Raspberry Pi controlled Lego car part 2

Not many pictures this time, because unlike last time I’ll rant a bit this time about getting the software on the Pi working. To start off: I did something rather stupid: I updated Raspbian. It took ages to update the OS and all the packages. The Pi isn’t very fast for that. I should’ve just downloaded a new image. Here’s how I lost a lot of time.

After updating the OS my wifi stopped working. I’m using a small TP-link USB wifi, since my Raspberry Pi B+ doesn’t come with on-board wifi. I did a lot of searching on why this would suddenly stop working, and found that, only in some cases, the B+ is incapable of providing enough power to the USB ports to make my particular model of wifi adapter work. The wifi did in fact work for just a split second after booting, and I was able to ping the Pi from another PC, but it almost immediately disappeared again. This I thought was a good indication that it was indeed a power issue.

I bought a USB cable from Amazon that combines two USB plugs, one for data, one for power, into one output, for the wifi plug. I was fairly confident that this would solve my problem. First I plugged both inputs into the Pi’s USB ports, but no luck. Then I tried plugging the USB power input directly into my USB battery pack, but that didn’t work either. It did have a weird side effect, in that if I disconnect the Pi’s regular micro-USB power connector, it miraculously stays powered through the USB wifi plug. Weird, but not useful.

So I did some more digging and eventually found out that for every Pi kernel you need to manually (re)compile your wifi plug’s driver. Ugh. I got started on doing that but it took ages. I eventually managed to find a site that offered precompiled drivers and simple installation instructions. Not exactly open-source but I’m definitely not going to wait hours for the bloody thing to compile.

With the wifi fixed and the motors super-easy to control via the Python GPIO library, I got to work on getting the Pi’s camera feed to work. The Pi supposedly does full-HD video capture at decent framerates so I had high hopes of getting a nice stream going. Unrealistically high hopes, it turned out. Recording decent quality video is one thing, but streaming it in real-time with little enough delay to control a moving vehicle, that’s quite another. I had to turn down the resolution all the way back to 640×480 to get <500ms delay, but after that it’s quite usable. The uv4l raspicam package comes with a built-in server to stream video, which is actually pretty nice when playing around with it on the local network, but since my final goal is to open it up to the internet I’ll have to find something a lot more secure than that. I’ll likely set up a separate Python server to forward the video feed, or stream it from the device directly. I hope it won’t introduce too much extra delay..

On the hardware front I’m playing around with some of Sariel‘s gearboxes. I bought a set of various Lego gears on ebay since my aging Lego Technic did not have many useful parts. I built this three-speed gearbox and then figured I might as well buy the Lego Servo motor as well to play around with.

Turns out that controlling a servo motor from the Pi is a lot more difficult than controlling a regular motor. To get the servo motor to go to a pre-set position you need to use pulse width modulation with a very specific duty cycle for each position. If you get the duty cycle slightly wrong the servo will jitter around the position and move back and forth a bit. The same happens when using the Python GPIO default module, which comes PWM functionality built-in, but just can’t be real-time enough to generate a stable signal. There’s loads of jitter if you try it that way. I ended up going with RPIO, which uses Direct Memory Access to get the timings right. I played with it for hours but in the end still could only get about half out of the supposed 14 positions to select correctly. I think that’s more of a problem on my side though, and I’m probably using the wrong duty cycles or frequencies. That said, I’m totally indulging at this point because the gearbox only needed the off position and full negative and positive duty cycles, so I didn’t even need to use pulse width modulation at all. It was an interesting side track though.

Once I got the three-speed gearbox working with the servo I slapped an XL motor on to it and immediately realized that this gearbox design will never work for my tracked vehicle. As soon as I applied only a little pressure on the output wheel the servo axle would fail and start rotating. It really doesn’t stand up very well to any decent amount of torque. Time for another design. I ended with a super-simple custom design for a 2-speed gearbox that I got off the internet, but all the simple designs, the designs that I actually have the parts for to build, don’t seem to be meant to be controlled with the servo motor. I played around with this for quite some time last Sunday and eventually managed to rig up some kind of controlling arm to push and pull the middle axle of the gearbox so it can shift gears. I haven’t tested this with load, though, so I’m not sure if it’ll hold up very well in the final vehicle. But I’m a bit more confident about it than I was about the three-speed servo gearbox.

