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Stubby the (Teaching) Hexapod

100% open source robot platform with accessability and affordability in mind: teaching children of all ages about robots & programming

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This project was created on 04/09/2014 and last updated 12 hours ago.

Description
Stubby is a 100% open source, extensible robotics platform. It features ultra low cost design (MDF frame, which you can cut with a scroll saw; $2 low torque servos; a single microcontroller; easily-obtainable electronic and mechanical components), can be controlled by a Universal Controller (over XBee) or a computer (over Bluetooth), and has a Processing API which can help children learn basic programming concepts.

My daughter, Princess Sparkle, and I have been working on it since February 2014, along with the help of some of my friends. Other hackers worldwide are working on their own versions, some of which are 3D printed, others are laser cut plexiglass, and at least one is hand cut from American Beech wood for what will doubtless turn out with a beautiful, natural look.

The Universal Controller interface is completed and working, and the Processing / Bluetooth API is well underway.

See http://stubby.digitalcave.ca/ for more information.
Details

Since we started, Stubby has grown from a simple, direct-driven 2 DOF (degree of freedom) per leg frame to a mechanically-assisted 3 DOF per leg design with a full inverse kinematics engine (which allows the processor to calculate custom foot positions for each step, rather than relying on a static loop).

This video shows off the latest version, including various features of the Inverse Kinematics engine:


Originally, the concept of Stubby came from the SG-1 universe's replicators (which, let it be known, are completely awesome!).  The name 'Stubby' was coined by Princess Sparkle, after seeing the first version (with 2cm long, oblong legs), barely able to limp along the carpet.

After the interesting parts (most notably the frame design and inverse kinematics engine) were completed, I wanted to expand Stubby's abilities.  The Hackaday Prize made me think about 'connected' projects... at the same time, Princess Sparkle was expressing interest in computers and programming.  In talking with her, we came up with the idea of making an API which would allow her to issue simple commands to control the robot.  

This is not the first time she has done this sort of thing... in her Grade 1 class, there was a unit on Lego Mindstorms robots, which taught the children to visualize arithmetic expressions by programming the robot to, for instance, move 10 units forward and 3 units back, and seeing where on a number line they were (10 - 3 = 7).  With Stubby, the plan is to expose more of the programming structure to her, teaching such things as procedural control, calling methods, assigning variables (by reading sensors), etc.

When finished, I plan on having an Ultrasonic Distance sensor (attached to a servo so it can 'look' up and down) allowing users to write code for autonomous operation, and an array of UV LEDs to allow for writing line following algorithms.  I also have an i2c header broken out, so that hackers can add completely new components.

The first Hackaday Prize submission video, outlining our plans, can be seen on Youtube.


For those who are interested in building their own version of Stubby, I have all the designs, plans, and theory available for all to use and modify freely.  There are two documents which encapsulate the majority of my work.  

First are the frame plans. The frame is one of the biggest advantages which Stubby holds over other, more expensive hexapods.  The first difference is the materials: Stubby is designed to be cut from 1/4" MDF using a scroll saw.  (However, the design is adaptable enough to be able to use other materials as well, and the community has modified these plans for use with a 3D printer, laser cutter, etc.)  The frame is quite easy to make; simply print the plans, tape it to an 8.5x11" sheet of MDF, and cut along the lines.  The second difference is how the servos are attached to the legs: Stubby uses push rods to convert distance to torque, allowing Stubby to work with cheap, low-torque servos (at the expense of being a bit more limited in leg movement).  This is the biggest factor in being able to keep below $150 in components (this assumes you have no parts in your parts bin, but does assume that you have all the required tools already).

The second important diagram is the circuit board schematic. This shows how to wire the control board so that the microcontroller can perform the needed calculations and tell the servos how to move.

All the hardware would be useless without software to control it. You can download or browse my git repository, which includes all software and libraries (written by myself and Warren), the QCad files for frame design and the KiCad files for schematic / board design.

Everything needed to make Stubby, both hardware and software, is licensed under a Creative Commons Attribution-Share Alike License).


