Arduino Uno w/ Motor Shield power questions

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adafruit_support_bill
 
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Re: Arduino Uno w/ Motor Shield power questions

Post by adafruit_support_bill »

So the motor assembly goes like this right:

Encoder on back of motor -> dual shafted motor -> gearbox on output shaft of motor-> our fixture
You would want the encoder on the output of the gearbox to measure the actual position. That removes the backlash from the positon equation.
So if I can get them in time I will be switching over to a motor with 0.9 Amps/Phase with 0.45 degrees per step, no gearbox needed
Going with a direct drive solution is even simpler. :)
If I am not mistaking two motors with 0.9 amps per phase, each equipped with an encoder and 4 lead wires, is compatible with Arduino Uno + Motor shield and would greatly reduce the cost of my project. I will still be equipping encoders, but in this case it simply counts the steps and thats all that matters right?
That should work - assuming you piggyback the L293D's to handle the 0.9A.

motorman12
 
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Re: Arduino Uno w/ Motor Shield power questions

Post by motorman12 »

So I was able to get the motors for the direct drive solution... so that's something!


As far as the encoders go, they have 5 pins coming out, 2 of which are for +5v and ground.

Do the remaining 3 pins go to the digital I/O's on the motor shield? Since there appear to be 13 digital I/O's I should have no problem connecting both encoders (6 pins), and I can put the 5v and ground pins in those two rows below the L293D.

Thanks again for all your help, I can safely say I have never recieved so much support before... this has me wanting to pursue a project of my own interest (instead of this boring contact lens business) after all of this is done :D

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Re: Arduino Uno w/ Motor Shield power questions

Post by adafruit_support_bill »

As far as the encoders go, they have 5 pins coming out, 2 of which are for +5v and ground.
Hmmm. Most that I know of have 4 pins: Power, Gnd, 'A' and 'B'. The A and B are quadrature encoded and can connect to digital pins.

The extra pin could be an index pulse which would be a good way to reference your zero position.

There is a nice little tutorial on encoders and quadrature encoding over at the Arduino Playground.http://www.arduino.cc/playground/Main/RotaryEncoders

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Re: Arduino Uno w/ Motor Shield power questions

Post by motorman12 »

the 5th pin as you said is an index pulse, I'll have to look more into that. We definitely need a good zero position reference so that sounds perfect.


Thanks for the tutorial I will check it out!

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Re: Arduino Uno w/ Motor Shield power questions

Post by motorman12 »

I am back yet again! Do you have any recommendations for applying a heat sink to the L293D? I will be piggybacking my motor shield soon but I'm going to put some heat sinks on the bottom L293D's just to be safe, because I have read/heard about some heat issues that arise from piggybacking.

Also these motors require a 24 VDC power input, will this cause any issues? I see that the motor shield is designed to run from 4 V- 36V, but does increasing this input voltage effect the system negatively?

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Re: Arduino Uno w/ Motor Shield power questions

Post by adafruit_support_bill »

24v should be no problem for the shield. Just be sure to remove the power jumper (next to the external power terminals) so that the 24v does not feed back into the Arduino supply :!:

There are clip-on heat-sinks for DIP chips. You would have to install them on the top-chips before soldering them to the bottom chips (use a dab of thermal compound on all mating surfaces). There are also glue-on sinks you can just attach to the top chip.

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Re: Arduino Uno w/ Motor Shield power questions

Post by motorman12 »

Could you post some examples of clip-on/glue-on heat sinks? I will probably go with the glue on option (if necessary) because I'm going to piggyback the chip now and don't have any clip on sinks ATM.

Thanks!

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Re: Arduino Uno w/ Motor Shield power questions

Post by adafruit_support_bill »

http://www.aavidthermalloy.com/product- ... d_depth=16
Select "DIP" in the "Select Package" option.

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Re: Arduino Uno w/ Motor Shield power questions

Post by motorman12 »

Alright so I've got everything and it works (for the most part anyways)!

I owe the majority of the success of this project to the great support offered on this forum, so thanks a lot! I even set up a cool GUI in MATLAB that makes controlling the motors very easy.

I do have one more question though:

I have a variable DC power supply unconnected and turned up to 24V. I turn it off, and plug it in to the Arduino EXT power terminals and then turn it on. Regardless of if it displayed above 9V prior to being connected to the board, it is unable to show me anything above 9V when connected to the Arduino board

Is this a problem with my power supply or am I doing something wrong? The power supply is pretty old so I wouldn't be surprised. The motors are still controllable and move and all of that, but I suspect I'm either missing out on some torque or the readout on my power supply is wrong.

What do you think?

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Re: Arduino Uno w/ Motor Shield power questions

Post by adafruit_support_bill »

Do you have the power jumper removed? You MUST remove that when using an external supply to decouple it from the Arduino supply.

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Re: Arduino Uno w/ Motor Shield power questions

Post by motorman12 »

Yes the power jumper is removed before attaching the power supply.

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Re: Arduino Uno w/ Motor Shield power questions

Post by adafruit_support_bill »

It could be that the power supply just can't supply enough current and sags under load.
I take it you have successfully run motors using different supplies.

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Re: Arduino Uno w/ Motor Shield power questions

Post by motorman12 »

Well I am trying a different supply at the moment, and it seems to be supplying more current than I want (when at the 24V). In order to stay around 0.9 amps (the listed amps/phase for the motors I've chosen) I can only give 7.2V from the power supply (while the motors are supposed to get 24 VDC).

The current values get up close to 3 amps when at 24V, and the l293d's get hot really fast at this current so I turned the supply off before trying to use the motors.

I'm thinking it might have to do with the way I wired the motors? It's a bipolar 4 lead motor

Red A Blue A' Green B Black B'

How does this translate to the motor driver? I just made sure I put the pairs together (so red/blue in the two terminals for M1, and green/black in the two terminals for M2... same for M3/M4)

Does the order matter?

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