# HELP: How to determine the speed of a small motor

• posted

I need help to determine the speed relation between a small 12Vdc capstan motor that turns at double speed i.e 3.75ips and another small motor that turns a 1600/3200Rpm I need to know if the the one that turns at 1600/3200Rpm is equivalent to 3.75ips......or a formula would be nice?

Thank you

• posted

Hi Eddy,

What is the diameter of the capstan? Is the capstan motor direct or belt drive? If belt drive what is the drive ratio? Does the capstan motor have feedback? Is its speed regulated?

You didn't say what this is for but I'll guess. "3.75 ips", "double speed"?? Compact cassette?

Reel to reel tapes run 30, 15, 7.5 3.75 and 1.875 ips.

8-track 3.75 ips Compact cassette 1.875 ips Mini and Micro cassette .9375 ips.

".small motor that turns at 1600/3200 rpm"? Multiple windings or different voltages? No load speed? Motor speed will vary with the load.

If the motor you have runs too fast you could try reducing the voltage with an adjustable voltage regulator or resisters to reduce the speed.

Jay

• posted

Jay, the shaft of the capstan motor is 2mm and is belt driven I don't know the ratio of the pulley from the capstan shaft to the drum. Feedback? I'm not sure.. but it looks like its speed regulated.(8.4-15.6V) This is for a double speed compact cassette & turns at double speed i.e 3.75ips The following specs are for the replacement motor... Rated voltage=12Vdc Operating Voltage=8.4-15.6Vdc Rated Load(g.cm)=10 Rated speed(rpm)=1600/3200rpm Ratedload current(mA)=83/89mA Load fluctuation(rpm/g.cm)=5.0/7.0 Starting torque(g.cm)=50 drift%=0.6/0.3

the motor model is Mabuchi EG-530KD-2B(2F)

let me know if all this helps Thanks

• posted

Hi Eddy,

It looks like your replacement motor is a good fit. All the numbers you've provided seem to agree. If your tape drives not working you have nothing to loose.

Good luck.

Jay

• posted

Hi Jay, I couldn't find calipers but I took a quick measurement of the pulley and the capstan drum(flywheel)with a tape measure and the calculations don't seem to jive. The pulley on the shaft is ~1cm and the flywheel ~4cm so the diameter would be ~1/4=0.25..I must be calculating wrong since I don't come close to the same RPM rating..could you verify if the numbers are ok? thanks again

-Ed

• posted

Hi Eddy,

Based on the numbers you gave me here's what I get.

2 Capstan diameter in mm 6.28 Capstan circumference in mm 0.247244094 Capstan circumference in inches

3.75 Capstan speed in ips

15.16719745 Capstan RPS for 3.75ips

4/1 Motor Pulley / Capstan Pulley ratio

60.66878981 Motor RPS for 3.75ips

3640.127389 Motor RPM for 3.75ips

1820.063694 Motor RPM for 1.875ips

Jay

• posted

Thats just wonderful!! Thanks Jay, have a great one...

PolyTech Forum website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.