Cheap four-legged insect robot

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This is a continuation of the journey started with #Tote to create an affordable walking desktop robot.

  • Cable Management

    deʃhipu5 days ago 0 comments

    Cable management is a big problem when you have a moving construction with eight servos. It doesn't help that by default the servos come with relatively long cables, and this three-pin plug on the end, that is hard to replace without special tools:

    Of course it would be best if you could just take that plug and plug it into the PCB, but then you need to do something with good 20cm of extra cable.

    We brainstormed about this problem, among other things, during the hackaday prize mentoring session with Kliment Yanev, and he came up with an ingenious solution that just might work. Yes, you need to get rid of the default plug, and the spurious cable, but then you are left with the problem of either soldering the remaining cable directly to the PCB, or attaching a different plug. Turns out there are plugs out there that are very simple to attach, and quite popular and easy to get. Kliment suggested I can use the plug that is commonly used for the ribbon cables:

    They have those blades in them, that bite into the cable when you press the tab on top, and make a secure contact. Furthermore, we are not increasing the price a lot, because you can use a single plug for multiple servos. Sure, this makes them harder to replace, which is a downside, but I think I can live with that.

    Unfortunately, this also means we will need a PCB redesign — the way this plug connects with the cables, we will need a completely different pattern of pins for it. Oh, and we can't put the sockets for those plugs in the same place on opposite sides of the pcb, not easily, anyways, so I will need to think about where to best place them. But I like the idea and I'm going to give it a try.

  • Yellow

    deʃhipu06/11/2021 at 22:07 0 comments

    The version 3 PCB has arrived, and populating it wasn't too bad. I didn't even use the hot air gun to solder the QFN chip — just drag-soldering it on all sides did the trick.

    Along with the new PCB I also received the parts for the new design of the legs. They are pretty much the same as the old, but use a little bit less space. And I got them made in yellow acrylic, to match the PCB. I also managed to find some orange servos, and I dug out some yellow pin headers:

    I'm wondering if I should remove those white servo horns and spray-paint them black, to complete the look.

    Tomorrow I'm going to cut the servo cables and connect them to the board.

  • Version 3

    deʃhipu05/26/2021 at 19:11 0 comments

    The previous two versions of this projects were kinda done on the side of #Kubik M0 to see if this approach even makes any sense. I finally decided to go for it, so here is a version three, with a new PCB:

    and an improved design of the legs (to make them use less acrylic, so you can fit more of them on a sheet):

    The PCB now includes, apart from the previous microcontroller, battery protection, battery charging and battery holder, also a tiny buzzer and a place to install an IR sensor — this way I can report the status of the robot with beeps, and control it with a TV remote.

    Any further sensors and other hardware can be added as FeatherWing shields to the front of the robot.

  • Configuration

    deʃhipu05/26/2021 at 18:55 0 comments

    While the #Tote robot was close to what I wanted to achieve back then, it had two major problems. First, the servos, even though relatively cheap individually, contribute to the total cost of the project considerably, because you need at least a dozen of them. Second, Arduino, while popular, is not the best coding environment for experimenting.

    I have long worked on making a version of Tote that could be programmed with Python — starting with #Tote HaD, that had an additional ESP8266 on board, through #Tote Zero that had a whole single-board computer, to the most recent #Kubik M0, running CircuitPython. Unfortunately, with the last I ran into a problem with not enough PWM outputs available on the chip I choose.

    I have also experimented with robots that require fewer servos, but can still walk properly, without relying on the surface of the floor having the right friction. It started with #Katka, a mammalian robot#µKatka and #Pony Bot, and more recently some experiments with the #Kubik M0. Turns out that it is possible to make a robot with only eight servos that still has an insect-like configuration of the legs. It can walk properly, keeping its feet firm on the ground, as long as it doesn't have to turn — because it can't move its legs sideways. But even for turning is not impossible, with some cheating.

    So this is how I came up with Fluffbug — a bug-like robot with Feather-compatible (or #Fluff M0-compatible) shields. The tiny SAMD21 microcontroller has just enough PWM outputs to control the eight servos, and the small PCB works nicely as the body of the robot, with enough room for a 16340 battery, and s FeatherWing on the front.

    The initial tests are promising, and I already have the basic code with inverse kinematics written in CircuitPython. The next prototype is going to have a little bit more useful components on the PCB, and an improved designs for the laser-cut legs.

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Dejan Ristic wrote 4 days ago point

Nice! I'm all on board with the affordable desktop robot concept.
Color scheme makes me think of the camel spider. But this one seems much less terrifying luckily.

  Are you sure? yes | no

deʃhipu wrote 4 days ago point

Thank you. To be honest, I haven't thought about the looks too much yet — most of the design is dictated by the mechanical requirements right now. There is some room for expression here — shape of the legs, shape of the PCB, etc. I imagine that it could also be made quite terrifying depending on how it moves — if you can reproduce the movement profile of spiders, for example, I bet people would get goosebumps just looking at it walk. The color scheme is probably not final — I had some choice here, so I went with yellow/orange, but the final version will probably be blue, because blue servos are the cheapest.

  Are you sure? yes | no

Dejan Ristic wrote 4 days ago point

Well as long as it doesn't bite :D
I also like the minimalism with 4 servos making up the thorax of the spider.
And the forward facing pcb. I'm guessing you can put on a shield with a distance sensor then?

  Are you sure? yes | no

deʃhipu wrote 4 days ago point

Yes, the initial plan was to put one of those time-of-flight sensors on it, but of course you could also use that huge ultrasonic sensor if you want your robot to look more steampunk. In fact, I'm even considering an adapter-shield for an #OpenMV 

  Are you sure? yes | no

danjovic wrote 06/12/2021 at 13:56 point

Awesome, specially in yellow!

Have you considered to make the legs out of PCBs?

  Are you sure? yes | no

deʃhipu wrote 06/12/2021 at 14:08 point

Thank you. I have, and in fact the previous versions all had the legs made out of PCBs, however, since the fabs nowaday charge extra for multiple projects in one order, and the leg parts look like multiple projects, this is no longer economically feasible. On the other hand, cheap laser-cutting services mean that you can get enough legs for three robots for less than the PCB, and it gets even cheaper in bulk.

  Are you sure? yes | no

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