A racheting type animation---

This may sound complex at first, but I am sure it's simple.

I need to create a relationship between two objects so that they both move together in a given (positive only)direction (say, X for instance) but reversing the parent object has no effect on the child. This is a spatial relationship, but in some ways it's much like the rotation properties of a rachet and bolt.

The bolt and wrench both move when turned clockwise- but when the user switches directions and rotates the other way- only the wrench (body) moves because of the racheting effect built into the device- (click click). (If you want to be precise, the socket head also is stationary) As the user stops and tightens again- the bolt continues from the same rotation value it was at before- and "adds" the additional rotation from the wrench as he or she applies more twisting to it.

In a nutshell, how can you link two objects so that they are parented in a given direction, but zero relation in the reverse direction...

How would this be set up???

Thanks...

Do you want the 'ratchet' to be able to push the 'bolt' further ahead than it itself travels?

For instance, if you slide the 'ratchet' from 0 to 10, the 'bolt' should also move from 0 to 10, and if you then move the ratchet back to 8, the 'bolt' should stay at 10. If you now move the 'ratchet' from 8 to 12, you've advanced it a distance of 4, but only 2 of those extend beyond the previous maximum. In this case, should the bolt move from 10 to 12 (starting once the 'ratchet' passes 10) or from 10 ahead to 14 (starting as soon as the ratchet does)?

An expression will work in either case. Here's one for the first:

float $trans = ratchet.tx;

float $oldTrans;

if ($trans > $oldTrans)

	$oldTrans = $trans;

bolt.tx = $oldTrans;

And for the second:

float $trans = ratchet.tx;

float $oldTrans;

float $diff = $trans - $oldTrans;

if ($diff > 0)

	bolt.tx += $diff;

$oldTrans = $trans;

Ask away if you need any part of those explained.

-Steve

My animation has nothing to do with rotation- it's all translations in a single direction.

Here's a picture of the racking system---

http://mywebpages.comcast.net/patane8/images/rack1.jpg

I was using the rachet analogy because it would have been cumbersome to explain the details of the actual device. But, here we go!


The animation represents two warehouse bays. (they are most likely off the ground- this is merely representational)Each of them is identical. Both have a center "platform" or sled-like device that sits inside the L-shaped tracks underneath the pallets. In its resting state, the pallets are all sitting on the rails with some space between the sled and the underside of the pallets. Simple, huh?

When raised, the platform causes the row of pallets to move forward exactly one pallet distance- whereby the forklift operator pulls off the "reachable" front-facing pallet. As seen in the image, the forklift operator has yet to come get the front one before the device can cycle the row ahead one place. (He's union, you know... a little slow)

If you imagine the front spot vacated- the platform will get raised up until the weight of all pallets is off the tracks- (almost like a mechanic's jack)- then the entire yellow unit (one piece) slips forward one pallet distance- lowers, thereby dropping them- then returns to starting place. I think the proper word is reciprocating. This is done until every pallet is cleared from the rack--- You can imagine the same in reverse for "loading" the racks.

The difficulty I was having was setting a relationship between the "platform" and the grouped pallets forming the pallet row. Essentially- it's a rachet type of animation whereby the pallets move ahead only, never backwards. Yet, the platform moves both ways.

Thanks so so much for the help. Let me know if you can see the image. No critiquing my render, either (grin) it's only rough... the plan is to animate both bays, (although you'd never operate a vacant bay) simultaneously so one can get a feel for what's not clearly seen under the pallets....

yeah my brain was all messed up. sorry