Advanced Turntable

[hansai]

Hi everybody,

I read this forum with great interest and I decided to recreate Walters great Turntable solution for my master thesis project, where I had to build an setup where I can scan 3D Objects with low-cost and as highly automatically as possible. Very soon the David 3D Scanner became the prefered solution and with this great community I was able to create a turntable in addition to the SLS2 scanner package.

A very important factor was the feature of taking controll over the software by clicking a button on the turntable that was added by Walter in his latest version of LEO2. Whit the help of his perfect circuit diagram and an unused circuit board for the pololu board I was able to build the hardware in 2 days. The software is as magnificent as the circuit diagram and it worked perfectly from the beginning. I changed the setup to an solution where the turntable and controlling is in one box and for that I used the old shell of a pocket record player. I planed to use some other parts of the record player e.g. the table or the engine but unfortunatlly the parts were useless for the turntable. After setting everything up I played a bit along with the rotating speed and the numbers of steps and I found the best settings for me so that I have to rewrite the arduino code a bit but that is no sorcery and absolutly doable.

In addition I search for a solution to keep small and also bigger objects with complicated forms on the turntable and so I created a stand with a clamp that could be placed on the turntable. The surface of the turntable is plastered with very rough sandpaper for the benefits of more grip and less slipping by the objects. Last but not least I had a gorillapod tripod at home and added this one to the setup so I am able to bring the flexible arms in position and place everything on it in the wished angle. Maybe that will help somebody for his own project and if somebody came along with other/better solutions for clamping/positioning please let us know and post it here.

So long, I add some pictures of the setup beneath but the credit belongs to WalterMo how shared this awesome solution for everybody to see and recreate. Keep posting and sharing your fantastical ideas.

Big thanks again to Walter who started this whole conversation!
Cheers

[hunkatibor2]

Hi hansai
Solution is a wood frame you glued bad CD. The CD is a double self-adhesive tape on my juice. This secures the object. I use the two-axis swivel my way.
Tibor

[hunkatibor2]

Hi

[hunkatibor2]

Hi
Vacuum at fixing flat.All interchangeable standard
Tibor

[WalterMo]

Hello Hans(ai),

Good to read that my how-to-do was useful and could help you building the turntable in a short time.

Can you please add some infos?
1. What stepping motor have you used? With a gear or direct coupling to the disk?
2. What kind of (micro) stepping gives the smoothest movement? Have you noticed missing steps?
3. What is the applied voltage to the Pololu board?
4. Did you supply the Pololu with a small heat sink?
5. What part should be better explained (by me)?

And finally, can you present a first scan on the table?

Walter

[hansai]

Hi everybody,

I have to wait at the moment for the SLS2 package, but I will add a example scan later.

1. My used stepping motor was the SMC12056 12V 0,6A from conrad.de. I don't used a gear and coupled the table directly to the motor.

2. I chooses the 1/8 step-mode and the table speed 8. When the speed became to fast, or the step mode smaller I had missing steps especially with a higher load on the table. Thats why I changed the micro switches to the slowest movement (i think both are off in my setup). I tried a lot with the micro switch and the step mode and delay time because it was important for me that the objects on the table are as steady as possible.

3. I used a 9V power supply for the board instead of 12V.

4. I ordered a heat sink for the pololu but I don't applied it on the board because I had no cooling-paste available. I checked the heat of the chip often and it was not too hot in my opinion. I also checked the heat of the motor and it became warm but not more than 60 degrees.

5. You explained every step very well so no shortcomings on your side. The program is very self explaining and just awesome. A bit problematic could be the choice of the motor, because the strength is very important in my opinion to not generate missing steps. I had some problems with the screen first, because I added the 3,6 Ohm resistant with an LCD with already integrated resistant so the background light was of. But I figured it out very soon I would highlight that a gear ratio could really improve the turntable because the biggest problem I see is the swing time of an object after it was turned on the table. For that anybody should check the delay-time after turning. In my example I changed it to 2 seconds. In addition I had some issues with the displayed angle, after I changed the micro switches. After a 45 degree turn it showed 90 degrees and so on, so I had to change the mathematics for the current angle from 0.9 to 1.8. But with the great explanation inside the code everybody is able to rethink this formulas.

