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Webot

The wireless quadruped made from $10 in parts and materials.

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This walker is a exercise in minimalism. Can I make robot for $10 that can be easily assembled with no adhesive? Can I make the instructions good enough that it can be assembled by middle school students and work every time? I want it to be elegant and the assembly to be a satisfying experience where every part just feels right. This should be a great starter project for soldering, Arduino, and digital fabrication at a maker space. This is completely open source and the files are all included.

My goals for this project are as follows:

$10 BOM cost, batteries not included.

No glue used in assembly

The parts should be made in 30 minutes or less

Parts should be easily shippable

Assembly should be manageable for a middle school student

Every piece should fit together with a sense that it belongs

Ideally I teach my daughter how to run a business from this project

Make it repeatable version of the very one off 

Tortellini the Turtle bot I made 8 years ago

Now it is time to do at least  as good I as I did with this bot in a reproducible way. The above bot was all glued together with 4 motors and 4 photo sensors. The MCU was 16F pic and it ran on an interrupt driven code but  it was definitely a one off labor of love. There was zero design for manufacturing incorporated in the design. 

Now that I belong to the Fox.build makerspace I have access to a laser cutter which makes very reproducible cuts. My initial goal was to make product it with acrylic, some off the shelf hardware and the other electronic bits and bobs from Aliexpress.  Now I am thinking about adding a few 3D printed piece if it would significantly improve the performance.

I have worked on it for over 2 years, made over 50 different revisions of the laser program but there was always something not quite finished. I decided to start to publish and rev as I go along. Once it looks solid, I can put it on Tindie and make that $1 I have in my yearly goals. I have bought the hardware to support a Tindie run of 50 pcs many times so I have boxes of hardware in the basement.

WebotV15 Drawing 1.dxf

This is the DXF file that can be used for laser cutting of the Step file below. Please note the scan and sew notes below.

AutoCAD DXF - 1.59 MB - 01/20/2019 at 17:29

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WebotV15.step

This is the flat pattern for all of the V15 laser cut pcs. The Leg gears need a scan pattern for the countersunk center. Some sew compensation (0.1mm) is needed for the Motor Gear with 0.5mm Module teeth and the code wheel.

step - 9.29 MB - 01/20/2019 at 17:05

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WebotRev15 v3.step

Here is what the board looks like after I added some components in Fusion 360. This is the first time I have made an assembled board and it looks very cool. Not sure if the colors will show up in the step file but I added a picture in the log.

step - 5.47 MB - 01/13/2019 at 11:49

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WebotRev15.kicad_pcb

Here is the KiCAD layout.

kicad_pcb - 112.10 kB - 01/13/2019 at 11:48

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WebotRev15.sch

Here is the schematic for my project. Added a 7805 Voltage regulator to allow higher voltages to run the motor without frying the Wemos

sch - 13.96 kB - 01/13/2019 at 11:48

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  • Version 15 Laser Trial

    shane.snipe6 hours ago 0 comments

    I have completed my CAD to do list.  I like the way I can work in Fusion but I have not found a good work flow to get the parts into a sheet form for laser cutting. I ended up exporting a DXF of each part, saving them all in one sketch. Extruding them all. Making a drawing. Saving the dwg. Not being able to save the dxf. Export the step file of the extruded drawing. Importing it into ONSHAPE. Making a drawing and saving the DXF. THERE HAS GOT TO BE A BETTER WAY!!!!  In Solidworks I had an assembly of the laser cut layout. If  I changed something in the model, it would change in the laser cut assembly and I would just output a dxf. The drawing would update automatically.

    In any case, here are the changes I made. It is a big rev so I hope it works.

    1) Changed from proprietary hardware to 3D printed axles and laser cut spring clips.  I printed out the parts but my printer was not having the best of days. We will change the Prusa back to direct drive and I think it will do better. I may need to open up the holes. I had to do a fair bit of filing to get in the spring clips.

    2) Added holes for plastic rivets to hold down the batteries.

    3) Change the board holder. Thanks to Kicad's mechanical output, I think it is in the perfect place. 

    Today  I will laser cut the 2.7mm acrylic I buy at Menards and see if I can get some nice friction free walking.  I have the new Li Ion batteries. (10440 x2) and the new board that will work with the higher voltage from these batteries is being fabbed at OSHPark.  

