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• Reviving the Skull Tote

  deʃhipu • 06/07/2018 at 19:04 • 0 comments

  I have a number of prototypes of Tote that I have built over the years, but the most presentable one is the one I pimped up in https://hackaday.io/project/6050-tote/log/48853-pimp-your-bot

  Unfortunately, that robot had a number of problems. Unlike all other Totes, it was powered with a 2S lipo battery, with a buck converter bringing to voltage down to 5V. That tiny buck converter would only work for a few minutes, and then starting to shut down when the current drawn by the servos made it too hot. Which would result in the robot having a seizure. I also discovered that the motor in one of the servos got stuck — rather common with the cheap SG90 servos — and would need to be replaced.

  So I decided to open up this robot, replace the power with a more standard setup (a 1S lipo connected directly without any voltage stabilization), add a battery charging circuit, and replace the servo.

  Here's the USB port for the battery charging circuit:

  And the replaced servo, primed with black paint, waiting to dry for a dry-brushing:

  And finally the whole robot, it all its robot glory:

• Gangsta

  deʃhipu • 01/15/2017 at 11:34 • 2 comments

  As I wrote in the previous logs, I'm going to be upgrading Tote to use some more expensive, but more powerful and easier to use components. But what about the poor students? If you are really concerned about the budget, the original Tote is almost what you need. Almost, because you would still need to order the PCB for it. Or would you?

  Of course not! The PCB doesn't have anything you can't easily reproduce on a vero/strip/perma board! Here's one example of a Tote on a strip board:

  Sure, you will need to remap the pins in the code, but that should be quite easy. Yes, I went wild in Fritzing, and it's barely readable. Here's a clearer picture of the strip board you will need to make:

  It even has the voltage divider for monitoring the battery. Oh, right, and don't use alkaline batteries like on the picture. Use a LiPo from a quadcopter or from an old cellphone.

  I have to admit that one thing they say about Fritzing is true: it sucks for making schematics:

  I wonder if I should fork this version off the main Tote, and keep a repository with the Arduino code for it, with remapped pins and so on...

• Programming the Spinal Cord

  deʃhipu • 01/14/2017 at 14:11 • 0 comments

  n the previous log I made a decision to use an Adafruit Feather board for the robot's brains, and a bare ATmega chip in a DIP package for its spinal cord -- that is, the servo controller. That's supposed to make the board much easier to solder even by inexperienced builders. But wait a minute! How are they going to get the servo controller program onto those chips? Will that not require some extra hardware? Sadly, yes.

  It will require six extra wires.

  The trick is to use the Feather board as an ISP programmer, using the "Arduino as ISP" example sketch from the Arduino IDE. You will need to make the following connections:

  Now, in your Arduino IDE go to Files→Examples→11.ArduinoISP and select that example. Then scroll to around line 68 and change this:

  // Configure which pins to use:
  
  // The standard pin configuration.
  #ifndef ARDUINO_HOODLOADER2 
  
  #define RESET     10 // Use pin 10 to reset the target rather than SS
  #define LED_HB    9
  #define LED_ERR   8
  #define LED_PMODE 7

  Into this:

  // Configure which pins to use:
  
  // The standard pin configuration.
  #ifndef ARDUINO_HOODLOADER2 
  
  #define RESET     0
  #define LED_HB    2
  #define LED_ERR   4
  #define LED_PMODE 5

  Then go to Tools→Board and select the Adafruit HUZZAH board, then do Sketch→Upload. You have your programmer ready.

  Then to program the chip, load the sketch with the servo controller, change the board to Arduino Uno, select Tools→Programmer→Arduino as ISP, and do Sketch→Upload Using Programmer. You should see some blinking lights on your Feather, and then your chip is programmed.

  In the end, I will probably make a Makefile that does the equivalent of the above procedure automatically, to streamline the experience a bit.

• Choosing the Brains

  deʃhipu • 01/11/2017 at 22:28 • 4 comments

  In the previous post I shared some of my thoughts about this project, and decided to pick a different development board than the Pro Mini that I have been using so far. Don't get me wrong, Pro Mini is great for all kinds of small and cheap projects, it's just that I want to make programming this robot as simple as possible. That, among other things, means using a platform that has a lot of computing power, not just enough, preferably one that has so much of it, that it can be used with a high-level language like Python. That also means something that has a USB socket.

