Archive: 14 posts

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Fairly shortly after I dipped into create mode on LBP PSP, (I've never played the PS3 version), I decided I wanted to make a walking vehicle. I tried everything I could think of and it was a disaster, so I gave up. After I'd got better acquainted with the editor I thought I'd give it another crack, using all the new tricks I'd learned, and it was a total disaster. I most often found things went pinging and jumping about the screen. I was determined though, so after a little while longer, I gave it another go and came up with something that worked. I was so delighted that I created my only proper published level so far on the basis of this discovery alone. Since then I've found a bunch of other ways of making things walk - some which work well, some which absolutely don't, and some which are sort of ok. Many people may already have worked this stuff out for themselves - however, since it took me so much trial and error, I thought I'd share some of my findings and methods with the community in the form of a "How To" guide. I have tried to include as much detail as possible, regardless of how mundane or obvious, however if I've missed anything or something doesn't make sense, please just ask. Part One: Simple Piston Legs This text guide is accompanied by a small level with some examples and ideas in it, nothing spectacular, which is titled: How To: Simple Piston Legs by SalieriAAX You can also see some walking machines my other publications: Colossal Calamity (using wobble bolts) AT-AT Walker The simplest walking mechanism involves legs that are essentially two pistons connected at right angles to one another with whatever material you want in between. Wobble bolts are a complete nightmare to work with in complex systems, so it's always good to be able to fall back on the old pistons. Here's an example of what a simple piston-driven leg might look like: http://i174.photobucket.com/albums/w120/kaloikagathoi/LegBasic.jpg The 'foot' section is quite long because, if your creature/vehicle is going to have only two legs, it's going to need all the help it can get to stay upright - they won't need to be that big if you have four or more legs. For the purposes of testing your legs it helps to lift the whole thing off the ground and turn the 'hip' section static, then you can watch your legs go without the often frustrating hindrance of the ground. You can acheive two different kinds of walking effect with a setup like this, depending on your timing settings - a 'smooth' walking motion where the feet sort of peddle along in near circles, or a squared-off, more mechanical motion (as on my published Star Wars AT-AT). We'll start with- Smooth Walking: You can set the travelling distances of the pistons to pretty much whatever you want, this will, unsurprisingly vary the size of the 'steps'. To make the leg 'walk' you will need to pay close attention to the timing and sync settings. The greater the time setting, the slower the leg will walk, set it to whatever you want for now, but for the purposes of demonstration we'll work with the default of 4 (4 also works out quite neatly with the maths later - don't worry, it's very simple maths). The most important thing with the time setting is that it's the same for both pistons and that you keep the pause setting at 0. The sync setting should remain at 0 on the horizontal piston, but to get the foot moving in the right manner you'll need to set the vertical piston's sync setting to one quarter of the time setting, which we'll call t/4 for the sake of algebra: 4/4 1 in our example. This will give you a nice, almost circular motion. You'll need at least one other leg, of course. In this instance at least the new patch is extremely helpful, so just copy and paste the leg you've already made and move it to the other laver. Of course now you have two legs that move in the same direction at the same time. This won't get you anywhere so we need the second leg to move out of phase with the first. Back to the sync setting. Set the sync of the horizontal piston on the second leg to half time, or t/2 ( 4/2 = 2 ) and the vertical piston to three quarters time, or 3t/4 ( 3*4/4 = 3 ). http://i174.photobucket.com/albums/w120/kaloikagathoi/th_SmoothLegSync.jpg (http://s174.photobucket.com/albums/w120/kaloikagathoi/?action=view¤t=SmoothLegSync.jpg) Set these in motion and you should have something that resembles convincing walking. If things don't seem to be going right, refer to the notes below on piston settings and materials in the implementation and potential problems section. You don't have to use exactly the set-up that I have used in this example. See the accompanying level for a few thrown-together examples of the same concept implemented in a few different ways. The next step is to make something to attach these legs to. But more on that later. 