    Here is what the layout looks like. Some how it is much sharper in real life.

  • Fasteners

    shane.snipe6 days ago 0 comments

    I had planned to use Chicago screws or book binding rivets. However, not only are they an additional cost and a impediment for someone to reproduce my work, the were binding when it was walking. The Chicago screws would come unscrewed and crash into the leg. Although I liked the feature that the robot could be disassembled, the has got to be a better way. 

    So after a few days of head scratching, I came up with a 3D printed and laser cut hybrid. First of all, this is more square pegs in round holes to try to reduce the points of friction. This robot does not go fast enough to worry about friction welding but the motors do not have enough juice to overcome a lot of friction.

    The second feature is the super low profile and simple to print shape. There is a bit of bridging but I think the Prusa will print it like a charm. I went line to line on the vertical walls and gave it and extra 0.3mm on the overhang length. Lets see if my estimation is good. 

    The other great thing is that this removes 4 of the 8 counterbores from the laser. It will speed up the cut by a few minutes because it takes a long time to scan. I hand added the counterbores to adjust to a specific rivet width.

    Here are some pictures.

  • Fusion and Non-Native Geometry

    shane.snipe01/13/2019 at 15:11 0 comments

    I am new to Fusion 360. I started working with it 45 days ago. However, I am blown away buy the ability to work with non-native files like step files. On Solidworks or Onshape, at Step file is just a piece of material. It does not recognize any features so you do not have much flexibility.

    With Fusion, you can click on a hole and delete it. You can click on surface and type Q for push pull and you can move it around. Thanks to this flexibility, I already have my PCB mounted and the pcb mount reworked. Thanks to KiCad spitting out the the file, I know exactly where it is rather about where it might be. Here is the top view. 

    And from the back.

    From the bottom.

  • CAD to do list

    shane.snipe01/13/2019 at 12:16 0 comments

    I have moved from Solidworks to Onshape and now to Fusion 360.  I am struggling greatly with the pin and slot joint in Fusion even though I got it to work in Onshape and Solidworks.  It works sometimes with contact surfaces but then it breaks. In any case, here are updates need to do for version 15. 

    1) I added 2 10440 Li ion batteries. One on each end. Some fastening method for the battery holder needs to be developed.

    2) I am not happy with the Chicago screws that hold on the gears and I want to design a 3D printed alternative. It will take $0.75 out and make the walking smoother if I do it right. I am thinking about a type of friction weld to hold the 3D printed rivets in place for the gear axles.

    3) Solidworks has the concept of parts and I could change the parts and the separate assembly that is all ready for laser cutting changed as well. Fusion is not set up like this. I read that people make a separate components for laser cutting using the same sketches. That way they update automatically. This makes sense and I want to try it.

    4) I need to hold the board in place better. Now that I have the 7805 dropping below the board  have something to hold on to so I may be able to hold it in place so the encoders actually work.

  • ECAD to Fusion 360

    shane.snipe01/13/2019 at 11:30 0 comments

    I have always kept my PCBs and electrical parts separate from my models. With KiCAD I learned how to output the 3D board with any components that were in the system. The output is an easily editable step file and I can add the component that were not in the library in Fusion 360. Here is a picture of my new board. 

  • Battery Power 2

    shane.snipe01/12/2019 at 12:00 0 comments

    Today  ordered 4 AAA Li Ion batteries and a charger from Amazon. 

    https://www.amazon.com/gp/product/B06X9TZ1CG/ref=ppx_yo_dt_b_asin_title_o00__o00_s00?ie=UTF8&psc=1

    I also bought some single battery holders. 

    https://www.amazon.com/gp/product/B07C2XT5C5/ref=ppx_yo_dt_b_asin_title_o00__o00_s00?ie=UTF8&psc=1

    By distributing the weight front and back, the balance will improve and the robot will not fall over while taking a step.

    By using the 2 Li Ion I will get 2 benefits.  Reduced weight over 4 regular or NiMH batteries and the combined higher voltage will give me more speed for my motors.

    The down side is I will have to modify my circuit to add a 7805 voltage regulator. Maybe I can use the 7805 part as a battery stop hanging below my board.

