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Other › Using a tach
02-12-2006 06:35 AM  12 years agoPost 1
davidgp

rrNovice

Orlando, Florida (by the mouse)

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OK, I bought a tach. I grabbed the Rex and stuck a broom through the skids and cranked it up to hover. Then I held the tach below the blades pointing at a light. Hmmm, 3600 rpms. That's not a blade count, just an AC count!!!

Next I tried lights out with a flashlight over the blades. Did I mention I was really nervous with my hands that close to the blades?

Speed jumped around but only maxed about 1800 rpm. I cranked up the hovering throttle knob to increase rpm, but the blades were really screaming!!! RPM just seemed to be too high. Am I doing something wrong? Throttle is set to 75% at hover with an Align 400 and Align 35 ESC, TP2100 battery, 13t pinion, and the Align yellow blades that came with the XL.

David

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02-12-2006 02:18 PM  12 years agoPost 2
exeter_acres

rrApprentice

Johns Creek, GA

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were there flourescent lights??

do it outside....

WITH A FRIEND

I'm old, bitter, and don't like people.... get over it

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02-13-2006 05:42 AM  12 years agoPost 3
davidgp

rrNovice

Orlando, Florida (by the mouse)

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Incandesant (sp?) lights. Unless someone cheated and put the flourescent "bulbs" in the light fixture. The real question here is it my imagination, or is the tach wrong. Should I just tach it at 100% throttle and see what I get?

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02-13-2006 06:18 AM  12 years agoPost 4
tihmed

rrNovice

Denver, CO

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My optical tach says that it must be used in sunlight. All indoor lights will have pulse rates of their own throwing off the tach. Try either by a window with sunlight shinning through or go outside and try it. Inside I was getting inconsistantly high and low numbers, outside it is much more acurate

Align.... it's not just a name, it's an instruction!

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02-13-2006 02:01 PM  12 years agoPost 5
WeatherB

rrVeteran

Toronto - Canada

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I had the same problem, you'll need natural light. Either go outside or wait for a sunny day when enough light comes through your windows.

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02-13-2006 02:36 PM  12 years agoPost 6
enginetorque

rrApprentice

North Wales

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whoooooooooo 3600
Unless you are running about 47S (battery)then not likely - you need daylight and you also need to ensure your tacho is not reading the paddles (or switch to 4 blade props)

two pumps and a squirt

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02-13-2006 07:21 PM  12 years agoPost 7
Willie 300S

rrApprentice

Birmingham, Al, USA

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Has anyone used an optical tach, where you sync with the blades until the image stops and then read the speed? Is this type tech more accurate?

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02-13-2006 07:24 PM  12 years agoPost 8
jcrack_corn

rrVeteran

End of Time

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willie, i havent seen an optical tach that goes high enough for our headspeeds yet....has anyone else (seems like it wouldnt be hard to make the drum spin a little faster)......

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02-13-2006 07:41 PM  12 years agoPost 9
aircrew1

rrApprentice

Midland, Texas

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Willie300S,
Yes, I have an optical tach that goes that high. I will look at it when i get home from work and post what it is.

TREX450SE / Fut 9CHP / GY401 / TP2100S Pro/ Kontronix40-6-18 / HS65's/Medusa 28-32-3400

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02-13-2006 08:42 PM  12 years agoPost 10
whtbronco

rrApprentice

Winchester, Virginia USA

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Here's my tach. [url=http://http://www4.mailordercentral.com/heliproz/prodinfo.asp?number=804260]

It only goes up to 2800rpm though. Truth is I have never used it myself. I always have to fly the heli and have someone else use the tach. The nice thing about the tach is that you can be 100 feet from the heli when taking the reading. I would not try using my airplane tach on a heli, too risky.

Chris Wish I was flying!

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02-13-2006 10:46 PM  12 years agoPost 11
aircrew1

rrApprentice

Midland, Texas

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Willie300S,
http://www.miniatureaircraftusa.com...l.asp?prod=0524

The optical tach i have is made by the above company.
It will read from 300 - 3000 RPM +/- 1 RPM
Its little pricey ($155)but is easy to use and accurate. I usually have my son tach while i fly. Hope this helps.

TREX450SE / Fut 9CHP / GY401 / TP2100S Pro/ Kontronix40-6-18 / HS65's/Medusa 28-32-3400

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02-13-2006 11:14 PM  12 years agoPost 12
Willie 300S

rrApprentice

Birmingham, Al, USA

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It does.
Thanks

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02-14-2006 12:41 AM  12 years agoPost 13
Squirrlybird

rrVeteran

Suffolk, Va US

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I have an optical tach that was only about $90. Cheapest one that I have found. Works like a champ too. My LHS now carries it "debbiesrcworld.com". It is the Modelavionics Sky Tach. Should also be at modelavionics.com.

Optical tachs are great. They allow you to see what your headspeed actually is while flying. You have to have a partner to use it though.

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02-14-2006 12:44 AM  12 years agoPost 14
Squirrlybird

rrVeteran

Suffolk, Va US

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Just looked at the modelavionics website and they are showing more than what my LHS charged me.

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02-14-2006 01:57 AM  12 years agoPost 15
Professor Fate

rrKey Veteran

Goose Creek S.C.

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Any indoor light will screw with a photo tach. As long you have AC current @60Hz powering a light source your screwed. I clamped down the Trex to my work stand, turned out the lights, had the Wife OP the Tx, held a flashlight in one hand and the tach in the other. Told her what to do while I shot the RPMs between the light and tach.

Welcome my son, Welcome to the machine

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02-14-2006 02:20 AM  12 years agoPost 16
lbowen

rrApprentice

York S. Carolina-USA

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Wish I could get my wife to help hold anything heli related - you are a blessed man!

lbowen

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02-14-2006 02:57 AM  12 years agoPost 17
tihmed

rrNovice

Denver, CO

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I got my tach from LHS. less than $40. small enough to fit in a shirt pocket. It reads within 20 rpm. when compared to a calibrated one we use at the hanger. "Hanger 9" by herizon hobby is the name. Must use it in sunlight only. only has three digit LCD but adding a 0 is math i can handle.

Align.... it's not just a name, it's an instruction!

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02-14-2006 09:52 AM  12 years agoPost 18
enginetorque

rrApprentice

North Wales

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HANG ON CHAPS
WHOA there - you are making this FAR too difficult

1 All you need is a plain old ordinary airscrew LCD readout tacho

2 Grab a lump of Blu Tac or silly putty and "stick" the tacho vertically to the bench/ground/table or whatever

3 Affix the heli to the same table/bench/wife/small boy etc

3 Stand well back and "fire her up"

4 Job done !

two pumps and a squirt

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02-14-2006 09:58 AM  12 years agoPost 19
Professor Fate

rrKey Veteran

Goose Creek S.C.

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"Wish I could get my wife to help hold anything heli related - you are a blessed man!"
She don't know it yet but she's getting an XRB for V-Day.

Welcome my son, Welcome to the machine

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02-14-2006 02:03 PM  12 years agoPost 20
lbowen

rrApprentice

York S. Carolina-USA

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Prof. Fate - that is a classy idea - I wish I thought of that - I spent a fortune on flowers and jewelery bling!

lbowen

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