Motorized rotary table

[tonyfoale]

I have put the code for the control on dropbox, here is the link https://www.dropbox.com/s/2021uz1x4s...Rotab.ino?dl=0

To load it into the Arduino IDE you will need to put it in a directory called Rotab (It must be exactly the same as the .ino file name.) That is an Arduino rule not mine.
On simple projects like this I almost never draw a schematic and I do not have one for this tool. I will recreate one by reverse engineering the code and I'll post that soon. In the meantime here are a bunch more photos with minimal explanation on most.

Click images for full size.

The first pic. shows the input spindle bush which has only been machined concentric with the bore for part of the circumference, as marked. I needed to use that for a location and wanted the OD to be concentric all the way around. That piece is cast iron and I did not want to machine it down too thin. So I just took enough off to locate a steel sleeve, the remaining gap was filled with epoxy. Here is the sleeved part. This piece is critical and is highly loaded because it takes the overhung weight of the motor.









At the time of building I did not know if I would end up using a Nema23 or 24 motor. They are very similar in size but the mounting holes are on a slightly different PCD. By drilling and tapping two sets of holes, each set with an angular offset from the other I could accommodate either motor.



These types of rotary table allow adjustment of the worm to control backlash, but there will always be some unless the adjustment is so tight that it is difficult to turn. Backlash is not too much of a positioning problem if you always drive the table in the same direction throughout a particular job. A brake is a reasonable solution and most come with simple clamps 180 degrees apart. I know some people who have made motorised tables put various forms of actuator on these clamps but I do not like that. I am sure that the clamp threads will have a short life. I have made an insideout drum brake pneumatically operated and the software automatically controls that via a solenoid valve. I do not seem to have photos of the finished brake (it was the last piece to be made) so I show the cardboard templates instead.

Ok for manual use but not so good for powered use.

I'll make another post about the control system. It is dead simple.

[metric_taper]

Very easy to read code.
Thank you Tony Foale.

Interesting brake add on. I assume you had some sort of friction material attached to the brake arms.

[tonyfoale]

Very easy to read code.
Thank you Tony Foale.

Interesting brake add on. I assume you had some sort of friction material attached to the brake arms.

No friction material, just aluminium. Remember this is a holding brake only. It only gets applied or released when the table is stationary. There is never any rubbing.

[Saltfever]

Nicely commented, Tony. For someone with zero experience with microprocessors I could even find the on/off code for the brake!

I'm looking forward to the rest of your information.

[tonyfoale]

Interesting brake add on. I assume you had some sort of friction material attached to the brake arms.

I did have a photo after all of the real brake shoes. Here it is showing torque testing of the brake.

[tonyfoale]

Oh my, Tony you could be at the F-1 race this weekend and here you are posting to HMT!

I was the works manager for a F1 team in the early 1970s just at the start of serious aero add-ons and Bernie's influence which coincided with the the end of interesting racing. I have no interest at all in F1, it is so boring. If you want good racing have a look at motoGP. Better yet the TT which has just finished.

[tonyfoale]

It goes against my usual way of working but I have drawn a schematic. If you are contemplating making something like this then here is not the place to ask about how to load the code or connect to an Arduino. Arduino.cc is full of helpful tutorials and guides on all of that basic stuff.

The motor and driver need to be sized to match the size of your table. I STRONGLY advise using a closed loop stepper motor. Nowadays they are not all that much more expensive than open loop but they are just so much better. The driver and motor are often sold as a pair and I have seen some offers with driver, motor and power supply as a package. I made my own motor power supply so I got the motor and driver only. You will need an 8 to 12 v DC power supply for the Arduino. This has a very low power requirement and you could use a 9 v DC wall wart or similar.

PS. I just noticed that on the drawing in the BOM I wrote "Brake solenoid" that should read "Brake solenoid valve".

Click for full size.

[metric_taper]

I did have a photo after all of the real brake shoes. Here it is showing torque testing of the brake.

Looks like a test setup to see what sort of force (provided by the test spring) was needed. Since you used an air cylinder to provide this force, and I assume air pressure of 90psi (6bar), how large a diameter cylinder did you use to get the brake lock force you wanted?

[tonyfoale]

Looks like a test setup to see what sort of force (provided by the test spring) was needed. Since you used an air cylinder to provide this force, and I assume air pressure of 90psi (6bar), how large a diameter cylinder did you use to get the brake lock force you wanted?

25 mm diam and 25 mm stroke.

[tonyfoale]

In comment #17 there is an error in the schematic. Pin A5 schould be labelled SCL not SDA as shown. Here is the corrected version.

Click on it for full size