Mildred the Hexapod

Yet another 3d printed hexapod, but this one is mine! (and it's matte black)

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Ever since seeing Matt Bunting's Dmitri hexapod I wanted to build one. This was a long time ago and I didn't have the budget (servos are expensive), the means (3d printers were not mainstream) or skills (that was pre C++ 11 or 14, I was doing ActionScript at the time) to pull it off.

So I'm back today with an admittedly heavily inspired by Dmitri's design for a start. It will evolve to become my own over time. I just really liked the stance that it had compared to other more reptilian leg designs so I knew that's where I would start.

The robot will first run tethered to a computer and PSU while I develop the software for it. It runs on ROS Melody using Ubuntu 18.04.

I will eventually upgrade it to have a LattePanda Alpha on it's back so that I can run ROS on board and experiment with vision/SLAM and an IMU.

I plan on making the CAD files available once all the issues are fixed.

  • 18 × Robotis Dynamixel XL430-W250-T Servo Motors
  • 18 × Robotis HN11-I101 Set Servo Idler Bearing Set
  • 1 × ColorFabb PLA - Semi Matte Black (0.75kg)
  • 1 × Robotis U2D2 USB to Dynamixel
  • 2 × Robotis 3P Extension PCB Serial and power distribution, hacked with make headers to solder power cable

View all 11 components

  • Startup Routine

    François Ubald Brien04/23/2019 at 18:53 0 comments

    I am currently working on the startup routine. I am coding a finite state machine to manage the different states and their transitions into one another. For example, I currently have idle, sitting, standing and walking states set up with events to transition from one to the other.

    I'm in the process of coding the standing state, which will consist of sensing where each leg is, bring them in a safe sitting position, then stand up.

  • Getting gazebo to behave

    François Ubald Brien04/11/2019 at 16:29 0 comments

    There won't be any cool build pictures for a while. I'll be working on the software until I'm comfortable letting it run outside of the simulator. I still have a bunch of stuff to do before I can do this. After tuning the model in gazebo I have to code a startup routine where it will sense its limbs and safely bring them into a "sitting" position before standing up. Then I'll need code to manage switching leg distance from the body, so that I can reduce the large footprint that the long tibias is causing during the standup procedure before walking.

  • Standing up powered

    François Ubald Brien04/04/2019 at 20:26 0 comments

    It can't move yet, but I made a first powered test to make sure that the motors were able to withstand the mass of the thing. It feels a little weak when I put it in a tripod configuration, I'll have to check if it's the motor or the power supply that's the issue on that one.

    An aggressive pose, just for fun

  • Connected the power supply of death

    François Ubald Brien04/04/2019 at 20:24 0 comments

    Disclaimer: I will properly fuse and mount it in an enclosure. For the time being, don't worry, this is in a tupperware so that neither me nor my cats can put their paws on the exposed live wires.

    Ugh, backwards again

    Every time I have to solder one of these I end up with the wrong plug on the wrong cable. The fact that the male metal plug goes in the female plastic plug confuses me. At least positive/negative are on the proper side, just don't connect a battery directly to a power supply or another battery by mistake.

  • Printed and assembled the tibias

    François Ubald Brien04/04/2019 at 20:19 0 comments

    2019-04-01 Printed and assembled the tibias.

    First solo test print
    10 hours into the remaining 5 tibias print
    This is heavier than I thought it would be

    I started to be scared that the servos wouldn't be strong enough at that point. I really ended up being heavier that I thought. I still have to eventually stick a computed on it's back and a battery inside of it. I could have made all the calculations in advance, but where's the fun in that?

    The tibias are too long

    Seeing it outside of Fusion360 for the first time I realize that the tibias a too long. It's not a practical position to start from in order for it to stand up. It can't bring the legs closer to the body like this and will use more energy getting up. It will also have to reposition its feet before walking as this is probably too wide of a stance to start with.

  • Printed and assembled the femurs

    François Ubald Brien04/04/2019 at 20:16 0 comments

    2019-03-31 Printed and assembled the femurs

    I must admit that I love the block-ish industrial machine look it has without the tibias. I have to revisit my design to be more in line with what I'm seeing here. I first thought I would go with a semi-organic insect look but this convinced me to go full sci-fi robot on my next design iteration.
    Trying to do smooth curves in the Z axis with 0.3mm layer height

  • Printed and assembled the coxas

    François Ubald Brien04/04/2019 at 20:12 0 comments

    2019-03-31 Printed and assembled the coxas.

