77 inches * 132 revolutions * 1 revolution = 1694 rpm's
revolution minute 6 inches
I definitely need to increase the rpm's. Maybe I could add another pulley. Maybe I should trade out the bike for a tandem so that two people can work together.
Today I worked on figuring the rpm's of the alternator pulley. I estimate that the rear wheel of the bicycle is making 132 revolutions per minute. The circumference of the wheel is 77 inches and the circumference of the alternator pulley is 6 inches. Calculating the rpm's of the alternator pulley:
77 inches * 132 revolutions * 1 revolution = 1694 rpm's revolution minute 6 inches I definitely need to increase the rpm's. Maybe I could add another pulley. Maybe I should trade out the bike for a tandem so that two people can work together.
3 Comments
Richard Ake
9/8/2014 03:06:58 am
Concerning your estimate on the RPM of the rear wheel...132 revolutions per minute of the rear wheel seems quite low. The speed at which the pedals are turned is called "cadence". The ideal cadence varies from person to person, but 90 RPM is a good rule of thumb. My road bike has 39 teeth and 53 teeth on the "chain ring" which are the sprockets at the pedals, and 12 to 25 teeth on the "cassette" which are the sprockets at the wheel. 90 (rpm cadence) x 53 (teeth/revolution) / 12 (teeth/revolution)= 397.5 revolutions per minute of the rear wheel in my highest gear (down hill with tailwind). To double check this math, the circumference of my rear wheel is approximately 2112 mm which is about 83". This makes the RPM of my rear wheel 254 (RPM) at 20 miles per hour... ( (20 {MPH} / (83 {inches} / 12 {inches per foot} /5280 {feet per mile} ) ) / 60 {minutes per hour}.
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Richard Ake
9/8/2014 03:08:42 am
I think this is a great project ! I hope you are not offended by my input.
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John
9/25/2014 01:29:56 am
Yeah I agree that adding another pulley is not going to help you. You already have all the gears you need on the bike itself. Unless you are in the highest gear (and you definitely aren't based on the speed you report of your rear wheel) you have more gears to make the alternator go faster but aren't using them because it's too hard to pedal. Adding another pulley will only change the gearing you need on the bike but won't change the ease-of-pedaling vs. difficulty you are already experiencing.
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