Don't Fix It In Software
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RectangleRoboticsSoftwarePresentation of a groupComputer animation
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Digital photographyExecution unitMaß <Mathematik>Metropolitan area networkInformation securityFigurate numberAuthorizationLecture/ConferenceMeeting/Interview
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Digital photographyPower (physics)Multiplication signMaxima and minimaFunction (mathematics)RoboticsLine (geometry)Hydraulic motor
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ForceSurfaceBitPoint (geometry)SmoothingForcing (mathematics)Computer animation
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Multiplication sign
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Programmable read-only memoryDisk read-and-write headForcing (mathematics)Thread (computing)Arrow of timeRippingVirtual machineComputer animation
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Transcript: English(auto-generated)
00:00
So hi everyone, my name is Katie Levinson and this presentation is called don't fix it in soft layer And you may be asking what happened what's happening here and the long the short of it is they just said I I got got drunk and mouthed off at DEFCON 17 and And you know something someone showed up a longer story
00:21
Is that somebody showed up when a speaker didn't show up and said, you know Whining about how his robot Didn't work in software and it didn't work and he was gonna use software to fix it And the problem was basically that his that he said it didn't drive straight and I'm finally like what's the ratio of your drive base?
00:40
And he's like, you know Are you driving the rectangle with the fat side forward or the skinny side forward? And he says the fat side and like if you look at the nice fat recti, I have a laser pointer This means I'm in charge When you look at the fat rectangle if you imagine wheels on the end of this as you go like As you as you go forward at all You're basically levering against yourself to walk down and it's not really magical that you're getting out of alignment
01:06
And if you if you want to only go straight, you know You drive it with the skinny side of your rectangle forward and then enjoy figuring out how to turn But you know, so this is this is the situation as I you know Goes on more questions and I wind up doing this this very academic intelligent rant
01:25
Which I'm I'm really sure probably look more like that But the long the short of it is afterwards security comes and takes me aside and this this makes me nervous because I don't have the best history with authority figures But you know, he says why don't you do that?
01:41
This is a talk and I was pretty excited because you know The bottle of vodka been offered and unfortunately some scoundrel absconded with my vodka I'm really proud. I got to use those words. It's like my vocab words of the day And and but now thankfully someone else would give me vodka props to you, dude But the long and the short of it is now we're coming up and we're gonna do this
02:02
Big list of all the ways in which I all the things I wish someone had told me before I started building robots competitively or professionally at the very least I can show you some pretty pictures I Do Photography and so most of these slides are pretty pictures. I'm really that boring It's just there's some pretty pictures for you to look at. All right My best qualification is the experience of doing stuff wrong as I'm sure you know
02:25
All DEFCON speakers are only admitted if they are exceptionally qualified So that that's how that's how things are these are qualifications, I'm probably more likely to put on my resume Just want to like say right now. Thanks to originate
02:42
I just started with them like a little bit ago and they're totally like yeah, you can do this talk That's basically self humiliation. You could do it in our name They often printed me an awesome hoodie, which I unfortunately left on the floor because I plan ahead But they are awesome. And if you are sick of your boss's shit consider replying
03:00
Yeah, so Basically, if you have a question just like ask and if we run out of time I'll have to ignore you and you can email me but I'd like just to be you know casual and Interactive as much as possible Was what? No, no. No, this was this was DEFCON 17 where I went up and like oh
03:24
That sounds terrible we should do something about that guys Q&A afterwards. All right Alright So the outline we're going through some good ideas We got some bad ideas and we're gonna go through some things that people generally just don't think through the whole way So starting right off with the good ideas
03:43
Let's go through physics Torque is angular force if you were to take a wrench and apply some force to a bolt in a in a in a nice In a nice, you know arc that is torque speed is how fast you do it Physicists will get snobby and tell me that I'm not saying this correctly. I don't care This is just a working definition for us idiots. Okay?
04:04
First item is pulse width modulation abbreviated to PWM Sometimes you want your robot to be going at a speed somewhere between zero and into max People frequently decide that the way to do that is to just feed less Energy into the motors and that's a bad idea. You really should not be doing that
04:23
Motors do not output power linearly. They you can see this straight line is actually is is That is the the force output you can see on the when it hits the side with the torque That's called the stall torque. That's where it's not moving at all where it hits the the the x-axis
04:42
That is called the free-running speed where there's nothing on it at all. And you know, the variations come in between there you can see the power that is output in total on the curved line and And you'll notice that like it is not the same at all points So you actually want to put it where it's getting. I'm sorry guys over there. I'm gonna laser this one
05:02
And try to describe as best as possible, but I apologize in advance You want to put it, you know somewhere near the top so you get out as much power as possible and Less inefficiencies All right So basically you want to pick a good point on that curve and stick with it as much as possible Gear your gear everything, you know how fast you want the robot to go
05:22
So take the motor at the torque and power output you want and just gear it so that the wheels actually turn at Approximately the speed you're looking for And the question is you know Oh, sorry, nope, we're looking at a picture now This is an oscilloscope looking at a PWM output And so you can see that basically the line goes up and down. It's about one third down two thirds up
05:44
So if you do this insanely fast to humans, it looks like the motors just running at a slower speed And so if there if the line is up two-thirds of the time It's going two-thirds of its max speed and this is a real way you control speed on Robots without totally messing up your power output
06:01
And the question is, you know, how do you pick the point that you run this square wave at? And the important thing to remember is that climbing takes force unless you're gonna be constantly operating on a perfectly smooth surface You're going to need a little bit extra boost to get over whatever you happen to run into And what happens very often is that people they put themselves right at this total peak and then they have to go up a hill
