Thread: Motor speed for vortex tunnell

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How do you guys figure the size of pulley needed to reduce the speed of a motor to get your vortex tunnell turning at a good speed?

I have a motor that runs at 1750 rpm.
I am using a 16" bike rim for my vortex to ride on.
My vortex ring is 9'5" in diameter...

What size pulley do I need to put on the motor to get my vortex to turn at a good speed? Probably anywhere from 5-10 rpm?

I have seen a few formulas but I just seem to be missing something.
Have any of you figured this or do you 'wing' it ?

Seems like its something about the rpm of the motor divided by the shaft pulley diameter. Then divide that by the bike rim diameter, divided by the vortex ring diameter? If thats the case... my vortex will just creep along! So, I know I am missing something.

Thanks for any help.. we may have to weld a pulley onto the motor shaft and I need to get this right the first time.

Lynn I don't think the size of the rings you are using factors into the motor speed and someone smarter than I am will have to help you get that motor down to the RPMs you want. I know you did your research on this project but everything I read said to keep the RPM at 6 or below.

I did find this RPM Calculator and according to the numbers you would need a .09 of an inch pulley on the motor to get the RPM down to 9.8 rpm if you are driving a 16 inch pulley/rim

That would be about the size of a piece of thread...using a 2 inch pulley would reduce the speed to 218 rpm. I know you can reduce that speed by using multiple size pulleys but someone else will have to tell you how.

Have you tried a wiper motor to see if it has enough torque to turn the tunnel? The monsterguts wiper motor turns at 52 rpm on high.....using a 2 inch drive pulley to turn the 16 inch rim would reduce that speed to 6 rpms

http://www.temecularodrun.com/ref/rpm_calc.asp

Thanks Max....
Finally got our vortex going! I actually got the pulley size right the first time! It runs at about 9 rpm which seem great to me.
I keep promising this but I will get pictures! We have the haunt done now and ready for our first night next friday.... so I actually have TIME to get pictures.

Another note on our vortex.... after much deliberation and worry... my son offered us 2 steel ibeams for our bridge! Its sweet and I owe him sooooooo much.
One other thing, now that we have all the fabric on the rings, there is one place that it kind of binds up, or slows down. I think we got the fabric so tight on the rings in an area that the ring binds up in one of the bike rims. I am hoping that with time the fabric will stretch a little and this will go away! So this is an issue that I don't think I have seen any mention of before so take note if you build one!