For more details and build instructions, please visit my website.

Components
  • 1 × *****SEE http://stubby.digitalcave.ca/stubby/components.jsp FOR BETTER FORMATTING*****
  • 1 × *****ELECTRONIC COMPONENTS (FOR REVISION 1.0 / 1.1 BOARDS)*****
  • 1 × ATMega 1284 Microcontroller (DIP package) (ATMEGA1284-PU-ND)
  • 1 × Control PCB
  • 18 × 9g Micro Servos (from Hobby King, about $2.00 each at the time of this writing)
  • 1 × XBee (Optional, an autonomous robot would not need this. Alternatively, you could use a different radio or connect to a computer
  • 1 × Universal Controller or other method of remote control
  • 1 × 3v3 LDO Regulator (MCP1702, Through Hole) (MCP1702-3302E/TO-ND)
  • 3 × 1uF Capacitors (1276-1066-1-ND) - Used for power supply + AREF decoupling
  • 10 × 1k Resistors (311-1.0KARCT-ND)

See all components

Project logs
  • Adding a Magnetometer

    a day ago • 0 comments

    While working on the Processing API with Princess Sparkle, we found that Stubby was having problems going perfectly straight; it would veer one direction or another, depending on the angle of movement.  After hours of research, we determined that the problem was due to slight variances in each leg.  When walking, these tiny differences in each step compound, and make for large errors in the outcome.  (This principle is the same as how, within a flock of female velociraptors with spliced frog DNA, some individuals will spontaneously change gender... oh wait, nevermind.)  Related to this problem, there are also inaccuracies when turning in place, depending on the surface that the robot is walking on (e.g. tile vs. carpet).

    Warren and I discussed a number of options on how to solve this.  The idea which seems most promising (both due to the simplicity, the low cost, and the low processing requirements) is to add a magnetometer.  This will allow Stubby to keep track of the direction it is facing; when moving, we will use the feedback from this sensor to make small course adjustments as the robot is walking (basic PID functionality, although the I component will probably not be included, and D, if any, will be minor).  The biggest unknown at this time is whether the magnetometer will a) be accurate enough and b) will work properly even though it is encircled by (admittedly small) motors.

    Since I have just ordered the rev 2.0 PCBs (which, BTW, are marked as Shipped, yay!), I bought a standalone i2c magnetometer from Sparkfun for prototyping:

    Assuming we can get things working as planned, I will add this chip to the Stubby control PCB itself.  In the mean time, I have a new top layer designed, which fits the new control PCB and has room for the magnetometer as well:

    Cheers

  • 3D Printed Frame + .STL Bugfix

    2 days ago • 0 comments

    Ellison, a hacker who is working on a 3D printed version of Stubby, emailed me yesterday to share his progress and to inform me that there was a bug in the previously uploaded servo layer of the .stl files - two of the screw mounting holes did not line up with the other layers.  He has graciously provided an updated file, and has permitted me to share the pictures he sent.

    I have added the updated .stl file to the 3D printer source files (I have kept Joshua Thomson's original design as well; the updated one is called Servo layer - Alternate.stl.  Anyone who prints their version should verify which one makes sense for them.)

    Ellison's version of the servo layer, along with a photo showing the alignment between it and bottom layers, can be seen below:

  • Processing Library Download and Instructions

    3 days ago • 0 comments

    For those who want to try controlling Stubby from the computer in Processing, I have attached the current build of the Processing library.  All planned features are not yet completed, but it is a good start, and is plenty to verify connectivity; Princess Sparkle is having a blast playing with the different options.

