Gearshift Display for a Rally Car

[Andrea] was helping out a local rally racing team with their car and was asked to create a device that would display the current gear on a big, bright display. Of course, a device like this already exists, but the team didn’t want to invest the significant resources into a ready-made product. Instead, [Andrea] was tasked with creating one.

The device is basically a pot attached to the gear shifter, but in testing, [Andrea] ran into a problem; between reverse and 5th gear, the shifter would turn 360 degrees, meaning these gears were indistinguishable.

The solution to this problem was a calibration procedure for when the driver starts the car. By setting a jumper, the driver puts the car into all gears, sorting out the reading and storing the analog values in the microcontroller’s EEPROM.

23 thoughts on “Gearshift Display for a Rally Car

  1. Is the Reverse-5th problem caused by a bad pot? A linear multiturn pot could deal with that.
    I would also go with shiftUp() and shiftDown() functions on the software side, keeping track of gear sequences. That way, if you start the car in Neutral, you could simplify or skip entirely the calibration process.
    Also, by mounting some serial driver on the 7 segment board instead of a parallel on the main board you could use a cable with less wires.

        1. Yes. It works exactly like a motorcycle. The shift rods that are normally pushed and pulled by the stick are instead guided by groves in a cylinder. There is a stop so that you can’t go from 5 to R, and many have a neutral position between R and 1.

  2. There are off-the-shelf gear indicators (mainly for the motorbike market) that work by comparing speed and engine rpm signals, calculating which gear you’re in from their ratio.

    That said, it is useful to know which gear you’ve stopped in though.

    1. “significant resources” is a matter of perspective. Your link, @ $300 by the time you buy a pot (listed, but not included at link price), I would not consider insignificant resources. – Especially if you can build an alternative with parts laying around your workbench, or less than $10, and learn something along the way and have fun designing it.

  3. Hall effect notch sensors would have made the whole thing simpler without requiring calibration. Using two modules, a display and a sensor module, with a TWI or (for better noise tolerance) a CAN bus between them would have simplified installation.

  4. I think a fairly simple boolean argument could keep the device from getting confused. Simply have it keep track of the previous gear selected. When the reading for R and 5 pops up, just have the software compare it to the last gear. It should be easy enough to know that it won’t be going from 4th to R without first going through 3, 2, and 1, if that’s how the transmission is sequenced (don’t know, as I’ve never driven a rally car, much as I would love to).

    1. This is a sequential gearbox, there is no visual or tactile indicator for what gear you are in. What happens when you bog the engine in first, assume you must still be in second, and shift down?

  5. Motorcycles have sequential gearboxes, those who ride or race them soon develop a feel for what gear they are using, any reason that would be more difficult for those driving a care with sequential gearbox? Grant motorcycle don’t have reverse. R doesn’t mean for race. Reverse even in rally racing doesn’t appear to employed that often, it seems to make sense to have control of reverse separate from the forward gears. Just pondering…

    1. I’ve been riding an ex-racebike for 29 years and haven’t developed that feel to my satisfaction. My bike has a tach, a speedo and a close ratio 6 speed gearbox. I’m often reaching for 7th gear or thinking 5th is 6th, especially after changing sprocket sizes. This year in the off season, I’m building a gear indicator (RPM vs. Speed).

  6. Andrea, this is terrific. Great work.

    The one thing piece of rally tech I’d *love* to do cheap is a trip odometer that the co-driver can read. my car is stock and OBD1, so I assume the odometer moves by a pulse sent X number of times per rotation of the drive tire. if that’s an electrical pulse coming down the line, there has to be some way to capture that from the car.

    I tell ya, if I can figure this out without GPS, that’s a game-changer for my car.

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