Tachometer mods

[mousewheels]

One thing that I am working on right now is that some Tachs have what I would call a lazy 1K, like my gauge, on my gauge the measurement between 0 RPM and 1 RPM is 27.3% shorter than the rest of the scale.
now that I have shrunk the scale down to fit more numerals, I am wondering if some of this lazyness has transferred into the 2k range setting the scale accuracy very slightly off, or if with the recalibration the lazyness will shrink down too....
I will test this I hope next week

Thank you - That's something I will check out on the Sun tach.

Wow, and here I was measuring it out manually, that app is awesome, will it have numerals as well?, I was looking for some small number stickers for my gauge, but have found nothing yet.....

I think a 300 or up dpi graticule output and an image editor to place the values would be quick/easy.

Some work has gone into numbers. Program currently has spacing issues with different fonts.

Font_Inside.JPG (14.66 KiB) Viewed 7114 times

Rotating_Font_Outside.JPG (15.1 KiB) Viewed 7114 times

[mousewheels]

Enough futzing with the graticule program, time for results.

-- Non-linear tach scales --
Breezy posted interesting info about non-linear scaling. I checked the Sun tach in this thread, and it too has a non-linear scale. It is squashed at the very low end. Yet in testing, Sun tach read 10% high at 1800 RPM - so it looks like the low end *not* being squashed might not be so bad... after all, our idle speed is 1800 rpm or so.

-- Test of a linear scale --
A paper copy of the graticule was printed with the program set for 27mm radius. That radius should fit the 54mm face of the Sun Tach. Roughly cutting out the face shows the program is doing fine at dimensions.

Tach_Scale_Test.jpg (20.77 KiB) Viewed 7100 times

To test the scale, a signal generator was used to adjust input frequency to set the tach pointer line up on each 1k mark of the scale. Results came out with all values off in the "too high" direction. By re-taping the face offset by about 350RPM, the adjusted error was calculated. Worst adjusted error recorded was +5.1%, a better than the original tach check. It showed about +/-10% error on the 8 cyl scale.

-- Results - Tach rescale shows increased accuracy, covers 0-10k vs 0-8k, works with 1cyl 2 cycle engine --

Sun_Tach_Rescaled_to_10K_1cylinder_First_Test.JPG (37.31 KiB) Viewed 7100 times

[abreen89]

Mouse these are very cool! Good job! are you going to be selling tachs that work better for these scooters like the one your working on if so let me know!

[noiseguy]

Nice work!

It's interesting that the error is as high as it is for a pure input. I would have thought they would have done a better job linearizing it... but now that I'm looking at the original scale, I'm getting it. No one cares about exact RPM for idle, you want to be able to see your shift points. Those happen at higher RPMs, so you want a larger scale out there so you can tell 6200 RPM from 6700 as the needle sweeps.

Now you're writing software... continuing to amaze. So, you'll have to work that compression into the lower numbers. Graticule... new word. I think you need to crank it to 11, though

[gyromaniac]

i am really impressed with what you have achieved with your sunpro. i just cant wait to put one on my gyro! that thing will look sweet in my gauge setup.

[mousewheels]

Thanks guys

-- Gyros --
Just like the Elite, we're looking for a way to get an auto tach connected without internal tachometer mods.

The Elite mod used AC headlight drive at 3x/rev - exactly matching '6 cyl' tach switch setting.
Issue here is Gyro's AC headlight drive is at the same frequency as the spark trigger.

-- Plan --
Double Gyro's ignition trigger pulses. An auto tach set to '4 cyl' (2 sparks/rev) should be scaled correctly.


Pics: Breadboard, and test setup

Pulse_Doubler_Breadboard.JPG (39.8 KiB) Viewed 7037 times

Gyro_With_Pulse_Doubler.jpg (191.53 KiB) Viewed 7037 times

Scope waveforms:
Far right pic, bottom trace shows the pulse doubler in action.

Note: Top trace - spark trigger signal is 10v/div. It's an issue caused by a divide by 10 probe. So the signal is actually +/-20v peak-peak.

Gyro_Composite_waveforms.jpg (133.77 KiB) Viewed 7037 times

-- Results --
Connected to the tach readings are too high. A Trail Tech Vapor was connected and reads too high. Computing RPM from the scope measurement gives an incorrect result {46hz, 60 and 64hz (~2800-3800 RPM)}. Gyro looks to be more than 1 pulse/rev. I'd like to confirm with a signal directly connected with crank rotation. (a reflective tach).

The Elite mod circuit was swapped in to provide a clean tach input, and Sun tach set for 2 spark/rev.
Photo: Trail Tech Vapor indicates 4k while the Gyro is at idle. Sun tach reads 2k.

Gyro_Test_Vapor_vs_Tach_set_for_2_sparks_rev.JPG (56.31 KiB) Viewed 7037 times

[gyromaniac]

Im not sure if understand this right. After looking at all of your data, is it possible to hook up the sun tach and just use one of the setting that comes on it without having to modify anything?

