motor advice for rotating crt setup

[Jimbo]

Hello all,

My project thread is here. I'm attempting a rotating setup on my cab. I have a 21" arcade monitor, weighing in at about 22kg, attached to a plywood frame, sitting on another plywood frame on casters at an angle of 45%.

I'd like to motorise the rotating, and I've thought the easiest way to do it would be as follows: -



I'd be putting a thin 3mm strip of rubber on the edge of the 18mm thick plywood monitor frame, then using a small DC reversible slow RPM motor connected to a small rubber caster/wheel to provide the friction to power the monitor rotation.

My questions are:

1) does anyone know what powered motor I'd need that will be powerful enough without being too big.

2) does anyone have one of these motors they want to sell me?   (or know where I can get one)

3)  Any other advice or opinions welcome (such as roughly what RPM range I should be looking for in a motor).

Thanks

Jimbo

[leapinlew]

odds are that after a rotate, the monitor will need a degauss since it's magnetic field in relation to the earth will have changed.

Use a LCD or plan on degauss after a rotate.

[brock.sampson]

I would check this http://forum.arcadecontrols.com/index.php?topic=62577.0.  I couldn't find any working videos though.

[Kangum]

i bet a cordless drill or a cheap 20 dollar electric drill would work. set the speed to slow sand hould be good to go. i wouldnt even take it apart. just rig it to a bit.

[knave]

How about the motor from a cheap Harbor freight hoist.  I got one to lift my Jeep top and it is slow and has forward and reverse buttons built in. It's on sale for $79 but I've seen it as low as $59.

http://www.harborfreight.com/cpi/ctaf/displayitem.taf?Itemnumber=40765

[bluevolume]

Any good sized 120v motor that includes the step-down gearing would probably work.   I don't think a DC motor would be a good idea -- how would you power it?  You'd need a pretty big transformer.

HarborFreight is a great resource for this type of thing, but make sure you wire everything up correctly and include appropriate fuses!  HF stuff is a little "smoke and burn" biased.

[DaOld Man]

If you use a 120 v motor, make sure it is reversible.

[bfauska]

You're also going to want to be careful with the placement of the motor.  If it is direct drive from the wheel to the monitor "frame" your motor (read big magnet) is going to be really close to your monitor.  I would think this is a good argument for a belt driven system. 

As far as size, you can get away with a fairly week motor since you are going to have some crazy reduction.  If you have a disk supporting your monitor that is about 24" diameter and a 3" diameter drive wheel that's an 8:1 ratio. 

[sac01]

Years ago I planned out how to do this, then lost intrest and just set up seperate vertical and horiz cabinets...My plan was to use a power window motor from a car.  Just go to a junkyard and grab one out of just about anything. They are 12v and don't require alot of amps to move something geared down than much (probably cost you $10).  Should be able to run off of a good 12v dc powersupply.  My other plan was as allready mentioned, use a cordless drill, plenty of torque and easy to power once again.  You can get a cheap one at any flea market or discount store.

[Kangum]

i like your idea Sac01 of the power window motor from a junk yard. pretty much self contained. easy to power, reversable, decent speed, and already has a switch that can be mounted anywhere. although i have to admit if i was to do it myself i would be to lazy to take one out and end up buying an electric screwdriver to chop up.

http://shbox.com/page/windowmotor18.html

is a pretty good shot of a stripped out window motor.

[bluevolume]

I saw a thing on the History Channel about how the thrusters in the Harrier work, and this might be a good idea for this project.  Adding gear notches around the monitor mount and running a chain to the motor.  Probably a lot more work but you would get pretty reliable performance out of it.  If it works with 21,000 pounds of thrust, it should work with a 60 pound monitor. 

[Anubis_au]

Jimbo, I've was having this very same discussion with my mech eng friends and the propeller heads at work today.

The top three suggestions that have come about are:

1. the motor connected to a caster wheel driving the rotation via friction. but, have the caster 'horizontal' under the rotating plate

2. motor with a cog married to a strip of cogs that's stuck on the outside of the circular plate. problem is where if anywhere to get this cogged strip. Worst case: get it laser cut at a perspex cutter etc (ie not cheap).

