Building a scale dynomometer.

[Nixholas]

Hi all!  I'm new!  I've done literally NO circuit design ever.  I have done solder repairs, even some basic SMD stuff, but rarely know what the components around the ones i'm replacing are for (I'd like to learn ).  I do have a cursory understanding of what resistors, capacitors, inductors, diodes and transistors do.

Onto my question:  I am interested in building a inertial dynamometer to measure the output of 1:27 scale RC cars (Kyosho Mini-Z).  The mechanical plan is a 25-50mm diameter steel roller for the driven wheels to spin up.  The mass of the roller will act as an inertial load for the test.

Electronically I plan to use a laser diode to pump(?) an LED to measure the speed of the roller.  I need to measure not just frequency, but the change in frequency during a 10-20 second run (thinking it'd be nice to be able record all the 'pulses')  I'd like to find the least costly method (starting from nothing) of gathering the data from the 'sensor'.

Thanks in advance!

[mikerj]

Have a look at the SimpleDyno software, which requires the absolute minimum of hardware by using the microphone input on your PC's sound card.

There is really no need to use a laser diode for optical sensing, a regular infrared opto-interrupter (aka photo interrupter) costs pennies and will do the job perfectly, just add a slotted wheel to the end of your roller.   Magnetic sensing tends to be more reliable however, particularly in dusty/dirty environments.

[Nixholas]

Thats a very cool project!  Sounds perfect!  The reason I thought about laser is I already have an LED, and i can get a laser pointer for $1 locally...  The way they show using a headphone and magnet for sensing is even easier though!

[grifftech]

this: https://www.amazon.com/DIGITEN-Digital-Tachometer-Proximity-Switch/dp/B00VKAT8A2/ref=sr_1_14?crid=2ZB01HTL95Z28&keywords=tachometer&qid=1573831873&sprefix=tach%2Caps%2C176&sr=8-14 (19 USD)