RC Radios, Transmitters, Receivers, Servos, gyros Discussion all about rc radios, transmitters, receivers, servos, etc.

Any simple way to check a tach's accuracy.

Reply

Old 06-02-2007, 05:27 PM
  #1  
karolh
Thread Starter
 
Join Date: May 2002
Location: Mandeville, JAMAICA
Posts: 6,602
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default Any simple way to check a tach's accuracy.

I have a fairly old Royal digital tach that is still in working condition. Is there any way to check if it is still accurate.

Karol
karolh is offline  
Reply With Quote
Old 06-02-2007, 05:34 PM
  #2  
GalenB
My Feedback: (18)
 
Join Date: Dec 2001
Location: Issaquah, WA
Posts: 2,140
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Point it at an incandescent lamp and read the value. The lamp will be "flickering" at 60 hertz and your tach should be able to read it. 60 hertz is 3600 RPM (60 per sec * 60 seconds). It may read half that for the two blade setting as 2 blips per rpm is how the tach may interpret it... I am of course dredging this up from memory as I am stuck at work today... []

I just noticed that you are in Jamica -- I don't know anything about AC power in Jamica so none of what I said above may apply...[:@]
GalenB is offline  
Reply With Quote
Old 06-02-2007, 05:48 PM
  #3  
Campgems
Senior Member
 
Join Date: Feb 2006
Location: Arroyo Grande, CA
Posts: 4,465
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

The same method applies only it would be 50 * 50 for 50hz power. 2500 I'm not aware of any primary power frequency besides 60hz and 50hz.

Don

ORIGINAL: GalenB

Point it at an incandescent lamp and read the value. The lamp will be "flickering" at 60 hertz and your tach should be able to read it. 60 hertz is 3600 RPM (60 per sec * 60 seconds). It may read half that for the two blade setting as 2 blips per rpm is how the tach may interpret it... I am of course dredging this up from memory as I am stuck at work today... []

I just noticed that you are in Jamica -- I don't know anything about AC power in Jamica so none of what I said above may apply...[:@]
undefined
Campgems is offline  
Reply With Quote
Old 06-02-2007, 05:49 PM
  #4  
4*60
My Feedback: (41)
 
Join Date: Mar 2002
Location: Shuswap, BC,
Posts: 1,749
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

50 * 60 since there are 60 seconds in a minute so 3000 or half that 1500. Let's get it right, eh!
4*60 is offline  
Reply With Quote
Old 06-02-2007, 05:49 PM
  #5  
GalenB
My Feedback: (18)
 
Join Date: Dec 2001
Location: Issaquah, WA
Posts: 2,140
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Wouldn't it be 3000 (50*60) for 50 hz power?
GalenB is offline  
Reply With Quote
Old 06-02-2007, 06:59 PM
  #6  
bruce88123
 
Join Date: Nov 2004
Location: Memphis, TN
Posts: 11,703
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Maybe they have 50 second minutes in Jamaica? Ya just never know.
bruce88123 is offline  
Reply With Quote
Old 06-02-2007, 07:06 PM
  #7  
pilotpete2
 
pilotpete2's Avatar
 
Join Date: Oct 2002
Location: Lyndonville, VT
Posts: 3,298
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Hey All,
First use a fluorescent lamp, not an incandescent lamp.
With a 2 blade setting it will read 3600 on 60 Hz. and 3000 on 50 Hz. The reason there is no conversion needed is simple, any lamp "flickers" at twice the line frequency, so at 60 Hz the lamp actually goes on and off 120 times a second, or 7200 times a minute giving you the 3600 reading in 2 blade mode.
Pete
pilotpete2 is offline  
Reply With Quote
Old 06-02-2007, 07:53 PM
  #8  
karolh
Thread Starter
 
Join Date: May 2002
Location: Mandeville, JAMAICA
Posts: 6,602
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Thanks guys. I just checked it against a 60hz fluoresecent lamp and it reads 3400, which is 200 or 5% lower of what it should read. Does this mean that it's time to put it in the trash can.