3. use a bike gear connected to a bike chain which is nailed to the outside of the circular plate.

In all three cases, these are suggestions put to me as how to couple a motor to the circular plate to achieve the desired rotation. No-one suggested anything about where to source said motor, but this thread has now revealed some ingenious sources (drill/screwdriver, electric window).

Don't forget Jimbo, I'm right behind you in terms of designing a rotating monitor cab. So good luck and don't fofget to share any of your findings. I for one, am watching *very* closely!!

[danny_galaga]

ok, ive done it on a smaller scale (15" crt) so i have some thoughts (",) . i myself would go for a cordless drill. set it up so that it can remain trickle-charged. thus all the 'grunt' work is done by the battery- no need for a huge transformer. this is what i will do if i ever build another rotator. mine being much smaller i was able to get away with an electric screwdriver sized motor. whatever you use will need to be geared and guess what? the drill will be just about right! i say forget about using AC motors. too big and complicated (and more chance of getting zapped somewhere along the way).

the other thing ive seen done is this on a 19" cocktail:

http://web.archive.org/web/20021016113027/http://home.attbi.com/%7Eelsmith2000/MAMECAB.htm

as you can see he's dropped off the radar, but wayback has some pics at least. im not sure what 12v motor he is using but i have heard somewhere that an electric window winder works well. again its already geared down.

about degaussing. being a pc monitor, mine degausses when its turned on and off. so when it rotates in my cab, i have it wired so that the monitor switches off while rotating. i dont know if they have anything built in on arcade monitors (i cant imagine the need for it).

edit: oh, and if you check out my machine, you'll see im quite partial to the exact drive setup you envisage! i used a wheel off a 1/12 rc car driving directly againt the ply turn table. i later added a thin foam strip to help with friction. i like this setup because if something goes wrong it will just slip rather than break something or burn something...

the gear ratio on mine pretty low. forgotten now, but including the roughly ten to one of the wheel to turntable ratio, it was in the hundreds to one. needs to be. if you have the power, and you had it spinning fast imagine the inertia on the monitor. a lot of un needed stress.

ooh, just remembered. heres mine spinning. i think its an acceptable speed. it allows for degaussing but also allows the 'oooohhhh!' fact to set in (",)

[urbecrisch]

To be honest I'm generally not a big fan of the rotating monitor, but this looks absolutely ****ing awesome.  Great build!

[Lilwolf]

for gearing down, couldn't you go and buy an old bike from a second had store?  Seems like it would be a good, solid and cheap way to do it.

And I love the idea of using an old drill.

[DaOld Man]

3. use a bike gear connected to a bike chain which is nailed to the outside of the circular plate.

I like your idea of using a bike chain as the driven gear and a bike sprocket as the pinion.
Just remember guys, the monitor only turns 90 degrees, so the chain or big gear does not have to go all the way around.

I have thought about using a rotating monitor on my cab.
I have drawn up an electrical diagram that uses relays to switch a DC motor.
Turn switch on, motor rotates to a certain point set by a limit switch and stops.
Turn switch off motor rotates backwards to another limit switch and stops.
This switch could be an output from the computer's printer port.
I was thinking of letting the computer automatically turn the monitor based on the game you have chosen.
I sorta put this on the back burner, but this thread has got me started again.
Oh, and by the way, Anubis, we call the mechanical types at my job "Flange Heads".
And they call us electricians "Watt Heads".

[ahofle]

That is so awesome -- nice job.
 

How did you get it to stop perfectly at 90 degrees?

[Cornchip]

  I'd seriously think about going with something that didn't use a 'friction drive'. Your monitor is at 45 degrees and might bind with all the mass hanging off the back. Consider a rear bearing if at all possible. The use of a 12V gear motor is the simplest due to it's high torque and simple polarity reversing (switch or relay). Also power window motors are worm gear driven...they will hold a load while stopped. Plan or rotating at something like 3 RPM. Sounds slow....but consider the weight involved (accelerate and decelerate count here). It's a whole other ball game with an upright cab vs. a cocktail. Do you have room behind the monitor for a chain drive as mentioned earlier? If that's a little complex for machining reasons I have another thought on something simpler not mentioned.

