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Thread: Steam Automaton Groucho

  1. #1
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    Steam Automaton Groucho

    Hi,

    I'm announcing this in hopes it can speed up my design.

    Part of the reason for building this is to give me a reason to learn ROS. Hopefully what I learn will appear on my blog once i set up a robotics area in there.

    The base for SA-Groucho is a very used Jet Power Chair. My thought is to remove the upper parts and use the base as is (mostly). The upper part will be constructed and will go approximately where the chair went.

    Much of the exterior will be decorated with 3d printed steampunk items. This will be the first bot I've built that I want to paint.

    The head will be small and oddly shaped, though I will do my best to put Groucho Marx' trademark features as much as I can, renvisioned for steampunk. However, the neck will be a robotic arm as long as I can make it, though that depends on my budget at the time. For now it will just sit in his neck like a normal head.

    Most of the computing power will reside in his torso. I have ordered a NUC and will use some BeagleBone Blacks for some control areas, along will some various Arduino clones I have. Perhaps if the Arduino Tre is inexpensive enough I could find a use for it.

    I plan to build him in stages so that I don't take on too much at any one time.

    SA-Groucho will also be the head of a Troupe of smaller bots, including Zeppo, Harpo, and Chico. Most of these will be wirelessly controlled from SA-Groucho.

    His purpose is mostly entertainment and art. I do plan on being able to take him for fairly long walks in my area just to see the reactions.

    Currently I have most of the parts except for the power system. Due to cost I'll probably use large amounts of SLA batteries. The ones in the wheelchair are a pair of 12V 75Ahr SLAs that are quite dead. I'm debating on replacing them with SLAs or with LiFePo4s. The one is lighter, the other cheaper. Plus the SLAs are heavier which will lower his center of gravity.

    Once I get some pics I will put them up here.

    The rest of the Troupe is even less well defined, though I intend for both Chico and Harpo to be Hexapods, while poor Zeppo will be a simple rover. All the bots will have sound, though Harpo will only be able to communicate through music and cartoon sound effects.

  2. #2

    Re: Steam Automaton Groucho

    From my experience, I'd recommend LiFePO4.
    Sounds like a fun project :-)

  3. #3
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    Re: Steam Automaton Groucho

    Question: Would you run the electronics off of a 12v source or a 24v source?

    Also, would you use two batteries (one for the motors, one for the electronics) or a single battery for both? If I use a single battery it makes charging easier. However, with two batteries I can choose the most convenient battery for my electronics. I think +19 and +5 should handle most of the electronics.

    Given 24 volts, though, how is it best to get high amperage 12v for my MX-64s for the arms and neck?

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    Re: Steam Automaton Groucho

    There are plenty of dc-dc converters that could drop the 22.4~28.8V of an 8S LiFePO4 down to a pretty well regulated 12V. There are TI 12~22V/6A converters at ~$23, Murata 12V/10A and 12V/17A converters at ~$50 and ~$70, respectively, and Delta 12V/17A at ~$63, but getting non-'board mount' converters pushes the price up a lot. There is an even wider selection of dc-dc converters to drop a solid 12V (or variable/noisy 18~36V) down to 3.3V/5V for all the embedded controller and sensor needs. Stepping a 3S LiPo (10~12V) up to 19V for a laptop or NUC/ZBox is a little less common so often more expensive, but there are several adjustable dc-dc converters mentioned on other threads that can handle a NUC/ZBox reasonably well.

    12V/5A is all that is needed for a DARwIn-OP with 20 MX-28 servos, but it will depend on which servos you choose, how many of each, and how heavily they are loaded. The servos are much less picky about the voltage tolerance of the 10~12V supply than computers and sensors with their 19V and 5V supplies, but any drops below ~9V because of over-current conditions in the power supply will cause issues.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
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    Re: Steam Automaton Groucho

    OK, I'm thinking then of using two LiFePo 24v batteries. The motor battery will be a 60 Amp-hr, and the electronics should be able to make do with a bit less - maybe a 30-40 amp-hr.

    As for the motors, there will be:

    1. A pair of wheelchair motors, 24v
    2. A "waist" motor to rotate the torso.
    3. The neck servos. This will be very similar to an arm in construction, except a bit longer. I'll be using MX-64 servos.
    4. Eventually there will be two spindly arms, but I'll only start with one.

