I have read through all the threads I can find on autorigs, and I understand that they are very complex HDAs. I will read about that and try to answer my own question. But I want to put it out here as well.

I've discussed a horse character I am working on in Houdini in another thread. At the moment I'm investigating options for rigging it. I thought it would be very easy to use a quadruped rig on it. I would have absolutely no problems rigging a horse in XSI or even using Character Studio in Max. In fact I've rigged a lot of quadrupeds that way in Max, even a sea turtle.

But Houdini's quadruped autorig only gives me two options for the feet - 4 toes or 5 toes. What about a hoof? Also, it gives me a lot more joints in the tail than I need for a horse. 2 or 3 would be fine. And as far as I can see it's the same even if I build the autorig myself from quadruped parts.

Does this mean I have to create all my own bones just because my quadruped is a horse and not a dog or a cat? How would I go about rigging an elephant?

A deeper question this brings up for me is how I should be going about learning Houdini. I'm a technical artist at a game company, I write tools for artists to use. I have 5 years of industry experience as an all-rounder in 3D animation. Should I be skipping the autorig completely and learning to build my rigs from scratch? Or would it be better to start with autorigs as a first pass?

OK, I've worked out that I can unlock the autorig and delete all the toes. But I'm afraid I'm now missing a joint I need to rotate the hoof. I still haven't worked out how to shorten the tail.

I'm also wondering, now, how to add ears to my rig. The quadruped tutorial conveniently used a model with no ears. I don't think that's very usual for a quadruped rig though :?

To add ears, I'd go into the auto-rig after you've unlocked it. Turn on point snapping, and make sure that a null or some such easily snapped to point is visible where you want your ear root. If you parent the null to somewhere in the rest of the skeleton, the new bones will be part of your capture heirarchy.

Now using the bones tool, (follow the prompts to get the parenting and root right), create your ear bones making sure you choose what kind of kinematics you want.

Then adjust bone captures and weights as usual.

Thanks! I'll give it a try.

Would the same thing work for creating a kind of a single custom toe for each hoof? They really need 3 joints from fetlock to hoof (inclusive), which curl together like a finger.

I guess I can experiment with it anyway.

Last night I tried to parent some nulls to the head so I could add ears. But the only part of the rig I could get any kind of access to was the head controller, and when I parented the ears to that they didn't follow the motion of the head properly. Obviously I would have to go deeper into the rig to do this, but levels beneath that seemed completely locked off and I couldn't find an option to unlock them.

Also, even though I deleted the toes from the autorig, after I generated the animation rig, I found that the toes have reappeared in the autorig if I go back to it. So they're not really delete-able.

It seems as though the quadruped autorig is only useful for a cat or dog character with no ears and a long tail. It doesn't seem general enough for all quadruped characters. Instead of saving time, it actually seems to be chewing up a lot of time trying to work out what I can do with it.

I'm going to follow some older tutorials and build a rig from bones.

lisae
Last night I tried to parent some nulls to the head so I could add ears. But the only part of the rig I could get any kind of access to was the head controller, and when I parented the ears to that they didn't follow the motion of the head properly. Obviously I would have to go deeper into the rig to do this, but levels beneath that seemed completely locked off and I couldn't find an option to unlock them.

This is tricky. I think it's a part of the Houdini UI which is very nebulous. Make sure that your DAs are Right Click -> Allow Editing of Contents. Then make sure that you are in the actual root of your DA in the viewport you are trying to add the bones to, (see the label at the top of the viewport). To select an object inside a DA, make sure you are using the POSE tool and not the SELECT tool.

lisae
Also, even though I deleted the toes from the autorig, after I generated the animation rig, I found that the toes have reappeared in the autorig if I go back to it. So they're not really delete-able.

They are, but I don't have enough experience with the auto-rig to tell you how to do it.

Thanks for your help, mrCatfish. I previously thought that if I enabled editing of contents at the top node of the rig, it would allow me to edit everything inside. I didn't realise each part of the rig was a DA as well.

I actually spent some time today browsing through the Python autorig utils and it gave me a better sense of how it works. Once I realised that all the parts were also DAs, I tried unlocking them (in the autorig, not the animation rig) and deleting some things I don't need - eg. the extra bones in the tail and the extra toes. But then when I tried to create the animation rig it didn't complete the whole process. From some experiments, it gets to the shortened tail and then stops. Is the number of bones in the tail hard coded somehow?

So then I tried working with the animation rig instead, and it seems as though I might have some success if I delete bones from that instead. But I haven't checked what kind of effect that has on the deformation rig.

I'm still leaning towards creating my own rig, but I would also like to understand the autorig better and work out how I can customise it. I would love to make a modified version of it that allows me to choose the number of bones in the tail, spine and neck, the number of toes, and also the number of head attachments I can have (like the “ponytails” you get in Character studio) to use with ears, elephant trunk, etc. I think that would be a big project, but it would be a nice way to learn more about Houdini.

I have also been frustrated by the lack of control over the curve of the neck bones. The neck needs tangent handles like the spine. And the head and jaw control in my horse's animation rig were not aligned to the head and jaw of my horse because there is not enough information in the placement of those nodes. Those are more subtle improvements, but I think they need to be made.

Edited to add: Oh, and I did manage to parent some nulls to the head bone during my last set of experiments