So I wanted to find out the maximum amount of amps that some motors I hacked out of a toy robot would consume. They are likely 9v motors, because the power output by a half dozen D-cells that the toy came with was 9v, and there was no circuitry in the entire thing to drop voltage. Basically just a couple of switches on a controller-thing to go forward or backward. Anyway, I hooked up 9v directly to the motor, and went to put my meter on it to measure the amps, and was going to have my wife stop the motor for me so I could measure the highest possible current draw, but once I metered it, it bogged the motor down entirely and read between 3 and 4 amps. :o Is that supposed to happen? I'm sure I know how to use my meter correctly, but maybe not... Any suggestions? I'm gonna try a different meter here real soon at work, but if that don't work then I'll be really confused. Any help appreciated. Thanks guys.
I'm sure I know how to use my meter correctly, but maybe not... Any suggestions?
Sure, describe the type of meter you used, the settings you used on the meter, and how you wired it into the circuit.
Know what? I figured out my problem. I need to set my meter right inline with the circuit. I've not measured amps in so long I forget that it's different. I set it on the '10A' setting, plugged my read lead into the 'amps' socket, but then measured across the motor while it was already running. It's a cheap-o $5 "CEN-TECH" digital multimeter. But it's served me well for the last year and a half. Course, all I use it for is checking the occasional voltage. And don't need super-precision.
I have a bunch of "CEN-TECH" harbor freight multimeters and they do 95% of what I usually need a meter for.
Know what? I figured out my problem. I need to set my meter right inline with the circuit. I've not measured amps in so long I forget that it's different. I set it on the '10A' setting, plugged my read lead into the 'amps' socket, but then measured across the motor while it was already running. It's a cheap-o $5 "CEN-TECH" digital multimeter. But it's served me well for the last year and a half. Course, all I use it for is checking the occasional voltage. And don't need super-precision.
I'm surprised you didn't burn that cheapo meter out - I love centech meters myself, too - I have a few of them kicking around.
BTW - what did the current reading come out to (and what toy did you get the motor from)?
current is one of those things I hate to measure with a meter
so do I set it to 200ma and it shows 140 ma, or do I set it to 10a and it shows 1.4 amps
blah! the main reason to have an auto range meter (otherwise they are frivolous)
so as in the case of my last trek, making a power supply for a model of digital piano cd rom - synth(that was not designed in house for software compatibility,... to what I don't know cause the library is humorous) I set the meter up to measure 200ma, and popped the fuse
super now I know its 1.4 amps and I have to find a PITA sized fuse from digikey and squander away another 5 bucks off my short budget
Oh yea. It was pulling 1.5 amps when I stopped it. It came out of a giant robot thing that my in-laws bought for me because they know I like robotics. It rolled around on treads and had arms that moved up and down and grabbed stuff. Controlled via wired remote. But the gears kept stripping on them poor things so you couldn't hardly pick up more than a dirty sock, and even then you had to prop it up just so. Needless to say it wasn't any good for helping clean up around the house. 
I'm going to use the treads as a base for my first homemade robot. Maybe later I'll put a turret of some kind on it. For now I'm going to just control it with a wii nunchuck so I can have fun with the accelerometer. Pretty excited. Then gotta find a way to do something with sensors and automate it.
so do I set it to 200ma and it shows 140 ma, or do I set it to 10a and it shows 1.4 amps
I always start with the 10a setting and work my way down as needed.
you can wire a 1 ohm resistor of suitable wattage inline with the motor and measure the voltage drop across it, 1mv = 1ma, 500mv = 500ma, this is useful if you dont have and amp meter, or for microcontroller measurements (up to vcc 5v), more than 5v you need a resistor network to divide the input /2 /4 etc..