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Thread: Robust GPS Speed Sensor

  1. #1

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    We've had issues making front wheel speed sensors live on our Bonneville Streamliner. The only GPS speed sensor that Holley makes uses a USB connector, and it only connects to the dash and not the Dominator ECU itself. This is problematic as it can not be used as an input the Dominator ECU. We need this as a robust speed signal to do things like control boost and compare real speed to rear tire speed. It will also be used for outputs to shift the transmission. It truly is mission-critical to have this be a robust signal.
    After a little research, I found a couple of GPS sending units that actually put out pulsed signal for GPS style speedometers, instead of GPS coordinates that need more math to calculate speed. I found a VDO unit that appears to fit the bill and I'm comfortable with VDO quality. It has an output of 200,000 pulses per mile. If we ever reach our goal of 500 MPH our last mile will go past us in approximately 7 1/2 seconds. That gives us a maximum of 26,666 Hz. Can the Dominator ECU speed sensor input handle this? It will be a square wave input and I'm waiting on the VDO technician to get back to me to confirm the unit can handle our target speeds? The question I really had for him was, "Is the square wave output a fixed duty cycle, or are the pulses all a fixed micro second?"
    I'm looking at GPS Speed Sender Part Number 340 786.
    https://static.summitracing.com/glob...do-340-786.pdf
    What do you guys think? Providing it is a fixed duty cycle digital signal, will this work?

    This unit can be configured for 4000 pulses per mile. It might also work.
    https://www.summitracing.com/parts/izl-s9020

  2. #2

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    For a one off vehicle, you need to build stuff. https://www.google.com/search?q=555+...w=1100&bih=567

  3. #3

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    Great idea. I can do this quickly with an Arduino to see if the ECU will support the frequency. I can also experiment with duty cycle of max frequency to see if it handles it.

  4. #4

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    I don't know about the VDO unit, but I believe that most handheld GPS units calculate speed based on position readings over a specific time period, like one second. Is a one second speed update interval sufficient for your purpose? And as you probably know, there are many factors that influence the accuracy of GPS position readings and therefore speed readings. Have you ever seen a GPS unit show a speed reading of 400 MPH while driving on the interstate, or show your position a half mile off the road? I have. Do you really want to trust the accuracy of GPS signals to control boost on an expensive engine at that speed?

    What type of speed sensors are you currently using?
    Are you using an Arduino to read the sensors and process the data? Charles

  5. #5

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    Charles, these sensors simply put out a pulsed signal over distance. Very similar to what I'm actually getting from the front wheel speed sensor.
    I do not need to have ECU calculate the speed, and I do not care about my actual position. We've had great luck with GPS speed before when we were using the FAST system.
    The problem with that GPS speed was that it was not a usable input that we could use for boost and other things like flap angle. It did give us very accurate data.
    We've been using MSD's cam sensor (Hall-Effect) on the front wheel speed. We do not use a rubber tire and we believe that the aluminum tire wheel combination is turning into a Van der Graaf generator and ruining the sensors.
    Also, the environment that the sensor has to operate in is extremely brutal. There is just wet salt everywhere in the wheel wells.
    We will continue to use the front wheel speed sensor, but we must make many runs and it must show better reliability before we go back to using it as an input for boost, flap angle, and comparing it against rear wheel speed for tire slippage data.
    BTW, we use the same sensor for the driveshaft speed and it works flawlessly.
    Our biggest issue is that there is absolutely nowhere to test this besides Bonneville, and that happens once a year and we better be ready for it!
    I talked with John at VDO instruments, and got him to inquire with the vendor that supplies the GPS units, to confirm that it will handle the speeds we're looking to operate in.
    We also found out that the sensor can be configured to deliver 16,000 pulses per mile versus 200,000 pulses per mile, which may be a bit better for our application.