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• New Year Reflections

  deʃhipu • 01/11/2017 at 16:15 • 0 comments

  Year's Summary

  This is one of my oldest projects, and definitely one that I have put the most total work into so far. With the year's end, I decided to reflect a bit about the progress made so far and the way forward.
  

  There wasn't a lot of activity, but some interesting things did happen last year.

  We had a workshop in Belgrade, where we built 20 #Tote HaDs. I have learned a lot about how (not) to source parts for such an event, how to run it, what parts are actually hard for people, etc. There were also some improvements to the construction itself contributed by the participants -- but only during the workshop. I'm a bit disappointed that nobody seems to have done anything with their robot after the workshop -- or, at least, I haven't heard about it. I think this is an important point to consider.
  

  There have also been some Tote-inspired builds out there. I helped to build at least two of them. There are even more unfinished projects, but I guess that's normal.

  On my side, I released another version of the PCB, experimented with some alternate brains (including the #Tote Zero with a Raspberry Pi), and made one of my prototypes look much better by giving it a chassis and some LED eyes, and a coat of paint. There has been practically no progress on the software side, despite some research on the CORDIC algorithms and servo PWM code. I also didn't experiment much with sensors and behaviors. The step-by-step tutorial is also empty.

  Overall, even though some work got done, and even though I gained some experience, I'm not particularly happy with the outcomes of the Tote project. I'm starting to realize that it's not enough to give people a platform to experiment with -- even if they do experiments and improvements, it's all for nothing if they don't share them.

  Wrong Goals

  I think that part of the problem is that I have been focusing on the wrong parts of the project. I need to pause and re-evaluate some of the assumptions I made, and see where that takes me.

  When I was just starting with Tote, I still remembered being a student and not having much of a budget for this kind of projects. So I made lowering the total cost the number one priority (well, apart from having it actually work, of course). As I look at this now, this might have been a mistake. Sure, when you are a student in Poland, price is the number one factor for anything. But it turns out that most people who do this hobby stuff actually don't mind spending a little bit more if that saves them time, makes things more convenient, gives better results or even just makes things look more shiny. If you are going to put hours of work into a project anyways, you don't mind waiting a little bit more to get the extra funds. So I am going to pay less attention to the price (but still try to keep everything frugal) from now on.

  By default, Tote is controlled with a TV remote, and has no autonomous functionality. I did that, because I figured it's the simplest starting point, and also shows off the hardware capabilities, leaving any software-side innovation to the users. Or maybe I was just lazy. In any case, I think that this has turned it into a toy, and discouraged actually programming it. There are some other decisions that also contributed to it: the need for an external programmer for programming, the main code written in C++, no easy way to update and debug the code. I think I should start putting more effort into making it easier to actually program this robot, and encourage it more. Fast iteration is the key to good progress. I have become painfully aware of that recently when working on the recent version #µBob biped robot, where I had to physically unscrew and detach the legs to access the chip for programming. That's the best way to make sure nobody ever changes anything in the program unless they absolutely must. So I need to try and remove all the obstacles for programming. And also finally finish the programming tutorial for it.

  Simplicity was another design goal (it always...

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• imath.h

  deʃhipu • 12/22/2016 at 14:48 • 0 comments

  It took me two evenings of pretty much randomly editing code, trying to make it as small as possible without breaking it horribly at the same time, but I finally have a library with three basic functions, iasin, iatan2 and isqrt, which are int16_t versions of the ones from the standard library. The angles are returned in the range of -1800 to 1800, and the input to asin is -1<<13 +1 to 1<<13. The whole library is around 700 bytes (644 at the last compile) and should be relatively fast on the AVR (although I didn't really time it). Oh, and the code is at https://bitbucket.org/thesheep/imath/src/tip/imath.c

  If you see any opportunity to shrink it even more, please tell me!

