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Offline Jon_WayneTopic starter

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Robot Power
« on: March 18, 2007, 11:34:27 PM »
Im a beginner and was wondering if my schematic appears to be ok, this is how i intend on wiring my robot. please submit feedback and let me know if im doing something wrong

http://i60.photobucket.com/albums/h28/jon_w_grimaldi/robotPower.jpg
« Last Edit: March 18, 2007, 11:36:19 PM by Jon_Wayne »

Offline hgordon

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Re: Robot Power
« Reply #1 on: March 19, 2007, 08:46:26 AM »
I would suggest wiring all of the ground connections together (charger, battery, microcontroller) -  then you only have to switch the +V side of your power.

How are you powering the microcontroller ?  You could use a voltage regulator to source power from the motor supply.
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Offline Jon_WayneTopic starter

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Re: Robot Power
« Reply #2 on: March 19, 2007, 09:29:39 AM »
im using a seperate 9v battery and regulator for simplicity for now, ill probably end up switching later on though.

Offline hgordon

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Re: Robot Power
« Reply #3 on: March 19, 2007, 10:33:25 AM »
No problem - in any case, I would suggest coupling all the grounds throughout the circuit, since they will probably couple through the motor controller anyhow.
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Offline Jon_WayneTopic starter

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Re: Robot Power
« Reply #4 on: March 19, 2007, 11:37:06 AM »
« Last Edit: March 19, 2007, 12:20:10 PM by Jon_Wayne »

Offline hgordon

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Re: Robot Power
« Reply #5 on: March 19, 2007, 03:40:00 PM »
Sure, but do it before the switch (i.e. ground the negative terminals of the battery and DC supply), and then you only need to switch the + voltage.  Also, make certain to tie this ground to the processor ground.
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Offline Jon_WayneTopic starter

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Re: Robot Power
« Reply #6 on: March 19, 2007, 09:50:42 PM »
ok, i kinda understand now, but the one thing that confuses me is the switching of the + voltage, sorry if this is a stupid question but doesnt current flow - to + ? and also, my robot will be almost entirely plastic, what should i ground the battery and the processor to?

Offline trigger

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Re: Robot Power
« Reply #7 on: March 19, 2007, 11:03:36 PM »
ok, i kinda understand now, but the one thing that confuses me is the switching of the + voltage, sorry if this is a stupid question but doesnt current flow - to + ? and also, my robot will be almost entirely plastic, what should i ground the battery and the processor to?

By convention, current flows + to -. 
There are 10 kinds of people in this world: those who can read binary, and those who can't.

Offline hgordon

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Re: Robot Power
« Reply #8 on: March 19, 2007, 11:59:37 PM »
You'll just have to run wires to connect all the grounds.   

Having a ground plane is a particularly good thing if your robot has a wireless connection - here's a starting point for reading about ground planes - http://en.wikipedia.org/wiki/Ground_plane
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Offline Jon_WayneTopic starter

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Re: Robot Power
« Reply #9 on: March 20, 2007, 01:25:14 AM »
So basically run a wire from the neg terminal of the 12v(motors) battery to the neg terminal of the 9v(processor)? sorry if im being a pain. i read a bit about the ground plane and i dont think i need that, that was talking about antennas and im pretty sure im not there yet.
« Last Edit: March 20, 2007, 01:27:22 AM by Jon_Wayne »

Offline dunk

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Re: Robot Power
« Reply #10 on: March 21, 2007, 03:26:12 PM »
hi Jon,
so don't worry too much about a "ground plane" or anything line that.
the important point is that all the negative terminals on all the different power supplies are connected together.
(for your purposes here, ground just refers to the negative power terminal.)

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Offline Jon_WayneTopic starter

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Re: Robot Power
« Reply #11 on: March 21, 2007, 05:13:21 PM »
thanks dunk. i was reading up on electronic theory and i still dont understand why i need a ground, granted, ill put one anyway but i just dont get why. the robots plastic so im not to concerned about elec. shock.

Offline dunk

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Re: Robot Power
« Reply #12 on: March 21, 2007, 06:30:35 PM »
so "ground" is just another name for the wire connecting the negative terminals.

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Offline gamefreak

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Re: Robot Power
« Reply #13 on: March 21, 2007, 07:34:19 PM »
Quote
Quote
ok, i kinda understand now, but the one thing that confuses me is the switching of the + voltage, sorry if this is a stupid question but doesnt current flow - to + ? and also, my robot will be almost entirely plastic, what should i ground the battery and the processor to?


By convention, current flows + to -. 

Bah i hate conventions, last year we "learned" about electricity in science class and the teacher taught the current flowed from + to -, since i already knew otherwise it confused the heck out of me, so bah to conventions, they are worthless.

and the point of grounding is:
Quote
A power ground serves to provide a return path for fault currents and therefore allow the fuse or breaker to disconnect the circuit. The power ground is also often bonded to the house's incoming pipework, and pipes and cables entering the bathroom are sometimes cross-bonded. This is done to try to reduce the voltage between objects that can be touched simultaneously. Filters also connect to the power ground, but this is mainly to stop the power ground carrying noise into the systems which the filters protect, rather than as a direct use of the power ground. See: NEC (Article 250).

