All work and no play makes Alex a dull tennis ball
All balls and no tennis makes Alex a tennis ball
Ball tennis and no balls make tennis a ball
balllllsss
Er. Sorry.
Medium close up
Close up
Oh goodness. I've fixed up the ball's rotation slightly, so now it begins to rotate after the first bounce. I think it's looking alright? I'm not sure. I still don't know if I'm terribly happy with it, and the more I look at it the worse it looks.
I think, in all honesty, I'm going to have to put a lid on this one for the time being - at least until I can get some outside feedback. It's still not brilliant, but there's only so much I can do with it using my own tired eyes. I'm feeling quite aware of the looming bowling ball and shuttlecock tasks, and if it's taken me this long to get a tennis ball going, I think I'm going to need to start getting on with those as soon as possible.
I'll more than likely end up coming back to it after I can get some feedback from others, but for now I think I can safely tuck it away.
Going to have to make this the last one for tonight. I should do a bit more and try to finish it off but I'm incredibly tired, and as previously evidenced, I make stupid mistakes when I'm tired.
I actually think the rotation on this one looks alright! It needs to roll just a teensy bit more towards the end, I think, but it's not too bad (as long as you don't think too hard about realistic physics). The problem comes when I try to apply squash and stretch...
It's the same rotation, just with additional squash and stretch on most of the bounces. I don't know why - maybe it's just me - but it looks really odd to me now. The way that it doesn't spin at all on the first bounce somehow seems very out of place when I add in the squash. Like the force of the contact with the ground should start it rotating? I don't even know! I've been staring at this too long. I've started to go blind.
I also noticed one horrible problem, I've managed to break the rig somehow - probably during my cock-up with the rotation keyframes. If you look closely:
The position control object has magically floated away from the ball and now sits somewhere in front of it. I have absolutely no idea what's happened - I don't recall the point it happened. In fact, I only just noticed when I went to adjust the position to maintain the ball's contact with the ground after applying the squash. It doesn't seem to have broken the animation at all but I'm starting to worry that moving it back into the proper place (when/if I can figure out how to do that) will mess things up. And that will be a whole day wasted. Note to self to ask Jon how to correct it.
Doh... I'm stupid.
Anyhow. I'm going to try one more time to correct the rotation tomorrow and polish things off a bit, then I'm going to need to move on for a while. I can only stare at this silly green ball for so long...!
Using the video I shot as a guide, I thought I might try and be really clever and use a quick diagram I drew as a Rotoscope image within Softimage.
I think it's actually looking a lot better. The biggest issue that I can see now is the rotation - it looks completely wrong, and nothing I'm doing seems to be fixing it. I've tried speeding it up, slowing it down, changing the points it starts rotating - nothing. It just looks weird. I think that the spin just seems to change speed quite randomly - for example, towards the end it doesn't spin much at all but then suddenly rotates quite a lot. I don't know. I'm really tired and I've been staring at this far too long. I'm starting to go blind.
I also noticed that I made a huge cock up and set the rotation keyframes on the translation control - I have absolutely NO idea how I managed that as I was 110% certain that I was selecting the rotation control each and every time. There was one point where, thinking I was being clever, I had two dope sheets open - one locked to display the translation keyframes, so that I would be able to see both sets simultaneously. It's probable that as I was keyframing the rotation control it was getting added to the translation dope sheet as well.
I'm erasing all the rotation keyframes from the translation control now; I just hope I've not somehow completely broken the rig...
Finally got my greasy mitts on a tennis ball that bounces properly. How exciting! I've now been able to shoot my own reference footage for the ball, which I hope will make my life just a little bit easier...
(Please excuse the mess. I've not hoovered yet - I swear I'm not always this grotty)
I did a number of drops, just to get an average. I'm guessing the carpeted surface may have affected the bounce somewhat; but I'm just going to say it makes it more like the grassy surface on the scene file!
I don't really know which shot I'm going to use for reference. It's tempting to do one that's a bit different instead of a generic bounce, but there's the danger that it wouldn't look right when viewed through one of Jon's preset cameras. I'm probably just going to stick with the last bounce on the first video... it's a bog-standard looking bounce, but it seems a fairly safe option. Plus I'm getting a bit sick of tennis balls by this point!
