bow rig help 3ds max
polycounter lvl 6
Hey guys,
I'm trying to rig a bow in 3ds max to bring into udk but I'm having trouble figuring out how I should set it up. In the image below I made some bones and an IK solver but it does not bend realisticly like a bow. any ideas?
I'm trying to rig a bow in 3ds max to bring into udk but I'm having trouble figuring out how I should set it up. In the image below I made some bones and an IK solver but it does not bend realisticly like a bow. any ideas?
Replies
With an IK solver, you're hoping for an "automatic" solution to a very simple problem, this is just a bow, not an arm or a leg. The animation of a bow is 2D and while a bendable IK would be nice, it's a bit overkill.
That said, spline IK's and wire parameters will get you a pretty nice "auto" bow pretty swiftly.
With Inverse Kinematics, the children influence the parents, you move the end of the chain and all other links are effected.
You aren't creating a real world simulation but bending a few points in 3D space to behave in the way you want with the least effort and complexity possible. The simplest solution is normally the best, especially when dealing with games where every layer of complexity can slow the game down and add to it another way in which to break.
You MIGHT be able to do this with two bones and control the bending of the bow/string through the weighting. One bone for the bow, one for the string, I would have to test it out and play with it.
Or actually you might need 4 bones, one for the string one for the bow and one for each tip. The two tip bones could be link constrained to the main bow and string, so as the string is pulled back the tips assume a point between the bow and the string.
Mark Dygert, I have tried 4 total bones (one for one side of bow,then one for half the string.then i mirrored that for the other half of the bow) but the few amount of bones make the bending real hard,not a smooth flow of the polygons on my model.
Two bones and adjusted weights.
It helped to animate the bones, and then blend the weights while it was in the extreme drawn back position. Making the rig more complex won't solve the weighting problem you will need to weight them effectively no matter how complex the rig is.
I can see making it slightly more complex if you plan to do a lot of bows and want to just easily skin all of those bows to some already animated bones, but a HI/IK rig might be harder to export correctly. You might have to bake the joint rotations or come up with a simpler rig that is constrained to the HI/IK rig, skin to that and export only the simple rig.
Personally I would rather just keep the bows simple, and adjust the weights with two bones. Less moving parts, less likely to break.
(the values here are the default ones)
Or just create a new, clean rig.
Not sure how else to help without making a specific video. If you're still getting stuck after building a new rig, you'll need to provide more information than "can't move the child bones".
Good luck, and don't over-think it.
Its a good example to learn from if you decide to put the time in but its a question of whether you need it done now or in a day or two...
A bone is just 2 points in space, when you parent one object to another the distance between the two pivots, gets locked by default.
To change this...
Click on the main bow bone.
Go to main menu > animation > Bone Tools.
Down at the bottom under Object properties uncheck "Freeze length" and set stretch to none. Now you should be able to move the string bow and it will still follow the main bone.
Doing this allows the length of the invisible bone between the string and the main bone, to change (you created a bone by linking the two objects, but it is not visually represented in the scene). I have no clue what this will do to an exporter, most games lock the length of bones and don't allow you to change the distance between them, some do but you need to flip some pretty deep settings to make it happen and it can come at a pretty high cost.
So if you are working with an exporter you should test this.
If you can NOT adjust bone lengths due to technical constraints...
You could try setting up a 3 bones and use a IK Limb solver. This is a little more widely supported by most popular game engines and it won't change the length of the bones but will allow you to side the end forward and back. A bit like your arm or leg, where it gets its name and common use from.
Note: it's important to put a slight bend in your chain because it acts like a rubber band, if your bones are perfectly straight it won't know what way to bend.
You can parent the base of this chain to the main bone and it will follow it while still allowing you to move the end effector of the IK limb solver. You can parent the end effector to the main bone also.
You might want to lock down its X and Y motion (hierarchy tab > Link Info) so it only moves on one axis.
This creates a few more bones than is necessary but you might be well within the number of bones the game allows for weapons, but again you should check and test this. If you are over, you might need to create another simplified rig, skin your mesh to that and export it, using this more complex rig for the mechanics.
