Engineering challenge for camera slider.

[cjdawson]

I while back, I started a project to make a camera slider.  Here's the thread.

 

That project has stalled, when I had trouble finding a decent way to drive the camera rotation part of the project.  This part is the trickiest past of the project, so I'm taking my time to get it right before I start building the sliding buggy.

So, I've found that Conrad do a nice 1:20 ration worm gear set, which I've just received and it looks great for the job.

Attaching the worm to the motor will be done via a 5mm to 4mm coupler.  The Worm will be on a 4 mm aluminium rod.   The motor is a NEMA 17 which will be bolted to the underside of the buggy.   The rod through the worm might also end up being secured at the other side to the motor, but I've not fully decided on that yet, it's an option if I feel there is going to be any flex when it comes to assembly.  (most likely won't bother with the support though, but not counting it out)

At this point everything is great.   The power from the motor is now now going to be increased, the distance per step is reduced and the torque will be through the roof, all good stuff.   Also by using the worm gearset the power will be translated through 90° meaning the axle comming off the wheel can go straight up through the buggy to the camera mount to provide the rotation.

 

(there's a picture below to help people visualise what I'm trying to do)

Now comes the tricky part.

The gear wheel on the worm gearset (the worm wheel I think it's called, it's the cogged wheel, not the spiral worm) has a bore of 5mm

From there I need to get the power up through the 3mm thick aluminium plate that will form the base of the buggy then into the bottom of the ball mount that I'll be attaching the camera too.

This is where I need help, as I'm not exactly sure how to do this.   I do an idea, but there are complications and could use some extra brains to help out.

 

Here's the details of the worm gear set

http://www.conrad-electronic.co.uk/ce/en/product/236942/Worm-wheel-set-module-075-Reely?ref=list

 

The ball head that I have is this one

https://www.bhphotovideo.com/c/product/743843-REG/Benro_BH0_BH0_Ballhead_with_Quick.html

 

 

So, here's my idea.

The ball head sits on top of the 3mm thick place, and is secured using a bolt or something like that  (this is the part I need help with)

The Ball head is fastened against one of these (thrust bearing to allow the ball head to rotate)

http://www.ebay.co.uk/itm/Needle-Roller-Thrust-Bearing-Complete-AXK0619-0819-0821-1024-1528-1730-2Washers-/272035297661

The reverse side of the thrust bearing is on top of the 3mm thick plate.

On the underside of the plate, is another thrust bearing

All of that is then secured in place, with a nut.

The thread then carries on into the 5mm bore of the brass wheel from the worm gear.

 

The plan is that the motor drives the worm and the camera will rotate.   Turn the motor off and the camera will be held in place by the amount of pressure that would be needed to make the worm gear work backwards.  And if that's possible, I can always use the breaking capability of the stepper motor. (It'll be almost impossible to move then)

 

So what's my problem?    In short it's the whole deal with the rod that will go from inside the ball mount to the worm wheel.   In addition I have concerns about the diameter of the thrust bearings -  I don't want things slipping other than the rotation axis.

First things first, the axle problem.

At the bottom of the ball head, is a standard tripod thread.  It's possible to use 2 sizes of thread, the ball head comes with an adapter for the smaller thread.

I believe that the smaller thread is 1/4" thread.

From there, I need to get out of the ball head, through the plate, past 2 sets of thust bearing before locking off with a nut.

 

From the nut, I need to then change size to a 5mm axle which I'll be able to file a flat part on to help the set screw in the brass worm wheel hold well.

 

On the underside of the mount the brass wheel needs to sit at the height of the worm, this is governed by the nema motor and it's mounting bracket.    It's about 2 and a bit cm from the place.   So there's not a whole lot of room to make brackets and things.

 

Here's a quick sketch of the part of the design

 

Where I have written "Help!" is the part where I need help.     What I need is something that will let me have a 4mm threaded rod at the bottom, that then changes to a threaded rod which will fit into the camera mount.

As I don't have access to the stuff that would be needed to make a custom part like that I need to do this with things that I can get hold of.   Or maybe someone would know of somewhere that could make up the vertical axle of this project?

 

Any ideas?