Another entirely unsuccessful attempt to procure a tennis ball today. You wouldn't have thought they'd be so damn difficult to get hold of. Looks like I'm going to have to exercise my imagination a little bit longer...
I've sorted out weird jumping-forward problem from the previous post, so now the ball rolls forward at the end fairly nicely. I made a few more timing adjustments as well, speeding up the drop on the second bounce. I also slightly adjusted the height that the ball reaches on its first and second bounce - it seemed to go a little too high before, so I dropped it down just a tad and it seems a little better. I think the bounces are slowly getting there - though I think the third bounce (and perhaps the entire set of small bounces) are a bit too slow, but I'm not entirely sure? Might look at speeding them up. This is hard without reference.
The other big change is the addition of a little squashing and rotation. The ball squashes a lot more than I'd originally intended - at first, I only squashed it a very tiny amount and because the impact with the ground is so quick and instantaneous it didn't really 'read.' I slightly adjusted the curve so that the ball would remain close to the ground for a fraction of a second longer and also increased the amount of squash - looking at the capture it stands out far more than I thought it would, so I may reduce it slightly. Tennis balls are pretty firm!
I'm not sure if the rotation is at all accurate - probably not! I think it looks alright though (so far at least) so I'm probably not going to do too much tweaking to it, unless necessary.
The other issue that probably isn't apparent from the angle of the shot is that the ball isn't actually touching the ground when it bounces. It's an issue I encountered whilst adding the squash to the ball - I could have fixed it straight away, but I decided to talk about it on the blog a bit first. I don't really know why. Maybe because it gives me an excuse to post some screen captures (which I've been neglecting so far)...
Basically, the rig seems to be set up in such a way that locks all its transformations to a local axis. The ball's centre point is positioned right on the bottom of the ball, so that when scaled along the y axis it squashes quite nicely. However, when a rotation is applied to the ball, the centre point follows - i.e. it's no longer on the bottom of the ball. This means that it scales from a slightly different point, meaning that the bottom of the ball is no longer touching the ground (as seen above).
It's not a big problem at all and I don't have any wonderfully clever solution - I'm just going to move the ball down so it's back in contact with the ground. I just thought it was worth talking about.
More timing adjustments! I used the region select tool to bring everything closer together so it's a little faster. I think it's looking better now actually - but there seems to be a weird jump right at the end. The ball seems to kind of... lurch forward. Not quite sure what's happening there - think it might have had something to do with the fact that I neglected to realise that I used the region select tool on the fcurves instead of the dope sheet. Ordinarily this wouldn't have been a problem, but I had it set to "isolate curve" so I only re-timed the keyframes on the y axis, so I reckon that the keyframes on the X axis are just a little out of sync. Hopefully it shouldn't be too difficult to fix...
Once that's all been corrected, I'm going to start looking at applying a little squash and stretch to the ball. Not too much, just enough to kind of emphasize the impact with the ground and the springy nature of this ball. Hopefully it will also help to highlight further problems with the timing and such.
Vimeo takes so long to process my videos that by the time it's done, I've already done another version. Ho hum...
Massively adjusted the arcs on the ball. It certainly looks better, but I don't know if it's at all tennis ball-like? I like the path of the motion a lot more, it's a lot smoother, but there are still issues with the timing. It's far too slow overall and there's no sense of force, or of acceleration/deceleration as the ball rises and falls. Again, these are all things that can be refined easily with the fcurve editor and the dope sheet.
I managed to tweak the ending so that the ball continues rolling for just a little bit after the last bounce. Rather than individually keyframing the horizontal motion between each bounce, as I had been before, I set the ball's final resting position on one keyframe right at the end. The ball could then continually move forward and would ease into the final keyframe right at the end in accordance with just one fcurve handle, saving me having to ensure that the flow of the curve was smooth between multiple keyframes.
It struck me that it would probably make more sense to take my captures using one of the cameras that the final render will be captured from. What looks alright from a flat, side-on view can look totally different (often broken) from another perspective - so working this way will help me to make sure that my final animation looks decent from the required perspective.
