Peristaltic Pump

There is an abundance of free 3D printable designs for peristaltic pumps. Many use a Nema 17 stepper motor. While some can be found using smaller stepper motors, I wished for something even more lightweight. With a few micro DC motors lying around, that happened to have gearboxes of suitable ratios, I decided to build a peristaltic pump around this type of micro motor. These micro motors are very common, but I was unable to find any existing design using these for a peristaltic pump.

pump without bottle

complete set

It’s common for peristaltic pumps to use rollers pushing a silicone tube against the wall of a circular housing. 3D printed ones often use ball bearings as rollers, as does my design. I learned through a couple of failed attempts, the micro motors are not as easy to use in peristaltic pump compared to the larger stepper motors. The axle out from the gearbox alone, doesn’t cope well with the force from the roller pressed against the silicone tube. It’s not impossible to have this load on the axle, but I think it’s pushing the small gearbox and its bearing to their limits. Something is needed to offload the force from axle.

There are several way I can think of getting the load off the motor axle. I chose a perhaps an odd method. Adding larger bearing in the center, with the smaller bearings resting against the larger one. The larger bearing is attached to the housing. This keeps the load off the motor axle. It’s not the most lightweight solution, with the center bearing being a large 22 mm one, but keeps the design simple and number of parts low.

The pump I designed is very slow compared to other 3D printed pumps with a larger motors. The flow rate is only around 10 ml per minute with a 30 rpm motor running on 5V. Not much more than few drops per second. I think this is close to the limit of what this type of micro motor can achieve. I didn’t try with a faster gear ratio, but at some point the motor will stall. It doesn’t seem far from the stall limit with this 30 rpm motor.

Video of pump in action. The pump gets its power from a USB type A connector. Works well from a power bank, the current draw is less than 100 mA.

pump without bottle

Sometimes you’re lucky. This sports drink bottle with a built in drip stop in the cap is perfect for a 5 mm tube. The tube through the cap without any modifications creates an air tight seal. The bottle gets flattened as water is pumped out, with no air entering.

electronics inside

A bit of a mess inside in this prototype. With some tweaking, it should be possible to fit a battery inside this housing. This version of the device doesn’t have an internal battery and isn’t waterproof.

inside pump

Inside pump, with rotor still in housing.

bearings

View of all bearings.

mouth piece

Simple mouth piece, for my intended use.

3D printed parts were designed in OpenSCAD. Source for parts available in https://git.sr.ht/~untaugh/peristaltic_pump01