Subject:
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Re: PnP, an NXT-based "industrial" robot
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Newsgroups:
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lugnet.robotics
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Date:
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Sun, 31 Aug 2008 19:12:29 GMT
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Viewed:
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8859 times
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In lugnet.robotics, Mike Hatton wrote:
> It is a nice action, is it accelerating?
> or fixed speed?, reminds me of a bird...
Yes, the motion reminds me a a bird as well sometimes. The speed of the arm
motions is under program control - it will slow down smoothly as it approaches
the target position, for instance, and some movements are set to accelerate &
decelerate. Actually, it will move much faster, but at the cost of being
jerkier. I don't have it set up right now to accelerate smoothly up to the
midpoint, and then decelerate smoothly afterwords (no reason I couldn't I
guess), so instead each motion has a user-defined "maximum speed" that it will
not exceed.
> I noticed you have a calibration with a
> limit switch under the 'place' rack, are
> your Pick racks also calibrated or fixed
> relative positions?
In this example, fixed relative position. In fact, it works best if you do not
attach the "racks" or "pallets" to the main structure, but position each
independently. Tied together, it's very difficult to get the exact spherical
symmetry required by the arm motions (although possible - adjustable connection
lengths with axles are great for this). As to sensors, the ideal thing would be
a sensor on the "finger" itself, but I didn't worry about autodetecting each
station - as in practice, each station might be doing something completely
different, and therefore need special code. It's a good idea, though.
> Also how are you detecting the last brick?
Right now PnP will not sort black - as that's the color of the of the "finger"
when it's empty. So if the arm waves in front of the sensor and the only
detected color is black, it assumes the EOAT is empty, and advances the internal
pallet counter. When it advances the pallet counter too far, it moves back to
the first, and repeats.
> Is this NXT-G still? (I know its your preference)
Yes - because it's bloody easy for a lot of things, and I actually think it's
kind of fun*. Also, there were several minor irritations that spawned this in
it's current form - one of which was the large number of people that I've heard
complain about how "poor" the NXT or NXT-G is at reliably positioning motors. So
I wanted to limit myself to a minimal set of "tools", and show that's it's
possible... not even that hard, actually.
> Its a very nice project I would be keen to
> see some closer pics/instructions
I'll toss some images onto BS when I get the chance. I should probably LDD the
PnP arm itself, as it has so few parts it would be pretty quick to do... but I'm
not sure all the parts I need are in LDD (the quarter ovals, for example).
--
Brian Davis
*Yes, I know many will think that's a strange, twisted, or even perverse
statement... but considering that we spent our time engineering using only small
plastic toys as a constraint, "because it's fun" seems a valid motivation to me
:)
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Message is in Reply To:
 | | Re: PnP, an NXT-based "industrial" robot
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| Nice work again Brian, It is a nice action, is it accelerating? or fixed speed?, reminds me of a bird.. perhaps Peck'n'Place... :) I noticed you have a calibration with a limit switch under the 'place' rack, are your Pick racks also calibrated or (...) (16 years ago, 31-Aug-08, to lugnet.robotics)
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