astistance with artist project: rotating table top

Hi Everyone,

I’m an artist and am completely new to aduino as well as stepper motors. I was wondering if there’s someone on the forum who’s a pro at these sorts of things that might be interested in assisting me with a project I’m working on. Please take a look and If you’re interested or know anyone who might be, please pass on my details. I will of course be happy to pay for your time (however sadly I’m not loaded).

The project:

In a nutshell, I would like to programme a stepper motor to rotate the top of a table at a very specific speed- one ration corresponding to the time it takes for the Planet Saturn to make a full rotation. 10 hours and 39 minutes.

The accuracy of the rotation is quite important and so is the smoothness- if possible I would like it to move imperceptibly.

The table is a small coffee table – see pics attached. The top of the table weighs approx 3 to 4 kg. (I plan to decrease the weight by routering out the excess of the bottom side. Once done I hope it should weigh around 2 ½ kg.

I would like to conceal the motor from view, so the length of the motor is a concern, but the width could be as large as is needed.

If theirs someone out there who’s interested, I would very much appreciate help with feasibility, recommendations on hardware to purchase and complete programming/coding.
It would also be a great to find someone not to far away in the uk.

I look forward to hearing from you

Thanks,
George

If you want someone to help you in return for payment you should ask in the Gigs and Collaborations section of the Forum.

Stepper motors move in steps. You can have very long intervals between steps for slow movement. if you want to reduce the impact of steps it would probably make sense to use gears so that a single rotation of the motor only moves the table a small amount.

How heavy is your table and how good is the bearing on which it will rotate? Those, and the gearing will affect how much torque you need from the motor.

Have a look at these links
Stepper Motor Basics
Simple Stepper Code

...R

Hi Robin,
Thanks so much for taking the time to respond to my post, and thank you for the link to the notes you made- there a great help!!

Ill def try posting in the Gigs and collaborations forum.

I’m guessing after reading your notes on stepper motors, you think using micro steps to turn the table top would reduce its accuracy? Is that why you suggest using gears? Would using gears be a way to reduce the speed of the motor without using micro steps or do they have another function as well?

Is it possible to buy such gears of the peg from a retailer, I found these on ebay http://www.ebay.co.uk/itm/Nema23-Worm-Gear-Ratio-7-5-10-15-20-30-Stepper-Motor-3A-L76mm-Speed-Reducer-CNC-/201606239526, do you think they or something similar might work?

the table top is hard wood –see previous pics (56cm diameter x 2cm thick) and weighs approx 4kg, once I know where I’m attaching the bearings I plan to decrease its weight by removing excess wood from the bottem side using a router, I hope to get it down to 3 kg.

I haven’t yet purchased my bearings, here are some I have seen that I thinking of ordering http://www.ebay.co.uk/itm/10-Inch-250mm-Lazy-Susan-Rotating-Aluminium-Turntable-Bearing-Engineer-LS250-/142040173061 but its hard to tell if the qualities up to much!

Thanks again
Best,
G

with a belt drive, a simple worm gear and a belt drive from a scanner, you could easily need to run 3 steps per second.
12:1 on the pulley, 10:1 on the worm and 1/4stepping on the stepper.

ebay has some 27:1 gear head steppers
coupled to a 10:1 belt, you would need to run your stepper at a decent speed. 6 steps a second ?

10hours = 600 minutes, = 36,000 seconds

27:1 x 10:1 = 270:1
200 natural steps x 1/4 stepping is 800 steps

270 * 800 = 216,000 steps per rotaiton

216,000 / 36,000 = 6 steps per second.

very easy to do.

I didn't mention microsteps in my Reply #1 because I thought it would be confusing at that stage.

You could certainly use microsteps. However for the very slow speed you want as well as your requirement for smooth motion I assumed you would need gears even with microsteps. Microsteps are still steps.

I think the first thing is to decide on the gear system. As @dave-in-nj says a worm drive is a good idea and it could give a very large gear reduction. Google should be able to find YouTube videos about people using worm drives for astronomical telescopes.

...R

Robin2:
I didn't mention microsteps in my Reply #1 because I thought it would be confusing at that stage.

You could certainly use microsteps. However for the very slow speed you want as well as your requirement for smooth motion I assumed you would need gears even with microsteps. Microsteps are still steps.

I think the first thing is to decide on the gear system. As @dave-in-nj says a worm drive is a good idea and it could give a very large gear reduction. Google should be able to find YouTube videos about people using worm drives for astronomical telescopes.

...R

I would not recommend designing with anything less than 1/4 steps. and the A4988 driver is a great chip for this project.

once you get into 1/8 steps, you have power delivery issues with the motor. microsteps are for smooth motor operation, not power delivery.

