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comanche



Joined: 22 Feb 2007
Posts: 22
Location: melburn


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Need help with wiring.

As you know from my previous thread, im building a tracked axe wielding robot for VCE.

Although im a bit puzzled with wiring the motors.
Im going to have 2 battery packs on board but can figure out how to seperate where the power goes. I want the axe motor to run on 12v, and everything else to run on 7.2v.



How would i wire that all together?

Post Tue Feb 27, 2007 9:18 pm 
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Spockie-Tech
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Joined: 31 May 2004
Posts: 3160
Location: Melbourne, Australia


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Connect the bottom right 3 boxes in your diagram.

Thats about as much detail as can be given right now based on your "Axe Control" and "Chip" (for your speed controller) diagram.

Presumably your Axe control will be some form of relay h-bridge or reversible electronics speed controller (ESC). your 12v battery will connect to it, and your "chip" will be some other sort of two-channel reversible speed controller. your 7.2v battery would connect to that.

Although I dont like your chances of finding a suitable reversing dual channel speed controller that runs well at 7.2v. Most Hobby Car ESC's only go in one direction, or have a fixed power reverse, or a reversing delay or something that screws up using them for a robot.

You could maybe make a relay hbridge and put a one directional hobby ESC underneath it, but you will still need mixing etc.

And your Axe ESC will need to be able to handle the stall current of your weapon motor, which will proably be well above most hobby ESC's as well (unless you are planning on swinging a doorknocker instead of a hammer)

A simple rule to remember when it comes to robots = precise control of high power motors = Big $. There is no way around that that we know of yet.

So First, pick your budget, then pick your motors, batteries and speed controller to suit, then we can help you with wiring diagrams

7.2v is a silly voltage to run any decent size robot on anyway. RC Cars only use it because they're very small and light and cant afford to carry many cells (batteries inside a pack). At that voltage, the tiniest inefficiency (excessive length, poor connection etc) in your wiring will cost you gobs of your power, and your ESCs will get very hot trying to push enough current to make any power in the first place.

12v is a minimum for for most robots, and you will find most of us are running 18-36v in our robots. power is much easier to make with higher voltage. dont choose some cheap 7.2v hobby motors and then try and build the robot around them.
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Post Tue Feb 27, 2007 9:29 pm 
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comanche



Joined: 22 Feb 2007
Posts: 22
Location: melburn


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Thanks for the advice

Ill restate what it is, not a competitive robot. More of a desctruction robot with the ability of a powered axe. Will not go into battle, its mostly all show. Its like the equivalent to a high powered r/c tank.

I didnt really understand the things you said below.

It wont need a relay because the "axe control chip" is the substitute for the turret control on the r/c tank that it was. I will have full forward and reverse axe control.

Im not sure if i want to try connecting all three because im scared the 12v will fry the main chip. It would cost hella much to replace. Everything pretty much working and no need for change (except the axe wiring of course).

I was thinking of wiring them all up and using just one 12v battery, but i think either the battery will run flat too quick, axe would be not at powerful or it may fry the circuit.

If i buy a r/c type rechargeable battery for the axe motor, will it still produce the same amount of energy and duration as the original drill battery? Im only thinking this becuase the drill batter is really heavy and im trying to get it as light as possible.

Post Tue Feb 27, 2007 9:59 pm 
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Glen
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Joined: 16 Jun 2004
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what is the main chip? some form of speed controller?

if so then itll have 2 motor inputs and a battery input (or just 1 motor input if its a single side controller). some have outputs for weapon thatll usually be open collector to ground that can power the relays and what not for an axe.

or you could just use a seperate speed controller for the axe. which is probably a better choice.


quote:
becuase the drill batter is really heavy and im trying to get it as light as possible.


for the energy it provides it is. but every other nicad pack and nimh pack is going to weight the same unless you change to A123 cells where youll save maybe 50% on the weight.. but thats getting quite complex right there if you have trouble wiring the basics lol.

if you can at least provide the docs for whichever controller youve got it might be actually possible to do you up a diagram.

in the very least the switch should be in series with the main power not hanging off the ESC (electronic speed controller).
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Post Tue Feb 27, 2007 10:03 pm 
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Spockie-Tech
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OK, Lets get in the same ballpark here at least.

How big do you think it will be, what sort of weight do you expect it will be (probably double what you think it will be Wink, What sort of things do you want to smash with your hammer ?

If we're talking RC car sized and the ability to beat up leggo, then it will be lots easier. If you want to be able to sit on it and ride it around and make people scared of it, then its a whole different game.

RC cars and Drills are different applications. the power you get out of either usually depends on the $ though. Cheap drills have cheap batteries that wont feed much in the way of high power for long... Ditto RC cars.

Electric Axes require a short (<1 second) very high amperage burst of current to accelerate the axe rapidly.

Try this -

Put a multimeter on the batteries you want to run your axe motor from and watch the voltage. Stall the output shaft of the Axe motor (hold it still with some vice grips or something). Connect the motor to the battery *very* briefly (about 1/2 second - maybe 1 second if things dont get hot quickly) while watching the meter. If the battery voltage drops by more than about ~30% then your batteries are going to seriously limit your axe power because they cant supply sufficient stall current without sagging.

Perhaps you could post some pics of the bits you have so far or a drawing with something for size comparison so I can get my thinking into the right scale ?
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Post Tue Feb 27, 2007 10:11 pm 
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Woody



Joined: 07 Oct 2004
Posts: 202
Location: UK


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I think you could use the turret output command voltage to operate a pair of SPDT 6 volt relays.

Connect your 7.2v battery negative to one side of both 6v relay coils..... attach a diode to each of the remaining coil connections ...connect the diodes so the positive will flow to the relay coils....... and connect your turret wires to them.