    You can download the library from my web site.  Once downloaded, unzip it to the Processing libraries folder, within the Sketchbook. (By default this is C:\My Documents\Processing on Windows, and ~/Documents/Processing on the Mac).  Within the sketchbook folder there should be one called "libraries".  Unzip stubby.zip to that location; you should see a folder structure similar to this:

    <sketchbook>/libraries/stubby.zip
    <sketchbook>/libraries/stubby (folder)
    <sketchbook>/libraries/stubby/library (folder)
    <sketchbook>/libraries/stubby/library/stubby.jar
    <sketchbook>/libraries/stubby/library.properties

    Restart Processing, and you should see the Stubby Control Interface library in the Libraries list:

    Go ahead and add it to your sketch, along with the Serial library:

    A basic program can include all commands in the setup() method, and can exit as soon as Setup is completed:

    All currently supported commands are listed below.  More are coming soon; you can always get the latest release of this library by downloading the Git repository, navigating to 'projects/stubby/processing', and typing 'ant' to build the library.

    /**
    * Turn the servos on
    */
    public boolean turnOn();
    
    
    /**
    * Turn the servos off
    */
    public boolean turnOff();
    
    
    /**
    * Move the specified distance in the indicated direction at the given speed
    * 
    * @param linearAngle Angle to move.  0 is straight forward, negative angles are right, and positive angles are left.  Angle in degrees.
    * @param rotationalAngle Rotational angle to turn.  Measured the same as linear angle.
    * @param linearVelocity Speed to move; unsigned 8 bit integer value between 255 (fastest) and 0 (slowest).
    * @param rotationalVelocity Speed to turn; same range as linearVelocity.
    * @param distance Distance to move (in mm).
    * @return
    */
    public boolean move(int linearAngle, int rotationalAngle, int linearVelocity, int rotationalVelocity, int distance);
    
    
    /**
    * Convenience method to walk in the specified direction for the specified distance.  See above for parameter descriptions.
    */
    public boolean move(int linearAngle, int distance);
    
    
    /**
    * Convenience method to walk forward.
    */
    public boolean moveForward(int distance);
    
    
    /**
    * Convenience method to walk backward.
    */
    public boolean moveBackward(int distance);
    
    
    /**
    * Convenience method to walk right.
    */
    public boolean moveRight(int distance);
    
    
    /**
    * Convenience method to walk left.
    */
    public boolean moveLeft(int distance);
    
    
    /**
    * Rotates to the specified angle.  Positive values rotate clockwise, negative rotate counter clockwise.
    * @param angle In degrees, with 0 being the direction the robot is currently facing.  Negative angles are to the right (clockwise), positive to the right (counter clockwise)
    * @param rotationalVelocity Speed to turn, between 0 and 255
    */
    public boolean turn(int angle, int rotationalVelocity);
    
    
    /**
    * Convenience method to turn right
    */
    public boolean turnRight();
    
    
    /**
    * Convenience method to turn left
    */
    public boolean turnLeft();
    
    
    /**
    * Convenience method to turn around 180 degrees (counter clockwise)
    */
    public boolean turnAround();
    
    
    /**
    * Convenience method to turn around 180 degrees (clockwise)
    */
    public boolean turnAroundClockwise();

    Cheers

View all 54 project logs

Build instructions
  • 1

    See http://stubby.digitalcave.ca/stubby/assembly.jsp for assembly instructions (Hackaday.io flat list style makes it hard to organize a hierarchy of build steps...)  However, if you really want to see it here, you can try to follow along below...

  • 2

    *****ELECTRONIC BOARD ASSEMBLY*****

    Currently this is dedicated to the Revision 1.0 / 1.1 boards.  This section is almost exclusively soldering.

  • 3

    Start with the 0805 passive components, like the resistors and capacitors.

    When soldering two pad SMD components, I found that the following approach worked best for me:

    • Start by tinning (melting a bit of solder) onto one of the pads on the PCB
    • Hold the component in place with tweezers
    • Touch the component / PCB pad with the iron, to melt the tinned solder. The component should now be stuck in place.
    • Put solder on the other pad. Use enough that there is a good solid connection to the board.
    • Go back to the first pad, and add more solder, such that it is about the same as the second.