The next challenge will be to duplicate the gearbox and make a design that allows the servo to change gears in both gearboxes simultaneously. Since I’m making a vehicle with independently-controlled caterpillar tracks (but only have one servo motor) I’ll need to have one gearbox for each track.

Lastly, I got one more thing wrong in the last post, about getting power to the motors. I had bought a USB-to-9V cable, which I thought didn’t work in my USB battery pack because the battery pack was smart enough to disable the port if it detected that no power was being drawn. That assumption turned out to be completely wrong. Instead, what happened was that the cable had a very shitty USB connector and after I let go of the connector it would drop a bit and disconnect. I duct-taped it into place and it works perfectly, so I can get away with using just one USB battery pack (with two USB ports) for my vehicle. Yay!

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Raspberry Pi controlled Lego car part 1

So, I have a fair bit of Lego lying around from my childhood days. Not a lot of technical parts, but enough to have some fun with. I also have a Raspberry Pi lying around after a failed experiment where I tried to use it as a security camera. Why not combine the two? I figured I could build a Lego car that I can control remotely via a little server on the Raspberry Pi, which would also stream its camera feed. It seemed easy enough, especially after discovering a page that explained exactly how to make the hardware part of it work. Never did I imagine it would take this much work to get it up and running..

This post will detail the hardware iterations and setbacks I faced. The next post will go into detail about the software side of things.

So, before starting on this project, here is the list of things I thought I’d need to make this work:

  • Bunch of Lego: wheels, gears, other technic parts and some generic bricks to connect it all up. (already owned)
  • Raspberry Pi plus camera module. (already owned)
  • A USB battery pack (already owned)
  • Two Lego power functions motors.
  • A 9 volt battery.
  • A motor controller.
  • Some Dupont wires to connect it all up.

Version 1

I bought the M motor starter kit and a separate M motor for my first iteration. I built a very nifty motor assembly and a very strong shell structure to house the components. Here’s how it looked like:

v1.0

It is thus that I found out that I should never overengineer before testing. While building the thing I discovered that I didn’t have the parts required to drive all six wheels, so I chose to just drive the middle wheels instead. I figured that by gearing down a bit it should be fine. Much nope. The M motors were way too weak to power the construction, which was already quite heavy from the USB battery pack, but weighed down even more because of its overengineered sturdiness. Having just the center wheels powered was also a terrible decision. Fail.

Version 2

v2.0

I built this is a test version to experiment with gear ratios and to see if in a lighter version the M motors would have enough power to drive the car. Answer: not really. I got it to go forward and backward pretty decently, but I still didn’t have the parts required to power all the wheels, so the motors were not strong enough to turn the whole thing without a steering assembly. Fail again.

So I had two options at this point. Option one was to build a rack-and-pinion steering assembly, for which I had the parts available and did end up experiment with, but in the end I wasn’t happy with its turning radius and how I’d either have to buy a servo motor or have an ‘unclean’ solution with a clutch gear to handle the stopping at the end of the wheel turning axis.

Instead, I went with option two: throw more money at it. I bought two XL motors and a crapload of caterpillar tracks. That’ll give me the power and the grip I need to build something really nice.

Version 3

..or not. It does look impressive though. Here’s a test build with the power functions battery box instead of the external 9 volt battery.

v3.0-test

At this point I was still powering the motors via a separate 9 volt battery. I figured that, since my USB battery had two USB connectors, I could use it to power the motors as well, so I ordered a USB-to-9-volt cable from Amazon. That should help me save some weight by not having to put in two batteries. Sadly, this did not go well.

USB batteries are pretty smart. So smart in fact, that they only output power if they think something’s plugged in. The USB-to-9-volt cable worked fine on a powered usb hub, but every time I’d try to hook it up between the battery and the motor controller it would simply not turn on. Crap.

