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tachometer optical vs digital?

Screwhead

Senior Heliman

Tucson Arizona USA

The optical tachometers seem higher in price though we use it to "see through" the hole to come up with the rpm? It sounds more cumbersome to get the rpm while a digital tach reads the rpm automatically at a touch of a button. Why the optical tach is consider better (if so?) and people prefer the optical to the digital? For example this costs only about $25 http://www.helidirect.com/hobbico-l...eter-p-2215.hdx and fully automatic and seems easy to use, but this popular optical tach http://www.helidirect.com/model-avi...eter-p-7027.hdx is $85, three times as much, and doesn't read the rpm for you automatically. You must "see through" it to get the rpm, then yada yada yada. Thanks.

10-26-2009 Over year old.
FlaG8r

Elite Veteran

Florida

This is why you don't want to use the digital tach, from the comments
"Hold tach 4 to 12" away from propeller"


Tough to do that when you're hovering and the blades are spinning at 2100 RPM.

Life is tough, it's tougher if you're stupid

10-27-2009 Over year old.
Screwhead

Senior Heliman

Tucson Arizona USA

Doesn't the optical one also require the same holding, aiming, etc while hovering whereas with the digital at least you aren't required to see through it. I've never used a nice optical one, but if the optical one is somehow superior, I'm willing to invest in one. I've heard a skilled person can just hear and tell an approximate RPM, which off course I can't do that.

10-27-2009 Over year old.
Farrell

Senior Heliman

Huntington Beach, CA

A regular tech needs to be close to the prop or rotor to give you a reading... it uses an IR sensor to look for "flickering" light... light that is obscured by the prop or rotor blades with each rotation. That is not practical for heli use as you can't safely take readings.

A optical tach is used on heli's, and you look through the hole in the tach and make adjustments until your rotor disk appears stationary.

I think Thunder Tiger used to make a regular tach that could be secured to your tail boom. No need for an expensive optical tach and no need to put yourself in harms way while using a regular tach... but it was a weird way to check headspeed. You had to look at the LCD on the tach / tail boom to get a reading, so it would not be very useful except to check hovering headspeed. I'm not sure if their tach is still available, I don't think it was very popular.

-Farrell

10-27-2009 Over year old.
HOMEPAGE  
Heli_Man_Bob

Senior Heliman

Miamisburg, Ohio, US

How would you be checking your head speed with the Heli hovering inverted with the non optical Tach.

Why an opticle tach? Safety is the reason as well as more capability.

With the optical tach you can observe the model in all modes of flight from a safe distance.

You do not operate the optical tach and heli by your self this is a two person task.

You don't necessarily have to own one just need to know someone who has one and will offer to tach your Heli.

If you intend to be in this hobby a while its a worth while investment.

10-27-2009 Over year old.
HeliFisher

Veteran

Verdi , Nevadafornia

Try this......

Have your buddy lift off into a steady hover. Now walk over to the hovering heli and hold your hand 4-12 inches from the main rotor.

I think the laser tach is for airplane props, where you can go full throttle and hold the plank (or plane) stationary while you tach the propeller. The optical tach allows you to remain a safe distance from your heli, since we need to be in a hover to get an accurate headspeed reading. You can also see the rotor disk bog with the optical tach. I dunno how useful that would be to see the bogging, but it looks cool!

I have found the headspeed calculators are very accurate as long as you enter all the proper numbers, as far as motor efficiency and that kind of thing.

The less a man makes a clarative statement, the less likely he is to look like a fool in retrospect.

10-27-2009 Over year old.
greenboot

Veteran

Marblehead, OH

It may be clearer when you understand what the optical tach does. It contains a spinning disk with a slit. You sight through the spinning disk and adjust it's RPM until the rotor blades appear stopped. At that time, the disk and your rotor are turning the same speed. Now you can read the RPM of the disk on the display. The heli can be VERY far away and it works fine. Of course you need a second person to operate it.

Tom

10-27-2009 Over year old.
JRjoe

Elite Veteran

Jonesville , IN USA #1

That cheap Hobbico tach is for planks. If you want to know rotor head speed you need an optical tach and a helper. No real way around it.


JRjoe.....
Indoor plumbing??? No, we don't need that!!!

10-28-2009 Over year old.
HOMEPAGE  
GyroFreak

rrProfessor

Orlando Florida ...

