| Gallery, Projects and General > How do I?? |
| Formulae for Cycle Computer to Read Metres per Minute |
| (1/2) > >> |
| velocette:
Hi to all "Mad Modders" I have been restoring a vertical bandsaw and have added a worm drive gearbox to the drive system for metal cutting. Planning on adding a variable speed DC motor to be able to cut at between 20 metres a minute to 70 metres a minute. what is the formulae to find the circumference to program into a "Cycle Computer" to be able to display Metres Min as Km Hr I. E. 30 Km hr or 3 decimal 0 Eric |
| andyf:
Hi Eric, I've done a few sums, and I don't think a bike speedo would work in this application. If the wheels around which the saw blade runs are 200mm diameter, you would need to program the cycle computer to think its actuating magnet was mounted on a bike wheel of an improbable 3.333 metres diameter. That is probably well over the permissible range of inputs. Dividing by 10 (so a reading of 6.7 kph represents a blade speed of 67 metres per sec) would involve programing in a wheel of 0.333 metre diameter, which is probably under the permissible range. Not would setting the thing to read in mph rather than kph help much, either. You would need to input diameters of 2.07 or 0.27 metres, which are still probably too large/too small. Of course, your bandsaw wheels may be not be 200mm, but unless they are of substantially different size it probably still won't work. Warning: my mathematics are not guaranteed to be any more accurate than they were when I was at school 50 years ago! Andy |
| DMIOM:
Eric, Further to the issue which Andy has highlighted concerning the necessary input being outside what a standard velocimeter might accept - can you let us know what the limits are for your unit? If if can't work as-is because of these limits, you may be able to bring it within range by using two or more magnets, so you have an electronic gearing. Dave |
| BillTodd:
--- Quote ---Dividing by 10 (so a reading of 6.7 kph represents a blade speed of 67 metres per sec) would involve programing in a wheel of 0.333 metre diameter, which is probably under the permissible range. --- End quote --- How about adding another magnet? i.e. two pulses per rev should allow a wheel of 0.66m or about 26" |
| PekkaNF:
See halfway down to this page: http://andysmachines.weebly.com/dore-westbury-mill.html This page: http://mikesworkshop.weebly.com/low-cost-tachometer.html http://psas.pdx.edu/ParaffinSpinCasting/BC500tachometer.pdf I have one cheap one as lathe tachometer, just to check, not in permanent installation and my bike computer did not care how bogus unists i fed to it. I didn't bump into build in input value limits. Mine had reed-switch, but worked fine whatever I threw at it (under 1500 rmp). I have heard that some can't go very high rpm. Pekka |
| Navigation |
| Message Index |
| Next page |