    Printing the coxas
    Such a long print with all that support
    Removing the support is so relaxing
    There are pieces of support material all over my apartment now.
    I like the look of this

    Unfortunately, I had designed the parts with enough clearance for a 0.2mm print but I decided to go with 0.3 at the last minute. So the slicer didn't round the values in my favor everywhere and I had to remove material with a knife to make the femur motor fit. Some screw holes even cracked as I was putting the screws in. It looks like it still holds for now but I definitely have to add more material around the coxas side tabs and maybe print in the other direction to make them stronger over the servo horn ones.

  • Printed and assembled the body

    François Ubald Brien04/04/2019 at 20:08 0 comments

    2019-03-30 Printed and assembled the body during the weekend.

    The kind of mess that I work with.
    All of this is boiling with potential.

    Soldered the power distribution to make headers that I hacked into the original board

    I didn't trust the original cables to be beefy enough for the power required to handler the load on 9 servos per board, so I replaces a connector with male headers onto which I soldered my power distribution. It will eventually have to change as my final goal is to have it run untethered with an on-board battery.

    The 0.3mm print really shows on parts like these

    The finish on a 0.3mm print is not that great but I wanted my parts to be more solid. On a positive note, the matte black PLA from ColorFabb looks so good!

  • Testing the motors

    François Ubald Brien04/04/2019 at 20:00 0 comments

    2019-03-28 Started testing, numbering and grouping motors by leg.

    Evaluating how everything will be connected inside the body
    I kind of like the rubber band colors on the motors. Maybe I'll try introducing a bit of color in the final design
    With a small work surface I have to tidy up pretty often. I wonder if I'll have enough room for the robot to stand.

  • Received the servos

    François Ubald Brien04/04/2019 at 19:57 0 comments

    2019-03-27 Received the additional fifteen servos and a bunch of accessories. This is starting to get real, I can't wait to build the robot now.

    I don't know why, I always enjoy having a bunch of similar objects that pack nicely together.

View all 11 project logs

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Seifert Johannes wrote 11/04/2023 at 08:17 point

Looks awesome! Do you share your 3D Model/3D parts of your hexapod. I'm planning to use dynamixel xl430s too, but cannot find 3D parts anywhere! Thx

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Louis Irwin wrote 04/14/2019 at 19:42 point

Brilliant project! I've always wanted to try some robotics, but I've never had the skill!

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Matt Bunting wrote 04/11/2019 at 05:29 point

Nicely done!  Love the design, but maybe I'm biased :)

Looking forward to seeing your progress!

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François Ubald Brien wrote 04/11/2019 at 18:26 point

Hehe thanks! I've always wondered why more people don't go for that longer leg design, it looks so good! I guess it has to do with the required torque (a thing I still haven't figured if I'm in the clear with my xl430s).

Thanks again for passing by, I'm not feeling any pressure at all now that I know that you are here looking ;)

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Tim Bitson wrote 04/10/2019 at 18:18 point

Awesome design, What a beast! I just sent Matt Buenting a link to this project.   

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François Ubald Brien wrote 04/11/2019 at 02:49 point

Thanks! I'd be humbled if he looks at my project. I'm such an amateur in this field.

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Matt Bunting wrote 04/11/2019 at 05:29 point

Tim!  Thanks for sending me the link!

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alireza safdari wrote 04/08/2019 at 21:00 point

Glad to see your project in here too! I thought you are only active on Instagram.

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François Ubald Brien wrote 04/10/2019 at 17:34 point

Thanks, I don’t know why I didn’t think about it earlier ;)

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Mike Szczys wrote 04/08/2019 at 16:52 point

Looks amazing! Glad you got the standing test to work. The modelling software is amazing, yet still interesting to me that it's not until the first version is printed that you really get an intuitive idea of scale (weight and leg length). Keep going, I love seeing it come together!

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François Ubald Brien wrote 04/10/2019 at 17:38 point

It’s my first time designing something that extensive in Fusion360, I guess those are things you get better at with experience.

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Mike Szczys wrote 04/10/2019 at 17:40 point

Maybe. But for me, the ability to zoom in EDA software just by rotating the scroll wheel means I can't really tell how big things are going to be. With PCBs I print out the board artwork to get a true gauge of the size. Your experience feels the same, which I like because it validates my thought that this is just how it is ;-)

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alireza safdari wrote 04/11/2019 at 03:48 point

I think it is great that you did not have enough experience! your spider looks so different from the other ones and I think this is what makes it standout. So to me, I am glad it turned out this way. I just hope your servos can handle everything. IMHO 80% of the love you have and will receive for this project come from its long legs and cooler look :D

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François Ubald Brien wrote 04/12/2019 at 15:40 point

I can't reply to your reply on my reply, but yes, how many times have I been zoomed in, adding .5mm chamfers to everything, only to realize it only looks pretty in the renders but will never show up in my .3mm 3d print.

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