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Thread: Next large robot

  1. #1

    Default Next large robot

    I've started the design work on my next creation which will be a bit different than the last few I've built. This robot will be a Hexapod based on a circular body. Each leg will have 3 drive motors and will use a design similar to the old Odex I (look it up if the name isn't familiar!). All moving parts will be on bearings or bushings, there will be 24 per leg. Linear actuators drive two axis and the third uses a large gear motor.

    I built a wooden version of one leg to validate the design,clearances and interferences. The CAD drawings were finished last night so the next step is cutting out the aluminum stock. Then it all goes into a CNC mill to make the parts!

    I'm using Parallax parts as much as possible but some things like the linear actuators were ordered elsewhere. The HB-25 motor controllersl are used to drive the 12 volt motors and 6 custom propellor boards will be used to control the legs. These controllers will be networked together with a master prop board running the show. The goal is to get the mechanical parts for a single leg together before the end of the year and have the basic individual leg programming completed before spring. I expect the final weight of the robot to be around 125 pounds and it will stand up to a maximum of around 4.5 ft.

    The rest of the legs will follow shortly after that (nice thing about a CNC is that design changes are easy to incorporate and reproduce!). I plan on using Rodney Brooks's behavioral programming ideas for this robot. So I have a lot of studying to do. My big goal is for it to be able to climb stairs with a minimum of input from myself. If I can do that, then it will be a success for me!

    This is actually my second Hexapod using this basic design but with access to better machining (CNC) capabilities and more modern electronics I expect to have more success this time around (the original was built in the 80's and had very limited capabilities)

    I'll add photos as I go along if anyone is interested.


  2. #2

    Default Re: Next large robot

    Absolutely interested!

  3. #3

    Default Re: Next large robot

    Sounds very interesting! Can't way to see this progress!

  4. #4

    Default Re: Next large robot

    I'm interested in the progression of your project, DiverBob. The whole description is interesting. Share as much as you can, as you proceed.

    Ken Gracey

    Ken Gracey | Parallax Inc.| Direct
    : (916) 625-3010 | www.parallax.com

    Follow me on Twitter

  5. #5

    Default Re: Next large robot

    Fantastic, DiverBob! I was a huge fan of Odex 1 back in the day and yours is a huge and noble effort. Def keep us in the loop on this major undertaking. My own efforts are much smaller these days: I'm still messing with OBC's simple "one servo robot" challenge. Gotta do something useful with the dozens of dollar Chinese relays I've been accumulating. Not hoarding, Ken. There's a subtle difference!

    For the uninitiated, see http://www.theoldrobots.com/odex.html

  6. #6

    Default Re: Next large robot

    Hello DiverBob,

    If I remember correctly I think I talked to you about your first hexapod robot at the second UPENE show. Sounds like your new project is going to be cool and I'd enjoy seeing pictures of your progress. Are you going to put a dome on the head like the ODEX robots? I have sources for those if you need some.


  7. #7

    Default Re: Next large robot

    Thanks for the encouraging words!
    Almost done with the CAD drawings, will convert them to G code for the CNC mill (I have a Tormach 770 for those that are interested). Most of the hardware will be custom built for this project. I am taking vacation all next week so I should be able to get a lot done. I'm also investigating aluminum anodizing, that would give the whole project a very nice look!
    I was inspired several years ago when I subscribed to Robotics Age magazine when a 1984 edition featured the Odex I. It was far and away more complex than anything I had attempted up to that point but I knew I had to try. The learning curve was steep and the price even steeper, but I finished a basic version back in the early 90's. Unfortunately it wasn't a complete success (it ran but only under full human control, the controllers I built and the available software wasn't up to the task -also all my money was going into this one project for several years!) due to a number of issues both mechanical and electronic. I blew my budget on it but it got me interested in metal machining and mechanical engineering.
    The propellor expo got my interest in robots going again when I saw the progress others had made and how far the level of controls have come. I believe my new design will overcome most of my earlier issues and computer control has come a long way! I'm using the propellor chip as the controller, it's put the 'fun' back into programming for me.