I'm using the IK Limb solver which seems to work well for the bending,to an extent. Before I can really test that i need to get the string bone moving so i can connect them to move at the same time.
I'm not sure limb IK will work effectively for the bow bending since it limits the number of bones you can have. A HI solver will allow you to have more bones and do the same thing making the bend (and default skin weights) much more smooth. Just don't go crazy with the bone counts, you could easily use half of the bones I used and still get a decent bend.
Then you just need attach all of the end effectors to the main bone so they follow along and rotate properly.
You will need to animate each of the 3 end points independently, unless you want to start getting into using reaction manager or wire parameters. While this would be a good exercise to learn those things, its more time than I can devote to this =/
None of it is all that complex to set up, it took me more time to make the gif than it did to rig and animate that example. If it exports great.
People always think the "pros" use these overly complex systems and that they need to make complex systems for simple things because that's how the pros do it. Well... the pros have a lot of work to do and they make the systems as complex as they need to be and no more.
The only reason I would go with my latest example over my first is that it gets the skin weights right. The reason I would use HI instead of regular FK, is animating 3 points is easier than rotating and managing the bones by hand. Granted you can rotate them all at the same time but then they curl instead of bend back. If the curl works great, if not you have to tweak it and that could take more time.
It's not like setting up a HI chain is a complex procedure...
Did you scale the bones? Because that will cause problems. Remake the string limbIK bones.
Select the Bones create tool in the command panel, under the IK Chain Assignment rollout, set it to IKlimb and check on assign to children, then create the two bones and right click to finish it.
If you need to adjust the bones, use Bone Tools > Edit Bone Mode.
Why? Scale is inherited by the children from the parents and anything skinned to the bones will also take this scale into account, DO NOT SCALE BONES, unless you specifically need those types of results for a very specific reason. 99% of the time its going to FUBAR your rig.
If you already have limbIK applied to the bones you need to delete it before you edit the bones. Click on the end effector (the "+" point helper) then delete it. This removes the limbIK chain from your scene.
Then go into Main Menu > Animation > Bone Tools and turn on Bone Edit mode, this will allow you to reposition the bones without effecting their scale, click on each bone and move it around it will stretch and distort but everything stays zero'ed out.
Then recreate the limbIK chain click the first bone and go into Animation > IK Solvers, pick IK Limb Solver and click on the last bone in the chain. This will recreate the IK chain. Or you could just delete the bones and recreate them, it doesn't really matter, I'm just showing you both ways to create it.
Did you link the end of the limbIK (the "+" point helper) to the main bone? If you linked the last bone in the chain that will FUBAR the limbIK by reordering and destroying the order of the bones.
So link the big +, (not the tiny bone nub at the end of the bone chain) to the main bone.
TL,DR:
I personally would turn on 3D snaps, set it to vertex, fire up the bone tool and recreate the 3 bone chains using the IK Chain Assignment option to automatically assign the HI and IK to the bones. It would take a min to recreate the rig and you would know that everything is fresh and clean.
Alright so I did that and the bones and all look like a decent motion now so there's one other issue i noticed about the skin. The string bends like your example but it is also being stretched sheet thin...
1) The verts in the center of the string are weighted to the bone at the end of the limbIK, which is rotating, so it twists the string.
2) The verts on the end of the string don't point toward the string bone, so they skew rather than rotate.
To get around this you could link bones to the last bone in each chain. Then assign "look at constraints" so they point at the right things.
The tips of the string look at the yellow string bone.
The yellow string bone looks at the main bone, so it won't ever rotate.
To assign a look at constraint select the bone, go Main Menu > Animation > Constraints > LookAt then click on the bone you want it to point to.
Then you add the new bones to skin, under parameters turn on vertex this will allow you to select and weight the verts, then click the wrench button and use the skin weights tool to weight the verts for the string 100% to the newly created look At bones.
OR
You could detach the string from your main mesh, apply skin to it and only add the yellow bones.
The rig is starting to get complex and fairly dense in bones. If you are under your limit for bones great, if not you probably need to think about a removing some bones from the bow, or creating a simplified rig that aligns and keys to this more complex one. I suggest looking at Jim Jaggers Animated Align script. It's what I use in those cases.
