Author Topic: Tach  (Read 117543 times)

Reply #75March 16, 2006, 02:05:22 pm

RabbitJockey

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« Reply #75 on: March 16, 2006, 02:05:22 pm »
this is awesome, once this is all figured to a 100%  a faq post must be made.
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Reply #76March 16, 2006, 11:55:25 pm

fatmobile

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« Reply #76 on: March 16, 2006, 11:55:25 pm »
I suppose after we get one built we need to calibrate it.
 I was looking for frequncy counters on ebay and saw a gadget that had a wire wound up in it.
 The plan was to set it on the engine (might have had a magnetic base) The wire would pull out like a tape and as it was pulled out it would vibrate from side to side. Pull it out a little more and the swing of the wire's vibrations would be reduced.
 Find at what length it moved the most and the device had a pointer that would indicate the frequncy.
  Each frequncy would be represented by a different length of wire. I don't know how accurate it would be. Maybe a very little difference in length would represent a large change in RPMs.
 Either way we are going to have to figure out an easy way to calibrate our tach conversions.
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Reply #77March 17, 2006, 02:02:02 am

mortskeg

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« Reply #77 on: March 17, 2006, 02:02:02 am »
When I installed my gas tach and signal converter, I simply figured out what rpm I should see at a given speed (60mph) in 5th gear.  I figured this out based on my tire size, gear ratio, and final drive.  If you'd like I can dig up these equations.  Of course I used a handheld gps to accuratly maintain the 60mph since the vw speedo is, well, a vw speedo. :)

It also helped that calibration was easy to do since I just had to bump the tach needle up/down by pressing the calibration buttons on the signal converter mounted on the kneebar which was then covered by the kick panel thing.

Hope this helps.


Reply #78March 17, 2006, 06:01:25 am

RabbitGTDguy

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« Reply #78 on: March 17, 2006, 06:01:25 am »
As requested (but replaced the pics on page 5 as well...) the 77-80 MotorMeter gasser tach for any of those of us having early MK1's using diesels with W's that might want to use this gauge.  







Joe
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Reply #79March 17, 2006, 06:05:15 am

regcheeseman

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« Reply #79 on: March 17, 2006, 06:05:15 am »
Quote from: "trev0rbr"
this is awesome,


The only thing awesome about it is the number of different PCB configurations that are coming out of the woodwork - I wish I'd kept quiet about it now.

 :wink:  :D

I've calibrated mine on the bench with a frequency generator with inbuilt counter. when I did this my variable resistor network measured 23.4K - so taking the fixed resistor of 10K out means the variable was set to 13.4K. Which is why I suggest midrange as a base setting.

I guess you could use a strobe on the top pulley

I was thinking either fit a w term alt onto a gasser VW and compare the diesel tach against the gassers one.

Or plug the tacho into another VW diesel that has a tach and a W terminal

Reply #80March 17, 2006, 07:19:54 am

regcheeseman

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« Reply #80 on: March 17, 2006, 07:19:54 am »
Rabbit GTD guy,

still had problems with your photos because they were at different angles but I gleamed enough to note it was exactly the same as BioBill's unit including the component designations so your instructions are exactly the same!

Reply #81March 17, 2006, 08:09:20 am

regcheeseman

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« Reply #81 on: March 17, 2006, 08:09:20 am »
Johnny,

Use the component designations as per below and you have exactly the same circuit as Biobill and RabbitGTD - so again follow the instructions I gave BioBill.

Leave the terminal marked ZA disconnected



Cheers!

Reply #82March 19, 2006, 10:52:45 am

johnny

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« Reply #82 on: March 19, 2006, 10:52:45 am »
Next weekend we will rebuilt the tach and install it, I think I'm going to use a strobe or make the variable outside of the tachunit so I can calibrate it more easily after the tach is installed in the dash.
I will let you know next week how it went.

Thanks again cheeseman  :wink:

Reply #83March 19, 2006, 06:23:19 pm

RabbitJockey

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« Reply #83 on: March 19, 2006, 06:23:19 pm »
we have these neato strobe lights at school that we used to see the rpms of little electric motors.  it had a read out of the rpm on the back and then you adjusted knobs until the mark on the wheel on the drive shaft of the little electric motor would "stay in place"  and of course, assuming the motor wasn't at double that speed, you found the correct rpm.
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Reply #84March 19, 2006, 08:29:03 pm

Kudagra

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« Reply #84 on: March 19, 2006, 08:29:03 pm »
Newer Bobcat loaders use a magnetic pick-up. Basically just a digital on/off switch. Think that would help anyone. I can probably get a few.
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Reply #85March 20, 2006, 06:27:38 am

regcheeseman

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« Reply #85 on: March 20, 2006, 06:27:38 am »
I took delivery of a set of A2 GTD clocks this weekend, I have just gone over the schematic (pretty tricky as board contains MFA stuff as well as tacho circuit)
But it is pretty much the same as the conversion board except for non important component value changes.

Anybody want a set of GTD clocks? Will fit A1 or A2 - some small loom mod required for A1 install.

Oh and all you motometer owners.... I not 100% sure on the original component values versus the VDO unit that I have succesfully swapped. It SHOULD be the same but I don't think it was every really answered.

Someone do a motometer.... if one type workswhen modified, they all should :D

Reply #86March 21, 2006, 04:50:04 am

johnny

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« Reply #86 on: March 21, 2006, 04:50:04 am »
Another little question:

does the voltage of capacitors matters or doesn't this have any influence on the tach. (I noticed I have one 100V capacitor and a couple of 10V)

Reply #87March 21, 2006, 05:38:43 am

regcheeseman

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« Reply #87 on: March 21, 2006, 05:38:43 am »
You should use caps greater than or near to the expected circuit value (12V ish in this case).

However my factory unit uses 10V caps - so you should be fine.

The 100v will be ok as well to use - aside from being slightly physically larger than the equivalent lower voltage version.

Reply #88March 23, 2006, 02:59:32 pm

alphawerks

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has this been beta (road) tested?
« Reply #88 on: March 23, 2006, 02:59:32 pm »
Has anyone had success with this in their car? Seems to be proving problematic at the moment. Just curious if it's me or the hardware.
(90 td, 83 gas tacho) Goes to 4k on power-up, then 5k running, with no change due to RPM. Checked the shematic several times, tried the 'conversion' instructions, and the 'original' td schematic setup. Any ideas?

Ryan

Reply #89March 24, 2006, 04:45:06 am

regcheeseman

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« Reply #89 on: March 24, 2006, 04:45:06 am »
I've got no car to try it with at the moment....



But I've ran it up to around 1000rpm with the altenator in a vice being turned by a drill.
And I've also simulated the W signal up to 7000rpm in the lab with no problems.

What tacho did you start with? Your problems are not something I have experienced during any of the development work except when I left a resistor in by mistake early on - it would whizz round to full revs showing without any w terminal signal applied.

I've built another conversion for a similarly afflicted caddy nut, but he has no way of testing it either....

 

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