Shop OBEX P1 Docs P2 Docs Learn Events
Servo Catapult Accuracy — Parallax Forums

Servo Catapult Accuracy

ercoerco Posts: 20,256
edited 2013-05-08 17:39 in General Discussion
I was so impressed by the "Positive Pressure Gripper" thread & video at http://forums.parallax.com/showthread.php?137966-Robotic-arm-uses-quot-positive-pressure-quot-to-work-its-magic&p=1074926#post1074926 that I wanted to see if my simple robot arm could shoot any baskets. But after rethinking the G-forces and resulting abuse involved, I left my 6-servo arm alone and made a single-servo catapult-style shooting arm test jig to see how repeatable a servo "sling" could be. Pretty dang repeatable. Futaba S3004 analog servo running on a 7.4V lithium battery and my fave, a BS2 HW board. The arm is 14" long, lightweight aluminum tube.

Comments

  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-02-21 05:19
    Good fun.
    Next step: Auto-loader.
    ?
  • Cats92Cats92 Posts: 149
    edited 2012-02-21 05:20
    whoua !!

    I build bots wit a group of kids , they will like a catapult.

    Please some details and close pictures .

    7,4 volts for a Futaba S3004 is it not a bit high ?

    Jean Paul
  • mindrobotsmindrobots Posts: 6,506
    edited 2012-02-21 06:20
    A while back, there was a thread asking "What's an engineer?" If it has to do with the practical application of theory and technology to a problem, then, sir, you are an Engineer!! What a great quick build teaching tool!!

    Multiple servos, multiple arms, multiple auto-loaders.......
  • Duane DegnDuane Degn Posts: 10,588
    edited 2012-02-21 06:52
    erco,

    Very Cool! That's impressive.

    Servos sure make easy for a uC to interact with the physical world.
    PJ Allen wrote: »
    Good fun.
    Next step: Auto-loader.
    ?

    Maybe this is where your (erco's) arm could help out?
  • GordonMcCombGordonMcComb Posts: 3,366
    edited 2012-02-21 07:45
    As Charlie Sheen would say Winning!! Great project.

    I agree, an auto-loader would be cool. So too would a turntable with two or three cups, and the chance that a ball won't make it in.

    -- Gordon
  • ercoerco Posts: 20,256
    edited 2012-02-21 08:28
    Great feedback, lads. I envision a second servo as a turntable to steer the arm to hit a variety of targets at diffferent distances, requiring different trajectories. This simple design puts a lot of stress on the servo. The "launch" sequence is simply slamming from one pulsout position to the next. The servo speed is limited, that's why I ended up with 14" arm and operating at 7.4 volts. It would be more efficient to use the servo to cock a rubber band or spring catapult and release it, but that would complicate things a lot and probably require 3 servos (cock, release, and change endpoints) to do what this one is doing now.

    The consistency is surprisingly good, but the servo power will probably degrade over time as the motor brushes & commutator wear. Such is life in the big city, but it's fun for now. Too bad the scale is so big. I'd like to nail everything down to a board. Like a 4x8 board!
  • ercoerco Posts: 20,256
    edited 2012-02-21 09:25
    Surely I didn't need to mention that a laser sight is in the offing!
  • RichKRichK Posts: 54
    edited 2012-02-21 11:02
    Maybe something like the old "Grand Prize Game" on the Bozo the Clown show. It was a series of buckets at increasing distance and the contestant tossed a ping pong ball into each bucket for better and better prizes. Top prize was a bicycle or something like that. There are clips of it on YouTube. Automate it with range finders, vision and who knows what else.
  • ercoerco Posts: 20,256
    edited 2012-02-21 11:13
    This guy still sets the standard.
  • ajwardajward Posts: 1,130
    edited 2012-02-21 13:18
    Nice! Just one thing missing... explosives!!!!!! =:-} (Tho' you might want a bit more range.)

    @
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-02-21 15:01
    How about those little wads of paper thingys, with the gun-powder, or whatever; they go POW! when they hit their target (floor, door)? What're they called again?
    I have some. Perhaps it's my turn.
  • ajwardajward Posts: 1,130
    edited 2012-02-21 15:22
    I've heard them called "cracker balls". Fun things. Used to fling them with a slingshot.

    @
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-02-21 15:44
    From a slingshot? They snap if you look at them cross-eyed.

    Well, anyway,... all I have is Parallax's standard servo, and it's not transiting anywhere near fast enough. Dang.
    Major depression sets in.