  Unfortunately, this is still way too large to make Tote fit in the magical kilobyte. I might try with int8 versions next, but those are not going to have enough resolution for a proper walk, unless I will play with the ranges some more.

  Here's a comparison of the values from those functions with the standard library:

  asin(-0.88)=-61.04 iasin(-7168)=-610 diff -0.04
  asin(-0.75)=-48.59 iasin(-6144)=-486 diff 0.01
  asin(-0.63)=-38.68 iasin(-5120)=-388 diff 0.12
  asin(-0.50)=-30.00 iasin(-4096)=-302 diff 0.20
  asin(-0.37)=-22.02 iasin(-3072)=-220 diff -0.02
  asin(-0.25)=-14.48 iasin(-2048)=-144 diff -0.08
  asin(-0.12)=-7.18 iasin(-1024)=-70 diff -0.18
  asin(0.00)=0.00 iasin(0)=0 diff 0.00
  asin(0.12)=7.18 iasin(1024)=72 diff -0.02
  asin(0.25)=14.48 iasin(2048)=144 diff 0.08
  asin(0.37)=22.02 iasin(3072)=220 diff 0.02
  asin(0.50)=30.00 iasin(4096)=300 diff 0.00
  asin(0.63)=38.68 iasin(5120)=388 diff -0.12
  asin(0.75)=48.59 iasin(6144)=486 diff -0.01
  asin(0.88)=61.04 iasin(7168)=610 diff 0.04
  asin(1.00)=90.00 iasin(8192)=916 diff -1.60
  
  sqrt(0)=0.00 isqrt(0)=0 diff 0.00
  sqrt(1024)=32.00 isqrt(1024)=32 diff 0.00
  sqrt(2048)=45.25 isqrt(2048)=45 diff 0.25
  sqrt(3072)=55.43 isqrt(3072)=55 diff 0.43
  sqrt(4096)=64.00 isqrt(4096)=64 diff 0.00
  sqrt(5120)=71.55 isqrt(5120)=71 diff 0.55
  sqrt(6144)=78.38 isqrt(6144)=78 diff 0.38
  sqrt(7168)=84.66 isqrt(7168)=84 diff 0.66
  sqrt(8192)=90.51 isqrt(8192)=90 diff 0.51
  
  atan2(0, 0)=0.00 iatan2(0, 0)=0 diff 0.00
  atan2(0, 1024)=0.00 iatan2(0, 1024)=0 diff 0.00
  atan2(0, 2048)=0.00 iatan2(0, 2048)=0 diff 0.00
  atan2(0, 3072)=0.00 iatan2(0, 3072)=0 diff 0.00
  atan2(0, 4096)=0.00 iatan2(0, 4096)=0 diff 0.00
  atan2(0, 5120)=0.00 iatan2(0, 5120)=0 diff 0.00
  atan2(0, 6144)=0.00 iatan2(0, 6144)=0 diff 0.00
  atan2(0, 7168)=0.00 iatan2(0, 7168)=0 diff 0.00
  atan2(0, 8192)=0.00 iatan2(0, 8192)=0 diff 0.00
  atan2(1024, 0)=90.00 iatan2(1024, 0)=899 diff 0.10
  atan2(1024, 1024)=45.00 iatan2(1024, 1024)=449 diff 0.10
  atan2(1024, 2048)=26.57 iatan2(1024, 2048)=274 diff -0.83
  atan2(1024, 3072)=18.43 iatan2(1024, 3072)=183 diff 0.13
  atan2(1024, 4096)=14.04 iatan2(1024, 4096)=139 diff 0.14
  atan2(1024, 5120)=11.31 iatan2(1024, 5120)=112 diff 0.11
  atan2(1024, 6144)=9.46 iatan2(1024, 6144)=95 diff -0.04
  atan2(1024, 7168)=8.13 iatan2(1024, 7168)=84 diff -0.27
  atan2(1024, 8192)=7.13 iatan2(1024, 8192)=70 diff 0.13
  atan2(2048, 0)=90.00 iatan2(2048, 0)=899 diff 0.10
  atan2(2048, 1024)=63.43 iatan2(2048, 1024)=633 diff 0.13
  atan2(2048, 2048)=45.00 iatan2(2048, 2048)=449 diff 0.10
  atan2(2048, 3072)=33.69 iatan2(2048, 3072)=336 diff 0.09
  atan2(2048, 4096)=26.57 iatan2(2048, 4096)=274 diff -0.83
  atan2(2048, 5120)=21.80 iatan2(2048, 5120)=216 diff 0.20
  atan2(2048, 6144)=18.43 iatan2(2048, 6144)=183 diff 0.13
  atan2(2048, 7168)=15.95 iatan2(2048, 7168)=159 diff 0.05
  atan2(2048, 8192)=14.04 iatan2(2048, 8192)=139 diff 0.14
  atan2(3072, 0)=90.00 iatan2(3072, 0)=899 diff 0.10
  atan2(3072, 1024)=71.57 iatan2(3072, 1024)=724 diff -0.83
  atan2(3072, 2048)=56.31 iatan2(3072, 2048)=562 diff 0.11
  atan2(3072, 3072)=45.00 iatan2(3072, 3072)=449 diff 0.10
  atan2(3072, 4096)=36.87 iatan2(3072, 4096)=370 diff -0.13
  atan2(3072, 5120)=30.96 iatan2(3072, 5120)=309 diff 0.06
  atan2(3072, 6144)=26.57 iatan2(3072, 6144)=274 diff -0.83
  atan2(3072, 7168)=23.20 iatan2(3072, 7168)=232 diff -0.00
  atan2(3072, 8192)=20.56 iatan2(3072,...