Take the COM relay connections (Common contact ) to the axe motor ...... connect one relay to one side of the axe motor and the other relay COM to the other side of the axe motor.

Then

Both NC ( normally closed ) contacts to one pole of the 12v battery and both NO ( normally open ) contacts to the other.


Hope I've got that right ........But I'm sure someone will correct me if I'm wrong.

EDIT:- Additional microswitch end stops might be needed to disconnect / stop the axe at the end of it's travel.

Post Wed Feb 28, 2007 4:29 am 
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comanche



Joined: 22 Feb 2007
Posts: 22
Location: melburn


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I dont think i can use a seperatre speed controller because everything is wired up handy and the controls are perfect for it. (plus low on cash)
Although if i get the money i may go with that idea.

So far the frame is 440x220mm, the axe should move quickly at bare min.

The drill motor = axe motor not drive motors.

Dont worry about the switching and stuff now because its simple and i can handle it.

Cant really get a pic since it is at school atm. Ill try and draw up a better picture.

Woody, im know how to do what your talking about but dont understand why.

Thanks forr the help

Post Wed Feb 28, 2007 7:00 am 
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Totaly_Recycled
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Joined: 15 Jun 2004
Posts: 1346


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What they are Trying too say is your rc tank controler will handle the small motor that was desighned for the turret (probaly 1 to 2 amps max ) .
But iff you replace it with a drillmotor that wants 30 plus amps to start moveing then you will see instant smoke from your turret control .Useing woodys advice the controler can be used to switch relays that will handle the higher power the motor needs for the axe . Then the turret controler is only switching relays on and off useing mili amps of power and the relays send the high power direct from the battery to the drill motor. ive done it before with realy cheap toy car controlers i used in a heavy weight .

Post Wed Feb 28, 2007 8:25 am 
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Woody



Joined: 07 Oct 2004
Posts: 202
Location: UK


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http://www.robowars.org/forum/album_pic.php?pic_id=1401

Hopefully this pic will give you the general idea.

Or ...reinstate the turret ....use that to mechanically operate a pair of SPDT switches on a seperate 12v circuit.

Post Wed Feb 28, 2007 9:52 am 
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comanche



Joined: 22 Feb 2007
Posts: 22
Location: melburn


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This is my interpritation of Woodys diagram
http://robowars.org/forum/album_pic.php?pic_id=1403
Is it right?

Thanks heaps

Today i was informed that i have to consider mechanical safety locking mechanism. Ive decided to attach the turret connections to a motor to mechanically lock the axe if necessary.

Instead of using the turret control for the axe, ill use the gun firing connections with a relay. From what ive heard, the relay fires then retracts when activated.

Im going to go with woodys idea. I can do it but dont know what the 85,87 etc mean. Im unsure about what the squigly lines are, black blobs and the need of 2 switches.

Post Wed Feb 28, 2007 1:23 pm 
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Totaly_Recycled
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Joined: 15 Jun 2004
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The numbers woody put on are numbers that relate to the conection pins on most standard relays .

Mechanicaly locking the axe means just what it says --you need a bolt or some other clamp or aparatus mechanicaly connected to the axe and the main body of your robot so that iff the axe is acidentaly trigered when its not in a safe place ( ie like on your school desk ) then the axe can't move and chop something you dint want choped like the ends of your fingers or your girlfriends foot ect Very Happy

Post Wed Feb 28, 2007 2:43 pm 
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comanche



Joined: 22 Feb 2007
Posts: 22
Location: melburn


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Ive already figured out my locking mechanism. Its just going to be a motor with a arm attached to it, blocking the axe from swinging.

Does it really matter what voltage the relays are? Because I can only seem to find them in 12v. How do i know how many connection pins there are?
I tried looking in Jaycar and DSE (i can order some for free) but cant seem to find the specific ones.

Am i looking for a 30A max one?
Any specific diode?

Heres some i thought maybe would work:
http://www.dse.com.au/cgi-bin/dse.storefront/45e522420aa682582742c0a87f9c072a/Product/View/P8005
http://www.rockby.com.au/searchres.cfm?select=21&subcode=472
http://jaycar.com.au/productView.asp?ID=SY4072&CATID=&keywords=spdt&SPECIAL=&form=KEYWORD&ProdCodeOnly=&Keyword1=&Keyword2=&pageNumber=&priceMin=&priceMax=&SUBCATID=

Post Wed Feb 28, 2007 5:31 pm 
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Woody



Joined: 07 Oct 2004
Posts: 202
Location: UK


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You may well have trouble finding a 6v 30 amp SPDT Relay.
You may need to complicate things a little with the addition pf 2 small 6v relays.

I suggest 2 off CAT. NO. SY4058 use these to drive CAT. NO. SY4074 both from Jaycar.

Explanation of blobby bits .......

http://www.the12volt.com/relays/relays.asp

Another pic showing the extra relays later.

Post Wed Feb 28, 2007 5:48 pm 
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Woody



Joined: 07 Oct 2004
Posts: 202
Location: UK


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Another pic .....I modified yours.
http://www.robowars.org/forum/album_pic.php?pic_id=1404

I'm not sure if you even need the diodes .....Perhaps someone will chime in with advice.

Post Wed Feb 28, 2007 9:10 pm 
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comanche



Joined: 22 Feb 2007
Posts: 22
Location: melburn


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umm i dont understand a few things.
-what is the square with the 'switches' in the middle?
-black blobs and squiggly lines = ? (not mentioned on site)

i was thinking of CAT. NO. SY4072
only because its cheaper since now i need to try and get 10.
will it work?

Post Wed Feb 28, 2007 9:58 pm 
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