So long.
Best
Hans

[WalterMo]

I had some problems with the screen first, because I added the 3,6 Ohm resistant with an LCD with already integrated resistant so the background light was off.

Hans,
Thanks for the feedback.

I think you meant a value of 180 Ohms for R3 and not 3.6 Ohms.

Regarding a fine working micro stepping:

The motor current must be limited by the motor driver board (Pololu) and not by the Ohm's law. That means if the motor coils are high-ohmic (2x20=40Ohms) then the supply voltage should be better 12V.
You can check this by looking onto the adjust position of the mini-potentiometer on the Pololu. It should not be in its max. position.

Walter

[VDX]

... I was recently dismanteling some of the old dental-scanners -- included is a really high resoultion turntable, which I've shown in more detail here in the 2nd post: viewtopic.php?f=9&t=5298&p=25233&hilit=dental+scanner#p25233

It's been driven by a DC-motor with attached encoder with 500 positions per rev. and a 25:1 reducing gear-box and further reduced by the tooht-belt ... so could be something like 3/1000 degrees mechanical resoultion and it's rotating/positioning much smoother than steppers.

Similar, but much cheaper DC-motors with encoders can be found otherwere, so maybe a more precise alternative to steppers?

Viktor

[qulet]

I did the driver of the rotary table on the basis of documentation contained on this website. Manual control works as described. Please tell me about how automate the scanning process. Please give step by step how to do it. Currently, when you select the correct COM port in the advanced settings., DAVID announces that scans but nothing happens projector does not change the image of the line. after disconnecting the USB cable, the program starts to scan ....
sorry for my English, I use translator. Use code leo2_2.

[qulet]

Problem solved the "start scan" was constantly shorted to ground.

Is a new problem.
Automatic scanning works well as I have not enabled "Alingn Scans". As the button is enabled in the automatic scan stops after one scan.

please help....

[qulet]

Problem solved the "start scan" was constantly shorted to ground.

Is a new problem.
Automatic scanning works well as I have not enabled
"Aling to Pravious Scan". As the button is enabled in the automatic scan stops after one scan.

please help....

[BigPines]

Regarding the table: It is equipped with two bearings: A conical roller bearing to carry the vertical force of the weight and a ball bearing to absorb radial forces. Latter will occur, specially at the lower end of the turntable arbor, if the emphasis of the load is outside the center of the table plate.

WalterMo, I am trying to replicate your wonderful table. I think I have most everything figured out thanks to your instructions. A couple of things I would like to know...

Based on your pictures, it looks like you have a belt tensioner in there to take the slack out of the belt. How did you build this? Did you just put a pulley on a steel shaft or did you put some kind of bearing in there?

How do I mount the other two bearings? I tried to see from your picture but I couldn't tell. Any information is appreciated.

[BigPines]

Also, how is the shaft attached to the platter? Some kind of mount with a set screw?

[WalterMo]

The platter is attached to the brass shaft by a flange. See the first photo.
You can also see the conical roller bearing. It has to carry the vertical load of the object on the platter. The flange has a cylindrical part which fits precisely in the conical ball bearing. At the bottom end of the shaft is a „normal“ ball bearing to absorb horizontal forces if the load is not exactly in the center of the platter and of course the force of the tensioned belt.

The cogged belt pulley of the belt tensioner has no ball bearing, simply a steel shaft.

The pencil sketch shows the drive of the turntable (first design). You see that K1 was originally designed as a ball bearing.

[BigPines]

Wow! Thank you WalterMo. That is much more of a response than I expected. I really appreciate it. You did some really great work there. I'll try to do as well.

I got to find that flange for the platter. I'll look around. Is it called something special?