Castors for rotating monitor rig - swivel-type or non-swivel?

[Anubis_au]

What's the best kind of castor wheel to use in a rotating plate monitor setup, like what Jimbo has done for his current project and what I plan on doing in mine.

Jimbo is using fixed castors. My friend, who will source me the castors I want, asked me which kind I'd want.

I'm inclined to go with fixed castors like Jimbo, but am wondering if people think the swivelling type of castor would not be better?

Opinions, people?...

[DaOld Man]

I would say that if you are following jimbos design, then use what he did.
Can you see an advantage to using swivel over fixed?

[Anubis_au]

I don't know enough to make an informed decision. There are some things I am woefully ignorant of... like motors, gears, and angular / tangential forces etc... in short, all the things that com into play designing a rotating monitor system

But, that's why we learn...

So, is there an advantage with swivel castors? I don't know, but the guy who's sourcing the castors for me asked the question, so I put it out there...

[bfauska]

For a setup where travel needs to change direction without going off course (as in a rotating monitor that rotates within a fixed path) a swivel caster would be a serious error.  When a swivel caster changes direction the wheel needs to pivot around IT'S pivot point which requires it to move perpendicular to the desired travel for a brief moment.

For an example look at the front casters on a shopping cart (trolley if you're from somewhere with less American English.)  Watch what the front end of the cart does if you try to switch from forward travel to backwards travel, the front of the cart will shift to the side while you change directions.  Now imagine that the cart cannot shift to the side, like it was pinned in the center, or trapped between guides, it will start to turn the caster and then drag it or make it wobble.

The drawback to a fixed caster is that if you don't get it aligned right (there is some room for error) it may drag as well, but lining them up with the direction of travel is not that difficult.

In theatre we frequently make large parts of the stage into turntables which act much the same as what we want a rotating monitor to.  Imagine a 30' (that's foot not inch) monitor rotating under motor power and hitting it's desired position with less than 1/2 inch of error and you'll picture what I'm talking about.  We use fixed casters to accomplish this, swivels would bind.

Not trying to sound all braggy and know-it-all, I just want you to know why I'm saying I know the answer and trust that I've tried and seen the results of both options.

AND fixed casters are usually cheaper.

[danny_galaga]

what he said! a 'fixed castor' is a mis-nomer since it doesn't actually pivot. basically its just a wheel, which is what you want. i used ball races myself...

[Jimbo]

For what its worth, the fixed castors work great on my setup.  Its a little noisy, but that's because I haven't sanded down the monitor frame yet to be a perfect circle. Once that's done, and I've put some sort of rubber/plastic trim on the edge of the monitor frame (and on the back of it where the castors run), I'm hoping it will be smooth as silk and quiet as a mouse!

[Anubis_au]

Thanks for the help guys.

One of my best friends lives in London but is back in Sydney in a fortnight for a mutual friend's wedding, so I have put an order in with him for the castors that Jimbo used.

Jimbo, firstly, thanks with the info on the castors you used, and also for the generous offer to procure them for me.

[danny_galaga]

are they that special that you need to get them from the UK?

[Anubis_au]

are they that special that you need to get them from the UK?

Well, in a way, yes.

The smallest castor I found here in Sydney had a total height of 64mm. The ones than Jimbo used and I am getting are 35mm.... roughly half the height, thus half the separation between the two layers of wood that make up a rotating monitor mechansim.

And since I am attempting to put this inside a lowboy cabinet, these castors will make a huge difference. If you've never seen a lowboy you may not appreciate just how small these things are. I need every millimetre I can save.

But, I kind of see where you are coming from... castors from overseas would seem rather over the top...

[danny_galaga]

like i say, i used ball races. nice n small diameter. buuutttt... they are a bick jumpy if you dont have a really clean surface for them to run on in which case i would do the same as you and get them from wherever you can. even pommy land!

[koz319]

FWIW, I actually used skateboard wheels.  Decent bearings, and a slightly softer surface that some of the hard plastic casters.  Do need to mount a little differently though.

Koz

[telengard]

I used non-swivel on my rotating monitor.  Can't imagine having used the swiveling kind but it may have worked, who knows.

~telengard