just going to be a wander through my personal builds and experiences.
I’m sure there are innumerable sources online for (much better) detailed discussions of the workings of peristaltic pumps. So I’m just going to hit the highlights, and I’ll try to remember to find some promising links and add them below, should a deep dive seem intriguing to ya.
The fluid being pumped is carried into the pump in a compliant tubing. This tube is routed around some portion of a circular/cylindrical path around the axis of the pump and then exits the pump. This is one interesting/attractive aspect of peristaltic pumps, the fluid never has to leave the tube that it is in, making these pumps well-suited to situations where contamination and/or leaks are highly undesirable. The housing that features the cylindrical wall that the tubing is being routed along can be considered the Stator, and that is generally the nomenclature that I tend to use.
So if there’s a Stator, there must be a Rotor…? Yup, the rotor includes some set of features that extend out to some defined gap between this feature and the Stator wall. These features, which in many peristaltic pumps are rolling element bearings, pinch the tubing to the point of sealing (ideally) the tube. As the rotor turns, this contact point proceeds around the circumference. Because the pinched point of the tube is sealed, the volume of fluid in the tube ‘ahead’ of the pinch point are, as a result, pushed forward. So, keep rotating, keep pushing….pretty much as simple as that!
Pros:
Cons:
A couple of years back, I had a concept for an in-line-mixing hydroponics system. The idea being that the supplies to the system would be just pure water and nutrient concentrates, and a series of pumps and valves would allow precise dosing mixes to each target plant in a system (I refer to this concept as Rail Yard Hydro, since it moves the fluids around the tubing network quite like rail cars are moved around a rail system. I’m planning to add a separate page diving into that one a bit deeper since it is the design scheme I am using in my current projects.)
Well, to facilitate this plan, I wanted to find an option for a dosing pump that I could integrate in to my control system (aka Arduinos and Raspberry Pi’s :)). Unfortunately, I quickly found that a servo-driven peristaltic pump could easily set me back north of $100….so I set out to spend many multiples of that making my own!
Actually, when I saw the pricing, I decided I should see if I could make myself a cheapo, manual version that I could use to just test out some basic questions on the Rail Hydro idea (mainly verifying that I could induce good material mixing in-line and that there was no cross-contamination between fluid reservoirs.) And so, ‘twas this endeavor that resulted in the pump I’m apparently referring to as “Test Build 1”
She ain't pretty (especially after a good while of getting knocked around), but the pic above shows the dual pump setup I rigged up for my testing needs. I was VERY pleasantly surprised that, other than a tweak to the hand wheel, these things worked pretty damn well!
I decided upfront that I was going to go with a resin printed build, because I thought the high stiffness and good surface finish throughout the 'pinch region' would give me a better chance. Since I was already going to have the good surface roughness, I might as well also integrate the main bearing into the printed parts.
In the image of the model, below, the Stator is the part shown in green, and the Rotor is shown in blue(ish.) Riding on the rotor are roller skate bearings to provide the contact with the tube. Race 1 has v-grooves on both sides of the race, providing the main constraint for locating the rotor, and Race 2 has a v-groove on the Stator, but only a single plane of contact on the Rotor side. This keeps from over-constraining the bearing.
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The absurdly overkill bolt running through the center is a real showcase of "using what I had on hand" :) in that these were the only bolt/nut sets I had on hand with the length I was looking for.