 

 Cornchip.

[sac01]

I was just looking at that drawing and I was thinking you could center the motor down under the monitor wheel, and do the same thing with the rope/cord, except not use the counter weight, and just have the cord wrap around a dowel connected to the motor wound in one direction, then it goes over the top of the monitor wheel (afixed at the top with a clamp or screw thru the cord) then it goes down the other side where you had the counter weight, but in place of the weight it wraps around the same dowel (dowel long enough to allow two windings of rope with something to seperate them like a large washer) in the opposite direction (counter clockwise if the other is wrapped clockwise)  Then when you run the motor to rotate to horizontal,  one side releases the cord and the other pulls the cord, when you reverse the motor to go to vertical, it pulls on the other side of the cord and releases the the opposite side)  Seems pretty fool proof, simple, and alot easier than a chain drive (probably quieter to)

[Cornchip]

  You could put the motor any where you like with this setup. Just use idler pulleys to redirect the pull. As for the main drum...just wrap either ropes in a 'right hand' and 'left hand' fashion. No need then of a second pulley. And your right about this being quiet. My chain was quiet by the way. It goes so slow that noise is not a problem. You do hear the motor. It's kinda the point.


 Cornchip.

[danny_galaga]

That is so awesome -- nice job.
 

How did you get it to stop perfectly at 90 degrees?

thanks  . it uses limit switches. works well at that size but if you have a look at how ive done it here:



i just use microswitches. the monitor turn table has a leg that hits one or the other. thing is, physically thats all that stops it! so eventually i imagine a switch will break. in this case easy to fix with just a bit of foam rubber on each switch lever.

[danny_galaga]

  I'd seriously think about going with something that didn't use a 'friction drive'. Your monitor is at 45 degrees and might bind with all the mass hanging off the back. Consider a rear bearing if at all possible.

i had forgotten about that. but you are getting me to think again ofr the first time in ages (",) . i had a thought and i reckon this is what id do if it needed to be a positive (as opposed to frictive) drive.

get a piece of bike chain and attach it so it goes around the circumference of the turn table. you only need a bit over 90 degrees. have a sprocket on the drive motor. and thats it!

[danny_galaga]

3. use a bike gear connected to a bike chain which is nailed to the outside of the circular plate.

I like your idea of using a bike chain as the driven gear and a bike sprocket as the pinion.
Just remember guys, the monitor only turns 90 degrees, so the chain or big gear does not have to go all the way around.

hehe. i guess i wasn't paying attention...

[Anubis_au]

I never wrote explicitly that you only need 90 degrees or so of chain on the circumference, but its obvious to all.

Seems this solution is gaining popularity... now we just need a tester...

The only problem I see with this solution over others, is that the bike chain adds to the circumference of the circular plate, which means your cab is even wider than it was with just a circular plate. the friction-based caster-roller solution, for example, avoids this.

Thinking out loud though, you could do a two-layer solution like Jimbo, with the second layer slightly smaller than the first, and the chain connected there, thus not adding extra to the circumference... that would mean one part of the plate would not have casters holding the plate up.... would that introduce instability to the plate mechanism?

[patrickl]

Wouldn't a bike chain give the monitor too much room to wobble?

[Ed_McCarron]

http://www.allelectronics.com/cgi-bin/item/DCM-287/400400/POWERFUL_RIGHT-ANGLE_DRIVE_DC_MOTOR_(USED)_.html

24vdc, 46RPM.

Cheap, slow-ish, and pretty strong for its size.  Nice large shaft.  Looks easy to mount.

[bluevolume]

http://www.allelectronics.com/cgi-bin/item/DCM-287/400400/POWERFUL_RIGHT-ANGLE_DRIVE_DC_MOTOR_(USED)_.html

24vdc, 46RPM.

Cheap, slow-ish, and pretty strong for its size.  Nice large shaft.  Looks easy to mount.

