Running 6 Servos from CBC

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ekmanb
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Need suggestions for running more than 4 servos from a CBC V2.

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Jeremy Rand
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If you can find a servo controller with a serial interface, you could plug that into the CBC's Create port. Alternatively, if you're willing to modify the CBOB firmware, you could probably rig something up using the sensor PWR/GND pins plus a GPIO pin to drive a servo. (I suspect that the former would be easier.)

Let us know what you find out!

-Jeremy Rand
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AdamF
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I'm not sure about servos, but it is easily possible to drive more than 4 motors from a CBC. You can plug a motor diagonally across the sensor ports. If you need to turn it off and on, you can easily put it in series with a touch sensor. My team did this to control 4 servos and 5 motors from one CBC this year. I will try to post a picture that explains how it works.

Theoretically you could use 1 servo to control 8 motors unidirectionally via 8 touch sensors, plus the 4 bidirectional motor ports already available. Not sure how this would affect the battery life though.

This works because each sensor port has a +5V reference line, a reference ground, and a signal line. Botball motors run on 5V easily.

Adam Farabaugh
Hampton High School

Jeremy Rand
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Wow, that's definitely in the hacker spirit, nice idea!

In 2007, Farz Hemmati and I got motors to run off the sensor ports by using the data pin as a digital output (setting to 1 shorts it to PWR, setting to 0 shorts it to GND). The XBC could sink a decent amount of current in the data pins without any problem; it wasn't nearly as fast/powerful as the actual PWR/GND pins, but Farz's team successfully used it to release a claw at the end of the game.

Disclaimer: using data pins to power stuff is a very bad idea in principle, and Farz and I were lucky that the XBC can handle it. We haven't tried it on the CBC, and we take no responsibility if you fry a digital pin by attempting this.

-Jeremy Rand
Senior Programmer, Team SNARC (2012-2013), Norman Advanced (2010-2011), Norman HS (2008-2009), Norman North (2005-2007), Whittier MS (2003-2004)
2012-2013 VP of Tech, 2011 President, Botball YAC (2009-2013)
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KIPR Matthew
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If you are running two servos to the same position at the same time (think arm) you might look into a servo splitter cable. It is a Y shaped cable that splits the signal to two servos. You might have to rig together an external battery pack to handle the power requirements, especially if they are high torque servos.

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Novatech
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Hello!

I am planning to start a training for group of students in a school, how can i get help for this

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Jeremy Rand
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@KIPR Matthew, why not just split the servo's PWM pin, and use the sensor PWR/GND pins to power the 2nd servo? Would that reduce the need for an external battery pack?

-Jeremy Rand
Senior Programmer, Team SNARC (2012-2013), Norman Advanced (2010-2011), Norman HS (2008-2009), Norman North (2005-2007), Whittier MS (2003-2004)
2012-2013 VP of Tech, 2011 President, Botball YAC (2009-2013)
Mentor, Alcott and Whittier MS

Jeremy Rand
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@Novatech, you should probably start a separate thread for that discussion. Welcome to the Botball Community!

-Jeremy Rand
Senior Programmer, Team SNARC (2012-2013), Norman Advanced (2010-2011), Norman HS (2008-2009), Norman North (2005-2007), Whittier MS (2003-2004)
2012-2013 VP of Tech, 2011 President, Botball YAC (2009-2013)
Mentor, Alcott and Whittier MS

suman
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I was using the USB port hub as an analogy for those who might not understand how parallel circuits work. In layman's terms, they both seem like they would be quite similar.

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