I finally have a chance to combine two of my favorite pastimes, robotics and theater. I am technical director for a production of Blithe Spirit at a local community theater and I am hoping to create some awesome special effects using things I have learned through robotics.
My first challenge is to make a table thump and shake during the seance scenes. I plan on using a couple of motors with off center cams to make this effect work.
My question is how to remotely turn the motors on/off in a simple, reliable, and inexpensive way. I can run a wire to the table from the tech booth which will end up being about 100ft of wire. Can I run wire from a battery to the motor that far and still have them work? Or do I need to setup some sort of switch driven by AC current and have the battery closer to the motors? If so, is there a simple way to set up the switch? A third option would be to convert AC to DC to run the motor but I’m not sure how to do that simply and inexpensively.
Appreciate thoughts on the pros and cons of the options I have mentioned as well as other options I haven’t thought of. Remember my criteria; simple, reliable, and inexpensive.
Richard,
You might want to use a 120 volt AC something from this page…
You can mount them on the table legs pushing down and one or two under the table for noise. Connect to a couple of non-dim circuits to energize as needed. You will need to make up an umbilical that can be easily plugged in between scene changes. For the ones mounted under the table, you might even add a chunk of metal or something else that the solenoid can bang against for extra effect.
You could use a relay near the motor to control it and have the switch for the relay in your control booth. Relays are inexpensive, and you would only need 100ftX2 of thin-gauge wire. You could run the motor’s power wire 100ft, but there would be a large amount of voltage loss, even in thick-gauge wire.
There are numerous AC-to-DC converters available fairly inexpensively, a quick search reveals many sub-$30 options on google products. I assume your stage lights are powered with AC electricity, perhaps if you connected the AC-DC converter to something already linked to lighting control you’d be done.
Bear in mind that if you used a CIM motor you would have vibrations in the 90hz range, which might be fine. You’ll also need a good bit of eccentirc mass, relative to the table, to get it thrashing around and not just vibrating. The large side-loads could damage the motor.
Al’s suggestion of using solenoids will probably give you the controllability and appearance that you’re looking for. Again I would suggest controlling the solenoids with relays.
Is there any reason you couldn’t go wireless, a la a VEX transmitter. The stage hands will be happier (and safer) if the table can be self contained without a tether. I am not familiar with the latest generation of VEX components, but you can probably find somebody around here to fill that gap. :rolleyes:
Thanks for all the great suggestions, I think Al’s suggestion of the A/C Solenoid wins for easiest implementation.
Good thing is the table stays on the set for the entire play, so no need for attaching/detaching umbilical. Controlling it from a non-dim light circuit also helps since there is a circuit to a nearby plug on the floor.
Follow up question, on the McMaster page for the solenoids, they have this attribute: Force, oz @ 1/8" Stroke. Any thoughts on what that means? For example if the solenoid has a 40oz Force rating and a 1" stroke, does that mean I get 320oz of force (40oz x 8)? Or do I get 5oz of force (40oz / 8)?
Richard,
I believe the specification relates to the non-linear force as the moving part of the solenoid moves through the magnetic field. The maximum force occurs when the armature passes through the 1/8" part of the total stroke. In most cases where you are positioning a mechanism, you would not want the armature to make full travel. Instead position would be controlled by something external like an adjustable mechanical stop. You would then design the system to make use of the max force specification. I think in your case, this will not be an issue. Once the table begins to move, you don’t really care if the armature bottoms out or not. If it does, that just adds to the noise. You can turn the pull solenoid upside down and attach a bar. When it pulls in, it will move the bar against the floor thereby raising the table. If you put one in each leg, and adjust them to contact the floor at different lengths, the table will have an other worldly look when it raises. I think you only want the table to move a 1/4" or so. Just enough to shock the audience but not enough to tip the table over. If the table has a nice long tablecloth, then you don’t even need to hide/camouflage the solenoids.
“Bear in mind that if you used a CIM motor you would have vibrations in the 90hz range” James you will have to explain that one.
So far here are the planned effects. This is theater in the round, so the audience is up close making the effects extra special. I linked a photo of the arena below…
Bumping table using Al’s solenoid idea
Swinging chandler (turning motor moves the light back and forth)
Moving furniture (putting one piece of furniture on a practice robot that has holomic drive). It will either spin or drive around arena, not sure yet
A large clock with crazy spinning hands
Some piece of set dressing being knocked over using a solenoid
Fog machine inside of fireplace shooting smoke out
Light changes and sound effects
Curtains billowing into entryways at 3 and 9 o’clock
The free-speed of a CIM motor is about 5500RPM according to http://www.firstwiki.net/index.php/CIM_motor
which is about what the motor would spin at if an eccentric mass (it’s not really a cam) were mounted to it. Doing a little math shows…
Richard,
Are you going to be able to power stuff at the floor without having power cords in the way of audience moving in and out? Is all lighting power overhead? It looks like you still will have some challenges. We have used electronic flash parts in some of our productions in the past. I built one into a piece of driftwood for a production once, I think it was Hansel and Gretel. The witch used it for special effects. A fan, a light, some logs and some thin red gel can make a realistic looking fire that you can control from lighting as well. The fan blows the red gel around so it looks like flames while the light backlights the gel.
@Al
I have four plugs in the floor that I can run from the light board and I am going to have a large area rug in the center of the stage, so there will only be a little bit of power cables exposed on the floor. Planning to buy some flat power cables and paint them right into the floor design. It should hide pretty well and with plenty of gaffer tape to prevent it from being a tripping hazard.
@Mark
Falling books are an option if I have the time
There is another option too. Have you heard of X10 lighting products? It is a product line that transmits commands and status over house wiring using 100kHz carrier current. It gives the ability to control several (128) devices connected to the same power. A small command console can give ON/OFF control or for home, you can control with a computer interface to add security lighting. Thee are also wireless remote interfaces available.
Hi all, just wanted to post some of the pictures from the play. The play has been a big hit with the audiences, especially when the map cabinet chases Charles around the stage.
http://www.rsisk.com/table.jpg
The seance table. The top portion of the table moves up and down on two solenoids that can be activated independently from the light board. Nice effect, just a little noisy.
http://www.rsisk.com/img_0094.jpg
Close up of the solenoid that moves the table. Lot of insulation in the table to try and absorb some of the sound from the solenoid.
Once again, thanks to everyone on the thread for your thoughts and ideas. It certainly helped us produce a successful play.
I just got drafted to fill in for a missing stage manager and take down blocking one night next week, but there’s no call for innovative set/prop design like you did.
The biggest problem was overcoming the weight of the table which was too much for the solenoids. Resorting to moving just the very top solved that problem. The weight also prevented us from using a motor with an off-center weight making the table jump. A cam setup might have worked, but the solenoids gave us a lot of control, both when the movement happened and how much.
The robot in the map cabinet worked great. It’s cool to hear the audience reaction when the cabinet chases Charles around the stage ;>
