Making a Magnetic Stirrer from an old Hard Drive - Page 1
Forum section: electronics / projects

author: mdszy
author_rank: Unknown
timestamp: June 07, 2017, 01:21:23 am
content: I want to get a magnetic stir-plate for making PCBs, it could be useful for agitating developer/etchant solution. I don't want to spend a hundred bucks on a stirrer, though... so I'm ripping apart an old hard drive and using its motors and magnets to make one! I made a video of part 1 of my project below, and awrite-up about it on my blog here.Here's a summary:1. Using an RC ESC to drive the brushless DC motor, with an Arduino (and Servo library) driving the ESC and a potentiometer for speed adjustment.2. The final project will use an ATTiny, since I basically just need a single PWM output and an analog input.3. I'll 3D print a mount for the magnets that will fit over the motor shaft.A couple of challenges I anticipate with this:1. The magnets might not be strong enough to penetrate the distance to the stir-bar in the substance it's stirring.2. The motor might not be able to spin slowly enough for reasonable stirring speeds. We'll see once I get it all implemented, but if the motor is too fast, it'll just be flinging liquid all over the place!Let me know what you think!

author: Silveruser
author_rank: Regular Contributor
timestamp: June 07, 2017, 02:14:45 am
content: I managed to get a couple stirrer/hotplates surplus for a decent price. I didn't see any mention of speeds. You'll need to get down to 50-500 rpm at the higher speeds you start to get a vortex forming which just sucks air into your solution. Depending on the depth, stirrer bar size, etc this could start at 250 rpm. That seems like an awfull lot to slow down a HD motor.Best of luck and let us know how slow you can go.

author: mdszy
author_rank: Unknown
timestamp: June 07, 2017, 02:32:32 am
content: Quote from: Silveruser on June 07, 2017, 02:14:45 amThanks so much for the insight! Hell, maybe I can 3D print some kind of gear reduction for it if it ends up too fast, but I'll keep you posted about the speeds I can get. Thanks again!

author: alanb
author_rank: Frequent Contributor
timestamp: June 07, 2017, 02:33:19 pm
content: This may be of interest, it uses old cd drive.https://youtu.be/AlNAmjprVys

author: mdszy
author_rank: Unknown
timestamp: June 07, 2017, 02:43:29 pm
content: Quote from: alanb on June 07, 2017, 02:33:19 pmInteresting, I'll give that a look when I have a chance, thanks!

author: james_s
author_rank: Super Contributor
timestamp: June 07, 2017, 05:13:56 pm
content: If you want brushless, there are lots of low speed brushless motors for multcopters and other RC stuff, you want one with a low kv rating (RPMs per Volt). For this sort of thing I think a plain old brushed DC motor may be the easiest though, or you could find a brushless pancake motor from a floppy drive.

author: mdszy
author_rank: Unknown
timestamp: June 07, 2017, 09:39:31 pm
content: Quote from: james_s on June 07, 2017, 05:13:56 pmI might look into that at some point, but honestly the main reason I'm doing this is because I have a few old hard drives lying around and want to make use of them.

author: BrianHG
author_rank: Super Contributor
timestamp: June 07, 2017, 11:34:22 pm
content: Quote from: alanb on June 07, 2017, 02:33:19 pm

author: cellularmitosis
author_rank: Unknown
timestamp: June 08, 2017, 01:36:58 am
content: Cool! I made a very poor quality stirrer out of a PC fan a few years ago:https://github.com/pepaslabs/PCFanMagneticStirrerIt worked, but just barely(the problem was getting the fan motor to spin slowly enough that it didn't "break free" of its magnetic coupling to the stirring pill)

author: mdszy
author_rank: Unknown
timestamp: June 08, 2017, 01:44:41 am
content: Quote from: cellularmitosis on June 08, 2017, 01:36:58 amHmm... Yeah, that's what I'm worried about too! But maybe I can 3D print some kind of gear reduction if that becomes a problem. We'll see!

author: CopperCone
author_rank: Super Contributor
timestamp: June 08, 2017, 03:19:59 am
content: Another fun one is a stir table, that rocks around an oblong axis. Sometimes you don't want a stirrer in a solution, this device requires some mechanical know how to make..google 'rocker table'

author: BradC
author_rank: Super Contributor
timestamp: June 08, 2017, 06:12:29 am
content: Quote from: cellularmitosis on June 08, 2017, 01:36:58 amI started out like that but found the radiated heat from my hot plate demagnetised the magnet and melted the rotor cap. I turned up a new rotor cap from mild steel and sourced some high temp cobalt magnets. The whole thing is stuck together with jbweld and has stood up to some 200C runs. The cobalt magnets also seem to couple better at distance. I can easily stir at full fan speed, although it makes no sense to do so.

author: Gyro
author_rank: Super Contributor
timestamp: June 08, 2017, 09:15:27 am
content: I'd try to find an old 5 1/4" floppy drive motor.These motors are self-contained with its drive PCB. It's a pancake motor so the whole thing is very thin and easy to mount in a narrow enclosure. On one side you have the disk driving hub with a recess which would be very easy to stick a bar magnet into. The back is a nice big rotating steel disk that you could mount multiple magnets onto (multiple stirrers?).Power supply is 12V. Some units have two speeds and very easy to modify the speed - the older ones are analogue with preset pots. They were designed to drag round a 5 1/4" disk in its liner at stable speed so would have no trouble spinning a stirrer.

author: P90
author_rank: Frequent Contributor
timestamp: June 08, 2017, 09:45:03 am
content: If the object is to agitate the solution, couldn't you just suspend a cheap electric toothbrush in the liquid to agitate it? Just a thought...

author: Emil
author_rank: Regular Contributor
timestamp: June 24, 2017, 08:06:38 pm
content: Many people have made magnetic stirrers using a computer fan with magnets attached. Very popular among homebrewers for stirring yeast starters. The fans are cheap and speed regulation is easy.