    Wish I hadn't torn down my SpinStamp stepper circuit.
    Plop.
  • ercoerco Posts: 20,256
    edited 2012-02-21 15:50
    According to ServoCity specs, a cheap Hitec turns faster (HS-311=.15 sec/60 degrees) than my cheap Futaba (S3003/3004=.19 sec/60 degrees). That's pretty significant in this application. Looks like I'm off to Pacific Coast Hobbies again for another HS-311 or two.

    @PJ: As I said, I had to use a long arm and 7.4 volts to the servo to achieve that moderate toss. I'm not above trying 8 or 9 volts either. Tune for minimum magic smoke...
  • PJAllenPJAllen Banned Posts: 5,065
    edited 2012-02-21 16:02
    I was trying to get by on the cheap.

    I still have one unopened box of "snappers".

    From the box:
    "D.O.T. Class C Explosive" - Talk to me.
    "A novel trick item." - Whatever
    "Recommended for outdoor fun." - Oh, stop already.
    "Please do not put in mouth." - I'm way ahead of you.
    pop-pop.jpg
    640 x 480 - 119K
  • Martin_HMartin_H Posts: 4,051
    edited 2012-02-21 17:47
    Cool project, but why do I suspect we'll see a flock of robots hurling snappers in the near future.
  • ercoerco Posts: 20,256
    edited 2012-02-21 19:58
    Might as well make it a UPEW contest! :)
  • mindrobotsmindrobots Posts: 6,506
    edited 2012-02-21 20:16
    At UPENE, OBC(Jeff) was hunted by Microcontrolled and his Nerf shooting Stringray.......the way this thread is going, 2012 might be a bad year for Jeff!
  • TtailspinTtailspin Posts: 1,326
    edited 2012-02-21 20:36
    Oh great! even more obstacles for the line following contest...
    now how can we incorporate these into the ELEV-8 air show?
    Catapults tossing snappers could add a whole new sense of urgency for the pilots in the baseball dropping contest...


    -Tommy
  • mindrobotsmindrobots Posts: 6,506
    edited 2012-02-22 04:06
    ...and so it starts....the ground pounders increase their air defenses...then the Airedales come up with ways to counter the new defenses (dropping nets to tangle the servo arms...then a new projectile system on the ground....oh the waste...the electro-mechanical carnage!!
  • ajwardajward Posts: 1,130
    edited 2012-02-22 07:40
    PJ Allen wrote: »
    From a slingshot? They snap if you look at them cross-eyed.

    Well, that was in the "good old days" when they made things more substantial.

    @
  • ercoerco Posts: 20,256
    edited 2012-02-22 08:06
    Duane Degn wrote: »
    Servos sure make easy for a uC to interact with the physical world.

    From this ME's POV, uC's make it easy for servos to interact with the physical world!
  • Nick ErnstNick Ernst Posts: 138
    edited 2012-02-22 15:48
    That lego launcher is pretty cool, but can it hold up against an air attack from an ELEV-8 armed with Estes rockets on it?....I think not!!!
  • ercoerco Posts: 20,256
    edited 2012-04-10 03:52
    YOU JOKERS ASKED FOR IT!

    Well, PJ anyhoo... just roughed out for Expo. Auto loader, IR remote, multiple target zones, etc. Might not have laser & sonar seeking yet for Expo, depends on timing...
  • LoopyBytelooseLoopyByteloose Posts: 12,537
    edited 2013-05-08 11:19
    That catapult is a great idea, but lots and lots of preparation.
  • ercoerco Posts: 20,256
    edited 2013-05-08 14:20
    About 4 hours total to build & program. Lots of superglue and "that looks about right"! Now I could do it in two. :)
  • Hal AlbachHal Albach Posts: 747
    edited 2013-05-08 15:26
    Perhaps you may want to look into a rotary solenoid to replace the servo. They can provide tremendous torque through a range of arcs (determined mechanically) and probably could hurl a missile quite some distance. Activation couldn't be simpler, a high current mosfet and a healthy 20-24 volt power source. By shortening the power pulse shorter distances could be realized. Since they are basically a very simple mechanical device with a coil they can take a lot of abuse.
  • ercoerco Posts: 20,256
    edited 2013-05-08 17:39
    Hal Albach wrote: »
    Activation couldn't be simpler, a high current mosfet and a healthy 20-24 volt power source.

    For the ultimate in simplicity, how about nothing, which the current servo requires? :)

    Additionally, the servo's trajectory (range of arcs) is all programmable using pulsouts.

    It works amazingly well over a variety of trajectories. The only change I'd consider making would be to increase the range by using a torsion spring. The servo would preload the torsion spring to a programmable amount, and then the lightweight catapult arm would be unlatched by a tiny release solenoid.
Sign In or Register to comment.