Hi,
Motors vary quite a bit actually, made for dc or ac.
For example, there are at least two types of AC motor: those with brushes
and those without brushes. The important thing here is that those with
brushes can be controlled using a triac while those without brushes can not.
A DC motor can be controlled using PWM.
Another option, as a last resort, is to try pulsing the motor at a very very
low rate...like once every second...so that the object (bed) appears to move
more slowly.
If you do end up with a brush type motor that runs on AC then you might
get away with the triac control by reducing the firing angle (same principle
that lamp dimmers work on). This also reduces the torque so speed/torgue
will still be a tradeoff.
The best way is to gear it down somehow, but i guess that isnt an option here.
I know it is sure harder to do this because all the parts have to fit just right.
Just curious, did you try connecting a large light bulb in series with the motor
(assuming the one you have now is AC)? If the size is right you will reduce the
motor voltage and the starting torque may still be high because of the nonlinearity
of the bulb. Since it doesnt have to run long this should not bother the motor
too much either. If you can not get say a 100watt light bulb to work with it
then try 2 100 watt light bulbs in parallel, then 3, then 4, etc. Just might work
if everything else seems too expensive. The more light bulbs in parallel the faster
the motor turns.