Other than that, not too much change. I've altered the curves slightly and tried to make adjustments to the timings so that the ball spends just a little less time in the air - I've shunted the keyframes a tiny bit closer together to try and improve the speed, but it still seems off to me. Something about the whole thing looks really, really wrong but I just can't put my finger on what. It almost looks like it bounces too much, or too many times? Something about the second and third bounce, I think... It might be the speed, again - it's just too slow. It takes too long to get from the apex of one bounce to the next.
This would all be so much easier if I had my own reference footage.
The ball now bounces across the screen rather than a straight line. It's definitely much easier to watch and, hopefully, to critique.
The problems become more apparent now that it's spaced out. Working backwards from the most obvious things, there are problems with the trajectory of the ball - towards the end it kind of lurches forward before coming to a very sudden halt which looks a bit odd. The ball shouldn't stop moving as soon as the last bounce occurs - it should probably still roll around or continue moving across the floor for just a little bit before slowing to a stop.
The timing in general seems to be a problem. The ball, to me, looks a bit weighty - it still doesn't have the energy and power of an actual tennis ball. I still don't think that it bounces high enough - potentially, it could just be a timing thing. If I increase the speed of its ascension it might look a little better. Tennis balls are fairly light and springy - they don't tend to fall too fast but bounce off surfaces with considerable force and speed, so I definitely think it needs to accelerate faster in order to capture that "springiness."
Thinking about spacing the tennis ball out so that it's not bouncing up and down in a straight line, I had a look back at some of the videos to try and get to grips with the pattern of the arcs after the ball first hits the ground.
Using the same videos as reference, I took the frames where the ball was at its lowest and highest points, dropped the transparency (acting as a sort of onion skin) and, from there, was able to loosely scribble the path of the arc that the ball took.
Forgive the horrible scribbly lines... I'm running Windows through an emulator which doesn't have native tablet support...!
Anyway, as you can see, the ball takes a sharp arc upwards but doesn't travel very far away from its original position. Each successive high point of the ball almost overlaps its previous downward path.
Slight difference in this one, the ball doesn't drop straight down after he drops it - presumably it's a bit windy or something - but usually, the ball will pretty much drop straight down, providing there's no other force acting upon it. The ball will be propelled slightly forward after its initial contact with the ground and will start to bounce away from its original position. Again, you can see it's quite a steep climb, but it doesn't really move very far away.
I also found this interesting image floating around online:
A stroboscopic/high-speed capture of... a bouncing tennis ball! It demonstrates the path of the ball very nicely... and you can even see the rotation. Interestingly, as the ball loses power, the arcs appear to get a bit wider and the ball travels slightly further. The bounce also appears to be a little slower, judging from the spacing, not quicker as I'd originally thought. (No idea why... thinking about it logically, it makes no sense. I suppose that if you just watch a ball being dropped because it's bouncing lower and lower it appears faster?)
Anyway! Very useful stuff, so hopefully I can now make a bold attempt at spacing out my animation and getting it to look a little nicer.
Redone ever-so slightly. I've tweaked the positions of a few keyframes and curve slopes to increase the hangtime of the first two bounces. I think the whole thing's looking a bit too slow overall, feels a little sluggish somehow. I don't know how much of it looks weird due to the lack of squash and stretch - I think that, once I've put that in there, it might start to look a little better. As I said before the strict up-and-down movement is problematic. I find it quite hard to look at and analyse for some reason - my eyes tracing the same path again and again in quick succession make it quite hard to read so it's a little difficult to pick out what's up with it.
I think the last series of bounces (the really small ones) are probably still a little sharp. They don't hang in the air at all - I don't know if tennis balls do that? As they lose energy, do they drop from the peak of their jump much more quickly? All things I'd failed to consider beforehand; back to the videos...
Rough sort of thumbnail sketchy-thing based on the timings observed from the reference footage.
It's messy and probably quite innacurate - it's fairly difficult to work from such limited footage. Hopefully once I'm able to shoot my own, I'll be able to put something a bit nicer together, but this serves as a sort of basis.