I found another USB battery, which is actually a battery used for starting cars that happens to have a USB port on it. This one did always keep the power on if I plugged in the USB-to-9V cable. Good! Except it only had one USB port, so I couldn’t also power the Raspberry Pi from it. So I ended up with two USB batteries and over double the original weight..

v3.0-final

The big green thing is the car-charging battery. Even without the second battery the 3:1 gearing wasn’t quite powerful enough to rotate this monstrosity when on certain surfaces, such as medium-thick carpet. Once again, fail. And once again, I spent way too much time overengineering the construction without testing it first with its full weight.

Version 3.5

I figured I’d try to keep the next version as small and light as possible and worry about motor powering and recharging issues later. I managed to build a pretty small prototype.

v3.5-test

Now, I had one option left to avoid the use of two batteries. The big green car charger battery did, in addition to its one USB port, come with a 12V output. It’s not the 9 volts that the Lego motors need, but I did find at least one link claiming that the motors should run fine on 12 volts as well. I had previously done this as a child when connecting an old technic 9V motor to my 12V Lego train controller, which gave it quite a nice speed boost as well. I figured this would be an acceptable trick. I butchered an old power supply, cut off it’s circular connector and used it to connect up the green battery’s 12V port up to the motor connector.

To avoid any more gearing issues I added another axis, bringing the final ratio down to 9:1. The build ended up much larger than I had intended, but still smaller than v3.0. With better gear ratios and a higher voltage to the motors.

v3.5-final

You may notice the second battery sticking out at the end of this bulky thing, despite the fact that the green battery has a free USB port thanks to the makeshift 12V connector. This is because the stupid battery doesn’t let you use both outputs at once. It just turns off one or the other. Not ideal!

I’m still annoyed at this but don’t have an immediate solution. The reason I spent so much effort trying to get everything onto one battery was because I intended to build a little wall charging station, so I can drive the robot into the charging station, which will connect the charging port of the USB battery onto a USB wall socket. I gave this a try with the double-ported battery while the Raspberry Pi was connected, and sadly it resets the Pi as soon as the charging connector is plugged in. Crap times two. I haven’t tried this trick with the green battery, but that’s pointless anyway since it only lets you use one device at a time. Looks like I won’t be able to charge the thing remotely while it’s running.

V3.5 still has a whole bunch of issues. It works great in terms of motor and track performance though. It moves and turns fantastically. even loaded with two bulky batteries. The motor placement isn’t great though; they’re way too close to the ground. I need to fix that in the next version. It’s also longer and wider than it needs to be. Once I get a solution to the two-batteries issue I’ll decide on how large the next version will be. I’m also thinking about buying the servo motor and using it to power a small gearbox, but I’d also need to buy more technic gears and axles for that, and I’ve kind of already spent way more on this project than I thought I would spend..

For now though, I’ll stick with this hardware design and focus on getting the software up and running. More on that next time.

 

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New hobby project

Turns out it’s really easy to control Lego power functions motors via a Raspberry Pi. I found myself a new hobby project

2017-01-08 20.24.33

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The 9gag data mining scam

(Or: what is your <insert meme here> name? Click here to find out.)

Perhaps you’re an occasional browser of 9gag or similar sites, and have come across images like these before:

Instagram-TropicalHouse-8dc5ec

People inevitably reply in the comments section with their hilarious name. Lately I’ve seen a lot more of these images than usual, and I’m guessing it’s actually an attempt at data mining by some hacker trying to dox people. The questions on the images vary; sometimes it’s the first letter of your name, sometimes it’s the date you were born, the month you were born, the first letter of your mother’s maiden name, and so on. People who are stupid enough to reply to these images with that data eventually create a very usable data trail that can be used by hackers to impersonate them on the phone. So yeah, have fun explaining to your bank that you publicly posted all details about your life in a poorly obfuscated manner.

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Responsiveness and Patreon!

