I purchased a Nerf Vulcan some time ago and was disappointed in the rate of fire. From the factory it chugged out a bit more than one round per second, or about 20 seconds to run through a 25 round clip. The battery pack is 6 D cell batteries for a total of 9 volts. I figured the motor should be able to handle more voltage, so I grabbed a couple VEX 9.6V batteries and wired them up. Everything went great until I reached 4 batteries, 38 Volts. The rate of fire was impressive as this video shows. It emptied the clip in about 3 seconds, twice. You can see how well the motor handled it below. The brushes came unglued, snagged the windings on the rotor, and made a general mess.
The motor itself is a standard size and shape toy motor with no markings. Just over an inch in diameter, and 1 1/4 inch long. Unfortunately in this state I had no way of determining any of its characteristics. I tried guessing the RPM by assembling part of the old motor in place and spinning the rotor with a pair of vice grips. That got old and the gear kept slipping, so I resorted in trial and error.
The first batch of motors came from The Electronic Goldmine, but unfortunately while they fit fine, they did not have the power or speed I needed. The best motor in that batch fired the gun at near the stock rate with 2x the stock voltage.
Second try was a success. I ordered a handful of motors from American Science and Surplus. The fastest of the motors runs at 13.5k RPM (at 12V) and will fire the gun at 4 rounds/sec at 27V. A 60 second test firing indicates the motor and the gun can handle this rate. The motor didn't heat up or smell funny after the test.
If you are looking for the motor, it is a Molon hobby motor rated at 6-12 VDC, at 280ma for 13.5k RPM. AS&S has it here: Hobby Motors
The only problem so far is that the motor is about 1/8 inch too long to fit comfortably in the gun. I'll need to use some longer screws to secure the orange top to the plastic standoffs, and Dremel out a little of the plastic to make it fit. I'll post more pictures and video when I get it put back together and shooting.
This motor should be a close replacement, although probably a little too big around.