Shifter Drum

[BMV_Deutsch]

Hi Everyone,

Has anyone thought about designing a custom Selector drum in the gearbox in order to get a different shift pattern to the default one?

Would i be too naive to say that this is only a matter of finding the right groove combination on the drum and have it machined on a drum that is identical to the stock drum? And then replacing the stock with the custom drum.

I'm sure there are other implications that i have failed to take into account. I'd like to hear from you all http://fsae.com/groupee_common/emoticons/icon_smile.gif

[Jay Lawrence]

It's definitely do-able. We had the option of either machining a new drum, or modifying the standard one. We modified the standard one by machining out a desired path that altered the original path, and by welding in new stops in the right places. This way we achieved n-1-2-3 shifting whilst still using the standard internal gears so we could maintain good final drive packaging. This was done on our 2009 car.

So long as your path is smooth and selects the right gears and there's no chance of selecting 2 gears at once, there's really not much else to take into account with the barrel.

[BMV_Deutsch]

I often wondered why they don't manufacture gearbox that has shift pattern that goes sequential N-1-2-3. That would save people, who decides to change this, alot of trouble!

Or perhaps there might be a reason behind having a shift pattern that is non-sequential?

[Boffin]

The only problem I know of is that you loose a gear.

We have custom barrels in both our RR and F4 and we have lost 6th in both boxes (N-1-2-3-4-5)

[nowhere fast]

Placing neutral at the bottom makes it more likely to unintentionally end up in neutral rather than first when shifting into first from a high gear. Some people just keep tapping the lever until it stops to find first and even if you don't you will sometimes make a mistake and end up in neutral.

The only reason I can think of for changing the position of neutral would be if you were using a pneumatic or electric shift actuator which couldn't find neutral.
Still, a simpler solution to this problem would be to add a mechanical lever to select neutral.

[woodsy96]

Our 2008 car was modified to N-1-2. Made it really easy to drive. Two of the gears were welded together to make it work with a tube between...unfortunately, after three months testing it gave up at the competion 3/4 through endurance and engaged two gears at once, causing much damage.

[PatClarke]

I often wondered why they don't manufacture gearbox that has shift pattern that goes sequential N-1-2-3. That would save people, who decides to change this, alot of trouble!

Or perhaps there might be a reason behind having a shift pattern that is non-sequential?


Once upon a time, a long long time ago, I raced a Kawasaki with neutral at the bottom. I don't remember much about the bike, but I remember what happened when I braked hard into a hairpin, shifting down through the gearbox. When I came off the brakes and opened the throttle, the bike simply fell over (in neutral). Those old enough to remember the TV show Laugh in will know what I am talking about! :-)
Thats why they dont put neutral at the bottom!

Pat

[nowhere fast]

I have heard that back when Bridgestone built bikes they neglected to put a stop on the shift drum so the shift pattern went something like: 1-N-2-3-4-5-6-1-N-2...6-1... and so on.

Mistaking 6th for 5th and thinking you still had a gear left would have been interesting.

[Sormaz]

Originally posted by nowhere fast:
I have heard that back when Bridgestone built bikes they neglected to put a stop on the shift drum so the shift pattern went something like: 1-N-2-3-4-5-6-1-N-2...6-1... and so on.

Mistaking 6th for 5th and thinking you still had a gear left would have been interesting.
Now if you really want to confuse your driver, make it symmetric: N-1-2-3-4-5-6-5-4-3-2-1-N....

[PatClarke]

What's wrong with random selection? http://fsae.com/groupee_common/emoticons/icon_wink.gif

Pat

[BMV_Deutsch]

I'm not sure if this is of any relevance, but what sort of material do you reckon best suits the shifter drum? Clearly the only wear I can think of is the metal to metal contact stress between the drum and the selector forks.

[NickFavazzo]

we do our own custom shift drums at UWAM, we have steel, aly and plastics, all have worked fine, though we have very very little time using the plastic ones in an engine, this may change.

[vandit]

Originally posted by woodsy96:
...Two of the gears were welded together to make it work with a tube between...unfortunately, after three months testing it gave up at the competion 3/4 through endurance and engaged two gears at once, causing much damage.

Just curious, do you have any pictures taken after welding the gears (before installing in gearbox)? and pictures of failure and damage caused?

Upto what temperatures did you guys pre-heat the gears before welding ?

[BMV_Deutsch]

Originally posted by NickFavazzo:
we do our own custom shift drums at UWAM, we have steel, aly and plastics, all have worked fine, though we have very very little time using the plastic ones in an engine, this may change.

wouldn't the elevated temperature in the gearbox be too much for the plastic shifter drum to handle?

Do we have to put much thought in the material selection or can we just go with any steel/aly?

[MalcolmG]

Originally posted by vandit:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by woodsy96:
...Two of the gears were welded together to make it work with a tube between...unfortunately, after three months testing it gave up at the competion 3/4 through endurance and engaged two gears at once, causing much damage.

Just curious, do you have any pictures taken after welding the gears (before installing in gearbox)? and pictures of failure and damage caused?

Upto what temperatures did you guys pre-heat the gears before welding ? </div></BLOCKQUOTE>

If you can imagine all the damage that you can do to a pair of gears, 4 pistons, a cylinder head and some dry sump pumps, that's approximately the damage that was caused.

[NickFavazzo]

Originally posted by BMV_Deutsch:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">Originally posted by NickFavazzo:
we do our own custom shift drums at UWAM, we have steel, aly and plastics, all have worked fine, though we have very very little time using the plastic ones in an engine, this may change.

wouldn't the elevated temperature in the gearbox be too much for the plastic shifter drum to handle?

Do we have to put much thought in the material selection or can we just go with any steel/aly? </div></BLOCKQUOTE>

Engineering plastics are pretty good, We are sponsored by a company called Dotmar, they helped us with the selection.

If you look at how the shift drum works, you want good wear properties, low friction and decent strength (if material is prone to chip/plastically deform) or similar to why we chose plastic you can have high(er) elastic deformation.

It depends where you are in your overall scheme of design, if you want to save a little weight and make all the little parts spot on go fr it, otherwise I'm sure time could be spent elsewhere, our older cars use the stock drum and they are no real problem to drive.