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Indy
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Measuring Vehicle Speed

I have a SpeedHut GPS Speedometer with an ouput that has a square wave of 4000 pulses/mile and 0-5 volts.

Can I measure vehicle speed with an Analog/Freq input or will I have to use a math channel?

Rick

http://www.speedhut.com/gauges/GPS-Speedometers/1:3

http://www.speedhut.com/instructions.i

AEM_NS
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Yes, if you supply a variable

Yes, if you supply a variable frequency 5v square wave to the AQ-1, you can record vehicle speed.  

Indy
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To configure the Vehicle

To configure the Vehicle Speed on input #8, the AQ1 needs to know Pulses/Rev, Final Drive Ratio/Scaler, and Tire Diameter. My SpeedHut speedometer outputs 4000 pulses/mile, so how do I configure these three parameters???

What formula is it using to calculate speed?

EDIT: The Pulses/Rev will only take a 2 digit number, how will I enter appropriate number for 4000.

AEM_NS
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Well I just spent a few

Well I just spent a few minutes doing a bunch of math to figure this out for you only to find that it won't work.  The AQ-1 is setup to calculate speed based on a driveshaft speed input and it's expected that you'd have some whole number's worth of pulses (1, 2, 4, etc).  Well, after calc'ing all this out for you, you pulses per driveshaft revolution is .72 which the AQ-1 won't accept.

So, you won't be able to log this as vehicle speed but you can log the raw frequency and then do some math in AEMData to convert frequency to speed.  The freq to speed calc is speed = .9 x freq based on the 4000 pulses/mile spec you gave.

Indy
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Why can't you use some number

Why can't you use some number for the "Final Drive Ratio/Scaler", it will take four digit numbers with two decimals places. Why can't that be used as a correction factor?

Where does the 0.9 come from in the equation given above? Just trying to make sense of all this info and get the end results of MPH?

AEM_NS
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How about you give me your

How about you give me your actual tire diameter and rear gear ratio so I can calc this out for you.  I'll post my spreadsheet when done.

The .72 was a "fake" number I calc'd assuming 4:1 gear ratio and 28" tire.  What the number actually winds up being won't matter because it won't actually be a whole number - it'll always bee some decimal value since the speed input isn't actually tied to a number of pulses generated by the driveshaft.  

The speed calc is from figuring out how much time there is to travel a mile in seconds at different speeds and then dividing 4000 by this time.  Pulses/seconds=hz.

Indy
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Tire Diameter = 30.38  , 

Tire Diameter = 30.38  ,  Rear Gear 3.7:1

I guess the torque converter slip will not effect this calc?

AEM_NS
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Set pulses per rev to 1, gear

Set pulses per rev to 1, gear ratio to 3.7 and tire diameter to 18.5".

Indy
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Cool, will do and report back

Cool, will do and report back!!!

Indy
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Not what I was expecting,

I did a run from 0-50, with constant acceleration. Not what I was expecting, what do you think?

VehSpeed is Sky Blue (at the bottom of plot area).

Indy
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When I went back to verify my

When I went back to verify my input numbers, the tire size was still on 30.38 instead of 18.5" like it should be. The number was easy to input, but it would not accept it when trying to upload to the AQ1. It would always revert back to 30.38. After rebooting things went better and it accepted the 18.5". I also went from recording at 1000/sec to 10/sec.

Please show me how to calculate these numbers so that I can refigure when I change tires or gear ratios. I can work with Excel spreadsheets if that's easier.

Thanks for all  your help, it's greatly appreciated !!!

greaser
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Looks like a bunch of noise

Looks like a bunch of noise in the vehicle speed.  What sensor, hall or mag?  Shielded wires?  Driven or non driven wheel.  I think you said GPS earlier, is that still the case and the result of that log?  What type of vehicle is it? Trans?

Where are you getting engine rpm from?  I calculate converter slip, converter clutch lock up slip, and wheel slip.  I use a stock nissan mag vss in my re401a as "driveshaft speed", i installed an abs ring on a non driven front wheel with a nissan cam angle sensor for "front wheel speed" and i used to use "engine rpm" from CAN transmitted from a series 2 ems.  Now i have "engine rpm" connected to a coil logic output.  Its faster, but not as fast as the other 2 speeds.  Once i did that converter slips were alot smoother. 

AEM_NS
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So it works?

So it works?

Indy
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greaser wrote:

greaser wrote:

Looks like a bunch of noise in the vehicle speed.  What sensor, hall or mag?  Shielded wires?  Driven or non driven wheel.  I think you said GPS earlier, is that still the case and the result of that log?  What type of vehicle is it? Trans?

Where are you getting engine rpm from?  I calculate converter slip, converter clutch lock up slip, and wheel slip.  I use a stock nissan mag vss in my re401a as "driveshaft speed", i installed an abs ring on a non driven front wheel with a nissan cam angle sensor for "front wheel speed" and i used to use "engine rpm" from CAN transmitted from a series 2 ems.  Now i have "engine rpm" connected to a coil logic output.  Its faster, but not as fast as the other 2 speeds.  Once i did that converter slips were alot smoother. 

Only in the first graph did I get lots of noise, that's not the case now, see the 2nd graph. The sensor is a GPS speedometer that output 4000 pulses/mile, actually it's for cruise control. The car is a TBucket with a 200-4R automatic transmission.

Engine rpm comes from a MSD distributor tach output. I would also like to see how much converter slip I'm getting, but that's down the road a ways.

The AQ-1 is located under the seat, not enough room under the dash area for the main wiring center.

 

Indy
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AEM_NS wrote:

AEM_NS wrote:

So it works?

YES ..... it works great!!! That is once I got the 18.5 number to stick so I could upload to the AQ-1.

Also I went from logging at 1000/sec in the first graph to 10/sec in the second graph. All the noise went away and was plenty fast enough to record vehicle speed.

Can you show me how to calculate the numbers, I might be changing the gear ratio or tires in the future ???

AEM_NS
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Sure.  Let me clean up my

Sure.  Let me clean up my spreadsheet some and I'll get it over to you.

Indy
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That must be some dirty

That must be some dirty software to need that much cleanup!

I know Excel pretty well, so I can work with it if you can just upload it.

Rick

AEM_NS
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Send an email over to emstech

Send an email over to emstech@aempower.com and we'll get it over to you.  Wasn't that it was dirty - wanted to add some notes so you can understand what I did.

Indy
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Sent Email !

Sent Email !

AEM_NS
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Check the email address you

Check the email address you sent to.  Nothing received on our end.  

Indy
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Ok sent email again, with

Ok sent email again, with subject line "Excel Spreadsheet".

 

Rick Miller

Indy
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Pyng Thai has responded to my

Pyng Thai has responded to my email.