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Formula SAE car gear indictator

  1. Jun 16, 2012 #1
    Hi, This may not being the right place for this but I'm giving it a shot

    I'm trying to figure out how to make a gear indicator for our university's formula SAE car. I just finished my freshman year and came in without any credits so I have a very limited knowledge of applying programming to a real world application or anything about electrical engineering in general. I'm also the only EE on the team so I'm more or less on my own here..

    To the point, our car uses a cbr 600rr motorcycle engine with a custom 4 speed transmission that's actuated by a steel cable attached to a gear lever in the driver cockpit. When you pull the lever back, it shifts up, when you push it forward, it shifts down. The position of the gear lever is independent of the gear you're in.

    I'm aware that there are gear indicators commercially available for motorcycles. However they rely on a program that calculates the gear you're in based on your RPMs and speed. This method has some issues such as it's fairly slow and requires the car be moving.

    Here is a list requirements I have for the indicator

    1: when you move the lever it changes the gear correctly
    2: it only has to be calibrated once so it follows our 1,2,3,4,N,N,N shift pattern reliably
    3: it has to somehow work even when the car is off, so if someone changes the gear when it's off it will save what gear it's in. even if the main battery is unplugged.
    4: the micro controller that dictates all of this must be able to run from it's own power source 24/7/365
    5: the display should indicate the gear the car is in and must only be on when the car's electronics are on and must draw power from the car's main battery

    Here is a list of how I think I can meet these requirements

    1: I'll have contacts or sensors or a magnet attached to the gear lever, so when you shift, up or down, a circuit is completed and the gear changes to the correct gear. A micro controller (programmed with an arduino or similar device) will sense the completed circuit and change the gear displayed to the driver.

    2: I'll figure out some way to activate a calibration mode in the micro controller, and then I'll have the car in first gear when the indicator is ready to be calibrated. After I’ll shift up from the 1st to the 7th "gear" and the calibration will be complete. We have 3 neutrals in our car as it used to be a 6 speed transmission, so that is why I said “7th”. Once calibration is completed, the car will cycle between 1st and the third neutral without issue as you pull and push the gear lever. I would like to also be able to recalibrate the gear indicator by pushing a button on the micro controller. That way, if I'm at a competition, we can recalibrate quickly and without any tools.

    3: I would like the micro controller to always be on so the gear position will be accurate for the life of the battery powering the micro controller. Moreover, if someone were to change gear when the car is off (i.e. put it in neutral to push it around) it will display the correct gear when it's finally turned on again. I was thinking that a disc battery (like they have on motherboards) could be used to power the micro controller but I'm not sure if it will have enough power to ensure the controller stays on for at least a few weeks.

    4: This kind of ties in with #3 but it's very important that the micro controller is powered independently from the rest of the car. This is because we're swapping batteries on an almost daily basis and I'd like this system to be reliable independent of the rest of the car to increase reliability and serviceability. I'd like to use a battery used in a motherboard because they're light, cheap and internationally available. However if I need a larger battery, so be it. Ideally I'd like the car's main battery to recharge the micro controller battery when the engine is running to minimize the amount of times we have to change batteries/calibrate the gears. This is a secondary objective though.

    5: The dash display that indicates the gear the car is in must only turn on when the car is turned on, and must run off the car's main battery so it doesn't drain the microcontroller battery. Of course, it must accept input from the micro controller so the gear is actually displayed. My idea for this was connecting simply connecting the power cable to the display to the dash harness and connecting the wires that control the gear displayed will be connected to the micro controller so the display is drawing power from the main battery and the main battery only.

    This is all a rather tall order, I know, and I'm not expecting anyone to do this for me by any means. These are simply my objectives and I'm using all my resources to learn as much about this as possible so I can make it a reality. You've probably been able to tell already, I'm embarrassingly ignorant.

    any suggestions/questions/comments are welcome.

    Thank you for any and all feedback.

  2. jcsd
  3. Jun 16, 2012 #2


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    Science Advisor

    Could you measure the input RPM from the motor and the output RPM, get the ratio between the two and then look up a table to see what gear the gearbox is in?

    Nicely written post.
  4. Jun 16, 2012 #3


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    Science Advisor
    Homework Helper

    If you want something completely indepedent of the gear change mechanism, that works when car isn't moving, you could try sensing the positiions of the gears or shafts inside the box. Capacitance based sensors might work, but I don't know if the gearbox oil would interfere wth them.
  5. Jun 17, 2012 #4
    I considered putting sensors inside the gearbox, but I'd have to open every motor and install sensors in every motor we use (we have 4). Moreover it just seems like that would add a lot of potential for failure, and seeing as this isn't a critical system for the car, I'd get chewed out like no other if my gear position sensor messed with our one off transmission.

    unless I'm misunderstanding what you said.

    @vk6kro we've tried that in previous years and we ran into problems where it wasn't 100% accurate. I also want it to work when the car is stationary/off. also I'm not sure if that nice post comment is sarcasm. maybe I'm jaded.

    I should also add if anyone knows of any literature that would be beneficial to learning how to do this, I would be very appreciative.

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