 

[cjdawson]

I just looked it up on wikipdia https://en.wikipedia.org/wiki/Tripod_(photography)

and the larger thread looks to be 3/8" whilst the smaller thread is 1/4"

 

So, I could find a place that did 3/8" threaded rod, which had an unthreaded 4mm part, that would do the job as I could use a 3/8" nut to hold the entire thing in place.  (3/8 of an inch is 9.525mm, so this looks doable with the right tools)

Same will work for a 1/4" thread as well. (1/4 of an inch is 6.35mm)

[Lonestar70]

16 hours ago, cjdawson said:

I just looked it up on wikipdia https://en.wikipedia.org/wiki/Tripod_(photography)

and the larger thread looks to be 3/8" whilst the smaller thread is 1/4"

 

So, I could find a place that did 3/8" threaded rod, which had an unthreaded 4mm part, that would do the job as I could use a 3/8" nut to hold the entire thing in place.  (3/8 of an inch is 9.525mm, so this looks doable with the right tools)

Same will work for a 1/4" thread as well. (1/4 of an inch is 6.35mm)

Hi CJ,

This is an interesting project, however, I can foresee several potential problems with your proposed design: -

1/ Thrust bearings are fine for axial loading but are not at all good for Radial loading which you will certainly have with a worm and wheel drive... these will almost certainly deflect sideways in a short space of time.

2/ The use of threaded rod for your shaft will also lead to problems given the sideways loading at the point where it passes through the thrust bearings and top plate... the sideways movement will lead to the threaded rod fouling,and eventually wearing away, the hole through the top plate... which will lead to further sideways displacement.

3/ There is a substantial unsupported length of rod below the bottom thrust bearing which will potentially lead to the shaft bending under load thus adding further sideways pressure on the bearings.

4/ Using an unsupported shaft for the worm will lead to problems with the meshing of the worm and wheel... it will not be constant, which could lead to the worm jumping a tooth on the wheel... this will vary with camera load.

I would recommend using flanged ball races rather than the thrust bearings... with 2 bearings spaced enough to fully support the shaft and pre-tensioned within a shaft housing (this would be achieved by using a nut and locknut just above the wheel) this would eliminate all the issues in 1-3 above.

Rather than using a separate reduction coupling between the motor and the worm shaft, I would suggest a custom made shaft with a 5mm bore at the motor end and the outer of the shaft reduced to 4mm at the worm location... Also this should extend beyond the worm and be supported on a small bearing which will eliminate the potential for the worm and shaft to deflect sideways as in 4 above.

I would also recommend this shaft be made from steel (stainless) rather than aluminium, which at 4mm dia. would bend like spaghetti.

These are the sort of bearing I am suggesting: -

http://simplybearings.co.uk/shop/p155036/FR168ZZ-Metal-Shielded-Flanged-Deep-Groove-Ball-Bearing-1/4x3/8x1/8-inch/product_info.html

http://simplybearings.co.uk/shop/p155047/FR6ZZ-Metal-Shielded-Flanged-Deep-Groove-Ball-Bearing-3/8x7/8x9/32-inch/product_info.html

Given the Outside diameter of your wheel (approx 18mm) I would suggest using a 3/8"(9.525mm) bearing at the top with a 1/4"(6.35mm) at the bottom which will leave enough room for the wheel to engage the worm whilst keeping the shaft housing long enough to fully support the shaft.

How long this shaft support could be depends on the amount of space you have beneath the top plate and the mounting arrangements you have for the motor.

The top of the shaft can have a larger diameter support plate for the ball head along with a 3/8" thread.

I have a fully equipped workshop and would be happy to make any necessary parts for you.

If this would be of interest to you then please PM me and we can discuss it in more detail.

Best regards.

Sandy.

 

 

 

[cjdawson]

I love the idea of using a flanged bearing.  Could insert this into the plate so that the rod going through has a bearing to run against rather than just the hole.

Deflection isn't something that I want to have, so with that in mind. I can see an idea of extending the 4mm rod that goes through the worm wheel.  This would then extend down and into another flanged bearing with a 4mm inside diameter.  This would hold the rod in place.  could also put a nut above and below this bearing to hold everything in place.  The rest could then be free to rotate, the ball mount could also be help in place with a nut, and maybe a penny washer.    With that arrangement, I'd not need the thrust bearings at all.

Adding a 4mm flanged bearing to the drive shaft, will stop any deflection of the worm.

Looks like a good improvement.