See all instructions

Discussions

axf33480 wrote 9 days ago null point

magnifique réalisation du superbe travaille il et possible de le fair avec arduino

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The Big One wrote 8 days ago null point

No it is not done with an Arduino; but it does use the same CPU family as Arduino does (the Atmel ATMega family of chips). A normal Arduino does not have enough pins to do what is required (drive 22 PWM signals), and the Arduino IDE is far too inefficient to do everything which needs to be done in real time.

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Dan Royer wrote a month ago null point

I have open source java code to teach a crab robot to walk. https://github.com/MarginallyClever/hexapod If it helps your cause, please tell your friends about my work!

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Jasmine wrote a month ago null point

Hello Wyatt and the Stubby team,
it looks like you've not updated the project in a couple of weeks. Now is the time to check and edit your project documentation on Hackaday Projects to give Stubby the best chance of going through to the next round of The Hackaday Prize.

I think you've got most of it covered, but this is the checklist of what must be on Hackaday Projects by August 20th:
- A video (check)
- At least 4 Project Logs (definitely check)
- A system design document. You have a lot of design docs. It would be great if you could highlight the main ones in the project Details.
- Links to code repositories, and remember to mention any licenses or permissions needed for your project. For example, if you are using software libraries you need to document that information in the project details.

Thanks for entering and good luck!

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The Big One wrote a month ago null point

Thanks for the tips, Jasmine! I have updated the project details with the two most important diagrams (frame design and control board schematics), and duplicated the links from the links section describing the repository and what is included, and clarified the licensing.

Cheers

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Souljacker wrote a month ago null point

Is this build in Arduino?

Would a programmer with no experience in robotics or electronics be able to build this by following the instructions?

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The Big One wrote a month ago null point

Hard to say when I started I had electronics experience but no robotics experience. 6 months later I had stubby. I would say that if you are patient and willing to make mistakes it would be very doable. Email me and I will help how I can. Everyone has to start somewhere and here is as good a place as any.

Cheers

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The Big One wrote a month ago null point

As for the arduino question, no it is not done with an arsuino, but it does use the same CPU family as arduino does (the amega family)

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Karl wrote a month ago null point

I'd love to build one - a little beefier, can be controlled via a cellphone app or PC, has a camera mounted on it. I have no idea how to do these things so that would be a nice learning experience. Do you think you'd sell them as kits? I have almost no access to the required parts - especially the PCB and the frame :/

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The Big One wrote a month ago null point

I have some pcbs left and have been sending them to a few people. Send me an email with your address and I can let you know the cost.

The frame would be a bit harder as I cut it by hand and it takes a very long time. Someone has posted plans for a 3d printed frame which you could try out. Anyway email me and we can chat. My aemail is on my digitalcave website.

Cheers

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GoatZero wrote 2 months ago null point

Hello Wyatt thanks for all the help, and for keeping updated your log and project page,

I already got most of the components already, i just have to find the xbee modules you used since i have never used radio communication modules before reason of why im a bit confused, i will get 2 for both the PS2 controller and stubby, wherever i look (mostly ebay) i find way to many versions of the xbee, and the breakout board, some are way to expensive others are not, im a bit confused about which one is it, could you point me out in the right one please?

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The Big One wrote 2 months ago null point

I had some XBee Pro version 1 modules from a previous project. There are a few things to note when choosing this:

1) Make sure you get Series 1, not Series 2. They are different, and not compatible. (Series 2 may be fine, but I have no experience with it and cannot say for certain)
2) XBee Pro have a much longer range than normal XBee. Long range is probably not required for this project, so you can go with the cheaper modules unless you think you may be re-using them for other stuff.
3) I think that these ones should work fine: http://www.digikey.ca/product-detail/en/XB24-AWI-001/XB24-AWI-001-ND/935965 . However, the ones I used are: http://www.digikey.ca/product-detail/en/XBP24-AWI-001/XBP24-AWI-001-ND/935968
4) Since you don't already have any RF stuff (i.e. no legacy requirements), you could really use anything that gives you a transparent serial port and runs at 3.3v. Basically, the interface Stubby is expecting is to be able to send data over the serial port. whatever radio you pick, it only needs to transparently send data which it receives over the serial port. For instance, I am working on using Bluetooth SPP modules for this (will be controlled by the computer).