'Mechanical' Walking: So, what about this 'mechanical' walking motion? The previous method combines vertical and horizontal motion simultaneously, however if you're making something robotic you might consider timing these movements seperately to make the walking motion squarer and more artificial-looking. To do this, we need to wade in with the pause setting. As an example, take the same piston and block setup that we used before. One unit of 'pause' time is equal to one unit of 'pause' time. I don't know whether they are seconds or what but it doesn't matter. Regardless, the important thing to note is that the time setting and the pause setting combine to make the total repetition time for the piston. That means that a piston with a time setting of 2 and pause setting of 2 will go in and out at the same rate as a piston with time of 4 and pause of 0, or indeed a time of 3 and pause of 1. Elementary, perhaps, but worth noting if you are not familiar with the pause setting. As an example, then, let us set the time and pause settings for the horizontal piston at time 6 pause 2, and for the vertical piston at time 2 pause 6 - it is important that the time for the one is equal to the pause of the other. This should now have the pistons moving, then stopping, then moving again. What we want to happen is for the foot to remain level while the horizontal piston moves, and then for the foot to move down while the horizontal piston is still. To do this, you will need to adjust the sync setting on the vertical piston to half of the time setting, or t/2 ( 2/2 = 1 ). Set it to run and it should produce a satisfyingly square step. For the second leg, the synch calculations are (t+p)/2 ( (6+2)/2 = 4 ) for the horizontal piston and t+(p/2) ( 2+(6/2) = 5 ) for the vertical piston. This should have the two legs moving correctly out of phase. http://i174.photobucket.com/albums/w120/kaloikagathoi/th_MechanicalLegSync.jpg (http://s174.photobucket.com/albums/w120/kaloikagathoi/?action=view¤t=MechanicalLegSync.jpg) Implementation and potential problems. So, you have the legs - now what? Firstly, unless you want to set your walker off to walk forever, you need to be able to control the legs. Switches set to on/off or speed will work, including getting your legs to walk backwards if you use a 3-way switch set to speed. Direction switches will not be any good to you at all. When sticking some kind of body to your legs, or vice versa, make sure it's only stuck to the 'hip' section, or alternatively do away with the hip section altogether and attach your piston direct to the body. Just make sure that the other parts aren't stuck to anything. Unsurprisingly - this stops things from moving properly. Most problems can be addressed by selecting appropriate materials and piston settings: "The legs appear to be overly sluggish and wobbly or the vertical pistons do not extend or contract to their proper length." Firstly try to avoid being tempted to double up pistons if their strength is already set to 10 and they don't seem to be able to cope with the loads. Doubling pistons, especially if set to 'stiff', can cause horrible problems (see below) and there are usually other options. Material selection is important. You may want your robot to be made of iron, or your massive walking colossus to be made of rock, but this probably isn't going to be practical, and there are often ways of making a much lighter material look the part using stickers (I am sure grey polystyrene was created for Star Wars fans). Generally, keep things as light as possible, even use peach floaty if it doesn't look too ugly, but failing that add rockets. It can make a great aesthetic improvement on certain things (like robots or sci-fi vehicles) to add some rockets that lightly lift the vehicle to take some weight off the feet(make sure they're facing directly upwards for the right effect). Tweak the power of the rockets through experimentation to get just the right amount of lift - have patience and you should be pleased with the results. See the aforementioned AT-AT or the AT-ST in the level that accompanies this guide for examples of rockets used to reduce weight. I have also found the legs to go all loose and wobbly after adding switches or magnetic keys to the moving parts of the leg. I have no idea why this would happen, but it does, so try to avoid it. "The legs appear to be operating correctly but my creation occasionally jerks about violently, jumps into the air, or appears to want to tip over for no reason." This kind of problem is usually caused by 'tension' in pistons. If a piston has a high strength setting and/or is set to stiff, but it's movement is for one reason or another impeded, it gets very upset and causes strange tension effects in the mechanism, including twisting and jumping about. It is worth noting that however heavy your object is, the horizontal piston's strength can be set very low, because the body can essentially move horizontally friction-free. Experiment to find the minimum strength setting that each piston will work with, and stick with that - be sure to test them going uphill if you intend to walk on an incline. A weaker piston should still fulfill all of your needs but will allow more margin for error and create less tension. Using floaty material or rockets as suggested above allows you to work with lower srength settings. "My bipedal walker keeps falling over." Make your feet as long as possible. However, there is a limit to how long a foot you can bear to use. As mentioned already, keep your vehicle light, but if it's already very light but still falling over, try changing the feet to a slightly heavier material, this will lower your creation's centre of gravity and increase its stability. If you are already using a rocket to reduce weight, make sure that it is positioned and angled appropriately and not too powerful, as this can actually cause your vehicle to tip over. If none of these tips help, consider using some kind of stabiliser. The friendly T-rex in the accompanying level is an example of this, as it is able to stand up only because its centre of gravity is between its legs and its glass-tipped tail, which drags along the ground.

