how to make two shafts rotate together... ???

[doctor ed]

ok, ive got 2 shafts which i need to install to run linkages dor 2 opposite banks of throttle bodies. the linkages need to pull towards the centre.

the shafts (onto which the linkages are fitted) need to rotate in unison (in opposite directions of rotation). they need to be linked precisely, and have the same amount, and rate of rotation relative to each other. not good if the banks of throttle open differently, ezpecially at low degrees...

the shafts are 10mm dia, and can have a separation of 100mm to 25mm

the easiest and most obvious way to make this work is with 2 meshed gears on each shaft. problem is, said gears cost $97 each. plus it looks ugly.

the alternative is to use a linkage mounted between a crank on each shaft. i happen to have some cranks that will fit the shafts, the length of the cranks are 30mm.

the question is, given that crank length, what should the sepration of the shafts be, and what should be the origin angle of each crank on each shaft (and obviously, what is the resultant lenth of the joining linkage).

this is obviously tough as due to bloody trigonometry, and the changing relative angles of the cranks and linkage through 90deg rotation, the ratio of angular movement between the shafts isnt quite 1:1 at all positions.

so far i have mocked up a few examples, and the best i can find so far is to have a separation of 67.5mm, a linkage length of 48mm, and radial origina of the cranks of 0deg and 90deg respectively. this seems to give the closest output of 1:1 mmovement, though there is a bit of wandering. obviously fidelity is most important around the first 20odd deg for smooth off idle throttle control...

the image below describes this 67.5mm separation. (this is the best ive com up with so far). the movement is referenced from the left shaft. as you can see, there is some tiny lag in the right shaft in the first few deg, which soon catches up, and overtakes, only to come back to nearly 1:1 at WOT importantly, see around 10-20deg, the movment is very 1:1



this following image is at 65mm separation (only 2.5mm difference) yet you can see that this has a big effect on the ratio of movement. specifically look how far ahead the right shaft gets even at only 20-30deg...



so, the question is!! can anyone come up with a BETTER way to link these shafts to provide as close to 1:1 motion over the full 90deg?? is there an equation that we can solve to determine the correct separation of the shafts, and the angular origins of the cranks to achieve this goal?

i have just been trial and erroring the diagrams and obsercing the effects changes to these dimensions has - however, there must be a mathematical way to describe this to yeild an optimal solution??

if not, does anyone have any other bright ideas as to how to link the movement of these two shafts???

perhaps a solution is to not have the cranks travel through 90deg at all, and simply change the ratio of the linkages to the throttles so that this 90deg shaft rotation isnt required ro achieve 90deg rotation of the throttle plate? (which is a pita as all my other cranks and linkages are designed for 90deg rotation!)

and before anyone says im mad for trying this, i got the idea from the toyota f1 linkage design:



so yeah, any thoughts!!

cheers
ed

[Zac]

Have you considered dual throttle cables or a single cable that splits into two?

[doctor ed]

yeah, but i want to see if this can work as it is the simplest and most elegant solution

there is limited space in the valley - if this works it will all be incredibly neat and compact

[Zac]

So it isn't a 7M-GE?

[doctor ed]

nup - sold project 7mge

now doing 1uzfe v8 into jza80 supra

n/a x8 throttles cams etc etc...

[doctor ed]

3d pic for calrification...

[blimpyboy]

Your idea seems to be the way that the oldschool quad weber linkages work.. http://www.redlineweber.com/html/for...nkage_kits.htm

[doctor ed]

now theres an idea i hadnt thought of...

[Jim]

yep, the above suggestion. or depending on room, have one pivot joint on each lever link down to one common joint, which then gets linked to the cable or whatever, so it is in a "Y" formation.

[doctor ed]

nah, had a play last night, tying the throttles together with a cross link wont work...

i still reckon im on the money with the original idea, just need to get the numbers right. any further suggestions as to how i might achieve this?

anyone have any pics of f1 linkage setups? perhaps showing in more detail the linkage as seen on the toyota engine above?

cheers
ed

[The Pupat]

you could run a dual cable setup like bikes use with cantilever brakes.

Otherwise the rose jointed adjustable linkage like the F1 team uses is the go. I'd make it adjustable since then you neither have to calculate the exact length nor drill it accurately either.

[260BC]

Do it like your drawing but have the cranks just clamped to the shafts initially. Clamped so the shafts can rotate freely with the clamps loosened off.

Then set the cranks in the positions you want with the throttle fully open or closed. Tighten the clamps to fix the final positions, then make the clamps secure by a means of your choosing.

I can think of another way too, by using circular 'clamps' fixed to the shafts. Set throttles fully open or closed, mark spots on circular clamps where a crosslink matches, drill holes..............

[doctor ed]

yeah, i think ill persists with the rose jointed thing as above... and build in some adjusabililty...

just trying to get the number kinda right to start with so i can plan some related parts of the manifold that depend on the locations of the shafts...

[HoonBoy]

What about two pulleys (or throttle cable holder thingy's) with a cable between the two like this?

[hotgemini]

A central pivot on a bearing, with equal length arms off each end, with the usual spherical bearings to the throttle shafts. MS paint drawing enroute.

Edit: picture