It's the Magnets!

[Karl]

So I added additional nickel-plated neodymium magnets to the drive shaft tonight, in an effort to make the speedometer response a bit smoother.  My car was delivered with one magnet.  I added 5 for a total of 6, and in a brief test drive around the block, it didn't seem to make an ounce of difference - the speedometer needle is still quite jerky.  So if any of you are contemplating this upgrade - it's not going to fix the jerky speedometer.

[bolus]

it's jerky because you are pushing down on the accelerator to quickly 

mine seems smooth.  could it be a problem with the dash?

[Karl]

Let me redefine what I mean by "jerky".  When accelerating from 0 to 20 mph, which usually only takes a second or two, the needle does not transition smoothly from 0 to 20mph indicated.  Instead, it will usually jump twice or three times, from 0 to 10, 10 to 15, etc.  This behavior is less noticeable at high speed (or perhaps I just haven't done enough testing at high speed), but is very noticeable at speeds ranging from 0 to 35 mph.  Whenever I'm coming up to a stop I watch the needle spaz from 35, to 30, to 22, 17, 10, 5, 0, in a very regular ~3Hz frequency.  It seems that, in programming the SPA dash microprocessor, SPA did not give the needles (yes, the tachometer too!) any "virtual inertia".  As a result, they can jump around all they like, but only as frequently as the microprocessor decides to update data to the dash display, which seems to be about 3 or 4 times a second.

[Bruce Fielding]

Yes. They're supposed to do that. Most race car dashes (that I've seen) do that.

If you look at the daft picture of Angie in Atomfun's car with no steering wheel, you'll see the dials showing that she's moving when she isn't.

[wisp]

[quote="Bruce Fielding"]
Yes. They're supposed to do that. Most race car dashes (that I've seen) do that.

[/quote]

That's understandable. It may have something to do with it being in a "race" car. If you're busy looking at the speedo then either you aren't racing or you could end up in deep shinola.

[bolus]

Huh... I dont think I ever recall looking at the dash between 0 and 20.  I'll have to try that

[dp35]

The GM powered Atoms might not have this problem, because they don't use a magnet on the driveshaft.  Instead, they use the OEM sensor inside the tranny. 

Mine does do some funny stuff at low speeds, including the occasional spaz up to 160mph when barely moving, but it doesn't seem as bad as what you're describing.

[silver]

could it have something to do with needing the capacitor fix.  the capacitor is a storage device for power, and maybe the power to the speedo is fluctuating on car's without the fix, therefore the speedo is erratic at odd speeds.  What i don't know is how is if the speedo is electronic, or if that even exists, but if it is electronic, and they know there are existing issues with the guages and that the capacitor fixes those issues, maybe it will fix this issue too.....any comments?

[Karl]

Thanks everyone for your input.  It most likely boils down to me being picky - there's nothing inaccurate about the speedometer, whenever the needle does move, it appears to hit the correct speed.  It's just that it only appears to move a finite number of times per second, something that I thought might be due to the sampling rate being very low (with one magnet).  It turns out that it's a hard-coded programming in the SPA dash.

[Karl]

Could one of you EcoTec guys go into the dash setup and figure out how many Trigger Points the EcoTecs have?

[bolus]

how do you do this?  I can try it later

actually, does anyone have a full manual for the dash?

[Karl]

Turn the car off.  Find the tiny little odometer-reset button on the left side of the dash.  Push and hold it.  Turn the car on.  When you see "Demo Mode" in the dash display, release the button.  Use the button to cycle through the various items in the dash display, until you get to "Trigg Points".  With "Trigg Points" shown on the display, press and hold the button until a number appears.  That's the number of trigger points.  Release the button and wait for the number to disappear again (be careful not to increment it!).  After the number disappears, shut the car off.

If you accidentally increment the number of trigger points, don't panic. Press the button to increment it again and again until you wrap around (99 -> 1) and get back to the original number.  Then wait for the number to disappear.

[bolus]

it says 5

[Karl]

Sweet, thanks for the info!

[Gage]

[quote="Karl"]
Let me redefine what I mean by "jerky".  When accelerating from 0 to 20 mph, which usually only takes a second or two, the needle does not transition smoothly from 0 to 20mph indicated.  Instead, it will usually jump twice or three times, from 0 to 10, 10 to 15, etc.  This behavior is less noticeable at high speed (or perhaps I just haven't done enough testing at high speed), but is very noticeable at speeds ranging from 0 to 35 mph.  Whenever I'm coming up to a stop I watch the needle spaz from 35, to 30, to 22, 17, 10, 5, 0, in a very regular ~3Hz frequency.  It seems that, in programming the SPA dash microprocessor, SPA did not give the needles (yes, the tachometer too!) any "virtual inertia".  As a result, they can jump around all they like, but only as frequently as the microprocessor decides to update data to the dash display, which seems to be about 3 or 4 times a second.
[/quote]

My speedometer doesn't do anything like that.  Its smooth.