As you may have noticed from the blinding orange link at the top of this page, I am now on Patreon

That said, I am fully aware that this is a personal blog with personal content, but on the off chance that someone enjoys my writing and would like to support me, I thought Patreon provides quite a nice way to do that. I’m perfectly happy to never get anything from Patreon and will still continue blogging, as I have done for the past 11 years. Yes, it’s been 11 years.. Interestingly that makes this blog the longest-lasting thing/activity/venture that I have in life. With possible exception of my iPod classic, those things last forever.

Creating a Patreon page was quite interesting. It really forced me to think further than ‘It would be great if people could throw money at me for writing silly stuff like this’. I had to think about what value this blog creates, what topics are the most likely things people want to see, and what is the best way to take payment. It didn’t make sense to offer payment per blogpost, since I would forfeit my freedom to write silly things that I wouldn’t dare ask people money for. Monthly contribution seems to make more sense. I assumed that of my writings, the cycling trip day-by-day travel reports are probably the most interesting to read, so any funding I get on Patreon will likely go to the cycling cause.

As a secondary effect, every time I think about increasing public exposure of this blog I get nervous about its quality. I can’t do much about the content after it’s been written, but I can do something about the styling and user-friendliness. So yesterday I wrote some css that will hopefully make this blog a lot more mobile-friendly. It’s still nowhere near perfect, but it’ll have to do for now.

Random life thing: I’m supposed to be preparing for the upcoming cycling trip later this month but instead I’m currently experiencing quite possibly the worst cold I’ve ever had in my life. I’m feeling myself start to recover, but it’ll be a few more days until I’m back to normal. I’ve got some ideas for posts lined up but nothing written down yet. There’ll be something new here soon. Stay tuned!

(ZEST)

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Why I won’t be moving away from WordPress

I’ve made some time for myself to do some personal projects, and one of the things that’s been on my mind for the longest time was to move this blog away from WordPress and host it statically on S3 instead. Serving a single static html page (plus a few resource files, but not many) from S3 would be so much faster than letting the shared hosting server parse endless lines of php, most of which I don’t even want. The benefit in that aspect is clear, but in other areas it’s less obvious.

Easy of deployment is one of the issues. I’m not bothered about not being able to post by email or mobile – whenever I have something to write I’ll usually have my laptop with me. It doesn’t bother me that it won’t be WYSIWYG either (which it wouldn’t be if I write my own blog software because I don’t care about WYSIWYG). The problem is always with the software and the libraries. My software of choice for my would-be static blog is python, but I’ll inevitably end up requiring some libraries that will need to be downloaded and/or set up on each machine that I want to publish from. Knowing myself, I will forget to do this before I go on a trip and end up having to download those libraries at ultra-slow speed at some hotel in the middle of nowhere. Or I might be on a public machine, which will be even worse.

Comments are another issue. If the blog is completely static I’d have to go for a javascript-based comment service. I also have old comments that will either have to be converted to the new commenting system or else inserted into the html somehow if I want to preserve them. Again, there are solutions, but they’re hardly easier than what I have with WordPress.

Finally there’s the issue of dynamic pages: the calendar, archive and search functionality. Calendar and archive pages are pretty easily generated, but I’d either have to remove the search function or rely on an external service for that. Bleh.

The system I had in mind would be a collection of small tools:

  • A converter tool to convert a wordpress database into raw blogpost/page files (the exact format of which I would have to think about).
  • A compiler tool that reads the raw posts and writes usable html
    • Inserts content into a predefined template, I was thinking Django templates. This doesn’t have to be fast.
    • Regenerates related pages (front page, archives, calenders, category pages)
    • Converts any markdown text to html
  • An uploader tool that publishes the generated html
    • Would upload to S3, perhaps pluggable so other providers would work too.
    • Would be smart enough to recognize linked images/files and upload those too.

I’d leave the template design and making the javascript commenting system work all up to the user, since that’d be a one-off job (for me, anyway). The goal of all this is to make my life easier, but it’s an awful lot of work for an awfully small amount of easiness.. Anyway, if someone else would also be interested in using something like this (or willing to pay for something like this!) then do let me know.