Hope this helps! Let me know...

Cheers

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David S wrote 2 months ago null point

Hey - if you still have extra PCBs, I'd like to buy one from you. I'm going to try your build with 3D printed parts :)

Are you sure? [yes] / [no]

The Big One wrote 2 months ago null point

Yep, I still have a few. Send me an email with your address and I can verify cost and provide details. My email address is in the contact section of http://stubby.digitalcave.ca.

Cheers

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GoatZero wrote 2 months ago null point

Wyatt, I have several questions regarding your project which im already in the process to replicate and if possible to improve in order to learn something more, Here come a bunch of newbie questions, please brace yourself for my ignorance

1.- What exactly which servos did you use?, I found this “$2” 9g servos in hobby king,

http://www.hobbyking.com/hobbyking/store/__32095__Turnigy_TG9_9g_1_7kg_0_12sec_Eco_Micro_Servo.html

Assuming I replace the top of the frame with some modified MDF roof in order to make it able to carry stuff around while it moves (Increasing the weight) would higher weight servos accomplish this?

3.- This one is just to make sure I understand how to use a Xbee, if the PS2 controller has been modified like yours , I will need another module of the Xbee placed into stubby, , module, Stubby will need another one right however since I don't have a model at hand ?

4.- I have programed PICs 18F… using a pickit2, however I wanted to ask you exactly which programmer and what software did you use in order to program the AVR pic

5.- At the component list for stubby “1x Control PCB” can be found however I find this confusing

6.- Any chance you post some pictures of the assembled and soldered PCB and the connection with the Xbee?

7.- What software did you use to make the MDF designs? i tried using Corel, Ilustrator and Autocad to open them and review them with no luck until now, they do open but all messed up

8.- I just noticed you just updated the Assembly Instructions in your project page, they are very detailed, great job Any chance we can get some high resolution pictures?

Are you sure? [yes] / [no]

The Big One wrote 2 months ago null point

Hi there.

No worries about questions... 3 months ago I was in exactly the same place! :-)

1) Those are the servos which I used. (The price has gone up a bit... when I bought them, they actually were $2, not $2.25. The blue version, http://www.hobbyking.com/hobbyking/store/__9549__Turnigy_TG9e_9g_1_5kg_0_10sec_Eco_Micro_Servo_.html , is a bit cheaper and I would assume that it works too, but I can't say for sure.)

2) If you wanted it to carry anything substantial (anything more than 25g or so - it is already borderline as far as weight is concerned), I would definitely want to use larger servos. The problem with that is that larger servos will not fit in the frame I designed, so you would have to modify it. Now, this is not very hard, but would involve using a CAD program (I used QCad and can highly recommend it), and that may have a bit of a learning curve if you have not used a CAD program in the past. More specifically, the coxa servos should be fine as they are, with the smaller servos (there is not a lot of load placed on these ones), The servos driving the femur and tibia should be larger, though.

3) Correct, you need two XBees to communicate with each other. The design really only calls for some sort of serial communication, though, so you could use any module that provides serial communication at 3.3v. I am planning on putting one of those cheap serial Bluetooth modules on Stubby sometime (in which case you would control it with the computer). Other options could include various eBay serial modules, or even just a cable for testing. You would probably have to tweak the software a bit, as right now it is relying on the protocol from my Universal Controller, but that is not a big deal.

4) I am using LadyAda's USBTinyISP programmer (http://www.adafruit.com/products/46). The software is AVR-GCC (compiler) and AVRDude (to upload programs). I have no idea how to get this installed in Windows, but on Debian it is easy (install avr-libc and avrdude) and on Mac I just use Crosspack (http://www.obdev.at/products/crosspack/index.html). I know you can do it on Windows, I just don't know how. To compile everything, clone the git repo, go to projects/stubby/source and type 'make'. To install, 'make install'. To set the fuses on the AVR, 'make fuse'. You can verify that you have everything installed properly before buying a single item, by trying 'make program'. It will fail to upload, of course, but the error should be from avrdude saying the programmer is not found, rather than from the OS saying avrdude is not found.

