RPM Sensors and Ratio?

DDragon · 11-28-2008, 08:19 AM

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.

Matt Jenner · 11-28-2008, 09:02 AM

AandP · 11-28-2008, 09:03 AM

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.

AandP · 11-28-2008, 09:09 AM

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.

DDragon · 11-28-2008, 09:19 AM

Quote:

Originally Posted by AandP

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.

Bell Bloke · 11-28-2008, 11:05 AM

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.

bcook01 · 11-28-2008, 03:11 PM

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.

Peter Rob · 11-28-2008, 04:16 PM

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
Peter R

Renfru · 11-28-2008, 04:54 PM

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?

bcook01 · 11-28-2008, 05:45 PM

Renfru

No. these are strong rare earth magnets

Bob

Renfru · 11-28-2008, 06:59 PM

Perfect then!

11-28-2008, 08:19 AM	#1
DDragon Registered Users Join Date: Aug 2007 Location: Canada	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. Attached Thumbnails __________________ Cheers, Deron. Too many helicopter and not enough time: Trex 744 turbine, PredWren, Trex 600, Trex 500, Trex 450. Anyone wanna buy a helicopter?

11-28-2008, 09:02 AM	#2
Matt Jenner Join Date: Jul 2008 Location: 00	.. Attached Thumbnails Last edited by Matt Jenner; 11-28-2008 at 04:02 PM..

11-28-2008, 04:16 PM	#8
Peter Rob Join Date: Feb 2006 Location: UK South West	Governor 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 Peter R

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11-28-2008, 09:03 AM	#3
AandP Registered Users My HF Map location Join Date: Aug 2006 Location: Chandler, AZ	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.

11-28-2008, 09:09 AM	#4
AandP Registered Users My HF Map location Join Date: Aug 2006 Location: Chandler, AZ	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.

11-28-2008, 11:05 AM	#6
Bell Bloke Join Date: Jan 2007 Location: ENGLAND A NATIONS PEOPLE UNDER CCTV	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.

11-28-2008, 04:54 PM	#9
Renfru Join Date: Aug 2008 Location: Wales	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?

11-28-2008, 05:45 PM	#10
bcook01 Registered Users Join Date: Aug 2007 Location: Ont,Can	Renfru No. these are strong rare earth magnets Bob

11-28-2008, 06:59 PM	#11
Renfru Join Date: Aug 2008 Location: Wales	Perfect then!