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Re: how much equipment needed for robot arm control?

by kgraf on Thu Feb 07, 2013 4:14 pm

We have more or less decided to get digital servos? Do you recommend a servo
control board? We are considering adding a rotating elbow, so we might have
7 servos to drive.
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Thu Feb 07, 2013 6:39 pm

I don't have any recommendations there. My experience with digital servos is limited.
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Re: how much equipment needed for robot arm control?

by kgraf on Fri Feb 08, 2013 10:21 am

https://www.adafruit.com/products/81
2 connections for 5V 'hobby' servos connected to the Arduino's high-resolution dedicated timer - no jitter!

Do you sell anything that can handle more than 2 servos?
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Fri Feb 08, 2013 11:28 am

Do you sell anything that can handle more than 2 servos?

Will 922 be enough? :wink: https://www.adafruit.com/products/815
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Re: how much equipment needed for robot arm control?

by kgraf on Fri Mar 22, 2013 11:07 am

6 weeks now and we still haven't gotten our servos. we cancelled and re-ordered this week.
Is it possible to create an additional IC2 connection into the arduino mega in addition to pins 20 and 21? we have 3 invensense gyros that don't have SPI - they call sda and scl TWI two wire interface instead of IC2. The gyros only have two selectable addresses. the gyros are invensense mpu-6050
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Fri Mar 22, 2013 12:09 pm

There is a link to a software i2c library here: viewtopic.php?f=25&t=13722
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Re: how much equipment needed for robot arm control?

by kgraf on Sun Mar 24, 2013 5:31 pm

A quick search of the XMega_Manual for TWI and I found
"up to four I2C and SMBUS
compatible two-wire serial interfaces (TWIs);"

Is there an xmega mcu available that has 3 or 4 I2C or TWI connections?
the 2560 board (from adafruit) I am currently using has only 1 at pins 20 and 21.

I do find some two TWI mcu's available
ATxmega256A3
ATxmega192A3
ATxmega128A3
ATxmega64A3
and another reference to 4 TWI
http://www.atmel.com/products/microcont ... xmega.aspx
High Integration — XMEGA devices integrate AES and DES crypto modules, up to 32 PWM outputs, 8 UART, 4 TWI (I2C) and 4 SPI channels, a CRC generator module, and more.
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Re: how much equipment needed for robot arm control?

by kgraf on Wed Mar 27, 2013 3:38 pm

asked and answered:

the ATxmega128A1U has 4 TWI on ports C D E F
pins 15 16 25 26 35 36 45 46

I do have another question:
Our digital servo and analog servo both test fine on a test code - rotate 180 degrees cw and ccw
then we hook the sensor to drive the analog servo and it works fine
then we hook the sensor to the digital servo and nothing happens
we check the signal on a scope and the signal is fine

does this sound like any common problem with analog compared to digital servo performance?
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Re: how much equipment needed for robot arm control?

by kgraf on Wed Mar 27, 2013 6:48 pm

asked and answered again!

We resolved the issues it turned out that the solar motors have a lower baud range than the arduino software assumes. The motors still go from 0 to 180 degrees but the difference in the the baud rate is lower. We got the motors to react properly to change in sensor readings so we just need to remember this when fine turning the code.
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Re: how much equipment needed for robot arm control?

by kgraf on Mon May 06, 2013 7:46 pm

concluding post:
thank you for your responses and info,
the project was moderately successful considering we only worked on it for 4 weeks because of a 7 week delay in getting servo motors. Anyone interested in the project can view the course required documentation at
http://www.eecs.ucf.edu/seniordesign/fa2012sp2013/g10/
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Re: how much equipment needed for robot arm control?

by adafruit_support_bill on Tue May 07, 2013 5:22 am

This has to be one of the longest running threads on the forum. Thanks for posting your results! :)
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