need help on my WIP

Discussion in 'Aircraft & Aviation' started by dvduh, Dec 17, 2008.

  1. dvduh

    dvduh New Member

    Hey guys, i am trying to design my own stir plate for making yeast cultures. a good example of what i am talking about can be found here. I am basically trying to take a project box, attach a nice motor to it (the tutorial above uses a computer fan, i want something that is sturdier) then have a magnet with a hole screwed onto the motors axel. Then i want to wire it through a rheostat so i can control the speed.

    My problem is i cannot find a motor for cheap enough, if a computer fan can do this there should be some really cheap motor out there that can handle it. If anyone can help me figure out what kind of motor i need that would be amazing. I also just need a good website to source all this stuff from, but i can seem to find one, i am fairly new to this hobby engineering field.

    Attached Files:

  2. dvduh

    dvduh New Member

    To the mods

    The reason i posted this in this forum is i figured that aircraft motors might be similar to what i need. If there is a more appropriate forum please move it to there, i just don't know where to put it.
  3. cdavenport

    cdavenport Member

    What RPM are you wanting to stir the yeast at? Also, do you want AC/DC?
    If it's the latter, a cheap can motor hooked up to an equally cheap DC train speed controller will meet your needs.

    If you want to increase the life of the motor and have greater control of your stirrer, put a sheave at the end of the stir shaft and connect the sheave to the motor shaft with a rubber band as the pulley. It'll work like a champ.

    You can get everything you need from Hobby Lobby.
  4. dvduh

    dvduh New Member

    i forget what the adequete rpm was, but is this something that would be listed on the motors box? I have never heard of a sheave, so i will look that up. Would the motor be affected by the magnet? Also, if i wanted to source these parts in the quantity of 100 where should i look.

    Thanks again so much for your help. I am a tinkerer and not formally trained : (
  5. dvduh

    dvduh New Member

    When i look for the motor, what would its normal use be?
  6. cdavenport

    cdavenport Member

    A sheave: Specifically, it's a pulley with a groove in it that fits at the end of a driven shaft to take power from the driver shaft. Look under the hood of an automobile; you will see a rubber serpentine belt connecting various engine accessories to the main driveshaft. the pulley at end of the accessory around which the belt rides is the sheave.

    As for the motor: Google "can motor". The magnet will have no effect on the can motor. You would have to be using an incredibly powerful magnet to affect the operation of even a small motor.

    As for the sheaves, Google "Small Parts" which is a company that supplies items for projects such as yours.

    I shouldn't think you will need a very powerful motor. In fact, if you have an old record turntable, you could make a prototype by cannibalizing the parts. I'll just bet 45 RPM is pretty close to what you need for stirring anyway.
  7. dvduh

    dvduh New Member

    i use a speed in excess of at least 180 RPM i think, that bar get spinning really quick and makes a crazy vortex. Thanks for the small parts site, i couldn't find can motors or sheaves on there though : (. Is this the right ?

    I really appreciate the support, i am headed to hobby lobby later today to look for parts
  8. Jim Nunn

    Jim Nunn Member


    Your question is not easy to answer without additional information. The big question is what is the maximum RPM requirements. Second item is what is the weight of the culture and container both of these factors effect the size and cost of the motor. Computer fan motors are actually brushless servo motors and you generally can not control the speed with a simple rheostat. If you open up one of these little $5 motors you will find a complex PC board and an IC chip that controls the speed of the fan.

    Next we have the rheostat if you are using a motor that draws 500 ma (1/2 amp) at 12 VDC you will need a 6 watt rheostat. A typical rheostat (potentiometer) is rated for not much more the 1 watt, need I say more.

    What I suggest is take a look at this web site
    They sell small low voltage gear motors (60 to say 300 RPM) for under $5. If you need a speed control then also look for the electronic kits they have and take a look at one of the PWM speed controls. These are very efficient and can control the speed of a DC motor (perhaps several) over a wide speed range with little speed droop under load.

    As for making a 100, you can do it cheap (and problematic) or buy used ones off the net somebody has to have these someplace.

    Jim Nunn
  9. cdavenport

    cdavenport Member

    look at this site. The toy motors will work just fine. You need a large pulley on the stirrer shaft to slow the RPM down and increase torque. A large rubber band will connect the motor shaft to the stirrer pulley. It's really that simple. If the motor burns out, just replace it. But, the Mabuchi toy motors are really quite dependable and for what you are doing, should last till Christ comes again.

    Once again, get a cheap DC train controller which will allow you to further control the speed.

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