Suggest an electric motor for a clock art project.

[Deeg]

I'm building an art clock. I want to have an electric motor drive some steampunk-type gears that will eventually turn an hour hand (no minute/second hands). The gears will mostly be scrounged from some old clocks and will chosen for their coolness factor so the motor speed will have to be adjusted accordingly. Currently I'm planning a motor speed of 600-1000 RPM but I'm flexible.

I can go to Digikey or similar and buy a motor but I'm not sure what would best suit my needs. I'd like a motor that was:

1) Easily adjustable so that I can make the clock relatively accurate. I can probably handle adding a motor driver if necessary.
2) Rock-steady RPM and reliable. I plan on running it 24/7.
3) Low voltage. The clock will be hanging on the wall so I want as thin a cord/wire as possible. Something like 30 gauge magnet wire (paired) would be ideal but I can use other wire if necessary.
4) Quiet.

Do you guys have suggestions on what/where I should look? Since it will be geared down so low I assume that I don't need much torque; just enough to overcome the friction of the gears. Is there anything else I should be considering?

Thanks!

 

[MikeMl]

To get timing accuracy, you will have to use an AC synchronous motor (like used in AC powered wall clocks or wall-clock timers), or a stepping motor. Unless you are willing to add an independent means of measuring motor RPM (opto-interrupter?) and a serious PID speed-controller, a DC Motor will never have the stability you will need.

 

[Boncuk]

Visit a junk yard and salvage the timing motor of an old laundry washer.

They normally have synchronous AC motors with some gear to program the duration of different wash cycles.

Boncuk

 

[picbits]

As above - either a synchronous motor or a stepper motor. If you use a 1.8 degree stepper, you get exactly 200 steps per revolution.

Alternatively if your electronics is good, you can put a sensor on one of the gear wheels and just use a normal motor. Count the pulses from the sensor and activate the motor for the required time to turn the gear "x" number of revolutions. Do this at exact intervals (maybe with a PIC microcontroller) and you're sorted.

 

[Deeg]

Thanks for the suggestions; I didn't realize I would need something like a stepper motor. I have a couple of follow up questions:

1) Since my motor will be spinning at a continual, constant rate does it matter how many degrees the stepper motor has?
2) How can I determine the max RPM of a motor? For example these catalog pages don't mention the RPM. Is there some way to calculate it?

 

[picbits]

You might get more visual effect if you run the motor as a start/stop device - objects that are still but suddenly start moving tend to catch the eye.

The max RPM of a stepper motor isn't much - it depends how you drive it though. I wouldn't bargain on getting much more than 1000 rpm out of one though.

 

[Mr RB]

Here's a "steampunk" suggestion.

Why not use a DC motor setup so it runs about 20% to 50% fast, then put a little cam on one of the steampunk gears with a little switch.

The cam is configured so once it starts to turn it runs one revolution (switch closed) and stops when the cam has a detent so the switch turns off. Then (the clever bit) you use any $5 clock module that makes a 1 second clock pulse... And use it to initiate the mechanical cycle.

The result is that the gear can have a big silly steampunk DC motor, and be synchronised to *exactly* one second per revolution to make an accurate clock.

 

[Boncuk]

Here is another "steampunk" suggestion.

Church clocks are widely used and synchronized with a nuclear master clock - hence they keep time very accurately.

Connect a micro switch to the church clock and have a solenoid advance a shark fin tooth wheel every minute.

Boncuk

 

[Boncuk]

As above - either a synchronous motor or a stepper motor. If you use a 1.8 degree stepper, you get exactly 200 steps per revolution.

Congratulations for that splendid idea!

How would you reduce the steps to indicate seconds, minutes and hours?

The division factor would be somewhere close to 1/33.33333333~

Boncuk

 

[wombweller]

I'm building an art clock. I want to have an electric motor drive some steampunk-type gears that will eventually turn an hour hand (no minute/second hands). The gears will mostly be scrounged from some old clocks and will chosen for their coolness factor so the motor speed will have to be adjusted accordingly. Currently I'm planning a motor speed of 600-1000 RPM but I'm flexible.

I can go to Digikey or similar and buy a motor but I'm not sure what would best suit my needs. I'd like a motor that was:

1) Easily adjustable so that I can make the clock relatively accurate. I can probably handle adding a motor driver if necessary.
2) Rock-steady RPM and reliable. I plan on running it 24/7.
3) Low voltage. The clock will be hanging on the wall so I want as thin a cord/wire as possible. Something like 30 gauge magnet wire (paired) would be ideal but I can use other wire if necessary.
4) Quiet.

Do you guys have suggestions on what/where I should look? Since it will be geared down so low I assume that I don't need much torque; just enough to overcome the friction of the gears. Is there anything else I should be considering?

Thanks!

Hi There
I am very interested in clocks and the thought of a Steampunk clock gets me going.

As you intend using clock parts and a motor then you need to understand how the gears work especially if your thinking of replacing some with a motor-
**broken link removed**


If it were me doing this I would find a Striking or even a chiming clock like a Westminster chime (quite cheap these days).You could remove the springs and replace with a constant force motors (seek advice on the best type of motors for this) then the rest of the wheels on the time side can stay as is even with a pendulum.

Where you can start and have fun is on the strike and or chime side of the clock.One thing that looks really spectacular is the Fly governor, this is located usually at the top end of the wheels and assists the strike/chime train to slow down after it has finished.If you removed the strike/chime linkages ie. to the gongs or bells and add lots of fly's anywhere on the two trains, you could go to town on that!! Anyway the results is that on the quarters and on the hours you get a flurry of little butterfly like fly's spinning, People will be amazed. The downside is it will take some doing on your part.
For an exaple on how Fly's on clocks can be used to spectacular effect please see this-
YouTube - Astro-skeleton, Dec. 09 (1).avi

To get the odd speed effect on the chime/strike train you could use faster motors that are stopped and started with a micro switch although by adding flys to odd wheels you will get flys that spin a differant speeds.

Just a thought

 

[wombweller]

To get the constant force wind motor connected you could 'with a lot of care' take out the springs in the barrel then cut the case down on the barrel so your just left with the toothed wheel.From this you could either add a sprocket to the barrel arbour and a chain to the motor or fix the now butchered main drive wheel to the motor.What ever way you find it would take some work.

 

[Mr RB]

Boncuk-

(re; stepper motor as a clock) How would you reduce the steps to indicate seconds, minutes and hours?

The division factor would be somewhere close to 1/33.33333333~

I recently did one here;
Linistepper 6-hour clock

Turning a stepper motor at exactly 6hours per rotation (synchronised to the mains). I used a linistepper which gives 3600 microsteps /rev so it's perfect for clocks.

If you use another stepper driver that does not divide a revolution evenly by 60, then you can use one of the bresenham systems on this page to produce extremely accurate low frequency output from any xtal;
Zero-error 1 second timing algorithm

As an example if you wanted a 6 hour rotation and your stepper does 400 steps per revolution;
6 hours = 400 steps, using 1 MHz xtal
therefore 1 step = 1000000 * 6 hours / 400
= 1000000 * 3600*6 / 400
= 54000000 TMR0 ticks for each stepper motor step

        // C code for PIC 1Mhz (4MHx xtal)
	// uses 1 variable; unsigned long bres
	// gets here every TMR0 int (every 256 ticks)

	bres += 256;		// add 256 ticks to bresenham total

	if(bres >= 54000000)	// if reached 1 stepper motor step
	{
		bres -= 54000000;	// subtract 1 step, retain error
		make a step();	      // move the stepper motor
	}