    I can use 24v motors for the waist and use a separate 12v converter for each set of servos.

    This also simplifies the charging station, because I will have, in addition to the chargers, 2 24v supplies to make the electronics and smaller motors happy during charging.

    The electronics are a bit less thought out at the moment.

    1. The main brain: an Intel NUC.
    2. (Deleted for being too silly even for me)
    3. A BBB to deal with the head itself.
    4. A BBB to deal with each arm.
    5. A wired/wireless router to enable the various parts to communicate via Ethernet.
    6. The wireless part will allow Groucho to communicate with the rest of the Troupe without depending on my home's wireless network.
    7. Various sensors including two or three webcams and a boatload of Sharp IR Rangers and sonar units.
    8. Some microcontrollers and LEDs for various decorations.

    Plus other things I can think of. I'll probably have some pistons that actually seem to do something.

  6. #6

    Re: Steam Automaton Groucho

    If I were using step-down converters from 24V to your 19V and 5V targets, I would not bother separating the batteries. I would put a high-power TVS (5KP26, 5KP28, perhaps even 15KP26 or -28) across the input to the step-down converters, and perhaps a big electrolytic at each (1000 uF or more) and call myself good. A single, bigger, battery, greatly simplifies charging, and makes best use of my money to get the overall runtime up, and balanced between electronics and motors.

    If you use Robotis or Dongbu servos, those are controllable by serial bus. Thus, you could use a single USB2Ax or similar adapter from the NUC to talk to the servos of both arms, no BBB(s) needed.

  7. #7
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    Re: Steam Automaton Groucho

    I can do the larger battery, but it is more of a pain. On the other tentacle I would have probably had to redo the battery tray anyway. The advantage of using a large battery is that it forces the CoG lower which makes going up and down my driveway more than a bit hairy. However, SA-Groucho should mass less than myself and I can make it down the driveway on Lee's powerchair.
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    Re: Steam Automaton Groucho

    Forcing the CoG lower to the ground (preferably below the wheel's diameter) decreases the chance of tipping over even with a large, unbalanced load on top. Overall weight is what affects traction and motor loading.
    Please pardon the pedantry... and the profanity... and the convoluted speech pattern...
    "You have failed me, Brain!"
    [git][mech][hack]
    gives free advice only on public threads

  9. #9
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    Re: Steam Automaton Groucho

    Thanks, Tician

    Unfortunately modern powered wheelchair wheels are fairly small. And I'd like to keep the battery tray about the level it's at, though I'll probably move it to the back for more stability. For this, I may have to do some math.

    I'm trying to balance the torso which sticks straight up. During normal travel, it isn't much of a problem, but our driveway is around 12 degrees, which doesn't sound like much until you take it in a power chair.
    -
    A little learning is a dangerous thing.

  10. #10
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    Re: Steam Automaton Groucho

    I would like to make a clarification. I've heard some people are wondering about how many projects I have and that I may be posting more than I should. I've been asking questions because I've been out of touch in robotics for a decade when I totally dedicated myself to taking care of Lee (my wife). I'm still her full-time caregiver but I realize I have to take time to do the things I need to do to keep sane and keep myself healthy as well.

    My main project currently is building one robot (SA-Groucho). Groucho is part of a set of four robots, also including Zeppo, Harpo, Chico, and maybe Gummo; I will be probably switching back and forth between these robots as my finances and interests imply. In addition there are other small projects that aren't really directly a part of a robot, but associated. This would be the laser harp I've been asking about; after all, Harpo Marx needs his harp...

    I'll admit that I'm going in a lot of directions all at once, but there *is* a madness to my method. Right now I'm in the design stage, so I'm still trying to work out what's going where. Sometimes I'm probably going to post in the wrong place. I do try to help people when I can. I also tend to ask questions where the forum seems to direct them. I do ask your forgiveness when I do things incorrectly. I will try to ask questions specific to Groucho in this project thread, but more general questions are likely to go anywhere.

    Thanks for listening,

    D. Jay Newman
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    A little learning is a dangerous thing.

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