    In my circuit, to make the motors go faster, more than 5V is helpful. 7-8 V might be idea. However, the Wemos can only handle around 6 V before letting out its magic smoke. I have a diode in the circuit now to reduce the voltage by 0.6V but I think I will replace the diode with the 7805 voltage regulator to allow the 2 Li ion batteries to be used at their full charge of 8.4V to their depletion charge of about 6V.

  • Syncronization

    shane.snipe01/11/2019 at 00:51 0 comments

    The diagonal legs need to move together.


    In the Turtle bot, this is accomplished by sensors.

    My initial idea was to use a fan gear and only run leg at one time on one side.

    I had sensors built in to synchronize the action. 

    Unfortunately, the sensors were limit switches that added load to the motion.  I could never get the motion synchronized.

    "If only I could link the diagonal legs!" 

    I tried to do it with a laser cut belt and cogs but it was not working well.

    Then I came up with the idler concept seen now with the dual driveshaft concept.

    This positively links the motion of the diagonal motors.

    The timing to run each diagonal is determined by the half relative and half absolute

    code wheel  that is on the shaft between the walls.  This runs through a ITR-9608, 

    possibly the least expensive and most forgiving photo sensor in the world. 

    The diagonals alternate taking steps for straight forward motion. Depending on the position of the inactive leg, moving the other diagonal continuously will turn in one direction or the other. This is the reason for the relative encoder with about a 10 degree resolution. I have not yet quite determined the best place to stop to turn each way.

    Again,  I will drop in some pictures to show all these steps when I get a chance.

  • Features in the acrylic.

    shane.snipe01/11/2019 at 00:40 0 comments

    Square shaft Round hole

    Getting the gears to press fit on the shaft was a 6 month endeavor.  I was using 2 and 3mm round shafts because I wanted to use an off the shelf 0.5M gear to dock with the gear on the motor. 

    Unfortunately, if I glued it, it came loose. If I press fit it, it would crack or come loose.

    I finally realized that I actually could cut the 0.5M gear on the laser cutter. It just took some seam compensation of 0.1mm to make sure the kerf of the laser cutter did not make the teeth too small.

    Once I found this out, I could make square shafts and square holes in the gears. I could make a stepped shaft so it would sit axially in the correct position. I made some clips to hold the gears on the outside of the gearbox although they could use a little optimization.

    Now I have very little friction and have completely eliminated the slippage issue.

    Pictures to come.

  • Battery Power

    shane.snipe01/11/2019 at 00:31 0 comments

    One of the biggest struggles I have had was regarding what kind of power to use. 

    To meet the $10 target,  I could not do anything more than provide a battery holder.

    This was good in the sense that it  ran 6V which gave the motors a little extra pep.

    The downside was the weight. On the recent versions the the battery pack did not 

    fit under the bottom drive shaft. I had recently extended the back.

    I made a version which would attempt to doc with a BL-4C battery. The Rev 12  acrylic 

    pattern has an attempt at holding this battery in place.  I did not have good luck in 

    keeping it in place while walking.  Adding the additional battery boost circuit was also cumbersome. In any case, here is a link to the acrylic. https://cad.onshape.com/documents/b10aa98723fb8ce297ce7b2f/w/d4d43d764bc67b14d7e563de/e/fad4e69b9bd54361983d38ae

    I will put the DXF in the files as Rev 12.

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Pat Helmers wrote 2 days ago point

I can see this being a great project for my middle school nephews. A lot of possibility for applied robotics with practical applications. I'm following closely.

  Are you sure? yes | no

shane.snipe wrote 01/13/2019 at 15:30 point

Does anyone know how to work Fusion 360 joints well. I really would like to make a video of my simulated walking gait but I can not get the pin and slot to work. I made it work in Onshape and Solidworks but Fusion wants the slot to be in a specific direction I think. In any case, I can not get the gear to move the leg and it slide in the appropriate slot. Here is the link in Fusion if any one wants to take a shot at making it move.  https://a360.co/2FnIfI9

  Are you sure? yes | no

Mike Szczys wrote 01/10/2019 at 16:39 point

Nice! The movement in the video is really entertaining (very turtle-like ;-D ). Can we see some pictures of the hardware without the shell?

  Are you sure? yes | no

shane.snipe wrote 01/11/2019 at 03:16 point

I will see if I can dig it up.

  Are you sure? yes | no

ꝺeshipu wrote 01/09/2019 at 17:22 point

That is so adorable! Great job!

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