From this, I put together a quick first draft laid out roughly according to the timing and spacing on the diagram. It needs a lot of tweaking but I think the basic principle is there.
It's pretty basic keyframing stuff so far with some minor tweaks to the fcurves to slightly alter the timings. Nothing major so far - no squash and stretch or rotation at all. This will all come later, once I'm happy with the timing and spacing and so forth.
Some things I've noticed straight off the bat - the ball doesn't look like it bounces quite high enough to me, especially on the second bounce. It appears to be a really cheap tennis ball - one that's heavy, comes in a 3-pack from Poundland. I'm going to increase the height of the successive bounces a bit, and I think it ought to hang in the air a bit longer at the top of each bounce, too. It seems as if it hits an invisible ceiling at the top of each bounce, coming to quite a sudden halt - I don't think I've given it enough time to slow into the peak of its bounce so I'll probably space out the keys a little more.
It kind of looks like it loses energy and power too quickly and too suddenly, so I might even look at adding maybe just one more bounce in there towards the end, just to make it a little more gradual. Part of the problem might also be the fact that it bounces in a perfectly straight line, up and down in a very mechanical fashion, which looks pretty unnatural. I'll probably space it out and have it bounce across the screen just a little bit.
Started doing a little planning for the first of the three ball bounce exercises - the tennis ball. I did try in vain to get hold of my own ball to film, but was completely unsuccessful. The only ones I could find that weren't professional grade were 74p from Pets at Home and didn't bounce properly - so, until such a time I'm able to get hold of one, I'll have to make do with raiding Youtube.
I did find an interesting website called Animation Physics that offers a large number of handouts covering details of real-world physics and their application to animation. It's incredibly heavy reading and very, very mathematical. Their handout on the physics of timing and spacing refers specifically to dropping and bouncing balls of varying types. It's very heavy stuff, with lots of precise formulae and calculations regarding drop speed and air resistance etc. I wasn't able to make complete sense of it but I did manage to pick out a few key pointers that I thought would be useful:
The spacing between poses of a falling object can be calculated using a principle called "the odd rule." Basically, it means that the spacing of the object will increase following a ratio of 1:3:5:7:9:11. So, following the first pose (or drawing, whatever) the second will be spaced three times as far, then 5 times, then 7, etc. etc.
To be totally honest, it sounds really convulted and confusing and mathematical - I think, to really dumb it down, what it's saying is "make sure a falling object gets faster." Which makes those last two paragraphs completely redundant. Oh well.
The tutorial does come bundled with some lovely reference clips however, including some rather excellent footage of a ball being dropped in slow motion:
It's fair to assume that it's probably not a tennis ball - it looks like one, but doesn't bounce as high as you'd expect one to. It only reaches a third of its initial height, when tennis balls tend to reach around half their original height (as shown in the videos below.) It is useful for analysing overall drop speed and spacing, however!
There's an astonishing lack of bouncing tennis balls online, but after a bit of digging I was able to unearth a couple of other decent clips:
This one is particularly interesting as it breaks down the speed of the ball's drop in a fair amount of detail. The video highlights the fact that the ball loses half of its height with each successive bounce - it's dropped from a height of 2 metres, which means that with each bounce it would hit 1 metre, 1/2 metre, 1/4 metre, 1/8 metre and so on until its energy is exhausted.
The height isn't specified in this video, but if we assume that it's also dropped from about 2 metres we can again see that the ball's height is roughly halved with each bounce. The ball bounces around 6 times until its energy is completely depleted and it comes to a rest. The ball takes around 16 frames to drop from its apex (peak) and hit the floor - using this as a basis we could assume that a ball dropped from 1 metre would take around 12 frames (half a second) to hit the floor. Giving the ball 4 -5 bounces until its energy is depleted would make the total time around 2 - 2 1/2 seconds (about 50 frames).
I'm starting to sound very mathematical, but I'm just using this as a rough guide to get me started, a basis to work from - I'd imagine that the final animation will end up deviating from these times somewhat! What's physically correct in reality doesn't necessarily look good on screen. A lot of the timings will be tweaked by eye in order to avoid getting something stiff and a bit lifeless.