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• CORDIC

  deʃhipu • 12/21/2016 at 16:20 • 0 comments

  Since the flu season began, I've been lying in bed sick quite some time. While I don't recommend doing coding with a fever (takes way too much time to track down the trivial mistakes you make), you do have some free time to explore some coding ideas that you didn't bother with before. One of such things on my to do list is rewriting Tote's inverse kinematics code to use only integer math, and I found a marvelous family of algorithms that can let me do it.

  If you look at my explanation of Tote's inverse kinematics at http://tote.readthedocs.io/en/latest/ik.html, you will see that I'm using two trigonometric functions (actually inverse trigonometric functions) in there: atan2 and acos. They both return an angle -- in the case of the standard library functions, in form of a number between -PI and PI (or was it 0 and 2PI? I can't remember). That's a pretty arbitrary range, that I have to then convert into servo pulse width in the range between 600 and 2400µs. Wouldn't it me great if they instead returned integers from 0 to 1800, so that I could use them for the servo pulse width directly?

  But how are such trigonometric functions calculated? There are several ways. You can approximate them with a polynomial, using a so-called Taylor series. You can also have a lookup table, with some interpolation for the values in between. But both of those approaches involve quite a lot of multiplications and divisions, and possibly floating point (or fixed point) numbers. Which is slow on a microcontroller such as the one used in Tote, not to mention a lot of code being generated (especially for the lookup tables). Fortunately there are the CORDIC algorithms, which involve only a lookup in a small table, some additions and some bit shifts. And of course you do it all on integers. Plus, you have very good control over the accuracy -- the more iterations of the algorithm you do, the better results you get.

  How does it work? The heart of the algorithm is a small mathematical trick that lets you rotate a point (x, y) around the center of the coordinate system (0, 0) by a fixed angle using just additions and bit shifts, provided you know the arcus tangent value of that fixed angle. So you make a lookup table with a dozen values for 45°, 22.5°, 11.25°, 5.625°, and so on (each angle half of the previous one), and you do a binary search for your value.

  Let's say you want to calculate cos(a). Imagine a length 1 line starting at (0, 0) and going to (x, y), with the angle between the x axis and the line being a. Then the value we are looking for is x. How do we find x? We will start with a line at angle 0° and coordinates (1, 0), and rotate it (using our additions and shifts) by 45° one way or the other, depending if our a is larger or smaller than 0. We will get some point (x1, y1) this way. Then we will rotate it again, by 22.5°, one way or the other depending on where the angle a is compared to our current angle. And we will repeat that, rotating by a smaller angle each time, until we get close enough to out angle a. At that point we have calculated our cos(a) (and also sin(a) at the same time).