  6. #6

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    Quote Originally Posted by robfrey View Post
    I do not need to have ECU calculate the speed, and I do not care about my actual position. We've had great luck with GPS speed before when we were using the FAST system. The problem with that GPS speed was that it was not a usable input that we could use for boost and other things like flap angle. It did give us very accurate data.
    I'm in the process of putting a Dominator EFI system on my car. When I had a carb on the engine, I made a little "black box" that used an Arduino to read the front & rear wheel speed sensors, compared the two, and controlled a light box that had green, blue, yellow & red LEDs. When the wheel slippage was 0%-green light, 5-10% slippage-blue, 10%-15%-yellow, >15%-red. When I get the Dominator EFI system working my intent is reduce engine power based on wheel slippage by retarding timing using the input from my Arduino.

    I assume you're doing something similar to what I did, by comparing the GPS speed to the speed calculated from the driveshaft sensor, and controlling various engine functions. I understand about Hall-Effect sensor signals & GPS output signals, and that the VDO unit converts the GPS speed signal to so many pulses per mile. So since you said that the ECU did not do the speed calculations, how you are doing the calculations? Charles

  7. #7

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    Quote Originally Posted by cbernhardt View Post
    I'm in the process of putting a Dominator EFI system on my car. When I had a carb on the engine, I made a little "black box" that used an Arduino to read the front & rear wheel speed sensors, compared the two, and controlled a light box that had green, blue, yellow & red LEDs. When the wheel slippage was 0%-green light, 5-10% slippage-blue, 10%-15%-yellow, >15%-red. When I get the Dominator EFI system working my intent is reduce engine power based on wheel slippage by retarding timing using the input from my Arduino.

    I assume you're doing something similar to what I did, by comparing the GPS speed to the speed calculated from the driveshaft sensor, and controlling various engine functions. I understand about Hall-Effect sensor signals & GPS output signals, and that the VDO unit converts the GPS speed signal to so many pulses per mile. So since you said that the ECU did not do the speed calculations, how you are doing the calculations? Charles
    Hi Charles. I apologize, we will be using the ECU and the VDO sending unit for calculating speed, but the ECU will not need to calculate speed from normal GPS data coming from updates on global positioning, it just has to do the simple math using frequency.
    I do like your idea of using the Arduino to compare front & rear sensors to detect wheel spin.
    I am doing something similar using the "Advanced" feature on the Dominator ECU. It is OK, but your Arduino may work bit better.
    I'm using 2D graph by gear and I can change how much wheel slippage can occur at different speeds.
    I can not have it pull timing or I will put my exhaust valves through my turbo in liquid form. LOL.
    This is because LSR runs last over a minute and if too much time in spent in Ignition timing retard, EGTs just go through the roof.
    I'm using the "Advanced" function to change target boost. It is a bit too slow, but it tries to help.
    Here is how I planned on configuring the 16,000 pulses per mile.

    GPS Speed input by CarbiniteLSR, on Flickr

  8. #8

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    Quote Originally Posted by cbernhardt View Post
    I don't know about the VDO unit, but I believe that most handheld GPS units calculate speed based on position readings over a specific time period, like one second. Is a one second speed update interval sufficient for your purpose? And as you probably know, there are many factors that influence the accuracy of GPS position readings and therefore speed readings. Have you ever seen a GPS unit show a speed reading of 400 MPH while driving on the interstate, or show your position a half mile off the road? I have. Do you really want to trust the accuracy of GPS signals to control boost on an expensive engine at that speed?

    What type of speed sensors are you currently using?
    Are you using an Arduino to read the sensors and process the data? Charles
    You do know that all airplanes have a GPS system, and their very accurate.

  9. #9

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    Quote Originally Posted by BITE_ME View Post
    You do know that all airplanes have a GPS system, and their very accurate.
    I agree. GPS units are accurate enough to find the airport and they are accurate enough for speed and location information at higher altitudes perhaps because there are no trees, buildings, power lines, and fewer atmospheric disturbances at higher altitudes, but are they accurate enough for instrument approaches? I have a private pilot's license with instrument rating, and the last time I checked, satellite navigation approaches required additional transmitters/receivers at the airports and were listed as NON-precision approaches. That was a few years ago though, so perhaps things have changed.

  10. #10

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