Karol
karolh is offline  
Reply With Quote
Old 06-02-2007, 08:53 PM
  #9  
RJConnet
Senior Member
 
Join Date: Jan 2002
Location: OR
Posts: 680
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Don't toss it till you pull the case apart to see if their is any kind of trim-pot or adjustment possibility on the circuit board. I have an old Hobbico unit that was reading 3500 rpm under the flourescent light, I found such an adjustment inside and was able to put it right on 3600.[8D][8D]........RJ
RJConnet is offline  
Reply With Quote
Old 06-03-2007, 03:19 AM
  #10  
Campgems
Senior Member
 
Join Date: Feb 2006
Location: Arroyo Grande, CA
Posts: 4,465
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.


ORIGINAL: 4*60

50 * 60 since there are 60 seconds in a minute so 3000 or half that 1500. Let's get it right, eh!
undefined


Well, I was half right.[sm=spinnyeyes.gif]undefined

Actually when you get to be an old fart like me, the minutes only have 50 seconds. So there.

Don
Campgems is offline  
Reply With Quote
Old 06-03-2007, 06:31 AM
  #11  
karolh
Thread Starter
 
Join Date: May 2002
Location: Mandeville, JAMAICA
Posts: 6,602
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

LOL ....don't worry you got lots of company there as we are all travelling on the same road, it's just that some are ahead and the others are behind

Karol
karolh is offline  
Reply With Quote
Old 06-03-2007, 06:48 AM
  #12  
TLH101
My Feedback: (90)
 
TLH101's Avatar
 
Join Date: Dec 2001
Location: Elephant Butte, N.M.
Posts: 6,707
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.


ORIGINAL: pilotpete2

Hey All,
First use a fluorescent lamp, not an incandescent lamp.

Pete
It works with either type of bulb. No difference.
TLH101 is offline  
Reply With Quote
Old 06-03-2007, 09:35 AM
  #13  
karolh
Thread Starter
 
Join Date: May 2002
Location: Mandeville, JAMAICA
Posts: 6,602
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.


ORIGINAL: RJConnet

Don't toss it till you pull the case apart to see if their is any kind of trim-pot or adjustment possibility on the circuit board. I have an old Hobbico unit that was reading 3500 rpm under the flourescent light, I found such an adjustment inside and was able to put it right on 3600.[8D][8D]........RJ
You were right on the money with this one. Guess they are made up pretty much the same huh. Thanks again.

Karol
karolh is offline  
Reply With Quote
Old 06-03-2007, 10:39 AM
  #14  
TLH101
My Feedback: (90)
 
TLH101's Avatar
 
Join Date: Dec 2001
Location: Elephant Butte, N.M.
Posts: 6,707
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

ORIGINAL: karolh


ORIGINAL: RJConnet

Don't toss it till you pull the case apart to see if their is any kind of trim-pot or adjustment possibility on the circuit board. I have an old Hobbico unit that was reading 3500 rpm under the flourescent light, I found such an adjustment inside and was able to put it right on 3600.[8D][8D]........RJ
You were right on the money with this one. Guess they are made up pretty much the same huh. Thanks again.

Karol
This is good to know, mine reads 3700. Time to "tweek" it.
TLH101 is offline  
Reply With Quote
Old 06-03-2007, 11:19 AM
  #15  
pilotpete2
 
pilotpete2's Avatar
 
Join Date: Oct 2002
Location: Lyndonville, VT
Posts: 3,298
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Hi Terry,
Most will read the incandescent fine, but some may have a problem as with an incandescent lamp, as the filament tends to buffer or average out the on/off cycle. Yeah my cheapy Tower Hobbies reads both spot on. As I remember my old analog Ace tach didn't like incandescent light.
Pete
pilotpete2 is offline  
Reply With Quote
Old 06-03-2007, 11:53 AM
  #16  
karolh
Thread Starter
 
Join Date: May 2002
Location: Mandeville, JAMAICA
Posts: 6,602
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Hey guys guess what. Now that I have tweaked it to give a 3,600 light reading it's gone completely wacko at the top of the scale, as it is giving readings on my engines that are just too high to be true. Maybe it's time to trash it after all.

Of the moderately priced tachs like Globee, Magnum, Hobbico and Tower, which is the best of the lot.

