Reddit reviews Signstek Digital Professional Automatical Switchover Non Contact Laser Photoelectric Photo Type Tachometer
We found 3 Reddit comments about Signstek Digital Professional Automatical Switchover Non Contact Laser Photoelectric Photo Type Tachometer. Here are the top ones, ranked by their Reddit score.
Auto zero adjustment, stores last, minimum, and maximum readings, values can be displayed by turn anytime.Measures the rotational speed with a visible red light beam from a powerful LEDThe housing has been carefully shaped to fit comfortably in either hand.High intensity class II laser measures from 2.5 - 99,999 RPMExtra large 5-digit LCD display, high accuracy of +/- 0.05%. Not include batteries.
That should work, and might be better since the regulator will be closed loop on itself. (And if you look at the DC motor equations it's DC voltage that matters).
You still want to create a PWM map because.
In order of accuracy:
Your school should have access to the first two. I'd ask around. You can possibly make a torque meter with a kitchen scale and a bar mounted to the axle. This is where you show off what you've learned and apply your engineering degree.
When you create the map make sure you go both directions with the PWM because of hysteresis.
Start off with a PWM signal of 0, record the torque or speed.
Repeat increasing by 5 or 10, record the torque or speed.
When you hit 255 go back down to 0.
Given the non-linearities of the system you may find that the motor doesn't even turn the wheels until the PWM is at a 25 or 50 (out of 255) and that 225-255 is likely flat. If you build your map correctly you can demand a torque or RPM in your program and get the accurate PWM output.
Im assuming one of the handheld laser tacs isn't an option?
http://www.amazon.com/gp/aw/d/B00EUY6FNI/ref=s9_top_hm_awbw_b1402J_g263_i3?pf_rd_m=ATVPDKIKX0DER&pf_rd_s=mobile-hybrid-11&pf_rd_r=0W25H233HV9HTG1HXAF6&pf_rd_t=30901&pf_rd_p=ca65a094-1622-5623-ad4c-0a28d6c7472b&pf_rd_i=15729791
Here's a cheaper one.
If you've got a spinner with dark/matte/satin finish, you might need to tape a thin strip of aluminum foil (shiny side up) to one arm of the spinner to get a good reading.
But really, isn't any amount of money spent on something that you'll only use once and don't really need in the first place going to be too much money?