Unless the design has changed radically over the last couple of decades, I think they’re just simple permanent-magnet brushed DC motors. These have an absolute upper RPM limit at which the rotor’s back-EMF matches the battery voltage, resulting in zero rotor torque; any drag (e.g. bearing friction or impeller load) results in a lower speed than that. So without any impeller load, you’d be somewhat closer to the motor’s max speed, but it wouldn’t run away on you.
I think the whole design thinking must be changed for vacuum. Take for example :
- The brushes of a motor - spark and you lose a little bit of copper each time. Now think about the sparks in vacuum - they will be huge and a lot more copper will vaporize (vaporization is a function of partial pressure)
- Cheap motors like these use PVC enamel on the coil windings. And plastics like PVC have outgassing and other problems and the windings may have shorted even before the motor starts. For that case, even the body of the Dustbuster would have problems with the plastic make and so will the numerous parts.
Hmm - do you get sparking in a vacuum?
I would be more worried about worn brush material building up between commutators, causing shorts.
Now, if you had one of those Starfleet dustbusters, you’d have more options…
It depends on the level of vacuum. Given a fixed gap, less and less voltage is require to get a spark with increasing vacuum; until you reach a point. Then the behavior reversed and you neee more and more voltage.
See here : Paschen's law - Wikipedia
Ok, so what happens when you release the dustbuster instead of turning it off?
You’d see the outside housing of the dusbuster start to spin, in the exact opposite proportion that the internal motor is spinning. Conservation of angular momentum. If we define the angular momentum of the whole system before we push the button as zero, the angular momentum of the whole system always sums up to zero. If one part starts to spin clockwise, something else has to spin counterclockwise.
The reason we don’t see this so clearly sitting here on planet Earth is that very often the angular momentum is transferred to the ground, or to the air, and so we naively think it just vanishes. It doesn’t vanish, it’s just hard to see. When you’re floating in a vacuum in zero gravity it’s a lot harder to lose track of which force transfers where.
I suppose the next question is what happens when you break open the dustbuster and take off every external part and just have the motor? Could the motor then spin clockwise? No. Unless something is spinning counterclockwise in an exact equal proportion, the motor can’t spin clockwise. That “something” could be the little shaft that used to connect to the fan. But without something that the motor can spin against, the motor can’t spin. If you take away everything and just have a bunch of copper wires with some attached batteries, it just sits there. That’s assuming you’ve got it rigged so it doesn’t spin the batteries. What you could never have is a motor that just sits there and spins clockwise with nothing spinning counterclockwise.
I figured that the dustbuster would start spinning around itself. But just before you let go of it you were also spinning as part of the system, and now what? Are you still spinning? Or is the reaction of letting go, no matter how careful you are to release the dustbuster cleanly, enough to stop you?
No, you’d continue to spin. Letting go of the dustbuster just stops spinning you faster, it doesn’t stop your spin.
With the human body as floppy as it is, there are various contortions that might make hard to clearly see that angular momentum is conserved, so before you do this experiment I suggest locking tight all the joints on your space suit to make things easier to understand.
I’ve seen multiple SF stories that have someone floating in empty space with a spin on their body, who go through various maneuvers of waving their arms and legs until they stop spinning. It bugs me every time I see it.
It’s a good time to be taken over by a demon. Exorcist girl could arrange for either her head or her body to stop spinning, as required. Then eject green vomit as reaction mass.
Re: Letting so while spinning.
Consider the situation of you and your twin connected by a rope and spinning in space around each other like bolo balls.
You let go of the rope, what happens?
You go flying off in a straight line and your twin goes flying off in a straight line in the opposite direction.
But … you were also rotating around your center of mass once per revolution. That doesn’t stop so you continue to spin as you fly off.
Same thing with the dust buster but it’s a lot more complicated. It depends on how you were holding it and the big difference in mass makes the effects less noticeable. So you and the dustbuster can move off in opposite directions (you very slowly if at all) and you continue to spin a bit (also very slowly). Again, it depends a lot on how you were holding it when you turned it on and when you let go. E.g., holding it so that the motor’s axis is parallel or perpendicular to your center of mass when you start it. In the parallel case after letting go you are all spin and no drift off.
IIRC early planes had propellers that turned in opposite directions to prevent torque on the aircraft.
Some did, maybe, but others actually had an entire engine that rotated. I’m not sure why that design would have been favored, but the effect was a very large angular momentum, and extreme gyroscopic effects whenever you turned.
If you could successfully address points 1-4, the motor would be spinning with hardly any load (no air resistance on the fan). Would that cause it to burn out?
Wikipedia has a list of aircraft with counter-rotating propellers. There are also some aircraft with contra-rotating propellers (both propellers mounted on the same axis).
The CH-47 Chinook helicopter has two counter-rotating rotors so that a tail rotor is not needed to offset the angular momentum of the rotor. Most quadcopter drones have two rotors spinning clockwise and two counterclockwise for the same reason.
No air to conduct heat away.
Yes, people say ‘space is cold’ but vacuum is actually an insulator, like an old-school thermos. Most devices made to use on Earth expect that the atmosphere will let them get rid of excess heat, in space they basically just keep getting hotter until they fail. (You can lose a bit of heat through radiation, but it’s not going to be significant.
What about the battery powered tools used on the moon and outside the space station?
Those aren’t devices made to use on Earth. The designers knew they’d be used in vacuum, and so designed in other ways for them to deal with heat.
But how?
I do recall an astronaut losing his grip on the space station and rotating with his battery powered wrench.