5) The control board is a PCB which I have designed and ordered from DirtyPCBs.com (the design looks like http://static.projects.hackaday.com/images/4964341397760277202.png). I have a few extra which I can send via letter mail for $5 if you are in the USA ($4 for Canada, a bit more for international depending on the country in question). This board uses a lot of surface mount resistors and capacitors, but is solderable using a normal soldering iron as long as you have steady hands. Look for Youtube videos on how to solder 0603 SMD components by hand. Alternatively, you can wire up everything by hand using a protoboard and through hole components according to the schematics (this is what I used at first, while still designing the circuit). The schematic is at http://stubby.digitalcave.ca/stubby/schematics.jsp.

6) Pictures are at http://stubby.digitalcave.ca/stubby/assembly.jsp

7) I used QCad for the frame design. I don't have access to any of those other programs, so have no idea how compatible they are.

8) Which pictures do you want higher resolution versions of? I kept them small to conserve bandwidth on my site (and since most of those pictures don't really need great detail, as they are just showing how things attach together), but I could link to some higher resolution ones if needed. Just let me know...

Hope this helps; please feel free to ask if you have other questions.

Cheers

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APBurner wrote 3 months ago null point

I am new at ordering boards. Which file do I send to the board service.

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The Big One wrote 3 months ago null point

Look at http://git.digitalcave.ca/gitweb/?p=projects.git;a=history;f=projects/stubby/kicad/gerber/stubby.zip;h=85ca159d7bad2bafbfc147f382d2850806c3176f;hb=HEAD . The file itself is stubby/kicad/gerber/stubby.zip. The one which I ordered is the older one (last updated 2014-05-21). I have since updated the design to include some fat capacitors on the bottom to help filter the large voltage drain that running 18 servos at the same time will do.

(Strictly speaking, you only need one of the three capacitors: the one which filters between GND and 3v3. If you don't have this one, the AVR will brown out when all the servos are moving at the same time. However, you could use the original design and just solder a cap on the expansion port, where I have already broken out GND, 3v3, VBAT, and A0-A2: this is what I have done.) I have the caps marked as 2200uF for the two capacitors on VBAT, and 470uF for the one on 3v3, although I am probably going to use a 2200uF one for all three. Currently I have a 470uF on 3v3 and that works, but larger wouldn't really hurt for something like this.

As to which one you should choose, that is really up to you. The original one is guaranteed to be correct, since it is the one which I had ordered. The new one should be fine, and has the advantage of some more capacitor holes, but I have not tried it myself.

Regardless of which one you choose, I would recommend uploading to a gerber viewing site (I use http://www.gerber-viewer.com/) and verify that things look right. (Look for things like holes not matching the solder mask, etc).

Finally, depending on where you are located, it may be easier / cheaper / faster for me to send you one of my boards. (You get 10 per order, and I only needed a couple). This would probably cost about $4 or $5 for one board, depending on exactly where you are located. Email me if you are interested. (Offer open to anyone pending interest and availability... first come, first served).

Cheers

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APBurner wrote 3 months ago null point

So I have started cutting out the pieces for Stubby and find the cutting very easy. The plan is well thought out. I have found something that will make it easier on those that try this. Before you cut the leg pieces off the board cut the holes for the servos. Then you have something to hold onto and can control the cutting better, Don't ask me how I know LOL. I am cutting it out of 1/4 inch Baltic Birch plywood, Only because I am a scroller two and have a bunch already on hand.

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The Big One wrote 3 months ago null point

That's a great idea... I cut them out after, and my hand was very close to the blade... it was a bit scary for some parts ;-)

Cheers

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brian kame wrote 3 months ago null point

I love it!

