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10-11-2005 11:08 PM  13 years agoPost 1
xJediXx

rrApprentice

Tucson, AZ

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I ran across it before, but cannot find it now. Is there a way to use a timing light gun to measure RPM's? Anyone have any luck with this cheap method?

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10-11-2005 11:30 PM  13 years agoPost 2
TMoore

rrMaster

Cookeville, TN

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Essentially this is a strobe tach.

We used to use this type of tach on NC machines to set up the spindle drives.

TM

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10-11-2005 11:49 PM  13 years agoPost 3
JiggerInc

rrApprentice

Arlington, VA

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I haven't used one before.. but I'm curious. A timing light gun picks up the EMI from plug 1 firing and flashes light to "freeze" the crank position so you can adjust timing, right? To get this working you would need an EMI source that you could accurately know the timing of... a pulse generator? That kind of kills the "cheap" approach. Is there another way to make calibrated pulses of sufficient current to trigger the light?

A homemade tach that could be used safely at a distance by one person would be a real boon to this hobby in my opinion..

-- Greg

PS - I've been looking around for supplies to make a DIY optical tach (LCD shutter style) on the cheap... any ideas?

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10-12-2005 12:13 AM  13 years agoPost 4
xJediXx

rrApprentice

Tucson, AZ

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I googled "DIY optical tach" and the 2nd result showed some confusing, yet interesting details. You may have already seen it, but just in case. I am also curious to learn more about this. I thought I had found my solution with the $5 Timing Gun Light, I bouht at a yard sale.

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10-12-2005 12:30 AM  13 years agoPost 5
JiggerInc

rrApprentice

Arlington, VA

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Yeah, that Google hit (here ) was very interesting.. but with all the images and schematics gone it was tough to figure out what they're talking about. I *think* they're using the term "optical tach" to mean like the $25 jobs where you stand right over the whirleybird and point it down into the rotor disk to "count" the blades going by.

My problem with that design is: a) its cheap enough to just buy one, b) its not particularly safe, c) you can't measure rpm in flight, d) you need a DC light source like a flashlight (or the sun). My last attempt to use one was a little rig that sat on the ground with the sensor pointed up, a flashlight rubber banded to it.. and then I'd hover over it to get a reading... it sucked to try and read that little display while I tried to hover.

I'd like to make one similar to the Miniature Aircraft version where a spotter looks through an LCD shutter and adjusts its flicker rate to "freeze" the rotors, similar to your strobe tach idea.. but maybe in a head-mounted version so a single operator could use it.

Back to the topic: your strobe tach would allow for safe measuring at a distance, but it would still need to be in relatively dim light, and wouldn't be effective in flight. It's still safer than the "hold it over the heli" approach... so I'd like to hear if you get something working.

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10-12-2005 07:17 AM  13 years agoPost 6
GTMAXX

rrApprentice

Canada

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Here's a tach that goes up to 2,800 rpms and works quite nicely - just need a second person to look through the view finder window at the main blades and work the up and down ranging button to get the blades to appear like they are standing still through the view finder while you're hovering your bird. They then look at the display and there's your head speed. We use them all the time for the nitro and gassers and it's the only way of taching headspeeds without the risk of getting bit as you can be at a safe distance during hovering to get your headspeeds.

http://www.deeteeenterprises.com/NS.Tool.Sky.Tach.php

Todd

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10-12-2005 12:36 PM  13 years agoPost 7
JiggerInc

rrApprentice

Arlington, VA

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Yeah, that's the LCD-shutter variety I was referring to. That particular unit only goes to 2800rpm.. which will probably just do for me at 2700-2750, but I know some folks here like to run around 3000rpm. At any rate, the $87 price tag is good for that design of tach... however, I think the original poster and I would like a DIY solution that can be made on the cheap... either LCD shutter or strobe.

I like the idea of a strobe tach, just not sure how cheaply one could be made. An automotive timing light is a good start, but you'd still need a calibrated source of pulses to know what speed you're strobing at. Any ideas out there?

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10-12-2005 01:50 PM  13 years agoPost 8
lineman55

rrApprentice

Connecticut

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I have a Hanger9 TACH I used for aircraft props for RPM readings.
Will this work ok with Heli's?

New to the TREX /

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