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Author Topic: Power circuit(s) for $50 robot  (Read 1139 times)

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Offline dattTopic starter

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Power circuit(s) for $50 robot
« on: March 21, 2009, 03:50:49 PM »
I recently got all the parts for the robot in the mail, and I am about to start building. I figured to make the circuit
board first so I can really see how big it will be for the chassis, and my question is about the power circuits.

First in the tutorial, what I understand is you can choose either a battery pack (which I have, 6v/2300mAh) OR the plastic AA battery case. I also read the Batteries section, which says you should always have a separate power circuit for servos and control circuitry.. So which way is the way to go? Also there was a forum link from the tutorial to a post (lost the link) where the poster attached a layered schematic (50$ robot.pdf). I will attach this here again for anyone who hasn't seen the original post. In this schematic, it calls for attaching a 9v battery (which seems like it could be less as long as it doesnt dip below 6ish) to the 5v voltage regulator, and a 4xAA battery pack is used as well. The regulated 5v goes to the electronics, but the ground wire from the regulator goes to the servo "power grid". The positive lead from the 4xAA battery pack goes to the servo power grid, and the negative goes to the electronics. Shouldn't the ground wires be reversed?
So...

So my question is basically how do I correctly wire the power circuit(s)?

Thanks

Offline SmAsH

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Re: Power circuit(s) for $50 robot
« Reply #1 on: March 21, 2009, 05:01:18 PM »
the $50 robot can be run off one battery which is the way the tutorial says isnt it? the reason some people like the two battery version is because if they are running a fair few servos they will most likely create electrical noise, hence the big cap to help with this.
and what do you mean about "shouldnt the ground wires be reversed"?? this circuit has a common ground meaning all grounds are connected. please explain further what you are asking?
and your last question:
to have one battery have the battery directly connected to the servo bus and the regulator connected to the sensor bus/mcu.

to have two batteries have one battery powering the servo bus and another powering the regulator which in turn powers the mcu/sensors.
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Offline dattTopic starter

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Re: Power circuit(s) for $50 robot
« Reply #2 on: March 21, 2009, 05:21:37 PM »
OK, I guess it doesn't really matter which ground wire goes where as long as they are all connected together somehow.

How many servos (or how much load in general) would it take to make a significant enough of an effect on the electronics that I would want to have separate batteries? If I go from the battery pack to the servos directly, and also from the battery pack to the 5v regulator then to the electronics, would the regulator clean out any noise? Is it possible to create two paths of "separated" power using the same battery source, so that no one path can interfere with the other?

Thanks

Offline SmAsH

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Re: Power circuit(s) for $50 robot
« Reply #3 on: March 21, 2009, 07:08:28 PM »
the main way people smooth out the noise is with a cap (like the 220uf). if you wanted to create a separate path from the battery they will still be connected as they both will touch the terminals although you may be able to do this with a diode, not sure though. im not sure how many servos would make noticeable spikes but generally you would be fine with a few (1-6) as long as they're not high powered or have crazy power needs.
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Offline Admin

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Re: Power circuit(s) for $50 robot
« Reply #4 on: March 25, 2009, 01:48:00 AM »
Quote
I also read the Batteries section, which says you should always have a separate power circuit for servos and control circuitry.. So which way is the way to go?
Quote
Is it possible to create two paths of "separated" power using the same battery source, so that no one path can interfere with the other?
What I mentioned in the battery tutorial about separate batteries isn't really true any more, as electronics are much more stable now than back in the day.

You'd only need to separate them if:
motors require much more voltage than electronics
motors place significant noise onto the power line

For small servo based robots, separate power supply typically isn't needed. Unless of course if you use the Arduino, where you need 7V+ for electronics, and 6V or less for servos. ;D

 


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