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GoatZero wrote 3 months ago null point

This is really amazing, just to see how much has this evolved from V1 to the current V3, i cant wait to see V3 with 2.0 legs

I noticed you wrote in your digital cave that you sent your PCB design to china and got it made there, I was wondering if there was a way for you to share where did you sent it, I would love to attempt to send my future PCB designs the same way and get them delivered if possible

Also, this is the 1st time I hear about using painters tape on MDF in order to cut it, I tried googling to find a technique that describes what you tried to explain with “cover your MDF with painters tape and glue the design to the tape” however I didnt really understood that step, i found lots of painters using it to make messy art tho

also, just curious, around how much time do the 4 AA batteries last in stubby??

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The Big One wrote 3 months ago null point

Thanks!

I used http://dirtypcbs.com/ to print this board (it was featured on HackaDay a few months back). In the past, I have also used seeedstudio's Fusion PCB (very similar). I can highly recommend both services. About 7 years ago I also got a larger PCB printed by working directly with a fab house (this was before hobby boards were really a thing); I would not recommend doing that, as it cost *way* more (IIRC it was around $100 for tooling costs alone).

Covering the wood with painters tape (or similar) is a fairly common approach when using a scroll saw. The idea is that you cover the wood with tape, and then glue the plans to the tape. You can then easily cut along the lines exactly as they appeared on the computer. When you are done, the tape removes easily without any residue. I have seen some people recommend covering the plans with a layer of packing tape as well, but I have not tried that. (I am quite new at using a scroll saw, so am not the best to ask about this... I am sure that if you ask in a scroll sawing forum, or possibly even ask APBurner (commented above), they could give you great info.

4x fully charged AA batteries lasted abour 30 - 45 minutes of continuous use in Stubby v2. I have not run Stubby v3 straight for that long, but given the fact that a) there are more servos and b) those servos are doing more work (version 2 was supported mostly by the joints; version 3 puts more load on the servos), I would guess that the batteries will last about half as long... I would be surprised if they last more than 30 minutes.

I have a battery monitor on this version, consisting of a voltage divider feeding an ADC channel. It is very interesting to see how much the voltage drops whenever Stubby moves. It may have actually been a good idea to use 5 batteries, but I didn't have the space or the battery holder to do this.

Cheers

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x3n0x wrote 3 months ago null point

Sweet! excellent work! I want to scale it up about 2-3x. You wouldn't happen to have an SVG or DXF of the parts would you? That would make it easy to scale up! Coupled with a different building material and some nice beefy servos, it would be a fearsome beast at the local RC gatherings...

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The Big One wrote 3 months ago null point

Yep, I do have a .dxf - look in my git repo (now with 42% more Web Interface!) at http://git.digitalcave.ca/gitweb/?p=projects.git;a=tree, and browse to projects/stubby/frame/frame_3dof_radial.dxf. I used QCad to design it, and have not used any other design programs so I can't say how compatible it is with Autocad, etc, but I would imagine it Just Works...

If you do end up building a larger version, please drop me an email... I would love to see an all-grown-up version of Stubby! ;-)

Cheers

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Joshua wrote 3 months ago null point

Good work, looks very well thought out. I like the name too, fits the cheerful whirring, buzzing and clacking along. I like the idea of unloading the servos as much as possible, simply design something well and use some proper mechanics rather than just going the easy way and bolting to the servo arms.
One thing I noticed was that sometimes the servo arms in the lower leg look like they get pretty close to the ground, just thought with some roll and translate positions they might catch stuff. Also have you tried rubber feet or does the slight degree of play in footing help to keep things unloaded?
I want to make a hexapod too. At the very least I will be repurposing some of my old PS1 and 2 controllers as you have. Thanks!

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The Big One wrote 3 months ago null point

Thanks!

The servo arms have not caught on anything yet, although they may if you walk in deep shag carpet or something.

