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I been searching for a while for information for this problem and have only realized how lost I am truly am.

For my project I wish to recreate the blurring effect of a high speed oscillation with a motor attached to an arm (video here). How I have achieved this so far is by using a oscillating multi tool like the "Chicago Electric Oscillating Power Tool"

I attached my aluminum arm to the tool and got the effect that inspired this project. The only problem is that the tool is hard to mount down, very aggressive, shakes a considerable amount and makes a lot of noise as a tool without the arm even attached.

What I need help with is figuring out how to select a motor that does what I need and not any more. The motor needs to have the power to oscillate at a high enough speed to blur the object to the human eye. The multi tool oscillates at "21,000" OPM for example. I have considered taking the system an alarm clock uses to oscillate and convert the RPMs of a motor into OPMs. oscillation example

How would I scale this up for a larger force? What type of motor should I be using? Why do motors get the RPMs they do? How do I start a search for a motor that has the RPMs and the power to do this operation?

To be even pointed in the right direction would be very appreciated.

Thank you

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You can buy normal DC motors (termed brushed, they have only two power pins and expect DC). If you attach an asymmetrical weight to the shaft, and have it soundly attached, your motor+weight will vibrate much in the same way you want to achieve when you turn it on.

Then the question is whether you really need the high-speed oscillation like the 21000 RPM you mentioned. It sounds a bit of an overkill to me. My advice would be to first try with the regular DC motors. They are usually limited to 6000 RPM, which is 100 Hz oscillation-wise. The human eye definitely wouldn't discern this movement - it would look blurry. If you really need the 21000 RPM, you can go with brushless motors, as their RPM limit is much higher. You can search for motors intended for remote-control cars/helicopters, and you should buy a matching controller as well, since they are much harder to drive (but once you get the controller - the ESC - it's again piece of cake).

A bit more on your question:

Why do motors get the RPMs they do

Brushed motors contain an interface between the stator and the rotor; you need to pass current to the rotating part, as well as to periodically switch the direction of the said current. This interface is called the commutator, and a set of graphite brushes act as a contacting material. They have to endure the friction. Running a brushed DC motor above its rated RPM leads to excessive sparking over this interface and the brushes wear out quickly. So the speed limit is not absolute, the motor can exceed it, but it's not recommended for its longetivity. Brushless motors don't have this interface, as the phase reversal and timing is done by the external circuitry - the ESC. This makes them both more durable, and also capable of much higher speeds. I don't know what is their limiting factor, but it could be purely mechanical.

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  • \$\begingroup\$ Thank you for your response. I looked up a few of those motors you suggested. I learned that the RPM of a motor will slow under load and tried to find a calculator that would help in figuring it out. I'm not sure I fully understand it though. As far as the vibration suggestion goes I am still struggling a bit on how I would go about it. I understand that a "eccentric" CAM is what I am looking for to copy that alarm clock's design. My biggest problem is finding motors that have a D shaped shaft that would allow for attaching said CAM to. \$\endgroup\$ – Ian Cochran Mar 22 '17 at 1:37
  • \$\begingroup\$ Well if the shaft is not the right shape, you can always subtract some material from it with a Dremel for example. On that the RPM will slow under load - yes, but not very much, and you'll find that weirdly the torque exerted on the motor actually depends on how "stuff" the thing that's holding the motor is. E.g. if you hold it in your hand, you'll find that stiffening your grip on the motor's body will decrease RPM :) You're having some fun experiments ahead :) \$\endgroup\$ – anrieff Mar 23 '17 at 3:22
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Q: "How would I scale this up for a larger force? What type of motor should I be using?" + Constraint: Slower.

Use a Washing Machine Agitator, the blur is a function of Shutter Speed if you are recording a Video. Since the Agitator is mechanical you don't want to speed it up (too much) best to rely on the Camera to fake what it looks like to the eye. Same with a Clock mechanism, designed for slow (and precision).

For the human eye (direct, no Camera) you'll want to be able to vary the speed so that it looks correct (using persistence of vision) and that motor may not be speed variable; at least it's mechanism is rated for that speed (which a Washing Machine Agitator is not).

Agitator and Motor of a Washing Machine http://www.applianceaid.com/images/beltagitate.JPG

More Info about Washers: http://www.applianceaid.com/how-inglis-whirlpool-kenmore-belt-washers-work.php

What is wrong with that Video, seems OK for what you are trying to do (do you only want slower, or to be able to use heavy objects)?

To produce linear motion at variable speeds, viewable by eye, consider the Variable Speed 1/2 Sheet Sander. Example: https://www.amazon.ca/Makita-BO4900V-Variable-Speed-Sander/dp/B0000789HT .

Makita Variable Speed 1/2 Sheet Sander

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  • \$\begingroup\$ Thank you for the response. The washing machine agitator would be a good idea except I visually prefer a back and forth motion. I would like to have it straight back and forth but I have not worked out how I would go about that. The arm in the alarm clock rocks back and forth on a pivot point but the straight back and forth would require something else. The final product won't be the video but a physical object. \$\endgroup\$ – Ian Cochran Mar 22 '17 at 1:46
  • \$\begingroup\$ Updated answer. \$\endgroup\$ – Rob Mar 22 '17 at 7:17

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