My question here is still how do you plan on powering that motor?  I don't see how you can get around having to buy another transformer.

[Jimbo]

Wow... what a great response! Thanks for your suggestions everyone, what an enlightening thread.

My cab's width is 28", and I can't really go wider than that else a) it won't fit through doors and b) it won't fit in the gap I have set aside for it. As already mentioned the bike chain idea is great, simply attached to a sprocket, but in my case it looks like I'd have to give up more space for the chain to fit round the monitor wheel... which, unfortunately, is space I can't afford in my build.

Cornchip's rope idea on the other hand is awesome and looks like it would work great in my situation.  I'm thinking a single motor (as sac01 suggested) mounted in one of the bottom corners would do the trick. I could probably use a bit of string and wind both ends round a drum in different directions (I'm thinking an empty cotton reel would be perfect) so one unwinds as the other winds as the motor turns. Man I love this idea!   I'm going to try and find a cheap car window motor, or failing that I'll get hold of a cheap electric drill and wrangle the motor out of that instead.

Thanks again for the ideas and suggestions, there's now light at the end of the tunnel.

[DaOld Man]

A car window motor is very powerful, thus it draws a LOT of current.
Not sure how much, but I used to have a Firebird that had the flip up headlights.
One of the motors failed, I bought a replacement and played around with it a bit before installing it in the 'bird.
Using a 10 amp battery charger for a power supply, it would peg out the amp meter on the charger.
If you could use a motor that wouldnt draw more than a 200 watt computer power supply you could use an old AT style power supply.
I think it has +12 and -12 volt that could be used to get 24 volts. (Its been awhile so I may be wrong on this.)
What about a windshield wiper motor? Seems like they would be less current demanding.
Looks like it's time to do a google search on motor current amps.
As someone mentioned earlier, you need to account for any high magnetism the motor may discharge, this is bad for crt's.
I really want to design one that turns automatically, based on the game you are playing.
Ive been experimenting with GLaunch. GLaunch can write a pre-command before running the game. I tried triggering a VB6 program that could turn on a printer pin, using it for an output to turn on the motor, but triggering the VB6 program screws up the vram file of the game. So that aint gonna fly.

[Ed_McCarron]

http://www.allelectronics.com/cgi-bin/item/DCM-287/400400/POWERFUL_RIGHT-ANGLE_DRIVE_DC_MOTOR_(USED)_.html

24vdc, 46RPM.

Cheap, slow-ish, and pretty strong for its size.  Nice large shaft.  Looks easy to mount.

My question here is still how do you plan on powering that motor?  I don't see how you can get around having to buy another transformer.

It'll run at 12v, with reduced speed and torque.  It'd probably still be enough to spin the monitor, considering the gear and friction-drive reductions.

[Kaytrim]

http://www.allelectronics.com/cgi-bin/item/DCM-287/400400/POWERFUL_RIGHT-ANGLE_DRIVE_DC_MOTOR_(USED)_.html

24vdc, 46RPM.

Cheap, slow-ish, and pretty strong for its size.  Nice large shaft.  Looks easy to mount.

My question here is still how do you plan on powering that motor?  I don't see how you can get around having to buy another transformer.

It'll run at 12v, with reduced speed and torque.  It'd probably still be enough to spin the monitor, considering the gear and friction-drive reductions.

According to the site it will work with a min of 14VDC so getting 12v off a PC PS won't work.

[Neverending Project]

What about using a couple of pistons from a tailgate or hatchback? The have a fixed travel, move slowly, and move heaps of weight. You could put one on each side (both pointing up so they are opposing in rotational motion) and make a simple mechanical release to unlatch them. When you want to rotate CCW, you would release the right one and it would rotate the monitor and compress the left one. Vice versa for CW rotation.

The only question is will the torque of one piston be enough to compress the other? Also, since they are so strong, you would need a relatively stiff frame so you don't risk crushing it. Maybe some metal L-brackets to reinforce?