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Offline Tsukubadaisei

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Re: Robot Power
« Reply #14 on: March 22, 2007, 05:07:07 AM »
One of the biggest problems in any electric/electronic circuit is noise. Noise can be an unstable current and the ground helps by taking or adding "extra current". Do like the others said but I think before you connect all the negative wires to the ground it is good connecting a resistor between the point where the wires are connected and the ground.
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Offline trigger

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Re: Robot Power
« Reply #15 on: March 22, 2007, 08:25:37 AM »
Bah i hate conventions, last year we "learned" about electricity in science class and the teacher taught the current flowed from + to -, since i already knew otherwise it confused the heck out of me, so bah to conventions, they are worthless.

Actually, in some materials, current really does flow from + to -.  Also, you can think of current as the movement of holes, rather than the movement of electrons, and holes go from + to -.  And to take it to another level, it's not the movement of a hole from the positive to negative terminal that creates current, it's a wave of holes "bumping" into successive holes that create current. 

But you're right--in most materials, the real charge-carrying particles are flowing - to +.  Oh well. :D

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Offline Jon_WayneTopic starter

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Re: Robot Power
« Reply #16 on: March 22, 2007, 10:44:57 AM »
Do like the others said but I think before you connect all the negative wires to the ground it is good connecting a resistor between the point where the wires are connected and the ground.

how do i determine what size resistor i should use? or will any be fine? and i just planned on having a ground wire from neg terminals of both batteries. should i just put a resistor between the two?

Offline Tsukubadaisei

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Re: Robot Power
« Reply #17 on: March 22, 2007, 08:45:29 PM »
From my experience, I would recomend anything between 1kΩ to 10kΩ. I usually ground with 2kΩ and it does fine . So you shouldn't worry very much about that. Just don't use a very big restance like 50kΩ or more because it will  act like an insulator and almost no current will flow and it will not stable the circuit.
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Offline Jon_WayneTopic starter

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Re: Robot Power
« Reply #18 on: March 23, 2007, 12:29:06 AM »
alright, got that all figured out now. my next question would be how do i put a heat sink on the h-bridge/motor controller? could i just rig it on there any old way just making sure it touches as much motor driver as possible?? i really dont want to use a fan cause thats just wierd for a robot.

Offline trigger

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Re: Robot Power
« Reply #19 on: March 23, 2007, 08:11:54 AM »
alright, got that all figured out now. my next question would be how do i put a heat sink on the h-bridge/motor controller? could i just rig it on there any old way just making sure it touches as much motor driver as possible?? i really dont want to use a fan cause thats just wierd for a robot.

Use a little bit of thermal grease to stick it on, and you're good to go. 
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Offline sdk32285

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Re: Robot Power
« Reply #20 on: March 23, 2007, 10:29:08 AM »
Thermal grease usually doesn't harden, so vibrations, movements, etc.. will shake it loose.
You probably want thermal epoxy.
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Offline Tsukubadaisei

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Re: Robot Power
« Reply #21 on: March 23, 2007, 11:09:47 PM »
For the heat sink I like the old way, because it is very easy. Get an aluminium rectangular plate. Then take your motor drive and you will notice that those big transistors have a hole or two. Those transistors are the switches for the current that will move the motors, so they are the parts that will get hot. In order to dissipate the heat you should then attach the plate to those transistors by making some holes in the plate and screwing the plate and the transistors together. The heat will be transfered because behind the transistors there are already small heat sinks that in contat with the big one you just attached will cause heat transfer by conduction.
But, honestly, I don't think you need a heat sink for 12v motors. The drive will get warm but not enough to burn itself.

here is a screen that I found of how it should look:

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Re: Robot Power
« Reply #22 on: April 21, 2007, 07:21:00 PM »
(sorry for the late reply, been traveling)

I dont use a ground plane on my circuits, but its useful for cutting down on RF interference if that is a problem for your circuit. I typically just use one long ground bus and connect all my grounds to it. My $50 robot uses my ground bus method.

Quote
alright, got that all figured out now. my next question would be how do i put a heat sink on the h-bridge/motor controller? could i just rig it on there any old way just making sure it touches as much motor driver as possible?? i really dont want to use a fan cause thats just wierd for a robot.

There are heatsinks that can screw onto the big hole on your IC, and other heatsinks designed to just slide right onto your IC. I avoid thermal grease cause it usually reduces the heat transfer rate to your heatsink (trust me on this).

Also, Im confused why you have a 12V battery connected to a 12V power supply. This can cause a problem because batteries change voltage - they are never at a fixed voltage. You should also consider using an LED and not a lightbulb (more efficient!).

This power circuit I use might help you (at the very bottom of the page):
http://www.societyofrobots.com/schematics_powerregulation.shtml

The switching regulator is optional . . .

Offline Jon_WayneTopic starter

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Re: Robot Power
« Reply #23 on: May 30, 2007, 08:13:35 PM »
its funny you mentioned the led cause i figured it out the hard way. i did end up switching. my bot has been in the the basement for awhile, havent worked on it cause of work and school, but should be able to work on it over the summer. saw the 100 dollar contest and think i might enter.

 


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