Gear position pot on shift drum, F4i

[Johughes]

Hey guys, this year I'm determined to get a pot onto our shift drum for gear position feedback for our electronic systems.

I know other teams have done this in the past. Questions I have are:
- Did you use a special type of pot to withstand the oil bath and high-temp?
- How did you physically mount the sucker in there?

Thanks,

John Hughes
Electrical Section Head
University of Manitoba Formula SAE

[jrickert]

Depending on what motor you are using it may already have a gear position sensor sensor. If not Penny and Giles makes some robust sensors that are designed for this sort of thing but rather expensive.

[Jersey Tom]

Is it really essential?

The quick and easy way to determine gear is by looking at wheelspeed data, engine RPM, and knowing the gear ratios.

If you gets lots of wheelspin it will throw the calculation off.. but for general data logging and display it works well.

[Kirby]

What engine does manitoba run?

[Johughes]

We're using a 600F4i.

It's obviously crossed my mind that I can simply "count" the up and down shifts, but I want to use gear position as a feedback source in my shift mechanism, and for traction control. I.E., I want to be 100% certain which gear the transmission currently is in, in case of missed shifts, etc.

John Hughes
Electrical Section Head
University of Manitoba Formula SAE

[JeffreyH]

You're better off looking at the exact position than using wheel/engine speeds + gear ratios. I've yet to come up with a good reason for wanting to look at which gear you're in once driving as you should be looking at the course, and when moving you should know what gear you're in anyway (as a motorcyclist I know that you just intrinsically 'know'). The most useful time I can think of is when sitting stationary with the clutch in and wanting to select a gear (or neutral).

In the past we have had systems which work out gear based on shifts and/or gear ratios, but it's not fantastic and really not worth the time. I would strongly suggest using an position encoder.

You could use a simple micro with a quadrature encoder to work out position, but that gets tricky as you either need to re-index on startup or have a very nifty routine to store position to EEPROM when your power is cut. There are better alterantives IMO, namely the use of absolute position encoders.

One manufacturer I'd recommend looking at is RLS. They're expensive, but IP68 and pretty awesome. There are a couple of other manufacturers of similar encoders as well, I just happen to be more familiar with RLS.


Hopefully that helps.

[Kirby]

IIRC, on the f4i (i think) under the shifting mechanism cover there is the "ratcheting star" which is part of the drum. you can extend out from this a shaft to attach to a pot, don't break the welds that it attaches to the drum with. this part of the shifter mechanism is dry from engine oil and such should be a reasonable place for a a pot. even then I'd go for a ceramet? or conductive plastic type over wire wound.

[JeffreyH]

Again, I would seriously look at a good absolute position encoder. They're only ~80 euros or something and are a much more accurate & repeatable option, which then makes any logic using the sensor a bit easier. I would expect to pay nearly as much for a good quality pot of any sort.

[Diablo_niterider]

Hey ,

we modified our shifter drum on the F4i to incorporate a gear position sensor.

What we did was manufacture 2 really tiny gears using the centre to centre distance of the shifter drum and neutral switch , remove the neutral switch and manufacture a hollow stepped adapter with external threads same as that of neutral switch and put it in the neutral switch hole. make a shaft of suitable diameter which passes through the adapter you put on the neutral switch hole and mount the gear on the shaft and shifter drum suitably , grind the shifter drum suitably and connect the pot on the other end of the shaft which is external. dont forget to use fibre washers and o -rings + sealant agents as precaution.
for retaining the gear on shaft you could use a circlip of that size available at remote control aircraft spare guys or 3.5 cc and so on engine manufacturers or thread it and grind a nut and loctite it.

on the other end of the shaft mount the pot , so make a stepped shaft with a groove for the pot shaft and mount the pot using the chain cover bolt or water pump bolt or both.

this way the pot is external and you dont have to worry about Temperatures.

We had thought of putting a Gear position sensor like the one on the stock gixxer (which is on the rachet attachment of the gixxers shifter drum) but there is no space as the shifter assembly and clutch basket fits closely.
if you still wanna try ,check out the assembly diagrams at bikebandit.com u will find the stock gixxer sensor there too.

we never had a failure till now in two years. Best of luck hope it was helpful

Hiren Patel
Powertrain lead '07 '08 '09
Technical Director '10 - ??
Orion Racing India
www.orion-racing.com (http://www.orion-racing.com)

[Kirby]

Originally posted by JeffreyH:
Again, I would seriously look at a good absolute position encoder. They're only ~80 euros or something and are a much more accurate & repeatable option, which then makes any logic using the sensor a bit easier. I would expect to pay nearly as much for a good quality pot of any sort.

No Doubt, but depending on ECU/Controller one Analog line is much simpler than the output of a absolute position encoder.

[JeffreyH]

Originally posted by Kirby:
No Doubt, but depending on ECU/Controller one Analog line is much simpler than the output of a absolute position encoder.


Are you sure? http://fsae.com/groupee_common/emoticons/icon_razz.gif

I take it you haven't looked at many absolute position encoders then. I know of at least two which output a linear voltage corresponding to absolute position. The advantage is that they're non-contact and sealed, meaning there's no wear on contacts, you're not affected by temperature drift (you will get this to a certain degree on pots), and it's going to give the same output every single time. Not that a pot is a bad solution, there's just better (in my opinion at least).

[Kirby]

Originally posted by JeffreyH:
Are you sure? http://fsae.com/groupee_common/emoticons/icon_razz.gif


I respectfully retract my comments. The one and only absolute position encoder I used was quite different to what you describe; Multi-way Digital output.

[JeffreyH]

Yea I was quite surprised when I found them. They're pretty neat. It's definitely more common to use the digital output ones though. Have a look at these: http://www.rls.si/default.asp?prod=re22

There's another manufacturer who makes something similar. I would definitely look at these over a good pot as your cost is likely to be similar yet these are non-contact and less susceptible to ... anything really. They're basically an LVDT as compared to a linear pot.

[Fred G]

John,

We installed a returning linear potentiometer in place of the neutral position sensor.

We had the luxury of remaking our shifter barrel to remove the Honda CBR 1-N-2-3-4-5 shift sequence to a N-1-2 etc. In doing so, we machined an inclined cam profile on which the potentiometer could be actuated.

Once installed, we programmed voltage boundaries to enable Motec to know which gear gear corresponded to these boundaries.

The pot cost a handful of dollars from a local electronic store. We also installed an o-ring to reduce oil ingress into the pot. The neutral position switch location was rethreaded and an adapter made for the pot.

Hope my rambling makes sense.

All the best.
Fred

[MarcusT]

On our Aprilia there is a gear position sensor that is actuated by the shift barrel. A small pin with a spring fits into the end of the shift barrel. The gear position sensor is basically a one wire "puck" with varying resistances pads. Depending on which gear the barrel has selected, the sensor grounds the sensor through the engine block. I used a microcontroller and a voltage divider to determine an output voltage and based off of that voltage used a seven segment to show the driver gear position display on the dash.

We were going to use the motec utility to determine gear based off rpm/wheelspeed, but opted for this route because we could tell what gear the car was in even when it was sitting still. Don't know if this is any help to you, but that is what we did.

Marcus
AUFSAE