[Ed_McCarron]

http://www.allelectronics.com/cgi-bin/item/DCM-287/400400/POWERFUL_RIGHT-ANGLE_DRIVE_DC_MOTOR_(USED)_.html

24vdc, 46RPM.

Cheap, slow-ish, and pretty strong for its size.  Nice large shaft.  Looks easy to mount.

My question here is still how do you plan on powering that motor?  I don't see how you can get around having to buy another transformer.

It'll run at 12v, with reduced speed and torque.  It'd probably still be enough to spin the monitor, considering the gear and friction-drive reductions.

According to the site it will work with a min of 14VDC so getting 12v off a PC PS won't work.

Whoops... Thats what happens when you assume.

OK, use the +12 and the -5 for 17v...  Kidding... The -5 is only good for a few ma...

So use a 24v ps.  Its not like they are all over ebay for $10...

[DaOld Man]

What about using a couple of pistons from a tailgate or hatchback? The have a fixed travel, move slowly, and move heaps of weight. You could put one on each side (both pointing up so they are opposing in rotational motion) and make a simple mechanical release to unlatch them. When you want to rotate CCW, you would release the right one and it would rotate the monitor and compress the left one. Vice versa for CW rotation.

The only question is will the torque of one piston be enough to compress the other? Also, since they are so strong, you would need a relatively stiff frame so you don't risk crushing it. Maybe some metal L-brackets to reinforce?

I think what you are describing is a perpetual motion machine. (Which is impossible due to physics.)
You will need a force applied to overcome the opposing cylinder.
Two cylinders acting against each other with no applied force in either direction will not work.

[DaOld Man]

What about using a couple of pistons from a tailgate or hatchback? The have a fixed travel, move slowly, and move heaps of weight. You could put one on each side (both pointing up so they are opposing in rotational motion) and make a simple mechanical release to unlatch them. When you want to rotate CCW, you would release the right one and it would rotate the monitor and compress the left one. Vice versa for CW rotation.

The only question is will the torque of one piston be enough to compress the other? Also, since they are so strong, you would need a relatively stiff frame so you don't risk crushing it. Maybe some metal L-brackets to reinforce?

I think what you are describing is a perpetual motion machine. (Which is impossible due to physics.)
You will need a force applied to overcome the opposing cylinder.
Two cylinders acting against each other with no applied force in either direction will not work.

But... you raise an interesting idea...
What about an air cylinder?
Pneumatics are used in several different applications. An air cylinder can move a lot of weight, it is quite, speed can be adjusted, and no magnetism.
Of course one would need an air compressor.

[Ed_McCarron]

The mechanics to get the linear motion of a cylinder to translate to rotary get tricky.  You can never make it that last few degrees without some wierd cam setup - the rotary shaft gets in the way of the cylinder shaft.

If you were to go pneumatic, you'd choose a rotary actuator - but things are getting way over complicated here.

[Neverending Project]

Hmm... my witty reply didn't seem to get posted. Probably a good thing, since I am sure it was more witty in my head than in the post.

Anyway, you are right. Converting the linear motion to rotational won't really be practical without putting the pistons in front of or behind the monitor. Which will either be very unsightly, or impossible. (Even if one ignores Newton's laws for a moment to assume that one piston could push another). 

Back to Professor Peabody...

[bfauska]

Linear motion to 90degrees of rotary motion is not difficult at all.  Start to creep up on 180 and you have some problems and the need for levers and the like.

I'm not necessarily advocating it, but it's not as hard as some would expect.  See the drawing below.

[Ed_McCarron]

Linear motion to 90degrees of rotary motion is not difficult at all.  Start to creep up on 180 and you have some problems and the need for levers and the like.

I'm not necessarily advocating it, but it's not as hard as some would expect.  See the drawing below.

I've done this, realworld, engineering high flow valves for robotic applications.  Use a small cylinder to turn a 90 degree ball valve.

They always tend to stick at one extreme or the other.  My throws are relatively small compared to your drawing.  On the order of 2-3 inches.

YMMV.

[DaOld Man]

Of course, you could also use the rack and pinion method. You could rotate the screen several turns, if you had the room for a long enough rack and cylinder.