Need to know more about what you're really measuring.

> What we are looking to do is make a d.c. motor test machine. It needs to
> do just a few things.
>
> 1. Test the rpm. No less than 10,500 RPM

I take it this is a pre-install test of a small DC wound field motor,
since you mention 6.2 amps.
Starrett or any number of other machine shop suppliers will sell you off the she
lf
mechanical tachometers.

> 2. Test the Amperes being drawn at that speed No More than 6.2 Amps.
fine - put a Simpson ammeter in the input line.

> 3. Torque it can handle.
I take it you want stall torque - go to the auto parts store and buy
a torque wrench and whatever collars and clamps you need to mount
it on the shaft. mount motor firmly on bench, and clamp torque wrench
in place. Think safety. Turn on motor and read off stall torque on wrench.

> 4. Horse Power of motor. no more than 1/8 H.P.
??????  This totally depends on the load. The horsepower
of a freely spinning motor is zero, as is the hp of a stalled motor.

No electronic devices needed here unless you're testing many, many of these,
in which case you have a robotics problem.

--
Anniepoo
Need loco motors?
http://www.idiom.com/~anniepoo/depot/motors.html