can someone explain to me how the variable speed control works

thanks, dave trimmer

all they to is reduce the power going to the motor at low throtle and increase it as you move the throttle up kind of like the volume control on the radio or tv

i notice that there are 3 cords on them, do they plug into the reciever or does a servo control it

one plug goes to the motor,one to the rx and one to the battery

thanks for your help, dave trimmer

On electric planes, the electronic speed control (ESC) takes the place of the throttle servo and plugs into the throttle channel of the reciever. There is also a pair of wires that connects to the motor battery and a pair of wires that goes to the motor if the motor is a brushed type of motor. Brushless motors need a brushless ESC and three wires go to the brushless motor.
Most esc's also feature a battery eliminator circuit that uses the motor battery to power the RX, eliminating the need for a separate RX battery. This is just a voltage regulator that reduces the motor battery voltage to 4.8 volts and sends it to the RX through the throttle channel output or whatever channel you choose to use to control the motor's speed.

You are aware that the battery that powers the reciever does not have to be plugged into the "battery" channel, it can power the reciever just as well plugged into any unused channel. That's why there is no separate reciever power lead out of the esc. It just powers the reciever through the throttle channel plug.

my last question, how do you determine which speed control to buy?

It has to big enough to handle the motor's full load amps and voltage. There is no harm in using a 40 amp ESC to power a 20 amp motor except for unnecessary weight. You must use a brushless ESC to power a brushless motor. Brushless motors can not be hooked directly to the battery. Brush type motors can be run directly from the battery through a switch if you want all or nothing control.
You can mix brands if you want. A Phoenix ESC will power an e-flite brushless motor just as well as an e-flite ESC.

The ESCs for brush type motors control motor speed by pulsing the power on an off very rapidly, one or two thousand times a second. That's why the motors make that high pitched squealing noise. The longer the on time verses the off time, the faster the motor goes.

Brushless ESCs do that also and in addition, convert the battery's direct current into 3-phase alternating current to run the brushless motor.

Thanks for that info BIF. Reading in this forum sure is educational for me-baylor