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Spike the Spider Robot — Parallax Forums

Spike the Spider Robot

ercoerco Posts: 20,256
edited 2014-01-30 21:15 in Robotics
Following Amanda's lead, I named my new robot per his main feature. She has Ted Tread and Wally Walker, so I have Spike Spider.

First test of modified Spider Robot chassis. ~$8 on Ebay: http://www.ebay.com/itm/200955719259

Two HXT900 servos modified for continuous rotation do the driving. No controller or sensors yet, just a simple servo tester used here. Servos are driven in opposite directions, so it just turns in place. More to come.
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Comments

  • ercoerco Posts: 20,256
    edited 2013-11-17 18:47
    Slightly bigger than mine, and you hardly even notice the truck underneath. :)

    Jump to 3 minutes, still a bit painful to watch.
  • Martin_HMartin_H Posts: 4,051
    edited 2013-11-20 05:48
    Erco, how did you couple the servo output shaft to the geartrain that was already in the robot spider? I imagine the input gear was designed to fit over one of those typical toy DC motor shafts.
  • ercoerco Posts: 20,256
    edited 2013-11-20 08:35
    Million dollar question, Pal! It's a hex shaft I cut & drilled out on a lathe; a 3/4" long 2-56 screw goes inside and threads perfectly into the servo screw hole. Slightly better view of the servo glued to one side at http://www.youtube.com/watch?v=aSnp58Uhhug
  • ElectricAyeElectricAye Posts: 4,561
    edited 2013-11-20 09:09
    erco wrote: »
    ...you hardly even notice the truck underneath. ... a bit painful to watch....

    I don't get it. I kept expecting it to walk off the truck lift. No?

    And what are all the dudes underneath it doing? Just going for the ride? Or.... please don't tell me they're all "driving" the thing.

    erco, where do you find the time to build all of these gadgets?
  • ercoerco Posts: 20,256
    edited 2013-11-20 17:41
    ElectricAye wrote: »
    erco, where do you find the time to build all of these gadgets?

    Who, me?

    Dang, it feels like I never have time to build anything compared to Duane, Martin, Rich and Gareth! I guess it's all relative. My building goes in spurts, especially when there's a contest or I'm writing a magazine article for SERVO or ROBOT (which has been exactly a year since either, so watch out). That Coasterbot took up more time than it should have, so I'm still catching up on honeydos. And Christmas is coming, cleaning and prepping that will slow me down until the holiday break begins.

    Hey, is there gonna be another "Hack the Halls" contest? :)
  • ercoerco Posts: 20,256
    edited 2013-12-30 11:47
    Finally something to show! First test, just walking in a circle. Open loop here, soon it will track around a center cylinder via ultrasonic sensor.
    http://www.youtube.com/watch?v=oVVGr6kQuHA
  • ercoerco Posts: 20,256
    edited 2013-12-30 12:02
    Grant makes me feel like a winner! Go right to the end to see the fail. Do not collect $200. http://www.youtube.com/watch?v=n0EOmati5_U
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-12-30 15:09
    erco wrote: »
    Finally something to show! First test, just walking in a circle.

    Looking good!

    I'm surprised those little servos are up to the task of powering that thing. Very cool. It looks like the original version just travelled straight?

    It seems like a simple task to get it to do a figure 8 now that you've got it going in a circle. Are you trying for the ultrasound challenge first?

    I have yet to make an entry in the US challenge. It's on my todo list (with lots of other things).
  • ercoerco Posts: 20,256
    edited 2013-12-30 15:33
    Yes, yes, yes, yes, yes, and yes.
  • ercoerco Posts: 20,256
    edited 2013-12-31 19:25
    Happy New Year from Spiderbot!
  • ajwardajward Posts: 1,130
    edited 2013-12-31 22:02
    Nice job erco!
  • Duane DegnDuane Degn Posts: 10,588
    edited 2013-12-31 22:34
    Yes, very cool!

    I love how it looks around.

    Is the distance from the bottles pre programmed or is it determined by the initial distance to the two bottles?
  • mindrobotsmindrobots Posts: 6,506
    edited 2014-01-01 02:33
    You should get some sort of Engineering award! You came in on time AND under budget!! We need a "Golden Erco" to give out on the forums!

    Very impressive!!
  • varnonvarnon Posts: 184
    edited 2014-01-01 05:33
    Nice. I love walking robots with leg linkages.
  • DiverBobDiverBob Posts: 1,110
    edited 2014-01-01 07:03
    Very nice setup, cheap too!
  • ercoerco Posts: 20,256
    edited 2014-01-02 16:04
    Thanks for your good words, guys. This bot retains one of my favorites features from my laser-guided Terminator bot. It uses just one Li-Ion cell (an AA-sized 14500 here) for power, visible on top of the PCB. A cheap Ebay USB stepup circuit provides 5V for the (noname) processor and sensors, while the servos run direct off the 4-ish volts of the Li-Ion. The little Spider robot has a lot of backlash in the leg linkages and I minimized weight at every opportunity.

