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My project involves creating an arduino midi controller that corresponds each note to a different servo or stepper motor, causing it to rotate a fixed angle. However, the difficulty I'm facing is that I want to ultimately cover 30 different notes, so I need to control 30 motors at once. From the research I've done so far (I am very much a novice), I doubt that I can make this work with one arduino, so any suggestions would be appreciated. Thanks.

EDIT (further explanation):

I want to place the motor (attached to a rubber or foam wheel) at the front of a row of rubber balls on a slope, and act essentially as a dispenser, so that it holds the balls back when motionless, and can rotate a certain angle to dispense a ball when signaled (I don't need it to generate a lot of force, but I'd like it to dispense fairly quickly). My only concern with servos is that I have not seen any servo with an axle to attach a wheel to. Other than that, I'm open to either servos or steppers, whichever would simplify the circuitry and electronics needed.

I've considered using the servo horn as an open/close dispenser instead, but I think that the balls would not roll forward fast enough (or at all, maybe, with rubber) if I don't use a wheel to push each ball forward away from the balls behind. I'll know for sure after I've tested this, but I'm betting that using the servo horn won't work.
« Last Edit: January 01, 2014, 01:29:36 pm by WorldWiz » Logged

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No problem with getting it to work with one arduino. You ether need a mega or a UNO with some external chips. Decide on if you want to use a stepper or a servo first then you can get solid advice.
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I currently have an UNO R3 in the mail, and I think I'm going to go with steppers. I'll be moving a light load briefly with each motor, and I can't imagine needing more than 100 rpm max. Most importantly, I want to keep the electronics/circuitry as simple as possible, and I prefer the lower costs too. I saw another thread that discussed multiplexing 50 steppers, so is that a good direction for me to go? Or does my need for a midi controller complicate things more? Thanks.
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You could use Adafruit's servo shield (http://www.adafruit.com/products/1411).  However, you'd need two of them as each one can control 16 servos. At least one of them you'll need to make stackable, which means purchasing stackable headers as well as 90 degree headers for the servo pins. You can look at my post for an example (second image) at http://solderspot.wordpress.com/2013/12/19/adafruits-servo-shield/.

If you need to use stepper then you are going to have a much bigger task. I'd recommend using servos if you can.

PM me if you need more info.

All the best.
« Last Edit: January 01, 2014, 06:02:03 am by solderspot » Logged


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Thanks for the advice. One thing I should add (if it makes a difference) is that if I go with servos, I will need to use the continuous rotation motors rather than the position control motors. They would need to rotate somewhere between 90 and 180 degrees each time (I'm still waiting for some materials to arrive in the mail to do some testing), but always in the same direction. Would servos still be preferable to steppers in this case? Thanks.
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I will need to use the continuous rotation motors rather than the position control motors.

Rotating continuous rotation servos to any specific position will be difficult.
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I don't think I need much positional precision. I realize now it would be more helpful to explain exactly what I need my motors to do. I want to place the motor (attached to a rubber or foam wheel) at the front of a row of rubber balls on a slope, and act essentially as a dispenser, so that it holds the balls back when motionless, and can rotate a certain angle to dispense a ball when signaled (I don't need it to generate a lot of force, but I'd like it to dispense fairly quickly). My only concern with servos is that I have not seen any servo with an axle to attach a wheel to. Other than that, I'm open to either servos or steppers, whichever would simplify the circuitry and electronics needed. Thanks.

P.S., I've considered using the servo horn as an open/close dispenser instead, but I think that the balls would not roll forward fast enough (or at all, maybe, with rubber) if I don't use a wheel to push each ball forward away from the balls behind. I'll know for sure after I've tested this, but I'm betting that using the servo horn won't work.
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is that if I go with servos, I will need to use the continuous rotation motors rather than the position control motors.
Using a continuous rotation servo in effect removes all the servo bit from it and in effect just leaves you with a DC motor. Controlling the position is not possible unless you add back the feedback mechanism you ripped out in the first place.   
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You could use a servo to move a two port gate to allow the balls to be released one at a time.
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Is it possible to attach a disc with a circle, or rather an arc, cut out of its side the radius of the balls. When the servos is in the 0 degree position the next ball rolls into the cut slot. Make the servo go quickly to 180 so the ball in the slot is shot forward. Then go back to 0 to set up the next ball.

The servo would need to be mount at the correct angle and height above the balls to work properly. Maybe it needs to be made of flexible material, like rubber. Depending how you set it up you'd probably don't need the full rotation of the servo.
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Is it possible to attach a disc with a circle, or rather an arc, cut out of its side the radius of the balls. When the servos is in the 0 degree position the next ball rolls into the cut slot. Make the servo go quickly to 180 so the ball in the slot is shot forward. Then go back to 0 to set up the next ball.

That sounds pretty good. My one concern would be the possibility that after the servo rotates to 180, the next ball in line would roll forward to some extent and cause the servo to stall when it tries to return to 0. However, now that I think about it, it's also possible that even if the next ball rolls forward a bit, the servo would just smoothly roll it back to the original position as it returns to 0. As soon as I get my materials in the mail, I'll try constructing a prototype of this setup, and post an update. Thanks, solderspot!
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BTW WorldWiz, as you are controlling so many servos and you'll probably need to be able to control the speed of each, you might be interested in these two libraries I've recently written:

https://github.com/solderspot/SS_Servorator
https://github.com/solderspot/SS_ServoTrim

Not sure what your programming level is or if you have installed libraries before but these might save you some time.

I created the libs as I'm working on animating a robotic arm that uses 6 servos and I needed speed control. I'm using Adafruit's 16 channel servo shield which I've written about in this blog post: http://wp.me/p493sy-2u. It might also be something you are interested in using as you can stack two of them to get the 30 servo controls that you need.

Pololu has an array of servo controller boards too: http://www.pololu.com/category/12/rc-servo-controllers

I'm sure there are other options but those are the two I know about.
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Thanks, solderspot. Initially, as I test and tweak, I'll be varying the speed, but in my final product I'll be keeping the speed fixed. I'll definitely take a look at your posts on adafruit's servo shields, though. Thanks again.
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This article I found on carnegie mellon's "vibratron" (http://blog.arduino.cc/2011/04/26/vibratron-robot-plays-out-midi-as-steel-balls/) seems like it'd fit my needs very well, so I'd like your opinions on a few things. Specifically, I'd like to know if I should get an arduino mega, which the article says allowed the creators to avoid having to multiplex I/O lines (would that be something I'd need to do?). Also, they used the midi shield from sparkfun (https://www.sparkfun.com/products/9595), so would I just stack that with a couple servo shields, or does my use of servos rather than solenoids complicate things? Thanks.
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Ah, I understand now what you are trying to build.

You'll want to the able to dispense balls from the same channel very rapidly and reliably. I think maybe a step motor or solenoid might be more appropriate. But this is way beyond my experience level.  You need a good dispensing mechanism. Not sure if servos are going to be fast enough or accurate enough.

I'm very curious how you will build this.
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