 

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The rational sacrifice

Check out this post on Elon Musk on Wait But Why. The post goes into great detail about how Musk reasons from first principle. By starting at the beginning and thinking about what’s best for humanity as a whole, Musk ends up being motivated to make reality renewable energy and travel to Mars. He didn’t just start there from scratch of course, and the article shows how he worked his way up from internet startups towards more lofty goals. It’s a good read, highly recommended.

Somehow, when I think about my own life in this way, and trying to be as rational as possible, I do not find myself reaching the same conclusions as Musk has. I think what Musk has done is, is you consider the human factor, not the most rational solution to the problem ‘what should I do with my life’. And that makes what he does all the more admirable. I’ll try to explain my reasoning with some personal life examples.

In my day job as software developer it pays off to be completely and coldly rational about your product. For example, even if you intend to be on a project for 6 months, it still pays off to focus on the extreme-long-term of the project if it was made to last long, even if you don’t intend to be on the project for that long. Rationally, what is best for the project is also best for you as a developer, because you are accountable for the state of the project. If the project goes well and continues to go well in the future, that means people think highly of you and will consider you again for future projects. Personal motivation and that of the whole are aligned.

Now compare that to Musk. He made his personal motivation to be the motivation of the whole. There is just no way that this can be an intrinsic, gut-feeling type of motivation, and he says so himself. He reasoned from first principles and arrived rationally at a conclusion about what he should do with his life. I know how this type of reasoning works; I use it all the time at work. In my case it means that I choose to increase test coverage, review code that someone else has already reviewed but I really want to be sure of, or spend a day debugging some hard-to-catch bug on production — all tedious tasks that don’t improve my knowledge as a developer. As a developer I can improve myself faster by learning new frameworks, trying new languages and venturing out into different areas of software. But I am employed for one particular project, and that project benefits the most from me doing what needs to be done, because no one else will do it.

I have no Musk-comparison for the opposite case: the case where you do something out of your gut feeling because you know it feels right, uncaring about the consequences, aiming towards nothing rational in particular but just wanting inner peace. But I do have an example of my own: that of cycling. Being on the road all day, seeing many things as I cycle along, with only room for one goal in my mind, sometimes pondering the book I’ve read the previous night. Cycling trips to me are a form of meditation, a way of clearing out my mind of unwanted thoughts and focusing on the here and now. It is a mental reset that, as far as I’m aware, I can only experience in that particular way, and it is a very powerful experience, especially when put into contrast against my daily life.

As someone who considers himself to be highly rational, I find it unreal that I am at my [best, happiest, most peaceful] when I am doing something irrational.

But then, rationally speaking, if I know that my mind and body can provide me with this peace of mind if I seek the irrational path, isn’t that the path I should rationally be pursuing? And isn’t everything else in my life second to that goal? It’s a deeply personal (even spiritual?) goal, one that is of no use to the people around me, society or humanity as a whole. I am no Elon Musk, and I can not rationally justify me sacrificing myself to save humanity. Or perhaps I just rate my chances of success pretty low. Either way, I know I will never be spiritually motivated that way, and I think neither can he be, which is why I think of what he’s doing as a sacrifice. I respect him for that, but I do not want it for myself.

—-

Reading back what I just wrote I realized there’s a contradiction between how I describe my goals versus the whole in the third and fourth paragraph. Although I wrote that I don’t want to sacrifice myself in the way Musk does, it appears that I’m doing exactly that in the smaller-scale context of my project. That’s probably not good. I think I can attain higher goals before resorting to a self-sacrificing position.

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Fascinating linkdump

Yup, I’m still alive busy moving apartments, but otherwise still interested in THE FUTURE.

I’ve also recently finished a Scalable Machine Learning course at edX. It was my first time trying out an online course and it turned out to be quite interesting. Especially the final week’s assignment produced some really cool results. Apache Spark is so much nicer to work with than Hadoop.

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