How to drive an NB speedo without a speed sensor - Page 2 - Miata Turbo Forum - Boost cars, acquire cats.

Welcome to Miataturbo.net   Members
 


ECUs and Tuning Discuss Engine Management, Tuning, & Programming

Reply
 
 
 
LinkBack Thread Tools Search this Thread
Old 01-21-2016, 03:36 PM   #21
Elite Member
iTrader: (3)
 
AbeFM's Avatar
 
Join Date: Aug 2006
Location: San Diego, CA
Posts: 3,048
Total Cats: 8
Default

Ah! I've been quite interested in this for years - never made it to the top of my "list of stuff I'll actually do".

I have no ABS, and I DO have the OEM VSS, but I've been wanting to make the MS apply my correction factor directly - as tire shape changes with speed (both larger from spinning and smaller from wrinkling), correlating GPS speed with pulses seems the way to go - then apply a correction algorithm to the input (be it ABS or VSS). I already take the VSS into the MS3Pro, but using the output to drive it makes sense.

Can you be more specific about this dwell time thing (or was that only for the tach)? As both have the same issue (https://abefm.smugmug.com/Miata/Modi...Tach-Response/) it would be nice to let the ECU just do ALL the corrections.
AbeFM is offline   Reply With Quote
Old 01-21-2016, 03:39 PM   #22
SADFab Destructive Testing Engineer
Thread Starter
iTrader: (5)
 
aidandj's Avatar
 
Join Date: Apr 2014
Location: Beaverton, USA
Posts: 17,999
Total Cats: 1,466
Default

We literally just connected an injector out with a 1k pullup to 5v, to the orange speedo wire. Set it up in MS3 and bam, it worked. Left the other yellow speedo wire floating

This has not been road tested, only tested up to about 45mph by spinning the front wheel.
aidandj is offline   Reply With Quote
Old 01-22-2016, 09:22 PM   #23
Elite Member
iTrader: (3)
 
AbeFM's Avatar
 
Join Date: Aug 2006
Location: San Diego, CA
Posts: 3,048
Total Cats: 8
Default

I should just try it. What really killed my motivation was the lack of scaling options in MS.
AbeFM is offline   Reply With Quote
Old 01-22-2016, 09:31 PM   #24
SADFab Destructive Testing Engineer
Thread Starter
iTrader: (5)
 
aidandj's Avatar
 
Join Date: Apr 2014
Location: Beaverton, USA
Posts: 17,999
Total Cats: 1,466
Default

Quote:
Originally Posted by AbeFM View Post
I should just try it. What really killed my motivation was the lack of scaling options in MS.
I'll borrow a function generator from work and see what speeds I can get out of my spare cluster.
aidandj is offline   Reply With Quote
Old 01-23-2016, 04:30 PM   #25
Elite Member
iTrader: (3)
 
AbeFM's Avatar
 
Join Date: Aug 2006
Location: San Diego, CA
Posts: 3,048
Total Cats: 8
Default

Oh, yeah, that would be good. I wonder if I have one? No. Spares of everything but what I need. :-)
AbeFM is offline   Reply With Quote
Old 01-23-2016, 04:57 PM   #26
SADFab Destructive Testing Engineer
Thread Starter
iTrader: (5)
 
aidandj's Avatar
 
Join Date: Apr 2014
Location: Beaverton, USA
Posts: 17,999
Total Cats: 1,466
Default

I have a spare cluster. And a MDO4k. It might even have a function generator output...
aidandj is offline   Reply With Quote
Old 01-24-2016, 06:54 PM   #27
Elite Member
iTrader: (3)
 
AbeFM's Avatar
 
Join Date: Aug 2006
Location: San Diego, CA
Posts: 3,048
Total Cats: 8
Default

I think when I was doing it I used the Jim Stim. Drove the MS and compared screen to physical tach gauge.

""I fed the tach known spaced tach pulses, and found that the tach is accurate at low RPM (1000), and from ~1500-~4000 is picks up linearly about 175 rpm of offset (it reads high). Then it stays there until ~7200 (reading ~7375) and by 7500 it's reading correct again, which it retains through 8000 rpm, which is as high as I tested.""

There's my super-scientific data. Enough to know something's wrong, not sure enough of it. :-) But both tach and speedo should have ~7 point tables or a simple formula to tweak the output. The MS should be able to drive all of it - and it already knows the engine/road speed, etc, so why not do it there?
AbeFM is offline   Reply With Quote
Old 01-24-2016, 10:46 PM   #28
Junior Member
 
Join Date: May 2007
Location: Atlanta
Posts: 384
Total Cats: 39
Default



Here are my manual tach corrections. Big pain in the *** since it's obviously non-linear. I'm using scaled piecemeal functions for the moment (imagine point to point lines). Need to check against my 2nd cluster to see if the results are valid and not some inherent manufacturing differences (and create a few additional data points). Don't worry too much about how this data is actionable, this is primarily to see if wolfram alpha could create a best fit line that looked halfway implementable (hint: it didn't).

Did I mention I have this on my bench reading data from megasquirt thru canbus right now? Too cold to work in the shop so I'm working on my bench. I need to get the LFX running to pull OBDII data, but I can compensate for transaction times and other gotchas via MS. Been playing with the timer0 prescaler to try and knock out some jitter. Needles aren't flapping but it could always look better through the scope.
Attached Thumbnails
How to drive an NB speedo without a speed sensor-tach_correction.png  

Last edited by gooflophaze; 01-25-2016 at 04:35 AM.
gooflophaze is offline   Reply With Quote
 
 
Reply

Related Topics
Thread Thread Starter Forum Replies Last Post
My solution for Oiltemp and Oilpressure input into Megasuirt (MS3) Zaphod MEGAsquirt 41 01-24-2016 01:25 PM
Back to Stock Part Out!! Turbo Parts, MS2 Enhanced 01-05, Suspension, and MOAR! StratoBlue1109 Miata parts for sale/trade 16 10-02-2015 10:39 AM
3rd Time's a Charm...hopefully. zephyrusaurai Meet and Greet 2 09-28-2015 11:59 PM
Got bad Crank Angle Sensor and Random Misfire codes, but runs fine. Greasyman General Miata Chat 2 09-28-2015 11:44 AM


Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off



All times are GMT -4. The time now is 04:30 AM.