Somewhat on that note, in general, I *am* pretty limited in what I can do with the Z axis. I cap the Z offsets at +/- 15mm in software; the hardware can do a little bit more, but not much (maybe 17mm if I am lucky). The limitation here is the servos: they are so small and weak that I needed to use push rods and trade mobility for torque in order to even get the thing to stand. If you have stronger servos, you could move the push rod connection point closer to the joint, which would allow for more movement distance for a given servo rotation; that would in turn allow for more height. The same torque limitation is what constrains the length of the legs: make the leg too long, and the servo is fighting against a lot more leverage.

I have considered rubber feet, and I may end up adding them, but this works pretty well already. It is much quieter in real life than it seems in the video (the problem is that the camera's microphone faces forward, and I was behind the camera when talking, so my voice is quiet and the footsteps are loud). The slight slippage does tend to help prevent overloading the servos (although that being said, Stubby works fine on carpet as well, and there is no slipping there).

I do notice that the roll math seems a bit off... for instance there is one point in the video where a leg is lifted right off the ground when demonstrating the roll. I should probably re-work that section (I am currently cheating and just doing two rotations on the XZ and YZ axis, rather than doing a single rotation on an arbitrary axis. My linear algebra is a bit too rusty to figure that out... I guess it has been too long since I was in University!)

Cheers

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Frankstripod wrote 4 months ago null point

Thank you for the push rod soldering video and pictures :)

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The Big One wrote 4 months ago null point

No problem, hope they are helpful!

Cheers

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Mike Szczys wrote 4 months ago null point

Remarkable fabrication!

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The Big One wrote 4 months ago null point

Thank you! Version 3 is coming along nicely, and is even more intricate than version 2 was... I am really wishing I had a CNC at this point! ;-)

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Mike Szczys wrote 4 months ago null point

I can understand how a CNC would help out a lot. But to tell you the truth, as your first CNC project i might take just as long as doing it by hand.

All my robot projects have been wheel-based. Seeing this I'm super tempted to try my hand at a hex build.

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jfw wrote 5 months ago null point

This looks great, I'd love to use this for inspiration.

The bolts-as-bearings look pretty chunky -- how come it wasn't them bearing the weight in V1, instead of the weight being transmitted to the servos?

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The Big One wrote 5 months ago null point

Version 1 didn't have the bolts / axels at all... the legs were directly connected to the servos. (This seems to be standard for most simple hexapod designs, just because it is stupid easy to assemble and program - see for instance the Sparkfun kit at http://letsmakerobots.com/node/34852).

You can see a picture of the old version at http://static.projects.hackaday.com/images/4646641397746524433.jpg

The new version is more than twice as heavy as the old one (almost 1kg, vs 400g previously), but essentially none of the weight is being borne by the servos, so it actually works out much better. The only downside is when walking on thick carpet: since it is heavier, it tends to sink in more, which means that the tips of the legs can sometime get caught when trying to lift up. Walking slowly can mitigate this, but even then I am more comfortable walking on smooth surfaces.

I currently have some el-cheapo ball bearing units on order from eBay; I am mulling over the possibility of changing the leg design yet again, to get rid of the bolts and use a real bearing assembly, plus add another joint for the third degree of freedom. Even if I choose to do this, these changes won't be for another month or so, though.

Cheers

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Eric Evenchick wrote 5 months ago null point

Neat to see a homemade hexapod build with the goal of being affordable, as opposed to the many that use off the shelf kits.

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The Big One wrote 5 months ago null point

Thanks! It has been very fun so far... I find the designing / making of a given project to be the fun part; to me, buying an off-the-shelf robot kit would only serve to rob me of the hours of pleasure I would otherwise get.

Once I finalize all of the build details I will be writing up instructions + BOM. I anticipate a total build cost of somewhere in the neighbourhood of $150 - $200, assuming you need to buy everything. I have been lucky to have much of what I need already (most of the electronics, wood for the chassis, etc); all I really needed to buy so far was servos (less than $50 inc. shipping), the aluminum for the v2.0 legs, and some hardware for the v2.0 joints. Assuming the design does not need to change much from where it stands now, I don't foresee the need for much else.

Stay tuned for more details!

Cheers

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