    @Duane: Orbit radius was hastily preset for this first run, but it could easily measure the distance and calculate its own radius, since it uses a built-in ADC to read the Sharp sensor. The sensor's "look around" scanning feature is borrowed from numerous other robots, I can't claim any originality there. I could have used multiple stationary sensors instead, but the servo scan motion adds a fun animation to the bot.
  • ercoerco Posts: 20,256
    edited 2014-01-02 16:55
    One interesting factoid I learned using that scanning method is that the Sharp IR sensor does not have a symmetrical view left & right. It has an IR LED on one side and a position sensing receiver on the other side, so that explains the discrepency. Compounding the problem, the sensor was positioned by a cheap Ebay 9g servo which didn't quite rotate the full 180 degrees. I mounted my sensor pins-up, which is upside-down compared to most installations. The flat top side was easier to bond to the servo horn underneath. In that orientation, it had a better view to the left (CCW) than right (CW) so I offset the sensor slightly clockwise to compensate. It was particularly sensitive in this application, needing to sense the leading edges of cylindrical bottles instead of a nice flat perpendicular surface.
  • ercoerco Posts: 20,256
    edited 2014-01-19 21:15
    Adam Savage's Spider robot is cooler than mine. Probably a little more expensive. http://www.youtube.com/watch?v=-vVblGlIMgw
  • ercoerco Posts: 20,256
    edited 2014-01-23 09:20
    Some specifics on modifying Hobby King HXT900 servos for continuous rotation. Having modified numerous types of 9-gram servos, this one is my favorite in terms of cost, strength, speed control, and ease of use. I like to use fixed resistors instead of a pot for stability, even though the null (stopped) pulsewidth may be slightly different than 1.5 ms, or PULSOUT n,750. That's easily calibrated in software. Alternatively, the three pot wires could be routed through a hole in the servo case to a small external multiturn 5K trimpot and adjusted accordingly.

    Part1: http://www.youtube.com/watch?v=wfmM3cuihJI
    Part2: http://www.youtube.com/watch?v=7pxRhxBPSUM
  • ercoerco Posts: 20,256
    edited 2014-01-26 18:35
    Ultra-simple tracking routine could be used on any robot, any processor.
  • ercoerco Posts: 20,256
    edited 2014-01-26 22:54
    Tracking to an object and maintaining a fixed distance.
  • DiverBobDiverBob Posts: 1,110
    edited 2014-01-27 13:16
    Cool, I need to add something like this to my hex when it's done.
  • ercoerco Posts: 20,256
    edited 2014-01-27 15:42
    DiverBob wrote: »
    Cool, I need to add something like this to my hex when it's done.

    This would be a 2-minute programming job on a 2-wheel BoeBot with a PING & servo. Thus, your amazing 6-legged walker should take about six minutes. :)
  • Martin_HMartin_H Posts: 4,051
    edited 2014-01-27 18:12
    This is neat.

    With my IR compound eye I had left, right, and center zones so I could infer the direction. But this sensor only has one zone. When you move your hand left or right how does it know which way to track? Does it guess and go the other way if it loses the object?
  • ercoerco Posts: 20,256
    edited 2014-01-27 21:50
    Another million-dollar question, Martin_H, you're sharp!

    It ain't smart at all. It just oscillates back & forth and stops when it sees a target. But it looks smarter than that when the object moves slowly back & forth, eventually they sync up. It eventually finds any object in range.
  • GarethGareth Posts: 278
    edited 2014-01-28 02:16
    erco wrote: »
    Ultra-simple tracking routine could be used on any robot, any processor.
    I just love the "Theo" style motion of this spider .... by the looks of it ; its intentions have already x-rayed your wallet and is already expecting an immediate upgrade......
    Q :- Do you do remove its batteries overnight.....? ;-)
  • ercoerco Posts: 20,256
    edited 2014-01-28 09:01
    In one of my non-posted videos, I said "it must be a girl robot, watching my wallet so closely", but I self-edited and opted for a more politically correct stance. Ladyada might be watching. :)
  • ercoerco Posts: 20,256
    edited 2014-01-28 21:51
    This flurry of experimentation & documentation is to support an upcoming magazine article on Spiderbot. It's actually easier to build a bot than write a construction article about it. I love writing, but it's difficult to judge how much detail to put into a technical article. Some readers need all the excruciating minutia if they actually want to copy the design. Others will never build, they just want the highlights. Overall, I probably tend to give too much detail, sort of a "no reader left behind" policy.
  • Martin_HMartin_H Posts: 4,051
    edited 2014-01-29 06:51
    erco wrote: »
    This flurry of experimentation & documentation is to support an upcoming magazine article on Spiderbot. It's actually easier to build a bot than write a construction article about it.

    That is so true. I've built plenty of bots but have never written an magazine article because it seems like too much work. At work technical documentation always seems to take the most time.
  • ercoerco Posts: 20,256
    edited 2014-01-29 08:37
    I had to go back and recreate a few things for photos & videos instead of ripping the robot apart (CA is great, but it's a one-way trip). Among other things, I modified another CR servo, and die-threaded another hex shaft for the videos I listed in post #20. Two steps forward, one step back.

    One pleasant surprise was my discovery of the photo editing capabilities in Windows 8 Photo Viewer. I don't have PhotoShop on the computer I was using to write the article & organize my photos. Some too-dark photos I took of the bot during assembly looked AMAZING after WIn8 did a single pass of auto-fix. Certainly saved me some time.
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