Robin2:
I didn't mention microsteps in my Reply #1 because I thought it would be confusing at that stage.

You could certainly use microsteps. However for the very slow speed you want as well as your requirement for smooth motion I assumed you would need gears even with microsteps. Microsteps are still steps.

I think the first thing is to decide on the gear system. As @dave-in-nj says a worm drive is a good idea and it could give a very large gear reduction. Google should be able to find YouTube videos about people using worm drives for astronomical telescopes.

...R

there is the question of power at the device. if this is just a visual effect and no one will touch it while moving, then a tiny belt from a scanner would work.

if anyone were to touch it, then the drive system has to be really-really strong. of has to have a clutch to protect itself.

Hi Dave,
Thanks so much for much for all the info!

I’m still trying to digest all the information you and Robin have given me but here are some initial comments/thoughts.

No one will touch the table whilst it’s running. The only added weight will be a glass of water that will be placed on the table.

The gear head/ belt combo sounds like an interesting solution! I am slightly concerned about using a belt though, although I have no real experience to ground my concerns on (just bad experiences with washing machine belts going wrong). How reliable are they? And what’s the benefit of using one instead of say an additional worm gear?

The only 27:1 headed stepper motors I could find on ebay are the Nema13 &17- do think they would probably be too small for my application? There also this Nema23 with a 50:1 gear box attached!-

:http://www.ebay.co.uk/itm/191884680329?_trksid=p2060353.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT
It might be a bit chunky though

G

thanks Robin, I had a look on youtube for those astronomical telescope videos but couldn't find any, found some interesting video of people using worm gears to control turntables for model railways though.

How about this, maybe drive another intermediate wheel to the inner lip of the table to slow it down more, or just blip the motor as needed to move it a little

Or this one
http://www.allelectronics.com/make-a-store/item/dcm-469/24vdc-gear-motor-45-rpm/1.html

This is the sort of thing I had in mind

I Googled "DIY telescope gears" (actually DUCK DUCK GO)

...R

Nice thanks robin! Really interesting, I'm not sure if I have the skill or equipment to fabricate my own worm cogs though.

Also found this project telescope project whilst doing some research- Motorizing a Dobsonian Telescope - YouTube
He has a blog of the making here: http://www.codeproject.com/Articles/657252/Motorizing-a-Telescope-Part

Do you know if the big fine worm gears are avalible to buy from anywhere?

if you have a way to make a circle in wood.....
cut two circles for the bread of the sandwich and one smaller.
make the sandwich.
mix epoxy and fill the void. let it start to harden. you do not want super fast drying.
put your sandwich on your axle and spin your threaded rod. it will make the thread in the epoxy.
use oil on the rod to prevent the epoxy from sticking.

instead of cutting the gears, you are forming them.

you are making your turntable first, then the gears. once it cures, it is ready to go !

another idea is to use a milling turntable

bolt your plywood on this and put on a pulley for your motor.
have to do the math, but the bits are easily worked with. no machining of gears or such.

Very little force should be required to drive your turntable and cheap adjustable plastic gearboxes can be had.

Lazy susan bearings are useful for your type of application.

They are often used for rotating displays although are of little use for machining or high speed operation.

Milling a flat on the underside may be required, a table top like that can distort with time ad can any wood including ply.
It may not be important for your application though, only noticeable as an up down motion when rotated fairly quickly.

As far as driving is concerned look at how railway modellers build turntables.

Ring gear, toothed belt, as search terms may be helpful.

I suspect that your requirement does not really need steppers as the movement is so slow as to be imperceptible anyway.

dave-in-nj:
if you have a way to make a circle in wood.....
cut two circles for the bread of the sandwich and one smaller.
make the sandwich.

That's a very neat idea for making the gear.

Another thought that had crossed my mind was to make a large pulley using that sandwich method and drive it with a belt from a very small pulley on the motor shaft. I think that would give a sufficient reduction without any need for gears. I think you can buy toothed-belt material by the metre to make up any length you need. You could even put a proper toothed belt pulley on the motor shaft but I don't think there would be any need for teeth on the big pulley. In any case mount the motor so it can be slid away from the other pulley to tension the belt. Look at the system for the alternator in a car.

A stepper motor provides a simple way to control the speed very accurately.

...R

Robin2:
That's a very neat idea for making the gear.

...R

I made a turntable using this.

Very little work needed just a small amount of turning to adjust the worm.

Thanks dave-in-nj, Robin2 and Boardburner2.
Apologies for the radio silence- I’ve had a really busy week but im really grateful for all the great advice and suggestions!

I’ve put together some draft drawings for the design of the gears, please take a look at the PDF attached If your interested. Any comments on the design would be very welcome!