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HSD Group - NSW
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Jaemus
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Joined: 01 Apr 2009
Posts: 2674
Location: NSW


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side note: i've always wanted to make a flipper that fires automatically (in addition to on radio command) by having a button strategically positioned on the flipper itself that fires it off if you happen to have the opposing robot contact it.

This is because you usually have fractions of a second to perceive the opposing bot is in a vulnerable position, react and fire

any lag between firing and the actual release of the flipper will be fatal here too

im aware you're not planning it as a flipper but the principle is the same
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<bovril> it collects data about the surrounding environment, then discards it and drives into walls

Post Mon Sep 19, 2011 11:25 am 
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frogbiscuit



Joined: 26 Aug 2010
Posts: 82
Location: Wollongong


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12V motor on 18V? really??
I know DC motors can take 110%, but 150%? Too chicken to try that without a temp probe on the motor.

Good call on the auto-recock. Fully intend to automate. Right now just motoring manually to cock & fire positions with forward & reverse pushbuttons. No time for such in a real fight. In future, one button to fire and then auto-rewind the 6 C-135 Bunnings springs. Could o' would o' should o' ...talk is cheap til I can put metal on deck.
Grandiose plans for sensors, optical and tactile. Farnell has cheap "sounders", piezo devices tha twork great as hair folicles.

Post Mon Sep 19, 2011 8:54 pm 
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Knightrous
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Joined: 15 Jun 2004
Posts: 8509
Location: NSW


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quote:
Originally posted by frogbiscuit:
12V motor on 18V? really??
I know DC motors can take 110%, but 150%? Too chicken to try that without a temp probe on the motor.


Hehehe, still stuck in that "Uni Robotics Theory" mode Smile How much you can over volt a DC motor is really dependent on it's construction and design. Some motors like the 12v scooter motors happily run on 36v without deathly results, others just fry from nominal voltage use Razz Although a temp probe on the motor is pretty good in theory, it's not as effective in practice. Especially with brushed motors, by the time the motor can heats up enough to trigger your thermal threshold, the armature can have already smoked, cooked and died spectacularly. And the other side of it, most builders would rather fry a speed controller or motor then be limited by software and control systems when ham fisting it out in the middle of a heated battle.
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Post Mon Sep 19, 2011 10:46 pm 
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haz



Joined: 15 Aug 2011
Posts: 169


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yes they can be run at 18v, i am in my featherweight with no problems

Post Tue Sep 20, 2011 1:13 am 
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Glen
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Joined: 16 Jun 2004
Posts: 9481
Location: Where you least expect


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Thats seriously cool, got any pics of the mechanism itself?

Drill motors are always finicky but giving an educated guess you could try 18v on that pretty safely. the motor doesn't sound all that loaded. When you stall them out they instantly start pouring out smoke though, so you'll want to avoid that at all cost with some limiting switches or something like that.

Hope to see it in some kind of robot soon Cool
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Post Tue Sep 20, 2011 1:45 am 
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frogbiscuit



Joined: 26 Aug 2010
Posts: 82
Location: Wollongong


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Ok, here goes:

http://s1116.photobucket.com/albums/k566/frogbiscuit001/?action=view&current=trebuchetframepan.mp4

The linear actuator is out of it right now being worked on, that actually makes it easier to see the mechanism.

Post Sun Sep 25, 2011 5:24 pm 
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frogbiscuit



Joined: 26 Aug 2010
Posts: 82
Location: Wollongong


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Define "...instantly..."

Like within a second of stalling? So a rotation detector would be better than temp probe?

Yeah, guess I'm stuck in retardo roboto 101...

Post Sun Sep 25, 2011 5:44 pm 
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Valen
Experienced Roboteer


Joined: 07 Jul 2004
Posts: 4435
Location: Sydney


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if your keen on doing it mathamagically you need to model the efficency of the motor, its heat disipation Vs ambient and RPM.
Also you need to measure amps and volts in.

At sane voltages your not going to explode the brushes in one hit or arc through the insulation.

As such you work out how much energy your putting into the motor vs how much its putting out and the left over is heat.
You want to keep the armature < ~100C and the magnets < 70 or so max.

Combine all that with a thermal probe to correct for drift in your model and you have the best current limit you can do.

I'd say you can go to 3x volts and 2x amps with a drill motor, but not at the same time ;-P

Too many amps and the brushes explode too many volts and they get eaten by sparks.
too many amps*volts and the winding cooks
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Post Sun Sep 25, 2011 6:05 pm 
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frogbiscuit



Joined: 26 Aug 2010
Posts: 82
Location: Wollongong


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Progress:

Established radio link. Motors turn wirelessly.
Upgraded PICs from 877s to J50's.
Full circle on encoders. Back to incremental, with neutral channel.
Weapon now with auto programmable load-cock-fire positions.

Post Tue Jan 24, 2012 2:38 pm 
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