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Microwave turntable motor

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Doubl3 Helix

Sat Apr 09 2011, 06:58PM

Registered Member #1548 Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61

Hello everyone,

I am planning on making a small "vending machine" that will dispense cans of soda. The only real hurdle that i've run into is how exactly I'm going to implement the mechanism that controls the dispensing. I have a few ideas floating around. What I thought would be good to use is the motor from a microwave turntable because it's already geared down quite a bit (maybe too much?). What my main concern is is whether or not its direction can be controlled. From my experience, its rotation direction is largely influenced by the position its shaft is in when it goes to start up. So I guess my question is if this is true or not. Also, if anyone knows how commercial vending machines do this, I think it would be awesome to know that! If anyone would like, I can probably put up my plans for this to get a better idea of what I'm doing.

Thanks,
Ron

James

Sun Apr 10 2011, 01:50AM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

These are small synchronous motors, RPM and voltage rating varies and there's a potential hurdle. The direction of rotation is random based on where the rotor happens to come to a stop. Also if you stall one by applying too much load, it will usually switch directions. Timers and clocks that use these get around the direction issue with a ratchet mechanism.

If you want a powerful, cheap, easily controlled and readily available geared motor I suggest looking at an automotive windshield wiper motor. You can get one for a few dollars at a U-pull salvage yard, probably a bit more on ebay. They also turn up at various surplus dealers.

I've never looked at how a soda machine mechanism works but if I were designing one I think I'd use a pair of solenoids, each linked to a pair of pins in a rectangular holding chamber below a stack of cans. To dispense one, you first engage the upper solenoid which drops a can into the holding chamber, release that solenoid to hold back the rest of the cans and then engage the lower one to retract the pins and drop the can out of the chamber down the chute. If you wanted to get fancy you could add optical or microswitch sensors to detect when a can is in position. I suppose a microwave turntable motor with a crank and a microswich to stop it in the desired position would probably work too.

Ash Small

Sun Apr 10 2011, 02:05AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

As James says, a crank and microswitch mean the direction of rotation doesn't matter, if it just 'pulls some pins'.

A friend of mine years ago had a two stroke AMF Harley (were they built by Cagiva?) and the timing was a bit retarded. He pulled up at some lights, it stalled and kicked back when he kicked it over, but it fired up, and when the lights changed he revved it, dumped the clutch, and shot backwards into the car behind.

(The retarded ignition caused it to run in reverse, apparently they had a habit of doing this when the timing slipped)

Adam Munich

Sun Apr 10 2011, 03:04AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

How about a stepper motor? They can be sped up to some high RPMs with the correct driving circuit, and they have a lot of torque too.

Doubl3 Helix

Sun Apr 10 2011, 04:24AM

Registered Member #1548 Joined: Mon Jun 16 2008, 09:22PM
Location: Ohio
Posts: 61

James, thanks for the awesome amount of info. I have considered solenoids as well. I'm really quite indecisive of how I'm going to go about this. Right now what I have as my best idea for simplicity is to have a motor move a kind of "U" shaped bracket to hold cans and release them as it cycles back and forth. Attached is what this bracket is looking like and a short animation kind of how I think it will work.

Using a windshield wiper motor seems like a great idea for this. Stepper motor would be good as well, but depending on price it might not be a great solution. I'm trying to build this spending the least amount possible. I might just abandon my current dispensing method just so I can use those MO turntable motors that I have...

1302409480 1548 FT112846 Dispensing Mechanism Drawing

]dew_machine_2.mpg[/file]

James

Mon Apr 11 2011, 06:48PM

Registered Member #3610 Joined: Thu Jan 13 2011, 03:29AM
Location: Seattle, WA
Posts: 506

Stepper motors tend to be quite low torque, they are good when you want to keep something in a known position without needing a feedback loop though.

I think the important part here is the mechanism. If you use something like I described with an intermediate chamber below the stack of cans, you can control the flow with relatively little torque. When the top pin is pulled, the cans will be stopped by the lower pin(s) and when the lower pin is pulled, the cans above will be retained by the upper pin. If the chamber is just big enough for the cans to pass through, the pins only have to protrude a small amount, say a half inch or so to hold them.

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