  Calculating the inverse trigonometric functions is similar, except we start with the line at (x, y), and try to rotate it to be as close to (1, 0) as possible, keeping track of how much we have rotated it so far. Once we got close enough to (1, 0), the total angle is our answer. Simple.

  All that is left for me is to actually write some code, test it, tune it to use the smallest types possible and to work with enough accuracy for my particular use case, and put that code in Tote. I will let you know when that happens, but first I need to get over this flu.

• Version 5

  deʃhipu • 12/07/2016 at 20:47 • 0 comments

  I've been asked for a Tote kit for a Christmas preset by a friend, and I realized I no longer have any version 4 boards. So I had to go and order some. But if I'm ordering boards anyways, why not make some improvements here and there? So here's a version 5.

  You can see the board is much simpler now. It's basically just the servos, the battery, the pro mini, power switch and ir sensor. There are still the optional battery monitoring, piezo, distance sensor and extra capacitor, but by default they are not used. I also switched some pins around, so now using the serial pins for servos -- but all the analog pins are free, and broken out close to each of the legs. That should make it easier to use them for sensors.

  There is also a new step-by-step assembly tutorial for this version at http://tote.readthedocs.io/en/latest/assembly_v5.html and slightly modified code at https://bitbucket.org/thesheep/tote/src/tip/v5.

  And I still have the other 9 boards to give away.

  Oh, right and a DirtyPCB link: http://dirtypcbs.com/store/user/preview/1154
  

• Pimp Your Robot II

  deʃhipu • 11/10/2016 at 11:09 • 1 comment

  So, today I hotglued the lenses with the LEDs, updated the software to let me switch the LEDs on and off, added a piezo to the robot, so it makes sounds, and painted some red highlights on the legs. The end result:

  And here's a short video:

• Pimp Your Bot

  deʃhipu • 11/09/2016 at 21:30 • 0 comments

  The winter is coming, and my robots need some maintenance -- after a year of traveling to various conferences and fairs, they accumulated a number of injuries. It's also a good idea to recharge the lipo batteries once in a while.

  I started repairing the robots, replacing broken servos, tuning them, etc. -- and at some point I realized that they actually look pretty drab. Just a bunch of wires and servos, really. Of course, the idea was to make them as simple and easy to make as possible, so that's just expected, but still they don't look like something you would actually want to have. That's when I decided to take one of the prototypes (incidentally, the one that I used for proprioception experiments), and make a chassis for it, to make it look a little bit better.
  

  So I went to the Internets and started to look through concept art of various robots. I'm quite surprised and saddened by how many of those are simply "a human in suit with a weird helmet". Oh well. Finally, I found one drawn by Paul Denton that fits Tote well and should be simple enough to make:

  It's a bit dark and gritty, but that's even better -- any mistakes I make will not be as visible. So I started with a plastic box -- from a set of toy blocks for kids. Of course I started by cutting the corners:

  Then I removed the legs from the robot, and installed the PCB inside the box:
  

  I had to cur the sides of the box, and also the "ears" on the servos -- to make them fit properly without colliding with the box or with themselves. Once I was happy with the shape, I hot-glued the PCB securely in place and started painting. I'm using acrylic paints for painting tabletop battle miniatures. It sticks pretty well to plastic.

  Once I had the base coat ready and it all dried, I started to dry-brush some of the wear and old paint on it, then dry-brushed the whole thing with metallic paint, to make it look like beaten metal.
  

  Next, I had to do something with the wires. They are way too long, there is not enough space inside to hide them, and they are the wrong color. After some deliberation, I decided to just cut them to size:

  And then I also painted them black. Some mor dry-brushing, and it's almost ready. I also made a hole at the top for the IR sensor for the remote to stick out.
  

  Next, I worked on the eyes. I found some plastic lenses for LEDs in my drawer, and some red LEDs:
  

  A bit of glue to secure the LEDs in place, some more to glue the lenses into the eyes, and some resistors and wires, and it's almost ready. Now I just need to wait for the glue to set...

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