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Unread 01-05-2002, 09:47 PM
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Talking Custom PCB

I am sorry, but I was involved with FIRST two years ago, and had to take a year off last year because I started a new job.....so this might NOT be a new item this year......

But is this CUSTOM board a new item? I am excited about it, ecen though I have not yet had a chance to see the ADDITIONAL HARDWARE list allowed on it.

What do you expect to do with it?

How about measure currentls of all motors to keep from popping breakers!

Can you do some signal conditioning on some of the sensors.....to either take some of the labor off the stamp, or perhaps somehow monitor stimulus or feedback that might otherwise been difficult to do. (accelerometers maybe?)

Who knows, but even with such a simple game, my imagination is running at 100 miles a minute!

I am only 20% finished with the download of that huge PDF file, and I only wish I could get at it right now to see what the limits on design freedom might be.

(I am experiencing a sort of mental salivation over all this as I sit and wait for the download)



Oh the torture,
-Quentin

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Unread 01-05-2002, 11:42 PM
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This is very new and it is WONDERFUL! Thank you FIRST!
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Unread 01-06-2002, 11:00 AM
Patrik Patrik is offline
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Amen!

I think this could make for some very cool robots, and definitely some more powerful ones. Is anyone planning on doing a custom circuit board? What for? Replacement of the entire control system? I'll post some ideas when I refine them a bit.

Patrik
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Unread 01-06-2002, 11:55 AM
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Wheel speed and current sensing dude...

I will be shocked if CD7 does not have a PCB.

To actually KNOW wheel speed and to KNOW motor current. These are wonderful things.

Now to find an EE in this building who can actually pull it off for me... ...where's my employee directory...

Joe J.
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Unread 01-06-2002, 06:06 PM
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In the past, we've contemplated making some sort of current regulator for our drivetrain to prevent popping circuit breakers. with the ciruit board, we may finally have a chance to use that idea.
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Unread 01-06-2002, 06:06 PM
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Where are the electrical specs

Are the electrical specs available anywhere for download, I can't find section 2 of the robot manual. I am excited about the circuit board also. Joe, you mentioned knowing currents and speeds, how do you plan on relaying this info back to the player station?
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Unread 01-06-2002, 07:58 PM
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Talking I never thought I would get so excited about a 6.5" x 4.25" plastic box!

I finally found Section 2 of the manual, and it sheds little light on the Custom Circuit Board.

I wonder if it has to be a hand soldered piece, or if you can go out and make a comercial PCB?

It doesn't sound like you can since that would NOT be from Digikey.....though if you went out and bought the copper clad board and etched it yourself, it might be fine.

Also, it looks as though ALL the custom work being done with this board MUST be contained on the board and within the walls of the Box. So if a wire wants to have say a current sensor on it, it seems the wire must come "through" this box.....since the detector would have to be within the walls of the box.

Am I reading too much into this?

-Quentin

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Unread 01-06-2002, 08:27 PM
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I am planning on making a counter curcuit and a timer to get speed in a digital format then using poor man's Digital to Analog Converter (I think a resistor network could work) to input a voltage to the sensor port.

I have to see how much $100 buys and what it buys.

60 weeks of stuff to do... ...6 weeks until ship date...

GO GO GO GO GO...

Joe J.
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Unread 01-06-2002, 08:37 PM
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Is section 2 online?

Did you find this section online? If you did, where is it?
For a current sensor one method is to use a low-ohm shunt to convert the current flowing thru the shunt to a voltage that could be measured. 10 gauge wire has about 1 ohm/1000 ft so you could use say 10 ft of 10 ga. wire with a "sense" wire at each end of the 10ft shunt. If we want to measure currents in the 20 to 60 Amp range...
V=I*R (voltage=current*resistance)
V=20 Amps*.001 ohms (1ohm/1000ft*10ft)
V=.2 volts for 20 Amps to .6 volts for 60 Amps would be our signal. That sounds like it is big enough to do something with. But how much power would be lost in the 10 extra feet of wire?
W=I^2*R (Watts=current squared*resistance)
W=60^2*.001 60 amps worst case
W=3.6 Watts, I can live with that.
Now what to do with the signal? How do you get the info back to the driver?
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Unread 01-06-2002, 08:44 PM
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I found section 2 of the manual in the paper copy handed out by FIRST.

It appears to be in the paper manuals, but not in the PDFs posted.
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Unread 01-07-2002, 12:08 PM
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Re: Is section 2 online?

Quote:
Originally posted by Allen Smith
For a current sensor one method is to use a low-ohm shunt to convert the current flowing thru the shunt to a voltage that could be measured. 10 gauge wire has about 1 ohm/1000 ft so you could use say 10 ft of 10 ga. wire with a "sense" wire at each end of the 10ft shunt. If we want to measure currents in the 20 to 60 Amp range...
V=I*R (voltage=current*resistance)
V=20 Amps*.001 ohms (1ohm/1000ft*10ft)
V=.2 volts for 20 Amps to .6 volts for 60 Amps would be our signal. That sounds like it is big enough to do something with. But how much power would be lost in the 10 extra feet of wire?
W=I^2*R (Watts=current squared*resistance)
W=60^2*.001 60 amps worst case
W=3.6 Watts, I can live with that.
Now what to do with the signal? How do you get the info back to the driver?
Umm... I think you missed a decimal point somewhere. Remember that
P=IV, so if you are pulling 60 Amps over a drop of .6 volts, that is
60 * .6 = 36 Watts, NOT 3.6 Watts. I'm not sure if 36 Watts is worth it...
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Unread 01-07-2002, 12:22 PM
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Custom PCB is OK ....

If you look at the additional hardware list under the "Control System" section, it lists "Custom Circuit Board". This tells me I can print and etch a PCB without including the cost in the $100 limit.
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Unread 01-07-2002, 04:42 PM
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Re: Custom PCB is OK ....

Quote:
Originally posted by Ed Sparks
If you look at the additional hardware list under the "Control System" section, it lists "Custom Circuit Board". This tells me I can print and etch a PCB without including the cost in the $100 limit.
The manual says "Electronic Components Up to $100 worth from Future FAI or
Digi-Key" then at a different line, it says "Custom Circuit Board must fit inside Plastic Enclosure for Custom
Circuit Board (see below), qty 1"

Express PCB http://www.expresspcb.com/ExpressPCBHtm/Costs.htm can do the PCB for as little as $59 incl. shipping (for a 3.8" x 2.5" board). However, I do not think the PCB cost is included in the $100 limit nor do you have to buy it from FAI or Digi-Key. BTW, they also give you software to design the circuit

-kai
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Unread 01-07-2002, 11:13 PM
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Re: Re: Custom PCB is OK ....

Quote:
Originally posted by Kai Zhao


Express PCB http://www.expresspcb.com/ExpressPCBHtm/Costs.htm can do the PCB for as little as $59 incl. shipping (for a 3.8" x 2.5" board). However, I do not think the PCB cost is included in the $100 limit nor do you have to buy it from FAI or Digi-Key. BTW, they also give you software to design the circuit

-kai

I don't think that counts....I think the idea is that you can either hand solder the proto....or you can perhaps buy the plated FR4 material and etch your own PCB if you want. (if you buy the materials from one of the approved suppliers.....at least the FR4 I would think)

-Quentin
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Unread 01-08-2002, 09:10 AM
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Exclamation Outside Help is OK ....

IMHO, use of an outside "Rapid Prototype" service for production of a custom PCB is OK. Many team even use outside services in the production of the robot. It's all on the up and up. It's a matter of how your team chooses to "Inspire".
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