id like to work out the best timing for my motor.
i have a good multi meter but i need some way of measuring the actual RPM of the motor...whats the best way to do this that doesnt cost more than the motor?
any cheap rpm monitors that hook into the sensor cable etc?

In fact, there are, like this one from G-Force: https://www.amainhobbies.com/gforce-...fc0107/p495878 , or from some copycat companies like this one: http://www.rcjuice.com/root-catalog/...r-checker.html . I have the G-Force one, & I find it very useful(especially in making accurate timing adjustments)....

I'm developing motor measurement tool that can measure RPM amp volt watt KV.
and it can use with boost ESC so I can know my motor values while boost active.
YouTube >> https://www.youtube.com/watch?v=ja09AWx2GwY

+ YouTube Video

and this is function "once measure for all values" in testing.
YouTube >> https://www.youtube.com/watch?v=j6XUHYqAveM

+ YouTube Video

with this tool I can know both "motor timing result" and "ESC profile result"
for details ... http://9turbo.com/motorpro/

You can get a photo-tachometer for about $10 on the evil auction site:
http://www.ebay.com/itm/Digital-Tach...Whc&rmvSB=true

To use with a brushless motor, get a green or yellow LED, wire it in series with a current limit resistor (470 ohms to 1K ohms is fine), and connect this to any two stator terminals on the motor. Face the LED into the tach, and off you go!

Here's one that I made a while back. I put the LED and resistor inside, held against the tach's photoresistor with some shrink tubing and electrical tape, and brought out the wires to a pair of alligator clips for ease of use:

I bet there are apps that measure rpm using your phone's mic.
Some pointers:
http://www.ymec.com/hp/signal2/motor1.htm
https://www.rcgroups.com/forums/show...and-microphone

how do you find it works? fairly accurate? i like this idea as i dont want to spend $100 to measure a $40 motor

The tach shown is quite accurate, since it is crystal-controlled. If I recall correctly, the resolution is 30 RPM. The RPM reading is much more stable than my GForce motor analyzer; it really bounces around!

The tach in the link (which I also own) specifies the accuracy at ±(0.05 % + 1 digit) with 1 RPM resolution.

motor RPM measure is very easy for Sanwa / Airtronics user. it have telemetry feature.
in fact Sanwa have infrared RPM sensor available for use with its RX461 RX462 already. but it range is very close about 1-3mm

in this clip I testing my infrared RPM sensor that increase detect range to 10-30mm
(using Sanwa MT4 - RX461)
YouTube >> https://www.youtube.com/watch?v=fkV5SUt5MVI

+ YouTube Video

see details about my infrared RPM sensor http://mt4el.com/mt4-sensor/index.html