Karol
karolh is offline  
Reply With Quote
Old 06-03-2007, 12:13 PM
  #17  
Gulliver
Senior Member
 
Join Date: Aug 2004
Location: Boulder, CO
Posts: 275
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Another $.02

The light bulb calibration method does assume that the calibration curve is linear, which it may not be. Might explain your deviation at the high end after you tweaked it.
Gulliver is offline  
Reply With Quote
Old 06-03-2007, 12:23 PM
  #18  
karolh
Thread Starter
 
Join Date: May 2002
Location: Mandeville, JAMAICA
Posts: 6,602
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

You might have a point there, and if that is the case, maybe it was originally calibrated to show 3,300 for a light reading. However I still need to know your choices regarding the tachs mentioned.

Karol
karolh is offline  
Reply With Quote
Old 06-03-2007, 12:24 PM
  #19  
4*60
My Feedback: (41)
 
Join Date: Mar 2002
Location: Shuswap, BC,
Posts: 1,749
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Try a new battery. That's waht mine needed when it read real high.
4*60 is offline  
Reply With Quote
Old 06-03-2007, 12:27 PM
  #20  
karolh
Thread Starter
 
Join Date: May 2002
Location: Mandeville, JAMAICA
Posts: 6,602
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

It's got in a new 9 volt battery. Come guys, what about the tach choices.

Karol
karolh is offline  
Reply With Quote
Old 06-03-2007, 01:20 PM
  #21  
Campgems
Senior Member
 
Join Date: Feb 2006
Location: Arroyo Grande, CA
Posts: 4,465
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

I had a Magnum tach that I liked, until I loaned it to one of the rotary wing guys and he sort of got to close to the blade and launched the tach. He replaced it with a GloBee tach with more features, but I don't think it gives as good a reading as the Magnum did. Either that, or I've got one screeming OS .40 two stroke. It peaked out at 27,000 the other day, but soon fell back to around 11,000. I am finding that a grey APC prop, or a wood prop gives a better reading than the black plastic ones. It also depends on the direction of the sun hitting the prop with the black ones. If I am pointing the plane at the mountain on the other side of the field, and with the sun off my left shoulder, I get some screwy readings. Turning the plane 90 degrees gives me a better light on the prop and a different background to read against. Some times you just have to play with it to get it reading right.

Don
Campgems is offline  
Reply With Quote
Old 06-03-2007, 04:04 PM
  #22  
pilotpete2
 
pilotpete2's Avatar
 
Join Date: Oct 2002
Location: Lyndonville, VT
Posts: 3,298
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

Karolh,
I have the Tower Hobbies which is the same unit as the Hobbico, hard to beat for the price
I was pleased to see when one of my flying buddies got the same one that when we took simultaneous readings we got identical readings, while not scientic proof of accuracy, was at least reassuring
Pete
pilotpete2 is offline  
Reply With Quote
Old 06-03-2007, 04:45 PM
  #23  
karolh
Thread Starter
 
Join Date: May 2002
Location: Mandeville, JAMAICA
Posts: 6,602
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.

The Tower price seems unbeatable, so I do believe that's the one I'm going to get. Plus I would not be surprised if all these low priced tach utilized the very same circuitry.

Karol
karolh is offline  
Reply With Quote
Old 06-04-2007, 06:58 PM
  #24  
JPMacG
My Feedback: (2)
 
Join Date: Jan 2002
Location: Ivyland, PA
Posts: 2,277
Default RE: Any simple way to check a tach's accuracy.

My Globee does great on florescent lgihts but doesn't give a steady reading on props unless I point the plane toward the sun. I don't know if other brands are any better.
JPMacG is offline  
Reply With Quote
Old 06-04-2007, 07:32 PM
  #25  
RTK
My Feedback: (1)
 
RTK's Avatar
 
Join Date: Apr 2003
Location: Left Coast , CA
Posts: 4,890
Gallery
My Gallery
Models
My Models
Ratings
My Feedback
Default RE: Any simple way to check a tach's accuracy.


ORIGINAL: karolh

Come guys, what about the tach choices.

Karol
If you want the best go with a TNC tach from Fromeco, not cheap but it will read accurately from about 5+ feet.
RTK is offline  
Reply With Quote

Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service