Results 1 to 7 of 7

Thread: Drum robot ... HELP

  1. Drum robot ... HELP

    Hey people!

    I'm very new to trying robotics and am probably way in over my head here, but I'm determined to work this out. I have an idea for a fully functional drumming robot made out of mostly pvc pipe and plastic custom parts made right in my garage. I've created the skeleton of his upper torso, arms, shoulders, and even his skull. I'm pretty sure I know how I want to make him move, but I'm not sure how to get the parts I need. So I'm hoping you can help me figure out where to start.

    To begin, he has four arms, which can swing 270 degrees on a y axis, and 270 plus degrees on the x axis (I only need 180 degrees of actual motion.) I had planned on using a bowden style cable system to pull the joints with two cables to each side of the arm, which will then attach to a motor in his chest with a pulley wheel to turn his arms and shoulders. Which brings me to my first question ... if his arms in total weigh around 5 lbs, what kind and size stepper motor can I use to turn and hold the arm in position? Also, how would I control it?

    His lower arms are going to be pneumatic air pistons, and only need to go fully in and out at the elbow and wrists, so that he can strike hard and quick. Is there a method of controlling this along with the stepper motors?

    I'd like to be as cheap as possible. My end goal is to have him actually play the drums via a laptop controlled midi interface so I could just start each song and he'll bang away, much like the drummer in the robot band compressorhead. As much information as I could get would rock.

    Thanks!

    I added a couple of photos of his torso for reference.Click image for larger version. 

Name:	20180821_095617.jpg 
Views:	8 
Size:	75.5 KB 
ID:	7323
    Click image for larger version. 

Name:	20180813_113448.jpg 
Views:	9 
Size:	76.6 KB 
ID:	7324

  2. #2

    Re: Drum robot ... HELP

    Neat! What are you using as rotating bushings/bearing/hinges?

    Won't multiple Bowden wires interfere with each other when they overlap in space?

    I don't understand how air pistons would strike anything -- are you hooking them up as "muscles" across some hinge joint? I'm not sure air pistons are the best choice for fast, accurate motion -- there's some risk you'll punch through the skin of the drum!

    In general, 99% of these kinds of projects end up failing because of cost. It turns out, moving 5 pounds across a span of a meter or two with precision and speed requires quite fancy control actuators, which cost a lot of money. If that weren't the case, there'd be a whole lot of more robots in the world :-)

    Answering a question about stepper motors is impossible without knowing exactly how fast you need to actuate the load, and with what precision, which in turn answers the question of how much gearing you need (which in turn needs gearboxes!)
    Also, steppers may be OK, if you can find a good way to automatically "home" them, but for fast, accurate actuation, you may end up needing servo motors instead, which adds the cost of position sensors.

    I'm assuming you know how to write software. If not, then ... you're unlikely to find a controller that get you where you need to go simply and cheaply, as this is a very specialized application.

    To "control" all of this, you'd need to use a microcontroller of some sort, that talks to USB to the host. If you want to use MIDI, then a microcontroller that easily lets you emulate a MIDI device would help; the Teensy 3.2 or 3.5 would be a good choice. Talk USB MIDI to the computer, and actuate the stepper controllers through the pins on the output. You'll need at 3 pins per actuator (zero, step, and direction) so whether to go with 3.2 or 3.5 depends on how many actuators you need.

    If you made slight changes, so that the arms are in "SCARA" configuration (vertical/gravity load is taken up by the joints) then you could probably drive that PVC with affordable servomotors like the Robotis MX-64 or XM-430. To talk to those, you can use a USB2AX or USB2Dynamixel straight from a laptop, but you'd have to speak Dynamixel protocol, rather than MIDI.

  3. Re: Drum robot ... HELP

    Quote Originally Posted by jwatte View Post
    Neat! What are you using as rotating bushings/bearing/hinges?

    Won't multiple Bowden wires interfere with each other when they overlap in space?

    I don't understand how air pistons would strike anything -- are you hooking them up as "muscles" across some hinge joint? I'm not sure air pistons are the best choice for fast, accurate motion -- there's some risk you'll punch through the skin of the drum!

    In general, 99% of these kinds of projects end up failing because of cost. It turns out, moving 5 pounds across a span of a meter or two with precision and speed requires quite fancy control actuators, which cost a lot of money. If that weren't the case, there'd be a whole lot of more robots in the world :-)

    Answering a question about stepper motors is impossible without knowing exactly how fast you need to actuate the load, and with what precision, which in turn answers the question of how much gearing you need (which in turn needs gearboxes!)
    Also, steppers may be OK, if you can find a good way to automatically "home" them, but for fast, accurate actuation, you may end up needing servo motors instead, which adds the cost of position sensors.

    I'm assuming you know how to write software. If not, then ... you're unlikely to find a controller that get you where you need to go simply and cheaply, as this is a very specialized application.

