How do the basic Tachometers work?

Namuna · Post by **Namuna** » Fri Oct 27, 2006 7:14 pm

So I'm on some wacky gauge kick. I dunno, I just dig knowing what all info they give you.

...Anyway, now that I've been toying around with Helicopters, I'm wanting to get a Tachometer to gauge the rotor RPMs.

But I DON'T want anything that has to tether to anything else to get a reading. I wanna be able to stand near the thing and have a gauge I can just point toward the rotor to read it.

Being ignorant to how the Tachs work, I saw this basic one over at BPHobbies:

http://www.bphobbies.com/view.asp?id=A0 ... id=W113578

Anybody know how this thing gets its' reading? I wish the damned site gave a little more info about that.

Thanks.

payaso · Post by **payaso** » Fri Oct 27, 2006 7:34 pm

The new telemetry units work off of magnets.

Have to mount the magnets on the shaft somewhere. I know for land based cars/trucks, they are counter sinkin em into the slipper clutches.

I'll see if I can find some extra info, as I haven't the $$$ to try it out first hand.

silla

Maxximum Attack · Post by **Maxximum Attack** » Fri Oct 27, 2006 8:00 pm

A couple years back I was doing a mechanical engineering class, and the tutor had a tool that used a strobe light to guage RPMs of the laithe. What you did was mark the rotatingobject with a piece of chalk and tried to sync the frequency of the strobe flashes with the RPM of the object. Once in sync the chalk mark would cease to rotate, it would apprea to be stationary. The device would already be calibrated to give an RPM out put on the display.

That's probly an arcaic method, seeing as we're not as technologically advanced as you guys. I just thought it was cool to add here

Maxx

sg219 · Post by **sg219** » Fri Oct 27, 2006 9:12 pm

Some use a laser and a reflective surface on the item that is rotating. Sorta like a cheap lap counter but way faster and more precise.

Magentic ones work on the same idea.

You could always stick a baseball card in it and count the clicks.

betty.k · Post by **betty.k** » Sat Oct 28, 2006 2:19 am

sg219 wrote:Some use a laser and a reflective surface on the item that is rotating. Sorta like a cheap lap counter but way faster and more precise.

that's my understanding of an optical tacho.

what maxx is refering to is timing adjustment, same as the timing on a 1:1 car engine.

Namuna · Post by **Namuna** » Sat Oct 28, 2006 1:48 pm

Hmm, then I wonder which type the one I linked to is. The description says you can easily switch between 2, 3 or 4 rotor reading.

Now, here's a wacky idea I had about using the Tach and my Anemometer (wind meter)...

Over on the RCGroups there's always talk about how some rotors produce more lift vs. others. I've been wondering how there might be a way to test for that and thought I could use the combination of the Tach and Wind meters to give a more objective comparison.

The constant would be to get a set of rotors to spin at a certain RPM (using the Tach to verify the speed), then measure the wind downforce (using the wind meter) generated at that RPM. Then throw on another set of Rotors and measure the wind downforce at the same RPMs.

beanoman · Post by **beanoman** » Sat Oct 28, 2006 2:21 pm

nammy...

http://www.bphobbies.com/view.asp?id=A0 ... id=V786359

lol...