Printable Peristaltic Pump
by asbach, published
I built this pump for reseach to gather basic hands-on knowledge of the inner workings.
If you have a MakerBot/3D Printer you can start right away. I built it in a few hours with common parts i had at hand.
Unfortunately you definitly NEED a very flexible silicone tubing, to get it really working. I did my first try with a short piece of tube i cut from our fish tank - this was definitely to hard for the ABS. unfortunately i was to eager to pump some water, so i did, but the contraption got too hot and broke.
The Pictures are from the rebuilt, but this time i'm waiting to get the silicone tube.
Currently there are no mounting holes for a motor. i used my electric screwdriver for testing. Gearmotor is planned, but i had to determine the required torque with this build.
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Most computer fans have 3 wires coming out. One is a ground wire, one is a power wire, and one is a sense wire. The sense wire outputs a certain amount of pulses per revolution (2 is typical) that you can measure with a microcontroller (like the Raspberry Pi) using a digital input pin. The sense wire can also be called a tach wire (tachometer). There are some computer fans that have 4 wires... the 4th is for controlling the speed.
To control the fan speed for both 3 and 4-pin fans, you would use pulse width modulation (PWM). The R-Pi can create a PWM signal on one of its digital output pins. Here is a link explaining PWM:
For the 4-pin fans, you can just supply PWM directly into the control pin. Can somebody double check me on that, because I'm not sure if a 3.3v PWM from the R-Pi has high enough voltage for 5v/12v fan's onboard speed controller.
For 3-pin fans, you would have to use PWM on the power wire. However, you can't connect the PWM signal from the R-Pi directly to the power wire of the fan because 1: CPU fans don't operate on 3.3V and 2: The R-Pi digital output pins can't supply enough current to power the fan. So you will have to feed the PWM from the R-Pi into a transistor that is connected to both the fan and a strong enough voltage source. I googled around, and this gives a good example of how to use the transistor:
You will have to do some calculations to get your transistor set up correctly, but it's not too hard. Try the concept out with an LED first, that way you don't fry your fan while you are learning :)
Once you have PWM set up, you can create a feedback loop that accurately controls the fan speed. Your R-Pi will continuously measure the actual fan speed using the fan's sense/tach pin, and then the R-Pi will continuously adjust the PWM duty cycle to make sure the fan's actual speed meets the desired speed. You can use a PID controller for this... here is a link explaining PID:
For starters, you can just trying a P controller and adjust the gain Kp:
PWMDutyCycle = (DesiredFanSpeed - ActualFanSpeed)*Kp
Almost excactly what I was looking for. Thanks for the files. Could you tell more about fans and how you control and monitor them? I'd like to connect the monitoring a the fan speed to a raspberry pi.
Do you happen to know where I could find ressources on how to use computer fans in a project ?
I'd love to be able to modify the speed of it (which I guess could be done by regulating the intensity of the electric current provided to it...#hoping #searching.
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While printing dismantle the Pc Fan amd harvest the ball bearings. Broken PC Fans are a great source for these. Either you remove the splint from the backside, which can be tricky, or - i prefer the hammer method - search for the upper end of the axle in the middle of the propeller. Use a center punch and a hammer and remove the axle from the propeller. the Fan will split up in its pieces.
If the fan says maglev let it be. those fans have a magnetic bearing, so nothing to harvest inside.
Take the pump base and insert the 8mm ball bearing from the fan in the center hole, just as much that it's even on the inside. put it away.
Take one X shaped part and screw it onto the M3x30(-40)mm bolt, add a M3 nut, one-two M3 washers and finish the stack with another M3 nut. You may tighten them.
Drill the center hole of the 2nd X Shaped part just as much so you wont have to screw it to the M3 rod. Take the blind rivets and cut thier shaft in 12mm pieces. insert them into the 4 holes on the 2nd X shaped part, using gentle force and a hammer.
Stack 2 M2 washers, one wheel and 2 M2 washers on each axle.
You can also only mount one pair of wheels or just one wheel, tis thing is made for experimentation.
Put the wheels X thingie on the long M3 bolt. Match the axles as good as you can and use a gripper to press the axles in the other X part's holes.
Finish with a M3 nut.
The wheels should turn, easily. if you tighten the last M3 nut and the wheels stop turning, you have to add another m3 washer in the middle.
put the roller wheel into the base and fasten it with a M3 nut.
Insert your tube and close the pump with the top cover and some plastic screws.
As tube i ordered a silicone tube outer diameter 6mm inner 5mm. i think this will be the optimal tube for a self printed pump, that should work without electric screwdriver in the future.
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