    To "control" all of this, you'd need to use a microcontroller of some sort, that talks to USB to the host. If you want to use MIDI, then a microcontroller that easily lets you emulate a MIDI device would help; the Teensy 3.2 or 3.5 would be a good choice. Talk USB MIDI to the computer, and actuate the stepper controllers through the pins on the output. You'll need at 3 pins per actuator (zero, step, and direction) so whether to go with 3.2 or 3.5 depends on how many actuators you need.

    If you made slight changes, so that the arms are in "SCARA" configuration (vertical/gravity load is taken up by the joints) then you could probably drive that PVC with affordable servomotors like the Robotis MX-64 or XM-430. To talk to those, you can use a USB2AX or USB2Dynamixel straight from a laptop, but you'd have to speak Dynamixel protocol, rather than MIDI.
    Thanks for the reply,

    Weirdly, I have made the hinges in the pvc so that they slide over each other with a little bit of grease and they seem to not need any kind of bearings. They pretty much spin perfectly and don't grind at all.

    The elbows and wrists will be the method of striking the drums, using a simple piston to push and pull like a tendon inside the elbow and outside the wrist.

    The joints move in a couple of weird directions. The first shoulder (the pieces in the center of the picture with the Ts close together both rotate left and right around the center rod and the second part (the Ts at the far ends of the picture) move up and down on their bones. So I really only need them to move between 15 and 180 degrees in either direction in large steps. Think of moving your arm from your waist height to putting it over.your head or moving your elbow from in front of you to your left or right. Ideally they won't need to be super accurate, considering anywhere close to the center of an 8 inch circle is a good hit. As for speed, they'd need to move up and down in about 1/4 of a second at the fastest I could ever imagine using them. The extra two arms will cover the movement needs a drummer would usually use speed to cover. So I'm not sure how to figure that.

    As for the bowden wires, I've got them configured in a way that they can be run down to one control box and the wires don't interfere with one another. I home made a bunch of them and they have bench tested really well so far. 4mm od, 2.5mm id air hose, with a double ended 4mm quick connect and some 200lb test fishing line seems to move them from nearly any position so far. It's a matter of motors able to pull them. I figure they'll feed down to a simple wheel to pull them 90 degrees on direction and 90 the other at most. I'd post pictures but I haven't put them all together completely yet, I'm still figuring out motor space first.

    Programming ... that'll be a tough one. I'm a quick learner though, and I do know SOME code, but not much. I do realize I'll have to program every single movement of his playing, but it'll be worth it. Lol.

    I've been mostly winging this project so far, and I've cobbled together everything I've tried from other weird sources like the igus robot arm and compressorhead music videos.

    I probably need lots of help with this, mental and actual, but I'm determined to do it. Thanks again for the reply and the help so far.

  4. Re: Drum robot ... HELP

    Oh missed one in there ... if you count the piston working his wrists, elbows, and feet ... he'll have 20 actuators all together. 4 per arm, 2 in the head, and one in the foot. 10 motors and 10 air compression.

    I might be over complicating this. Lol

    I'm basically going for a cheaper and smaller version of this https://youtu.be/qKAWBNl4MeA
    Last edited by HiMM; 2 Weeks Ago at 07:33 PM.

  5. Re: Drum robot ... HELP

    I'm basically going for a cheaper, lighter version of this: https://youtu.be/qKAWBNl4MeA

    Mine will have 10 motors for positioning and 10 air piston for striking (elbows, wrists, and feet)

  6. Re: Drum robot ... HELP

    I'm probably rambling now, but I have five of the ten joints rotating horizontally ... using a SCARA set up, how would you get vertical lift on the arms? Would I have to add some kind of gear box to move the horizontal motion to vertical, like a crown gear or something? Even then how would it carry the weight?

  7. #7

    Re: Drum robot ... HELP

    I have made the hinges in the pvc so that they slide over each other with a little bit of grease
    PVC bushings, then! That will work, as long as you don't put too much sideways load/torque on them.

    using a SCARA set up, how would you get vertical lift
    You don't. SCARA arms typically have a separate mechanism for lift, such as a ball screw/linear actuator. But for drumming, you can position the snare and toms along one vertical axis, and the hi-hat and cymbals along another vertical axis, and you only need sideways motion, plus striking.
    If you don't want to compromise like that, and want the "human" set-up, then you do need some lift, which in turn turns into a speed-and-torque limited assembly, which may be expensive to actuate.

    For 20 actuators, you'd need 60 pins of control, so you'd actually need multiple microcontroller boards, OR you need to use some kind of serial bus, where there's a small microcontroller driving each separate actuator (or a small cluster of them.)
    Couple the need to not punch through the skin of the drums, with the need to drive lots of actuators, and it's starting to look a lot more like a servo network (Dynamixel bus, or CAN bus, or RS-485 bus) and less like simple stepper drivers ...

    I'll be really interested in seeing how it goes! (And how it sounds :-)

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •