DIY Magnetic Stirrer Version 3 - Final Victory?

My previous attempts at a DIY magnetic stirrer to use as a resin wash worked moderately well, but not on par with even the cheapest one you could buy on Amazon. So of course I had to come back with a third attempt, this time rocking a mighty drill motor and hard drive magnet.

Music from Uppbeat (free for Creators!):

Music from Uppbeat (free for Creators!):

3d Printers:
Robo3D R1+
Matterhackers Pulse with Olsson Ruby nozzle
Monoprice Mini Delta
Monoprice Maker Select Plus
Lord Chungus Humongous (heavily modified Geeetech A20M)
Creality LD-002H
Creality Halot-Lite

[roosterhout]

Did you already figure it out? The motors you use run 10.000 rpm or more. Taming them is a problem. An asyntronic motor on mains runs only 3000 rpm. I think that is the main problem. Another problem is that the zone your magnetic field works is very small. Therefore you lose contact very easy: place your magnets further apart, bridge them under the magnets, and make the stirrer as long as the distance between the magnets. That make a very powerful magnetic circuit. Experiment until the stirrer wants to be exactly in the middle and goes back to the middle if you try to displace it. ( I would choose either rotor, or stirrer to have magnets, and the other one steel) Succes!

[skraushaar]

It's the repulsive force when like poles meet up as the stirrer outpaces the magnetic stirbar. The screw never has to deal with that.

Why don't all stirbars just use an unmagnetized bar? Because at slow speeds the stirrer would get dragged in a circle instead of spinning. Same problem if you use a single pole base.

1) Get a stir bar with a central pivot point if you don't have one
2) Try a bar which is longer or equal to the distance between base magnets.

This issue happens with very nice stirrers at high speed. Your instinct to slow down the acceleration was right.

[j.justin]

I know bumpkis about dingus but what I DO know is you're very entertaining and interesting to watch. Enjoyed this very much. New sub!

[yeyuan]

The ptef stirrer has magnets inside it as well, the screw how ever on one hand it’s a lot lighter and it generates less traction force as it’s just a ion nail, the other hand when the magnates sweep over the nail, it’s will generates vortex electricity to counteract the external change of magnetic field. In our case it will lift the nail a a little bit, that’s why they use a ceramic mag embedded in a aluminum frame in some German made hot plates.

[preputium]

I experienced the same problem using different magnets. And I'm about to go crazy like you. The magnetic stir bar is acting weird.

[anthonystewart]

Too much resistance from the water in its static state, PTFE bar is round and can effectively slice through the water until the boundary layer affect catches up. You’re design is trying to push a lot more volume before the boundary layer has a chance to form

[jakewarner]

Okay, firstly, you need a more powerful bottom magnet. With that the speed and syncing issue will go away. Then to get a good vortex use a cylindrical vase for water or any circular container.

[thelivingkiltedpirate]

Have you tried using a circular brace (for lack of a better term) hard mounted around the stirrer bar? Or using more magnets in the case to possibly help with the synching issue? Another idea would be to try one larger magnet instead or two or more as there would not be a gap as the motor spins.
I imagine that when using more than one larger magnet, the revolution of the magnets creates a pulse like wave that with a straight rod would cause hiccups in the bar's rotation cycle.
You cokd keep the 2+ magnets on the motor and use a larger magnet embedded in the propeller. I would also keep the permanent wall to help force the vortex.
Also, redesign the fins so that they're slanted. Think of water propellers.

I'm not an engineer, but these are some ideas I had while watching your videos on this project.

[liviu-adrianmunteanu]

You have more than one problem sir:
1. Magnet on magnet - the distance between poles isn't big enough and the high frequency of the magnetic field change isn't allowing the magnets to sync and thus throwing the free one of its rotation axis.
2. Magnet on metal - still not big enough distance between poles to force the metal bar to sync when having load (e.g. plastic turbine which creates a drag force within the liquid thus standing still). The wood screw alone spins because it doesn't have that much resistance moving through liquid as say a turbine

Your solution should be:
1. Inside the box, instead of having one magnet that spins, just 3D print a support for two magnets further apart from each other.
2. Insert a metal rod in your turbine. The metal rod should be the same length as the distance between the magnets underneath. Also you should put a small pin in the middle of the turbines bottom surface, this pin is meant to prevent the turbine from sitting flat on the surface thus reducing any unnecessary drag (e.g. whirligig)

Good luck! Would like to see the result

[xyphoidprocess]

"because I don't know what logarithmic means"... That's a phrase I often use...

[MrFish]

It would be better to get a cheap Arduino so you can simulate a soft start and stop with a bit of simple code, you could also use it to damp speed increases from the speed knob to avoid sudden speed changes when adjusting the speed.

[NakedSageAstrology]

Use a more powerful magnet with field lines that align with those of the magnet in the source.

A larger bar magnet would do much better. With your four way blade, I would suggest alternating one for each blade.

[NuttyGeek]

7:18 messed the polarity, it has to be (+) ---- (--) at the top of the plate and the same config have to be on the magnetic rod. (Unless you've got a monopolar rod, which is really uncommon). But I am pretty sure you had aleady figured that out :)

It suffers to hold to to the field of the rotor side magnet. the rod itself vibrates violently eben when idling. that means the moving magnetic field changes its character rapidly and breaks the flux while spinning. there must be something that interfers during the rotation. let's try to guess: high currents flowing through the motor coils or brushes give sparks which interfere the magnetic field contingency.

Disclaimer: don't blame me in case my explanation sounds gibberish, I am not a professional scientist, just had some related eperiences a bit more than a decade ago. Since then I found and thoroughly studied ca 50 -ish patents of "stirring apparata", found a couple of monographic works on the topic and elaborated a couple of working configurations. First of all, the leading magnet (rotor side) usually is made of a medium strength magnets of the following forms: ring with continuous magnetic field or double rod (two directionally arranged ambipolar rods). A cpuple of terms to fast forward in problem exploration are: magnetic hysteresis and coercivity

[walidkhier]

Create a fixed axis of rotation for the impeller.

[carpio]

pulse width modulation for speed control

[keithjohnson]

I would say that it is the magnet. use two magnets and put the magnets on the stirrer to see if the stirrer is set to the correct polarity. Just a suggestion. Did you ever get it worked out?

[NotPhil]

Hey! How could we get the stl files if we want to try this out?

[kollchris]

see i want one to mix my resin better lol . ima use an ultrasonic for cleaning

[toxomanrod]

Hey Ken what filament is that? I've never seen an icy blue sparkly looking filament before!

[nowar]

Hey brother, the magnet size, shape and positioning om the motor also plays a huge roll, also the size and magnet strength of the stir bar, if cheap stir bar magnet may be weak inside and cause poor overall performance, get a few diff sizes and few diff priced ones for assessing best suitable for ur app, might be better getting 2 round neos and fastening them opposing each other instead of the hard drive mag..

If u still want to improve it id def start here moving on, been thru the whole thing tryna improve a cheap model.