Dear Core & community,
I need some help finding the right goBILDA components for a project. I have found some components that look right, but I need help with sizes and the correct connectors to interface these components. Also, please feel free to suggest better solutions.
TLDR Objective:
Make a miniature motorised rotary stage / platform / lazy-susan using goBILDA components and for a 20mm prism.
Driven by micro servo & controlled by Arduino/Raspberry Pi.
Off the shelf example:
Thorlabs and other optomechanical manufacturers sell motorised rotary stages driven by worm screws. These are too expensive for my application. I don’t need this kind of precision.
Details of my proposed solution using goBILDA parts:
Hopefully showing you the goBILDA components will make the design clear:
1. Base plate:
This will be screwed down to the main fixture plate. Springs or crimped washers between the bearing block and the main fixture plate, and the screws will be partially tightened for fine levelling. I’ll most likely only use three screws (but 4 springs / crimped washers).
2. 12mm shaft through the bearing: This I haven’t been able to find. Would like some help here.
3. Mounting a gear wheel to the base plate bearing: HELP NEEDED HERE
This will attach to the bearing via a shaft.
It will serve as the platform for mounting the prism as well as the interface with the servo.
Unfortunatley the bore hole of the gear wheel is 14mm, but that of the bearing is 12mm. So I need a similar gear with a 12mm bore to mount it to the common bearing shaft Alterntively some kind of a collar or adapter to mount a 14mm bore gear to a 12mm shaft.
4. Mount prism onto the gear disk This i suspect is the easier part. It can be done in a number of ways. My idea is to machine two ABS or aluminium plates with triangular recesses. One above the prism, the other below. The bottom one will have tabs to screw down to the gear wheel. The top one is attached to the bottom one via some twisted coppor wire. Here are some Thorlab solutions using tension clamps.
although Thorlabs components are too large
5. Mount a smaller gear on a servo:
**6. Finally mount the servo beside the main rotary table, and mesh the servo and main wheel.
Constraints
- This whole arrangement needs to fit within a volume of 50cm x 50cm x 50cm (excluding the servo) and maybe 80 x 50 x 50 with the servo.
More as I think of them,.
Alternative ideas
- Mount the prism directly onto the servo, but I suspect that may be too wobbly.
- My main fixture plate is a 300mm Arca Swiss rail. I’d consider a goBILDA channel if you think that is rigid enough for an optical application.
Many thanks!!
Z B
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You mention GoBilda, but you indicate that you are still looking for parts, and might make some, so it is not clear whether the project has to be restricted to GoBilda or that is just a design choice.
As the purpose is presumably to rotate the prism, the important specs are the range of rotation, the resolution and the precision. That will determine your options for a driving motor - stepper, analog servo or digital servo, and also whether or not the drive is direct (which would be much simpler than belts or gears).
A stepper will give unlimited rotation with high precision but resolution generally lower than a servo, although geared steppers can give very high resolution at some cost in precision. An analog servo will give high resolution but low precision, while a digital servo will give high precision and high resolution, but at a higher cost. Some servos have limited rotation. Both servos and steppers are available in sizes that would be sturdy enough to securely mount a 20mm prism, which would be the best option for precision.
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Hi Zaeem
Do you mean 50mm??
50cm is half a metre, Quite a big volume.
Cheers Bob
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@Jeff105671 Thanks for the quick response and the questions.
I’d like to use as many goBILDA components as I can.
- Conceptually I am building a miniature lazy suzan for a 15mm x 15mm x 15mm prism.
- Angle of rotation is up to 30 degrees.
- I don’t want to attach the prism directly on the servo.
- The lazy suzan will be bolted down to an optical bench.
- A micro servo will be mounted next to the lazy suzan.
- Gear on the servo shaft will somehow mesh with the lazy suzan to turn it.
- In my plan so far: the goBILDA 12mm Bore, Heavy-Duty Flange-Mount Bearing Pillow Block would be perfect base for the miniature lazy suzan. I can bolt it down with wavy sprung washers or even springs for levelling.
- Next, something like a goBILDA hub mount gear mounted on the bearing would be perfect. It will serve two purposes:
- the platform of the lazy suzan, and and mounting surface for the 15mm (half) cube prism, and
- a gear to mesh with the servo gear.
Where I am stuck:
- How to mount the hub mount gear onto the bearing.
- Ideally I could press a 12mm shaft into the bearing and mount a large gear with a 12mm collar onto the shaft.
- goBILDA hub mount gears have 14mm bores. I can’t find a 12mm collar to attach to the gear.
- Does goBILDA have 12mm shafts? I can’t find one.
- I like the goBILDA hub mount gears because I can use them to reduce the gearing of the servo and increase the precision of the rotation.
Hope this clarifies my setup. Very glad for the responses so far. Thank you!
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@Robert93820 - oops, yes indeed, I meant 50mm. There is some flexibility on the total size, but roughly the size of a small potato 
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That link to the bearing above in your original post shows some drawings of typical applications with a 12mm “REX” shaft and some gears etc mounted on it so they must be available. This bearing is almost the size of your suggested limit at 40mm square and 12mm is quite a large shaft to support a 17mm prism or is it a bit heavier than one would imagine.
Cheers Bob
When you blow up the pic the “REX” shaft is actually hexagonal.
Add on:
Be aware also this bearing is not a thrust bearing. That is if mounted horizontally it is not designed to support any weight vertically. so don’t rely on it to support the total weight of your assembly. Mount the drive motor etc solidly then this type of bearing will supply lateral stability. Have a close look at the couple of drawings in that link to get an idea of how it is used. If you are going to drive something then the motor will have to be mounted in a stationary fashion anyway.
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Hmm - the drawings with the goBILDA bearing seem overly complex for my needs. They seem to require clamping collars on both sides.
I need to mount the bearing flat on a reference surface (optical bench) and press fit a gear wheel onto it.
Any components/collars/sleeves that will allow me to do this?
Any simple way to mount the large gear wheel to the bearing?
Any options other than goBILDA available?
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Is Core Electronics staff reading this? Can you please help finding the correct components.
To simplify the problem,
- I want to mount the 12mm Bore, Heavy-Duty Flange-Mount Bearing Pillow Block onto a flat optical bench.
- I want to somehow mount one of the large geared wheels on the bearing so it can turn freely without play.
- The gear will also serve as a lazy susan for a prism.
- I chose the hub mounted gears because they are larger than the bearing block, and can mesh with a pinion gear on a servo. The servo will drive the lazy susan.
Ordinarily I’d machine some press fit components and even gears for my needs, but I don’t have access to a machine shop currently, so looking for off the shelf components. I was hoping goBILDA would have components that could easily be made to fit together. Appears not. Please help!
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Hi Zaeem,
Welcome!
Core just got back to work today (Its Monday here).
Since goBILDA dont give tolerances I’m not sure that you’ll be able to build an assembly like this without some back-lash in the gears.
An assembly like this, would be the mechanically stable with the addition of another bearing supporting the REX shaft (and what Bob was refering to with the thrust bearing):
Source: 1613 Series Thrust Ball Bearing (12mm ID x 21mm OD, 5mm Thickness) | goBilda GB-1613-0521-0012 | Core Electronics Australia
To eliminate slop in the system from gears, belts would be your best bet, though it doesn’t seem there is a pulley with a suitable OD:
I’d say a combo of goBILDA parts and 3D printed gears would be the best option (unless you can expand the 50mm x 50 x 50 volume constraint