06:26
So now they're moving slower. So now they get pushed down this side of the curve They're outputting less speed. It's coming out as torque now the motors less efficient so they can shove further down the curve and further down the curve further down the curve and they're just Wailing in place and really not getting anywhere
06:40
So you want to optimally pick a place a little bit over towards the speed side is so if you hit a bump You don't wind in this horrible downward spiral of getting nothing done at all And the expected terrain will change Approximately where on the speed side of the curve you want to set your running point generally speaking
07:02
Yeah, I hope I'm going at okay speed this is you can see at the bottom these things here These things at the bottom these are PWM's usually do this as a hardware object you buy them the internet sells them They're like a hundred bucks. They're cheaper if you like fire
07:22
but like You know a good trustworthy Like I would feel comfortable putting this on my robot and it will probably not be the thing that catches fire about a hundred bucks This guy removed all the cooling systems because he likes fire. That's his prerogative You do get to at least see the insides of them, which is interesting to some people
07:43
All right next item I Really shouldn't have to have a whole series of slides on this but software people think threads are just kind of magic It's like I've I've applied if a bolt to this problem and now all my physics are solved and it's like no people major in
08:03
This shit and it's kind of complicated So the once-over lightly this is a bolt this is not a bolt Every time you call this a bolt I die a little inside and I need to drink
08:25
This is a screw. The end is pointy You don't have to drill a hole first when you put it in you don't put a nut on the end so I don't know what this chicks problem is, but You don't need to put a nut on the end of this also Bolts need to have something on the other end to hold them on you either thread the piece of metal or wood or whatever
08:44
That you're putting them into or you put a nut on the end This is wrong You're just gonna rip the head off the bolt here. You see the arrows imply the force you're gonna rip off the head of the bolt and you're gonna rip the the the twirly Okay, the threat yeah, we're we we are extremely technical around here
09:07
You're gonna rip the threads off the screw if you do this don't do this. Okay? This is also wrong this is a machine that does nothing but bend your screws and By screws, I mean bolts
09:30
All right. This is gonna get a lot interesting really fast
09:46
All right. This is wrong This is also wrong In this one you are not bending your bolt But you're going to share it because you're using the bolt as the major pieces that keeps it together And they weren't actually in the same way that you know
10:03
You're up off the head. You'll just share these things in half. They're like zinc plated shit Like they're really not made for this. Okay, don't do this. This is also wrong This is uh It's Miller light dude. This is right. Okay. This is how you do it
10:29
The bolt is actually not the object that is holding the pieces of metal together The bolt is the object that holds the pieces together enough for static friction to take over and actually do your major holding force
10:43
Like it's it's like you don't like that the force should not be physically in the bolts the forces in the fact that Static, I'm just gonna repeat myself. You got it. Okay All right. Next. This is a puppy because we're changing ideas and People say I talk too fast, so I just put puppies and kittens and those things in whenever we have to transition ideas
11:03
I hope you guys are cool with that puppies are awesome though. So I really hope you are Next item drivetrain ratio. Okay, we're gonna consider the the places where the wheels we're gonna assume the four-wheeled robot here Because we're simple. Okay, so assume that the the points where the wheels touch the ground are points
11:21
You make them into a shape If it's a square then you're you know, you can go forward and turn You know if you if you want it to be super agile, you know You have the big like crazy angle thing or you drive the rectangle with the short side forward if you just want it To go straight almost all the time This is not terribly complicated. But a lot of people are just like I'm making a robot
11:42
I'm gonna put some wheels on some plywood, you know, so think about this when you're setting up your stuff Okay, the other thing that people default to is a car though And you know all of you who drive though that cars aren't actually like Particularly nimble objects. They need to lady. That's just like trying to turn a bicycle They need to go forward in order to turn
12:03
Also making the wheels swivel properly is a pain in the ass So unless you have a good reason for this This is probably not the default that you want to go to even though it's what you see most often in your daily life Tank is actually a pretty good default. Just put the wheels down the side
12:20
Put them all forward to go forward put these guys forward and these guys backwards to turn turns on a dime pretty clean It'll scuff up everything If you care about that because basically the whole art of it turning is it doing little micro hops? So and it particularly if you have large tank treads and then you previously had rug in your house
12:44
Some people will do like two wheels tank driven and then Casters or omni wheels on the front as a slightly less brutal alternative That that will that will save your carpet significantly, but no guarantees man Omni wheels unless you have a good reason you should just buy these so many people want to make them I
13:08
Warned you So they're helpful with the resistance They permit like some people will do Like they will have a set of wheels going this way on the robot and then a set of wheels going this way on the Robot and what you can do is by driving different sets of wheels independently
13:23
You get a robot that goes this way and goes this way without turning cute trick Terrible lateral traction for pretty obvious reasons this thing in the middle here is an omni wheel I'm gonna I I'm sorry the speakers in the way. I really can't even see that one. I'm so sorry guys But yeah this thing towards the middle is an omni wheel and as you can see it's a yo-dog
13:44
I heard you like wheels so I put some wheels on your wheels These little black things are free-floating so This is why you can have the wheels go opposite ways of each other and not have anything actually fight This is also the transition side towards vector drives, which are these things with like the miniature hair curl hair curl or rolling pin things
14:06
You'll notice these are at an angle which means that this wheel when you turn it most people when you turn it They just want to go forward this wheel wants to go forward and also in the direction of the little hair curlers And so when you look at this if you put four of them on they're like default state
14:23
Is that they all have a a direction? They all have two directions that they're pushing and if you balance them, right you actually now have a like fully