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Old 11-28-2008, 08:19 AM   #1
DDragon
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Default RPM Sensors and Ratio?

Hi Folks,
I received my Seagull Pro Eagle Tree wireless thingy from HobbyCity.com (They have two left for $345 BTW) and it arrived safe and sound and as advertised.

Anyway, trying to figure out where to place the RPM sensor for HS sensing and Bob has been helping me figure this out (Thanks BOB!).

I figure I can make a collar (on my lathe) that fits over the stock mainshaft (bottom) collar (see attached photo) then make a bracket for the sensor that fits under the boom block.

I think it will work... but I'm wondering. When setting up the software you set the gear ratio... in the manual is says that if the sensor is on the main shaft you use 1:1 ratio.

OK... here's the crux of my question... if you have a rotating circle... isn't the rmp of a point faster as you get closer to the hub. Or in other words, it takes longer to go around the circumference if you are on the outside as opposed to closer in towards the center?

I know this is basic physics, but does the software need to be changed from 1:1 depending on this mounting position? Or is it still 1:1 ... and why? Trying to wrap my head around the physics of it.
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Old 11-28-2008, 09:02 AM   #2
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..
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Old 11-28-2008, 09:03 AM   #3
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The RPM remains constant. The farther a point is out from center the faster (MPH) it will have to travel to get around the increased circumference.
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Old 11-28-2008, 09:09 AM   #4
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The main gear and the blades rotate at the same RPM. The tip speed of the blades is much higher than the teeth of the main gear because the blades have to cover more distance at the same rate of rotation.
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Old 11-28-2008, 09:19 AM   #5
DDragon
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Quote:
Originally Posted by AandP View Post
The main gear and the blades rotate at the same RPM. The tip speed of the blades is much higher than the teeth of the main gear because the blades have to cover more distance at the same rate of rotation.
A light just came on!

Thank you for this explanation. I'm no longer confused! I was confusing MPH and RPM.
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Old 11-28-2008, 11:05 AM   #6
Bell Bloke
 

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When I had a Carvec on my Predator I mounted the rpm sensor onto the main gear. I did this by drilling into it by the depth of the magnet and then glueing it in, simple.
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Old 11-28-2008, 03:11 PM   #7
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Quote:
I did this by drilling into it by the depth of the magnet and then glueing it in, simple.


Yup. That is the way I did it and the method I recommend as well.

..........Why complicate life.
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Old 11-28-2008, 04:16 PM   #8
Peter Rob
 

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BB, was that a Preditor gasser, on my Sectra G I have the GV1, with a stator gator which uses the pulses off the magnito, works extreemly well
On the X-cell Tempest the GV1 had magnets in the maingear unfortunatly they never seemed to stay in place for any length of time
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Old 11-28-2008, 04:54 PM   #9
Renfru
 

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I was going to suggest gluing the magnets into two tiny holes drilled onto the top surface of the aluminium collet above the main gear but would the ferrous grub screws in the collet upset things?
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Old 11-28-2008, 05:45 PM   #10
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Renfru

No. these are strong rare earth magnets

Bob
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Old 11-28-2008, 06:59 PM   #11
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Perfect then!
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