DIY Peristaltic - Again - The Planted Tank Forum
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post #1 of 60 (permalink) Old 01-15-2011, 07:52 AM Thread Starter
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DIY Peristaltic - Again

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Originally Posted by mistergreen View Post
Have any of you tech heads thought about making one? ...

Any thoughts?
I didn't want to crash mistergreen's thread so I started a new one.

I imagine I can put together an open source miniature molded plastic peristaltic pump and controller (MMPPP&C) for, well let's see:

Motor: $6
Bearings: 7*$1=$7
Custom molded housing: ~$2 worth of polyurethane
Misc hardware (tubing, screws, etc): $5

Total per channel: $20

6 channel Timer/Controller: ~$15

I am going to need something like this for my CNC Nano, and if I put a little extra work into it I can make it reproducible in small quantities. I really have no desire to mfg these, so I would probably make the custom parts available for purchase from Shapeways and BatchPCB, along with a BOM so anyone who wanted to could buy all of their own parts, or buy batches and resell them.

Does that sound like a decent price point for an autodoser setup? I there's interest, I could post a more detailed description tomorrow.


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post #2 of 60 (permalink) Old 01-15-2011, 01:30 PM
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Do you have a picture of one constructed?
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post #3 of 60 (permalink) Old 01-15-2011, 04:01 PM
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Nice to see you back robotguy.

Do you know what kind of torque that little motor can produce?
I found that the motor should be fairly strong to push onto the tubing.


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post #4 of 60 (permalink) Old 01-15-2011, 05:20 PM Thread Starter
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Quote:
Originally Posted by Gatekeeper View Post
Do you have a picture of one constructed?
It's still in my head, but you should see it. It's really cool!

Quote:
Originally Posted by mistergreen View Post
Nice to see you back robotguy.

Do you know what kind of torque that little motor can produce?
I found that the motor should be fairly strong to push onto the tubing.
Thanks! Good to be back. Can we call this the GreenDoser? It's your idea after all.

That particular motor (GM3) produces 50 oz*in at 5V. It's from Solarbotics, and they make quite a line of small plastic gearmotors. I am actually hoping I can get away with a GM6 which can put out 20 oz*in. The GWS continuous rotation servo produces 39 oz*in at 6V. Does that sound like about what you used, or did you have a high torque servo?

I am hoping that by using the motor with the small shaft, I can fit one of the 3mm bearings on the central shaft to keep everything running smooth. Plus I have a couple of those and a bunch of the bearings laying around already, so I can start prototyping.


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post #5 of 60 (permalink) Old 01-15-2011, 05:33 PM
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I got this

http://www.sparkfun.com/products/9347

it's 3.3kg/cm at 5V and 4.8kg at 6V.

I think anything lower would have a hard time with the friction ( to make a proper seal on the tubing). The GM3 is worth a try since it's fairly cheap.


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post #6 of 60 (permalink) Old 01-15-2011, 05:59 PM
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Quote:
Originally Posted by Robotguy View Post
Can we call this the GreenDoser? It's your idea after all.
heh, It's not for me to say.. I want it up and running on an actual tank first though.


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post #7 of 60 (permalink) Old 01-15-2011, 07:07 PM Thread Starter
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Gotcha! 4.8 Kg*cm is 66 oz*in so we are at least in the ballpark with the 50 oz*in.

A quick rummage through the lab turned up these supplies for prototyping:


The tubing is Top Fin silicone airline tubing:

OD: .25"
ID: ~.150"
A quick test shows it needs to be compressed to .075" to stop air when I blow through it.

The piece I had with the circular pocket is 1.742" ID, so the outside edges of the bearings should be on a (1.742-2*.075)=1.592" diameter. The bearings are .394" (10mm) diameter, so their centers will need to be on a (1.592-.394)=1.198" circle. Split the difference to get the diameter of the plate they will ride on (1.592+1.198)/2=1.395

Something like this:


Eventually I want to add a small channel around the ID of the body to hold the tubing so you don't need a front plate, and a dovetail on the outsides so that multiple heads will snap together into a single unit.

Quote:
I want it up and running on an actual tank first though.
Fair enough.

Here's my plan for "production." I am going to prototype what I can on my CNC, then when I am confident in the parts, I will get a set from Shapeways (and make the parts public so anyone can buy them). I will use those parts to make a silicone mold and then cast at least 3 sets for myself. Then I will probably cast a few more to send to people who want to help test. Finally if everything is working I will offer to send the molds to someone who would be willing to cast and sell parts.

Well, it's time to put together a monthly menu and go grocery shopping, but I'll try to get some more done tonight...


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post #8 of 60 (permalink) Old 01-15-2011, 08:30 PM
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Definitely go with latex tubing. I tried silicone tubing and it was surprisingly rigid. My servo couldn't handle it.


