How Do I Spin the Dish on My Time Machine

What are you using as a powerplant, DC motor, AC motor or ICE? To spin the dish, you can use chain drive, belt drive or a gear box coupled to your powerplant. Also, do you want a fixed or variable angular velocity? If you're using a DC motor and you want a variable speed spin, then you can adjust it simply by varying the resistance. If you're using an AC motor and you want a variable speed spin, then you'll need a VSD to control the motor speed, and if you're using an ICE, you'll need a throttle mechanism to control the fuel flow rate. Likewise, if you're using a variable speed gearbox, you'll need a clutch mechanism to enable you to change the gears while running.

By the way, you can simply buy an actual functioning time machine, not just a working model like you're building from KrisDel^®. I'm not sure whether the have they famous HG Wells model though.

Yep. Try the KrisDel^® one. Don't infringe their copyright, though, or they'll send the heavy mob round....

Our unit uses a Squirrel cage motor.
But seriously, to spin a disc shouldn't take too much power, if the bearings are good, for safety I'd use a small DC motor, simplest answer is to try it and see.
Actually a manually (or pedally) operated mechanism would seem appropriate.
Del

Thanks Del the Cat. The bearings are very good and you are right. It does not take much to get the dish spinning.

Thanks DVader. The dish I'm looking to spin weighs around 50lbs. I tried to determine the required torque to get it going. I used the method of placing a weight a foot from the axis and came up with about 19 oz.in. The bearings I'm using are very good smooth bronze sleeve with a dry lubricant. Picture this: The motor will sit on the wooden base platform of the Time Machine, output shaft pointing up. A 5/8" steel shaft attached to the motor goes up about 3 feet and makes a right angle towards the back of the Machine via a 1:1 right angle gearbox. A shaft from the gearbox goes back about 1 foot and attaches to the dish. The rotation is controlled by a single lever which has a neutral position for no rotation. As you push the lever forward, the dish begins to rotate clockwise. I guess I need to use some sort of pot so the speed of the rotation increases as the lever is pushed forward. Top speed of the dish should be around 100 RPM. Pulling the lever back rotates the dish counter clockwise, again with varying speed. If you go to this YouTube page and click 6 mins. in to the video, you will see the original Machine with the dish rotating. [http://www.youtube.com/watch?v=AmFxri4KQnU&feature=related] I'm guessing what I need is a DC stepper motor (24 volts?) with about 50 oz.in. of torque connected to some kind of controller? and a power supply? (120v AC input and 24v DC output). It's important that the motor is pretty quiet. Do I need a slipper clutch in the drive chain? I'm thinking because of the inertia of the dish if the rotation deceleration is too quick, it would put undue stress on the motor, but maybe that's not true with stepper motors?? Is there some reason I would I be better off using an AC stepper? Or none of the above?

seeing our comments crossed and reading this I've had a better idea, a cordless drill. Is there anyway you can get a mechanical connection from your control lever using bowden cable (bicycle brake) to the trigger? A cordless drill has everything built in, variable speed etc. if you allow access to change batteries you can have spare batteries on charge or charged already and exchange them. The only thing you can't do is reverse the direction unless you couple the lever to the mechanical button on the drill.....

oh well, it's food for thought.

HUX, I like your cordless drill idea. But lets take it to a different level.

First: Take the drill apart, find the reverse switch. most are DPDT w/ center off switch with center contacts from switch and negitive of battery. the two out side contacts are crossed and then go to the motor. switch in first position motor spins clockwise, second position motor spins counter clockwise.

The lever is pushed forward trips the switch one direction causing the motor to spin CW. The lever pulled back trips the switch the other way after a pause in the neutral position to let the disk to stop spinning. The switch is flipped the other way causing the motor to run CCW.

Now to use the variable speed switch out of the drill, Take it and position it under the lever with a couple of rollers attached to the lever. So as the lever moves in the forward position the roller pushes the switch down further making the motor spin faster. Same thing in revers.

The only modes would use heaver gauge wire from the switch and trigger to the batter and motor.

I hope this helps you.

Charles

Thanks, Charles. I will not be using a drill motor but I'm going to apply your mechanical switching idea to a dc controller. Glad HUX brought up the drill idea. Great!

glad I could help.

Charles

Stepper motors are mainly used for precision control. You can use them, but they're not cheap. Unless you have a need to be able to stop the dish at precise points, it would be better to use ordinary motors. Anyway, your torque loading is very low, so you won't need a very large motor for this. Not being a mechanical engineer, I can't say for sure exactly what you'll need, but it will be a small one.

