Rotating Monitor Help

[torridpsu]

Hey guys.  I need some help with my rotating monitor

I have a 24" 16:10 flat screen mounted with a lazy susan bearing and a pololu motor, mimicking the design of topjimmy and DNA Dan, with 2 exceptions mentioned later.  I've managed to get the monitor rotating successfully when laying flat.  When I set the whole mechanism 85 or 90 degrees, the monitor only successfully rotates clockwise.  Counterclockwise, the wheel rotates full speed, but the platform doesn't rotate at all.  Complete slippage.  I have to *really* press down on the motor to get it to rotate, and at that point the motor is bogged down due to the pressure. Also to note, I have the spring hinge preloaded to 90 degrees to keep pressure on the wheel.  

So the two main differences in my design so far are 1. I have no supporting casters and 2. I have a widescreen 16:10 monitor.  I know the weight distribution is different than a 4:3, but I'm not sure how much that matters.  

So as for questions, do you think I need supporting casters?  Has anyone had similar issues with rotating monitors?  Any other suggestions?


Here's a video that shows the rotation in both directions.  you can see at the end that, standing up, it doesn't move, and setting it flat it does.

[youtube][/youtube]



DNA Dan's rotating monitor http://forum.arcadecontrols.com/index.php?topic=110471.0;all
Top Jimmy's monitor http://forum.arcadecontrols.com/index.php?topic=112424.0

[Turnarcades]

Obviously it seems that when tipping the monitor up to a viewing position, gravity is playing a part but not in the way you want. The supporting castors on the other designs seem to keep the rotating plate planted evenly against the bearings, or at least enough to keep friction high. Try roughing up the bearings or the surface contact area to increase friction and help it 'grip' when trying to rotate. This may put extra load on the motor but could be necessary with your design changes.

[TopJimmyCooks]

Gravity kills.  When you're flat, the bearing plates are coplanar and the monitor disk can spin freely.  this is the situation the Lazy Susan bearing designers were planning for - normal operation.  when you're upright, the weight of the monitor disk causes the bearing plate attached to the disk to rotate down and pinch the ball bearings that are at the bottom, increasing resistance.  the bearing wasn't designed to work vertically like this.  it's counterintuitive, but as DNA dan figured out for us, you have to have a couple of castors or wheels at the bottom to support and space the disc out and keep the two bearing plates co-planar.  My rig has 2 small castors within 2" of the drive wheel on either side, they're just hard to see from the back. 

Then, if your motor pressure spring is stout enough to push the monitor disc away from those castors, you need a third one on the other side of the disc opposite the motor to keep the disc from being pushed too far in the other direction and therefore binding at the top.  Clear as mud, right?  if this doesn't get you what you're looking for I can update a sketch and post it up.  good work, keep it up.

[torridpsu]

Nope, I understand.  That was my first thing to try tonight when I get home.  I have to find these casters with the nut on them that you guys described in your post.  I briefly looked at Menards and only found casters without a bolt to release it. 

So with the two casters, you're placing them at approx 4 and 8 o'clock right?  And if you had 3, you would place the 3rd at 12 o'clock?  Any tricks to determining the depth to mount them at?

 

[TopJimmyCooks]

The small casters I bought were swivel castors and had a plate on them with ball bearings, etc.  I drilled out the rivet that held that plate on and got rid of the swivel, ball bearings and mounting plates, then stuck a bolt through the hole in the caster frame.  It's harder to find small non-swivel casters, but those would work fine. 

My two casters are right to either side of the motor drive wheel, say at 5 and 7.  DNA dan had his at 4 and 8, either way will work.  you don't need anything at the top, the disk is pulling away from the cab at the top.  I considered putting a 3rd wheel at 6oclock on the monitor side, to keep the motor drive wheel from pushing the disk away, and giving the opposite problem, but it turned out the pressure spring relaxed a little and I don't need it. 

Depth to recess the caster into the support frame equals height of castor minus the thickness of the lazy susan bearing.  So if the bearing is 1/4" and the castor is  1 1/2" tall (after modification), you want to recess it 1 1/4" into the cabinet side of the assembly.