[Breezy]

Hey Mousewheels,

Will this graticule program be available for download/purchase?, I would be interested, at the end of the day I think my plan for my tach will be to adjust the 11,000 RPM correct and all the measurements below will be slightly incorrect. Im finding it very awkward to adjust and get my markings right via my car.

Just an idea, this could be printed onto translucent plastic paper like they use for school overhead projectors, then sand off the markings of the old graticule and glue the new one on top.
Was thinking the translucent paper might be good so that the back light could shine through and it would be readable at night

Another idea is if this could be made to have back rounds incorporated onto the print out, like pictures or custom brand names

[mousewheels]

Im not sure if understand this right. After looking at all of your data, is it possible to hook up the sun tach and just use one of the setting that comes on it without having to modify anything?

I want to verify this, but it looks that the Gyro is 2 pulses/rev. Thus the 4 cyl setting is scaled correctly.
On the electrical side, I'd recommend limiting the tach input signal. The pulse trigger coil measured -/- 30 to 40 v peak to peak in the scope photos posted earlier. The other source - AC Headlight drive goes both negative and positive.

For a pickup from the AC Headlight drive, circuit for the Elite should work. Will test on the Gyro this weekend. It limits the input to the tach to between +12v and about -0.6v. Its small enough to splice into the wires and heat shrink over.

[mousewheels]

<Will this graticule program be available for download/purchase? I would be interested, at the end of the day I think my plan for my tach will be to adjust the 11,000 RPM correct and all the measurements below will be slightly incorrect. Im finding it very awkward to adjust and get my markings right via my car>

The program is still experimental, it might be fun to complete it. Original goal is to make/post meter faces for the Sun at 9/10/11/12k.

For your tach, what is the diameter? I will work on a face for it. You have good info on the non-linearity. Looks like 4k an up it's getting right onto your calculated markings.

[Breezy]

<Will this graticule program be available for download/purchase? I would be interested, at the end of the day I think my plan for my tach will be to adjust the 11,000 RPM correct and all the measurements below will be slightly incorrect. Im finding it very awkward to adjust and get my markings right via my car>

The program is still experimental, it might be fun to complete it. Original goal is to make/post meter faces for the Sun at 9/10/11/12k.

For your tach, what is the diameter? I will work on a face for it. You have good info on the non-linearity. Looks like 4k an up it's getting right onto your calculated markings.

Thanks Mouse, The Diameter I have is 48mm and needle sweep range is about 240 degrees, but I wouldnt worry too much for now, pens and vernier callipers work fine for me and my testing at the moment, I was just thinking about making it look good once I have it sorted.
I might have a go at making an electrical signal producer, I have posted some links on my thread, If you could advise if I am on the right track that would be great

[mousewheels]

I might have a go at making an electrical signal producer, I have posted some links on my thread, If you could advise if I am on the right track that would be great

The links in your thread would work fine with some changes. Circuit is missing a frequency adjustment pot, and frequency may be outside your range. Oease post your build of that too

Some low effort calibration sources:

1) Wall Wart cal
Output is 2 calibration frequencies based upon AC line frequency. For a tach set up for 1 spark/rev, output is 3600 RPM and 7200 RPM (or 3000/600 for 50hz AC).

Wall_Wart_Calibrator.JPG (46.18 KiB) Viewed 6970 times

Top trace - 120hz bridge rectifier output
Lower trace - 60 hz half wave output

Wall_Wart_Calibrator_Waveform.jpg (60.17 KiB) Viewed 6970 times

2) Serial Port calibrator
A computer with a serial port (or USB serial adapter) is an accurate calibration source. The serial port clock is crystal controlled.
By changing serial port settings, 1500/1800/2000/3000/3600/4000/6000/7200/8000/12000 RPM calibration points are achieved.

Write up for how to set the serial port, data used and freeware terminal program will be in a following post.

RS-232 signals are about +/- 12v. All that's required is to restrict the negative going signal.

Serial_Port_Tach_Calibrator.JPG (40.99 KiB) Viewed 6970 times

[gyromaniac]

Any progree on getting the sun tach to work on a gyro.

[mousewheels]

Any progree on getting the sun tach to work on a gyro.

Sorry for the delay. Sun Tach is working with an AC headlight signal source. Set to '4 cyl', no internal mods required.
Couple posts back we were talking about using the parts reduced circuit drawn for the Elite. I tested this on the Gyro today, it works as expected.

This circuit is easiest to build as a 'splice in' to Sun tach's green wire.




Connections:

• Splice yellow wire to the Gyro Stator Headlight wire (Yellow)
• Black wire to ground.
• Green Tach input wire to green wire of tach input circuit

(Not shown)

• Tach Red wire to +12v switched
• Tach Black wire to Ground

Tach_Input_Limiter_Installed.JPG (61.52 KiB) Viewed 6919 times

[gyromaniac]

I am more of a visual guy myself. I have a hard time picture how to do something when some one puts it in words. Could you post some cloe ups of how you hooked the gyro up to the sun tach. Sorry for the inconvienence.