You would only need a clutch if you were using an ICE to generate motion and stop motion. In any electromagnetic motor whenever the torque generated by the motor is insufficient to move or stop an item no damage occurs as long as cooling still happens. (That was a verbose way to say, as long as the motor is not frozen you're fine.) Also, a stepping motor will just complicate things for no advantage.

having spent some time looking at the work you have put in, you don't want to make a hash job of it. At my last place there was a 1908 electric motor we used to spin up. It was pretty and ornate. It seems to me you should go for a dc motor for safety's sake and make some external cladding to make it look like a period piece. 12 Volts is a good figure to play with, and although not recommended for long runs due to the lack of ball bearings, a motorcycle starter motor with a friction drive may do the trick. As for power source you could try looking at an old laptop. Hack the guts to take the voltage out and you have the mains charger to connect when it gets a bit low, but it will work from a charge so there are no wires visible. A laptop is slim, has easily replaceable battery modules and power supplies in the event of loss or damage, and may fit underneath the seat quite well. Don't omit a fuse (Edison's overlooked invention).

For the speed control you want to use pulse width modulation, some other contributor can suggest where to go for a module which can do this, use a foot pedal with a variable resistor (precision rotary potentiometer on ebay) as an input so you can get the disc spinning from a seated postion. You can make this invisible with care.

Good luck, you seem to have spent a lot of time on this; is it true you can make time with a time machine?

If you drove it from the edge (hidden down at the bottom) instead of the centre, you could use an electric drill with a small pram (buggy?) wheel attached. Without close inspection the movement would appear to be "magic" (self induced or autonomous, you know what I mean).

Wow you do beautiful work. Can't wait to see the finished product. I have some friends that are going to go Ga Ga over this piece of art work when they get the link.

So what are you going to do with it after its finished?

OK, I'll bite. Just exactly why do you want to build a replica of an old movie prop? You do know that you can't actually time travel in it don't you?

It started out as a gift to his family then became a hobby. Don't you ever build things just for the fun and accomplishment? Are you telling us you have nothing around your home that is there "just because" you liked it or wanted it.

Actually we are all time travellers, but only one way and at the same pace.

actually none of us is traveling at the same rate because we all have a different velocity, strictly speaking. But hey, thats really splitting hairs, or maybe billionths of a nano-second. Anyways, there are thousands of ways to get your hands on cheap DC motors (definately go this way). Undersize the motor a little bit and add some heat sinks. This way the RPM will appear to be smooth (dc brush motors have a hard time running smoothly at low rpms). I doubt you'll be running this 24/7 so undersizing the motor shouldn't be a problem. a little 1/16 or 1/32 hp motor should work plenty fine. maybe even a 1/64... get yourself an RC car battery and various resistors from radio shack and hardwire the appropriate resistor into the circuit. Or you can install a pot for variability. Either way should be simple.

Thank you all for such a great response and excellent suggestions! I did consider a drill. Simply and ready to go, but too noisy. I also thought about powering the disk from the outside edge but I was also concerned about noise and changing the look of the Machine. It's not that I need the motor to be silent. In fact if it had the "right" sound it could be a plus. But I'm going to be adding my own audio to the Machine to mimic the original in the movie. It has become clear that a DC motor and not a stepper is the way to go. Based on your suggestions I have presued this, I looked at Bodine, Baldor, Bison and others. I have found a company that claims to have a very quiet, compact DC motor (Midwest Motion) which I will explore today. Thanks HUX, DVader, Del the cat, Redfred, Randell, scotchdrnkr, and Jason something. I will let you know how it works out.

I suggest you look at a windscreen wiper motor. They are intended to run for protracted periods, certainly hours, and are pre-geared down.

best of all, they can be got for peanuts from a scrap-yard

Chas

Interesting you should mention that, I used a wiper motor off of a junkyard Toyota, as an animation motor on a Bolex 16mm camera. Worked great. But the speed is a bit too slow for the dish. Thanks.

How about an overhead ceiling fan motor with a variable control. They can go in either direction and are very quiet.

I believe that a fan motor would not have enough torque to turn the dish. Thanks for the thought.

From "wiki" - "Fans use a capacitor start motor owing to the high torque required to start the fan after which the torque required lowers. it has single phase induction motor which need starting torque.for that purpose capacitor is used to make phase shift b/w running and starting winding." Just FYI. Nice work by-the-way!

Hi Tom, I have placed an order for a DC motor from Midwest Motion, but you got me curious. I'm going to look more closely at a fan motor.