2010-02-17 16:55:00 Author: SalieriAAX Posts: 421

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Thanks for sharing! Pretty clever, using rockets to lighten the load. Have you ever tried holding it up with a "balloon" (off-screen floaty attached by invisible rope)? That might work if you don't want rocket smoke. This makes me want to build a walker.

2010-02-18 09:30:00 Author: Rogar Posts: 2284

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Hi, salieri! Thanks for lessons! It is very usefull. Do you plane to continue it in future? And one more question - can I publish translate of you lesson on our Russian LBP community site -http://lbprussia.ucoz.ru/ ?

2010-02-18 11:03:00 Author: Domik12 Posts: 838

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Hi, salieri! Thanks for lessons! It is very usefull. Do you plane to continue it in future? And one more question - can I publish translate of you lesson on our Russian LBP community site -http://lbprussia.ucoz.ru/ ? Hi. Thanks. Yes, I'm going to do another one at some stage about other methods of making walking legs, but first I'm going to do a guide to 'advanced' vehicle controls and logic. Sure, go ahead with the translation, you're more than welcome. Rogar. I have experimented with the offscreen balloons, and they do work pretty well. However, they're not ideal as you have to make sure they don't snag on any scenery, and I have a thing about 'cheating'. If I were to do something like that I would prefer to make a vehicle that looked like there was a good reason for attaching balloons, and have them completely visible.

2010-02-18 11:12:00 Author: SalieriAAX Posts: 421

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This guide is incredible. Very detailed and extremely well written. Thanks for putting it together!

2010-02-18 17:31:00 Author: Taffey Posts: 3187

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And thanks for the great level! (I love the T-rex ) I also love that steam powered thing. Do you plan to make a whole vehicle in that style? That would be amazing!

2010-02-18 17:35:00 Author: Arrestor Posts: 363

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Thanks Taffey. On reading it back it is a little rambling. Could have covered all the info in les than half the words. I suppose that's a benefit of 'proof reading'. ^_^ And thanks for the great level! (I love the T-rex ) I also love that steam powered thing. Do you plan to make a whole vehicle in that style? That would be amazing! Cheers, and I already have, along with about 80% of a level to go with it, but it'm having lag issues in the busier sections. I know I can solve them by doing away with some of the moving parts and excess stickers, but I'm having to take a bit of a break before I can bear to part with them.

2010-02-18 17:46:00 Author: SalieriAAX Posts: 421

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Yes, it's perhaps a little rambling.... No worse than every single textbook I have ever read though. If someone really wants to make their own walking creature (and I do now, thanks to your awesome guide) they will very much appreciate all the detailed explanations.

2010-02-18 17:49:00 Author: Taffey Posts: 3187

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Excellent guide! Very useful for those who want to create walking creatures. Thanks for sharing your knowledge.

2010-02-19 12:38:00 Author: Lleonard Pler Posts: 277

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Hmmm... I just had another look at this and for some reason the word 'legs' has been censored in the uploaded version. LEGS! There, I said it, lock me up! LEGS! Seriously, what's going on?

2010-02-27 21:33:00 Author: SalieriAAX Posts: 421

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Just played. Great tutorial, good graphic too. Now you made that T-Rex you MUST put it in a chase scene in a prehistoric level you WILL MAKE

2010-02-27 21:40:00 Author: Unknown User

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oh great! nice tutorial. you could call that level Jurassic sack (that comment above me)

2010-11-12 07:47:00 Author: jimydog000 Posts: 813

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Salieri, u seem 2 know how, plz join this: https://lbpcentral.lbp-hub.com/index.php?t=42887-mech-wars

2011-01-12 11:57:00 Author: dylan-is-cool123 Posts: 54

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*cough* shameless advertising*cough* but i will have a look as well. ps i reccomend that you send someone a message if you wish to contact them rather than the way you just used

2011-01-12 23:01:00 Author: unXpectiD Posts: 1132

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