  8. #8

    Default Re: Next large robot

    Sounds like an awesome project, please post your progress...

  9. #9

  10. #10

    Default Re: Next large robot

    Raw material (Aluminum) for one leg is cut to size, (used 81 inches of 1 x .25 stock, 8 in of 3 x .25, 12 in of 2 x .375, 4 in of 1 x 1) started validating the G code for each piece and optimizing the cutting sequences. This is important because if all works out OK in testing then I have 5 more legs to produce!

    Initial test cut ended up breaking 2 end mills, going back and verifying the cutting speeds and feeds are correct for type 6061 aluminum.


  11. #11

    Default Re: Next large robot

    Hey Bob!
    I remember you were talking about doing this at the UPENE. It will be fun to follow your progress. I think it would be neat to see the milling work as well as the construction. Have fun!


    PS what was the name of the spider in the "Lord of the Rings" that bit Frodo?
    My wife is very, very understanding

    Prospero: Robot Farmer

  12. #12

    Default Re: Next large robot

    Quote Originally Posted by vanmunch View Post
    Hey Bob!
    I remember you were talking about doing this at the UPENE. It will be fun to follow your progress. I think it would be neat to see the milling work as well as the construction. Have fun!


    PS what was the name of the spider in the "Lord of the Rings" that bit Frodo?
    I told my wife that your Hexapod was the motivating factor last summer to get back into Hexapods again! I won't introduce you to her at the next expo, there could be trouble!
    I'll try to run some videos from my iPhone during machining. I'm heading back down to the man cave to run the next tests go the G code. I spent a lot of time last night updating the CAM info, now to see if it pays off.

    The spiders name was , I had to look it up in the book. That might be a good name for a large Hexapod?

    I started a blob in this forum to put in more details of the build, kind of a diary. Let me know what kind of information you would like to see.


  13. #13

    Default Re: Next large robot

    The last two days have been filled with milling out the various pieces for the robot. The main leg supports are complete along with various connecting parts for the leg kick and lift system. I finished building the first motor mount tonight. Parts are being deburred and then put in a vibratory bowl to remove machining marks. Eventually I want to anodize the parts, the hard anodize layer will reduce the number of nicks and scratches and generally give the end product a more professional look. Here are some photos that I took of the process.

    The photos show the raw stock on the floor prior to cutting and then the cut material. The next photo is my original leg design followed by a full scale wood prototype leg. The motor mount is being machined in the mill and the last photo is polishing the parts after milling.

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  14. #14

    Default Re: Next large robot

    You're diving right in, nice! Would like to see some photo details of your motors & leadscrews. Great project, DiverBob!

  15. #15

    Default Re: Next large robot

    Hey Bob,

    Thanks for the update. I think it's neat to see how everything is created. If its any consolation for your wife, you've inspired me that I really "need" a CNC. Someday.... Have fun and did you see that Speedy Metal is having 10% off this Friday-Sunday and 15% off next Monday?


  16. #16

    Thumbs up Re: Next large robot

    Busy days but productive! The photo below shows most of the major parts that go into a single leg (with a few exceptions that are still being polished). The top round piece is the part of the foot of the leg that touches the floor. The next 2 are the main leg supports, just above the ruler at the bottom of the photo are the upper and lower swivel attachments. These screw into the holes on the right and middle of the main leg supports. The 2 3D parts are the motor mounts that also attach to the upper and lower swivels. Right under the main supports on the left are 2 parts that are part of the pantograph, actually all the remaining parts are part of the pantograph. The two parts on the left side under the main supports are the upper portion of the leg foot assembly (missing from the photo is the part that connects the foot and these parts together. The curved parts on the right side are part of the kick arm assembly, this uses a motor to allow the foot to 'kick' out. The large holes in the parts are where all the bearings and bushings go.

