A 220v question

[Shopgeezer]

I want to use 3D photogrammetry to model engine parts, print them on my 3D printer and try lost PLA casting. I built a light box and gave it a try. Works great. I copied and printed several various objects around the shop.

The process involves taking lots of overlapping pictures of the object from all angles. The software then stitches the photos together to form a 3D model that can be printed. In order to facilitate all the turning you have to do I bought a cheap turntable from Ebay.

This is a display turntable for shop windows. It had a normal 110v plug but when I plugged it in it just sat and buzzed. Checking beside the power switch revealed a little sticker saying 220v. Weird that they would use a 110v plug. I have lots of 220v in the shop. I rigged up an adapter and plugged in a foot pedal from the odds and ends drawer. All works fine, except for one thing. Stomping on the foot pedal makes the turntable turn just fine, but the next time you hit the pedal it turns in reverse. Or not. It seems to be random. Since I need to take specific shots of my engine parts in order, having the turntable reverse all the time is driving me crazy. I can only guess that the motor is grabbing opposite phases each time it reverses. What can I do to fix this?

 

[mfrick]

Hello the 220 v single phase motor needs to come to a complete stop before you can reverses it if you just hit the reverse switch it will run the same direction that it was just running.

Mike

 

[Shopgeezer]

That is what I want. I want it to run the same direction every time I step on the pedal. There is no reverse switch. Just on/off. The turntable always comes to a complete stop as I take the picture.

 

[tornitore45]

I think you need to open it ans see what kind of motor you have. Most likely a shaded pole. Shaded pole motor have a copper turn on a portion of the stator to create a minimal rotating field favoring one direction. if the copper turn is for some reason cracked or open then it behave like an induction motor with a missing start capacitor and has no preference once it manage to start in any direction.

 

[BaronJ]

Hi Guys,

A standard microwave turntable motor will do this because there is nothing to control the direction.

Put a small flap under or on the turntable edge so that the flap only allows it to turn in the direction you want. A bit of cardboard and blue tack will work to demonstrate the principle.

 

[mnay]

What software do you use to do the stitching?
Thx Mike

 

[Ken I]

Its probably a synchronous motor which can go either way - if you force it one way and switch on - that's the way it will go.
You can force it to go one way with a ratchet - if it starts wrong it "bounces" off the ratchet and goes the other way.
Ice making machines often use such motors to cycle between stops without having to fiddle with reversing switches and the like.
Regards, Ken

 

[Shopgeezer]

What software do you use to do the stitching?
Thx Mike

Its called 3DF Zephyr. I tried a number of different programs and this one is by far the best. Great tutorials on the web site. You get a free copy that is limited to 50 pictures. You are supposed to use many more than that but I have had good luck with 50. I intend to buy their minimum level software that gives you 500 photos. That should be plenty.

 

[Shopgeezer]

Interesting about the ratchet idea. That will be a bit of a head scratcher. This is just a little plastic turntable that you can't open up without breaking. Not made to repair. A ratchet would have to drag on the side of the moving table and prevent it from backing up. So mount it on the frame just below the moving table and have it drag on the table. It allows the table to move one way but not the other. Maybe a metal finger with a fairly sharp end that grabs the table if it tries to move backwards? A spring? A wedge? A bearing clutch that only rolls in one direction would work but don't have one.

 

[Ken I]

Use a spring loaded rubber wheel cam lock into a tapered gap - it only locks one way and imposes virtually no load the other.
Can also run inside or under the turntable.
Regards-Ken

 

[Noitoen]

Old washing machine programmers used small synchronous motors with this problem. There one way is just a small spring wound around the shaft with one end tied up. If the shaft rolls in the wrong direction the spring tightens and blocks the shaft.

 

[Shopgeezer]

That is like the speeder handle on a micrometer. I bought a used 1” Mitutoyo micrometer on Ebay. It is an expensive model but this one is pretty beat up. It was very had to turn so I took it apart, removed the adjuster and opened the fingers that tighten on the shaft. This reduced the effort needed to turn the barrel. I noticed that there was a small spring on the end of the barrel when I slid the speeder grip off the barrel. The spring had one end trapped and the other free. I didn’t understand how the speeder grip racheted but your explanation of the washing machine makes sense. The spring on the micrometer handle tightens one way and drives the barrel, but loosens the opposite way snd lets the sleeve slide. Cool.

I really don’t like this feature. You can turn the barrel in quickly by ratcheting the speeder handle but there is no way to move it back out unless you grab the barrel at the numbers. This is hard to do with oily fingers. I think I will remove the spring and just loctite the sleeve to the barrel. Far easier to use that way.

 

[mnay]

Its called 3DF Zephyr. I tried a number of different programs and this one is by far the best. Great tutorials on the web site. You get a free copy that is limited to 50 pictures. You are supposed to use many more than that but I have had good luck with 50. I intend to buy their minimum level software that gives you 500 photos. That should be plenty.

thanks for the info. Looks like fun to try.
Mike