I would simplify the rig to just two bones on both the top and bottom side for the bending of the bow but the reason I havnt is because already when the bow is fully bent it looks blocky.and there's a decent amount of geometry there. If I lesson the bones it will be worse.
It looks like you need to create the yellow bones from scratch, and skin the string to them. The center looks to be skinned to some of the old bones in the LimbIK which will rotate pinching the string, they need to be skinned only to the yellow bones and that center yellow bone needs to be looking at the main bone so it doesn't rotate.
http://www.mediafire.com/?hlc811oes8w3moe
Sorry about that...
So everything seems fine but the verts in the middle of the string are rotated oddly. Go back down the modifier stack to edit poly, vert mode select those verts and hit "Y" next to the Make Planar button. It will straighten those out, exit sub-object mode and click on skin and everything should be fine.
Or you could mirror the bow string so you have verts that slant in both directions on either side of where the arrow goes. But that adds more geometry than what is probably needed.
Sorry for the thread necro, but this is a really interesting idea, and an issue I am working to learn now. I noticed the OP ended up using a whole bunch of bones, but is it possible to just use the few bones you proposed?
And would that look something like this diagram?
If you use a "Position Constraint" on the position track (not the transform node) it will allow an object to get it's position from a mid point between several objects, like the main bow and string bones.
Position constraint has a weight that you can blend but it has a fatal flaw that needs to be solved, it would only move the points backward.
At that point you might as well use two bones?
I guess you could experiment with animating the position constraints weight, that might affect its trajectory a bit and cause it pull in, but that's probably not that predictable and a pain to animate. You might be able to automate it but that's a pain too.
I think using two bones would work fine in a lot of cases, if you really need the tips to bow in as the string draws back use simple rotations, like I talked about in this thread.
If you're allergic to doing things simply and must use something more complex this thread is littered full of convoluted ways to rig a bow, heh.
Thanks a lot for the response and the great insights. This is really helpful to better understanding the different caveats of how to do this.
Re your comments on link vs position constraints-- being still a beginner, I am a little unclear on the nomenclature and was simply parroting the language you were using, but thank you for the clarification and for the gif.
As far as turning this into actionable items go, I think running with the 'vanilla rotation' execution makes the most sense. Again, this is my first run at this, so I really appreciate the feedback.
One thing that's bothering me though is what are those circular nubs in both the examples on the x axis?
1. Set up bone system (2 upper bones + nub, mirror at center pivot for lower bones).
2. Create the 'circular nubs' (helpers?)
3. Link IK HI solvers from bone closes to nub to the 'mid-bone'
4. apply Orientation Constraint from bones closest to nub to the (helper) at mid point on bow string.
5. Apply transform constraints to the (helper) only able to move on x-axis.
6. Link the two mid-bones to the (helper) on the right/outside of the bone.
Sorry if this is a little too granular, but I have been drilling into the Autodesk video tutorials and I'm struggling to turn what I have learned into something actionable.
A bone is technically a distance between two points (the child and the parent), if a bone doesn't have some kind of child at the end, the bone is just one point with no length, even if the visual representation looks like it has length.
Even though the upper bone looks like it has length, its really just a single point, it needs a child linked to it in order for it to actually have length.
1. Set up bone system (2 upper bones + nub, mirror at center pivot for lower bones).
2. Create the 'circular nubs' (helpers?) (single point bones)
3. Link the two mid-bones to the (helper) on the right/outside of the bone.
4. Select the bone chains, set the pivot gizmo to local, turn on autokey and rotate the bone chain to draw it back and rotate it while animating.
You don't need the HI solvers, simple bone rotation is all you really need (step 4).
You don't really need the look at constraints for the string, unless you run into problems with the string losing volume. But there are a few other ways to handle that with skinning and smart use of geometry, rather than just throwing more bones at it.
What additions would I have to make?
[/post edited for clarity, check new post for update]
I have a couple questions:
1) What is linking the two mid bones to the outer nub meant to achieve? It doesn't even seem to be mentioned for actually animating the bones-- the end user has to select all the bones, and then rotate them.