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post #9 of 60 (permalink) Old 01-15-2011, 08:31 PM
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I was doing some dismantling of peristaltics so here are few pictures, maybe youll get some ideas. BTW , im also cnc operator, wouldnt it be cheaper to produce housing on cnc, rather than mold with plastic?

This is cheap peristaltic from ebay, about 40$. Difference from first one i have, this one has hose clamps, so when in action hose doesnt "travel" or doesnt suck in by the rotation of pump



Axis


Internal



Difference between hoses. Cheap peristaltics come with left one. Right one is normal air hose. Maybe its easier for motor to run with left one?



This is peristaltic from inkjet printer. Notice the same hose and just one pressing part

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post #10 of 60 (permalink) Old 01-15-2011, 10:30 PM Thread Starter
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Quote:
Originally Posted by mistergreen View Post
Definitely go with latex tubing. I tried silicone tubing and it was surprisingly rigid. My servo couldn't handle it.
The best would be if I could find a way to make silicone air tubing work because most aquarists have a bit or at least know where to get it. If I can't get that working, I'll have to switch over to latex. It looks like Pololu actually makes their own version of this motor that can put out 100 oz*in at 6V, and can be driven up to 12V. I wonder what the torque is at 12V? It also says that there is a clutch that keeps it from stripping gears, so there will be a maximum amount of torque we can expect from this thing.

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Originally Posted by majstor76 View Post
I was doing some dismantling of peristaltics so here are few pictures, maybe youll get some ideas. BTW , im also cnc operator, wouldnt it be cheaper to produce housing on cnc, rather than mold with plastic?
Thanks for the pics. They should be useful.

I believe for hobby quantities, casting polyurethane in a silicone mold is cheapest. I've done a bit of that with robot parts. For larger quantities, CNC is best. For really large quantities, injection molding would be the way to go.

I pushed off grocery shopping 'til tomorrow, so I updated the model a bit:

For a size comparison, each body is about 2" X 2".

I just got Solidworks, so I am having a lot of fun learning how to use it. Can you tell?

Should I work on reducing the cost as much as possible? For example, would it be worth it to use 2 sets of bearings instead of 3 to save $2? Should I make the molded parts use as little polyurethane as possible to shave off another $0.50 if I can, or is that not worth the effort?


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post #11 of 60 (permalink) Old 01-15-2011, 11:00 PM
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I just got Solidworks, so I am having a lot of fun learning how to use it. Can you tell?
Types of programs like Solidworks i would not describe as fun to learn

Quote:
Originally Posted by Robotguy View Post
Should I work on reducing the cost as much as possible? For example, would it be worth it to use 2 sets of bearings instead of 3 to save $2? Should I make the molded parts use as little polyurethane as possible to shave off another $0.50 if I can, or is that not worth the effort?
Hm, if theres no structural or any other compromise i dont see why not product would not be smaller and/or cheaper.
Its question how would thing operate with just two bearings? Most cheap peristaltics have 3, and i have industrial one with 2.
Would motor and axle be under strain just on two bearings?
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post #12 of 60 (permalink) Old 01-15-2011, 11:29 PM
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I'd focus on the bearings for cost reduction.

If the design can be modified to use common skate bearings, they can often be purchased for lower cost; especially in bulk if someone's going to be putting together complete kits for sale. If builders are going to have to get parts from different sources, skate bearings can be obtained locally, saving a shipping charge.

But are steel bearings necessary? The motor might drive simple nylon rollers with no problem.
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post #13 of 60 (permalink) Old 01-15-2011, 11:37 PM
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Quote:
Originally Posted by Robotguy View Post
Pololu actually makes their own version of this motor that can put out 100 oz*in at 6V, and can be driven up to 12V. I wonder what the torque is at 12V? It also says that there is a clutch that keeps it from stripping gears,
what does 90-Degree Output mean for this motor? That's a strong little motor.

And the more bearings you have, the more points of contact & friction.
2 works great.


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post #14 of 60 (permalink) Old 01-16-2011, 12:10 AM Thread Starter
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Quote:
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I'd focus on the bearings for cost reduction.

If the design can be modified to use common skate bearings, they can often be purchased for lower cost; especially in bulk if someone's going to be putting together complete kits for sale. If builders are going to have to get parts from different sources, skate bearings can be obtained locally, saving a shipping charge.

But are steel bearings necessary? The motor might drive simple nylon rollers with no problem.
These 3x10x4mm bearings were the cheapest ones I found at VXB ($0.99 each). My guess is that nylon rollers may be possible, but might put the motor under more stress and shorten it's life. No reason it couldn't be an option though.


Quote:
Originally Posted by mistergreen View Post
what does 90-Degree Output mean for this motor? That's a strong little motor.
I think they just mean the output shaft and the motor shaft are at 90 degrees.

So far:


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post #15 of 60 (permalink) Old 01-16-2011, 03:45 AM
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That pump is just too cool.
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