Get an Eagle Tree on board data logger. Then you have a record of your rpm all through the flight. No need for a 2nd person and it is about the same price.

I think about the hereafter. I go somewhere to get something, then wonder what I'm here after ?

10-28-2009 Over year old.
Screwhead

Senior Heliman

Tucson Arizona USA

Thank you very much folks. You gave me lots of helpful hints and information regarding my possible purchase of a tach. I'd probably scratch the idea of digital tach. I have heard that reading of the rpm with an optical tach may take 2 persons. I'd also read about the Eagle Tree on board data logger. I may consider that if not expensive. If the logger is expensive however, I shouldn't get it because I may crash and break the whole heli including the logger.

10-28-2009 Over year old.
Screwhead

Senior Heliman

Tucson Arizona USA

Hi, this review of Eagle Tree data logger says there are types of RPM sensors available.

http://www.rchelisite.com/eagletree...gger_review.php

The optical "second" type is being said not usable for measuring the heli headspeed, which works in the similar manner as the digital tachometer, as you explained to me (therefore not great for helis.)

Which would you think better between the electronic RPM sensor "third type" (to be put between the ESC and motor) and the magnetic "first type" (a physical sensor installed near the rotor blades) better? The article recommends the third type.

10-28-2009 Over year old.
OICU812

rrMaster

Edson, Alberta, Canada

"IF" you want to consider a fantastic sky tach look at the western robotics chinook. Brushless motors, large window, they work a treat I really enjoy mine!

...Once upon a time there were Nitros, flybars and frequency pins...

11-05-2009 Over year old.
Smok

Senior Heliman

Antwerp, Belgium

There is also a third option - a governor or speed controller
which allows to set the RPMs in all idle-ups.

Futaba GV-1 can do that and also CastleCreations Phoenix controllers.

Both work fine for me ..

Smok

11-05-2009 Over year old.
HeliFisher

Veteran

Verdi , Nevadafornia

Also......

If you have an I-phone, you can download a tachometer app. I used my buddies the other day and it worked well.

The less a man makes a clarative statement, the less likely he is to look like a fool in retrospect.

11-05-2009 Over year old.
Screwhead

Senior Heliman

Tucson Arizona USA

Hi, The western robotics chinook have been mentioned in my research to look for a good quality optical tach. OICU812, your comment confirms that. Thank you. I'm leaning toward the Eagle Tree data logger that some of you mentioned. Thank you for useful recommendations, folks.

11-06-2009 Over year old.
skytrekin

Senior Heliman

Glendale, AZ

The iphone app does indeed work. I was skeptical but tryed it, it works pretty good!

12-26-2009 Over year old.
Screwhead

Senior Heliman

Tucson Arizona USA

I've heard the audio based RPM analyzers generally work, including the ipod program. I may as well try if it's cheap enough. Thanks for your input.

12-28-2009 Over year old.
perfeet

Heliman

Oslo, Norway

Why not fasten the digital tach to a stick (about 1/3 length of helicopter height) and stick it in the ground?

Then hover next to the stick. Alternatively just spool up the heli next to the tach on stick?

Land and spool down. Walk over and check the reading.

Then you can even do it alone.

04-27-2010 Over year old.
oteskate

Senior Heliman

Long Island, NY - USA

As a few of the guys were mentioning, the optical tach is the way to go. You need another person to use it effectively, but what's nice about them is that you can watch the heli throughout an entire maneuver and see exactly where and by how much the heli is bogging down.

I personally use the Bantam Checkmaster and like it alot. Always very accurate and offers a few other "tools" such as servo tester, temp sensor, digital prop tach and also reads heli RPM's up to 4,000 RPM! I think the others only go to like 3100 or so, generally.

Here's the link if you want to check it out:

http://www.rcaccessory.com/bantame-...4khelitach.aspx

Jeff
Team Hirobo/MRC, KBDD, RC Booya, Switchglo, JGF, Castle Creations, Magnum Fuel

04-30-2010 Over year old.
Screwhead

Senior Heliman

Tucson Arizona USA

My wife bought a Ipod touch, and supposedly the tachometer application that meters the RPM accoustically works decent only for a few dollars, and I'm investigating now.

04-30-2010 Over year old.
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