    The aluminum is a dirty gray color after the first round of polishing, this step just deburrs and removes most machining marks. Once all the pieces finish the first stage of polishing then they will be polished to a higher luster using ground walnut shells. After that step they will be ready for anodizing. I probably won't do the anodizing for a while, still have to study up on that before I jump into it.

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    Here are photos of 2 of the linear motors being used. One has a 2" throw and the other is a 4" throw. Both are capable of moving 110 lbs and holding 550 lbs. All this and only 12v and less than 10 amps! They have integral internal limit switches and output potentiometers. I have both pistons fully extended in the photo. The piston moves .5" per second.

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    This is a photo of the CNC Milling station in my workshop. This is a Tormach 770 I got last spring. It is designed from the ground up as a CNC mill for prototyping. I have been very impressed with what I have been able to do with the machine so far. It far exceeds the capability of my older and smaller CNC milling system (custom designed several years ago using a Sherline mill). It took a while but I finally out-grew the old system and upgraded. (Know anyone looking for a working, used CNC mill? )

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    Next steps are to finish making several smaller parts that connect everything together. Even the lathe got a workout tonight making connectors! Then I'll be heating all the parts to around 250-300 degrees and then press fitting the bearings. Once the bearings are installed then I can do an initial assembly and see if everything fits together the same way they did on paper! In other words, this is when I find any math mistakes I made in the calculations!


  17. #17

    Default Re: Next large robot

    I did an initial test fitting of the parts and most everything is going together as expected. I have several notations on the plans for changes to the design but this test leg looks like it will go together well enough to start installing the motors and electronics. I need several sizes of fasteners that I thought I had but didn't so I'm putting together a list of items to order in the next few days. I can make due with some of the fasteners I have just for testing but I want a uniform look to the project.

    I'll get some pictures posted of the assembly process later.


  18. #18

    Default Re: Next large robot

    Have you considered how your sensor array will interface and where the sensors will be located?

    If you are looking for it to go up and down steps then I would suggest using a combination of several differnt devices for sensing. For example a dual or tri axis accelerometer to keep it level, sonar and IR for object avoidance, bump sensors just in case something goes horribly wrong, a gyro for additional balance or leveling, perhaps even one of the laser range finders.

    Also if you want to get fancy you could run wireless transmittors and recievers to send and get information, location, new instructions or even dump onboard memory (or use thumb stick memory) and overlay a GPS so you can create maps.

    If you really want to do it big, get a CMU cam and use the color detection to have it locate and follow or track an object, give it a RFID to gain access to doors properly equiped and an onboard charger so it will find an outlet and plug itself in when it needs to recharge and give it PINK capacity so it can communicate via the web to a remote terminal.

  19. #19

    Default Re: Next large robot

    Sensors for the project are planned but I haven't really gotten into figuring out everything I need/want. It will probably be a gradual process instead of adding various sensors as the need for them arises. One advantage of a large Hexapod is there is plenty of space for installing sensors, weight is not a serious concern (the motors I have can move about 330 lbs) and the batteries will be fairly large. The initial sensors will be to determine leg position and identify when the leg is on a surface that will hold its weight. The next layer set sensors will be 'bump' sensors on each leg so it knows when a swinging leg encounters an object.

    Since I plan on following Rodney Brooks behavioral programming as a guide, I should be able to layer in new sensors that will automatically interact with other sensors in unique ways.

  20. #20

    Default Re: Next large robot

    Quote Originally Posted by DiverBob View Post
    Here are photos of 2 of the linear motors being used. One has a 2" throw and the other is a 4" throw. Both are capable of moving 110 lbs and holding 550 lbs. All this and only 12v and less than 10 amps! Bob
    Of course, ~10 amps times 12 or 18 linear actuators can add up pretty quickly... what's your planned power source, maybe a liFePO4 scooter battery?


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