Linear potentiometer for a racing car gearbox


Thread Starter

David Halpin

I am remachining the shifter drum in a sequential gearbox to improve racing. I want to be able to identify current selected gear and plan to do so by replacing the 'neutral light sensor' on the engine with a potentiometer. I will machine in 7 different protrusions on the drum to correspond with each gear. However, I only have a depth of about 10 to 12mm to play with so I will have to make 7 discrete steps of about 1.5mm each. Does anyone know of a device that will reliably give an output that I can process through a microcontroller to give an output to a LCD?
Hey Bob! We have six gear positions and a neutral. We are restricted to a 600cc engine and therefore have chosen a Honda CBR600 motorcycle engine. However, because the shift pattern on the bike is 1-N-2-3-4-5-6 with 'half-shifts' between 1-N and N-2, I wish to machine a new shifter drum so that we can go N-1-2-3-4-5-6 with the half shifts out of the way up around 4,5 and 6 as the car will only use gears 1 thru 4. The class of racing is Formula SAE. To learn more, have a peep at - we are the first Irish entry. The operation of the drum means that there is no external way of determining current gear at any moment. The bike has a neutral indicator which is turned on by a spring loaded switch being depressed by a raised bump on the drum. By producing a series of these bumps on the new drum, I hope to be able to feed the potentiometer voltage into a micro so that it can decide what gear we are in. If the circuit resets at any stage, the micro will be able to detect current gear without having to refer to memory. Sounds like a bit of a task, but I love a challenge! Dave
Hello Dave. I see - maybe look for Magnetostrictive indication. It is used in our industry - but you can get a better price from hydraulic industry. This device is used to measure the stroke of a cylinder eg. Robotics or some type of accurate control. 0.0001 of an inch. Look around on your side, as systems are available from palm size to huge. You would have to drill a boss in the case so the tiny actuation rod could be inserted inside while the small sensor is attached external. I would imagine F1 would use this technology for throttle position sensors. Also – you guys have some hot 125 shifter karts running – lots of good electronic stuff on your side. Looks like your going to need an airline sponsor to get that SAE car over here. You’re looking at a steep learning curve for that class. Someday – one of you guys will finally figure out that a variable transmission (snowmobile) is the only way to go. Properly set up it can’t be beat. Probably not legal anyways. The picture looks like your using a #35 chain. Nice and light and better for high speed. You could always use a double row if it breaks. SAE uses heavy breaking – have you thought of double-faced self venting brake disks. Once again – the kart industry has them. I’ve seen several SAE cars but never an event. Spending a day with you guest speaker is worth a year of thinking if you listened to him. You guys have a lot of talent. Work hard and good luck. Thanks Bob Hogg
Use three sensors at the same time and count the gears in binary? Then you could use three narrow but equal height bumps on the drum. FWIW, Ed Speaking for me, not for Starbucks. . .