Rotating an object on its own axis

Youve got it mate !
If you look at the centre wheel boss on my Britannia model, the connecting rod does a real herky-jerky !
No-one has pointed it out though yet. Looks like i got away with it !

Kim Durose
[img:162awlos]http://www.kimsim.co.uk[/img:162awlos]
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This may sound like an extremely thick question, but does anyone know how to rotate an object around one of its own axis rather than the world axis ?
I am trying to animate some Caprotti valve gear which has some inclined drive-shafts and I wish to make the shafts rotate.

Thank you,

Kim Durose
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Cheers Kim – actually I figured out what the problem was by looking at M$’s Scotsman model. Your answer makes sense too:

I was trying to rotate the piston-rod from where it pivots at the centre wheel – not by the piston itself – this was meaning that the inaccuracies were showing themselves up near the obvious piston travel which has to go in a straight line to look right.

If you let the inaccuracies happen near the centre wheel imaginary pivot, they are barely noticeable. (only if you are looking hard, which of course I am!)

I was also getting in a knot trying to shift the objects in animation – which tends to get ignored by the animator – I had to physically move them!

The reason for tangents is that I was working the angle out based on the distance down the rod had to travel.

I’m not sure I totally get your method of angle calculation!

anyway, cheers for the advice – like you say – once you work it out it’s easy!

JonG

Thanks for the advice chaps. I’m still using version 4.24, is the andquot;use objects axisandquot; button in this version ? I’ve had a poke around but cant find anything (again I’m probably being very thick).
Animating Waalscherts is a bit of a pig at first but once you find a system its incredibly easy. I keep meaning to do a tutorial on it but never get round to it !
You seem to be going about it the hard way really. I animate in this order:
Coupling rods
Connecting rods
Slidebars / piston rods
Following these i do all of the other bits and bobs. Once you have all of the keyframes in place for the main components its just a case of rotating the other bits so the imaginary pivot points line up again. Ive explained that terribly, but its easier to do than it is to explain !
There should be no working out of tangents and suchlike to be honest. If you imagine that your eccentric rods and combination levers etc. are rotating on a circular plane (even though they dont rotate the full 360 degrees) you wont go far wrong.

Kim Durose
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Yes, you’ll need 5.0 (or higher) for the Object Coordinates mode.

5.0 is a free upgrade for all registered users.

Richard

You’ll have to do this by hand but it is possible. On the main toolbar there is a button called andquot;Edit using Object Coordinatesandquot; (or something like that) that allows you to work in object coordinates rather than world coordinates.

It might be a bit tricky if you need to get exact angles.

One thing to remember is that to get a proper rotation you don’t need to animate all key ( 0-8 ). In fact, that just makes it harder. All you really need is to get key frames 0,2,4,6,8 right. ( Or possibly 0,3,5,8 )

Richard

odd to see you, Kim, of all people asking for advice!!

I’m not sure what you mean, but isn’t it a case of setting the rotation angle in the correct axis in the object properties (or is this the world axis?) I know there are a number of buttons on the top toolbar which say ‘edit using world co-ordinates’ etc – maybe it’s a case of selecting one of these!! No doubt Richard will be able to help anyway!

I’m trying to animate Walschaerts valve gear for my A4 and it’s doing my head in to be honest! I totally get the principle – it’s quite easy really, but trying to find the exact angles is very difficult. I’m probably only out by half a degree here and there but it’s noticeable! I’ve used trig (tangents) to calculate my angles but it’s not as accurate as I would have thought. I have the main con-rod, no problem, and the crank also no problem, but the piston rod ‘bounces’ slightly and I’ve yet to try all the trig again on the valve rod. Many long evenings to come I feel!

You’ve always done excellent valve gear animation, got any tips?

JonG (jonrach73 on uktrainsim)