2) What is the purpose of the the rear nub/bone? It's not mentioned at all in the process.
3) In the outer nub creation, you mentioned deleting the bones the nubs were originally attached to. Do the nubs have to be on the same chain? I created two sets of bones, roughly matching them with my eye
My objective: create the rig emulating this gif that @MarkDygert posted:
My rig has few bones based on this gif:
Here's the series of bones I created, with their hierarchy also displayed:
The two bow bone-nubs have a look-at constraint applied to the IKLimb goal. Obviously, that isn't sufficient to drive the rest of the bones to curve as the bow string is bent.
I could be wrong, but I feel very close-- what am I missing? Do I need to add the bones that were in the OP's mesh (a bone and a bone nub aligned and linked to both IK HI goals)? The OP's bow was not bending like either of the bows depicted in the GIF fyi.
Appreciate any feedback!
That's for the string.
No the nub was just a simple bone, the end point of a chain after I removed the chain. I copied it to make the string bone.
Nothing in that HIsolver example drives everything, it is 3 pieces animated separately. You still have to animate the end effectors and the bow string independently. To have one thing drive everything you end up spending a lot of time with reaction manger or wire parameters or scripting to make those connections work. That's a lot of time wasted when you could be animating and no professional is going to waste time on something like that unless the absolutely have to.
Still if you're interested in figuring it out just for the sake of learning, reaction manager is probably the most straight forward way to do it without knowing any scripting. Set the string bone position as the master, and the bow bones rotation as the slaves.
Create 3 states:
State1 = Bow in natural position.
State2 = Bow drawn back.
State3 = Bow over extended.
But to dial in each state you have to sit there in reaction manager and edit the values, which is a lot more tedious than just rotating the bones when you're animating. Plus by using reaction manager you're locking the bones to these pre-defined states, if you want to change it you can't just grab the bones and tweak it, you have to come back in and adjust the states.
I'm not even going to bother going into scripting or wire parameters, that's a lot more complicated and has a lot more prerequisite knowledge than I want to cover.
I kept thinking in the back of my mind, the rig created in this example:
http://vimeo.com/29973835
But you're right, it looks like he is using wire parameters as well as HI solvers.
Edit: I see your point about the reaction manager boondoggle and the need to animate this regardless, so might as well go back to that.
I apologize if I look like I am running around in circles, but I am interested in returning back to your original suggestion of using the rotate tool-- the issue I had when I first tried this was that trying to rotate the bones by selecting the mid bones and rotating the z-axis.
but if I understand correctly, in the original simple rig, you're saying that I should forget about all the IK solvers and just rotate each individual bone's z-axis, manually transform the bow bone's x-axis and then weight those bones to the mesh (using skin modifier) accordingly?
Also, I tried linking the single bow bone/nub to the chief bone and I can no longer transform the nub-- how do you link the bone so that it follows the parent but still can transform?
If both sides don't rotate the right way, they where not mirrored correctly. You can remirror them using bone tools, try ZX first that should do the trick but it really depends on what viewport you drew the bones in as to how their pivots are oriented.
To solve this you go into the Bone Tools menu, expand "Object Proterties, select your root bone and the string bone, uncheck "freeze length" and set Strech to none.
This needs to be done for both bones in the link that you want to free. By linking the string bone to the main bone, it creates a bone (that is invisible), bones have their lengths frozen by default so they don't stretch, but you can turn that off in bone tools, but it has to be done on both ends of the bone.
I tried that last time, and it just ended up turning into a haymaker, with each bone spinning from its pivot, but looking nothing like that GIF.
Here's a screen grab of what I have, after just trying again:
edit2: just redid the mirror after re-positioning the mesh/bone chain-- I was mirroring the bone chain just on the Y-axis when I should have mirrored on the YZ-axis.
That seems to have done the trick!
Edit 3:Well as an update, the bow and arrow has been skinned and animated. Thanks a ton for the advice, Mark! You're right, once I figured out the shenanigans, it's a much faster solution.
I'd like to figure out how to create a controller so I don't have to select all the bones each time I'd like to animate though...