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61  General Category / General Discussion / Re: 3D printer question on: November 18, 2012, 08:51:55 pm
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Kinda to add onto what cr0sh is saying, when I built my scrap CNC mill a few years back and I know I certainly underestimated the effort required. You spend so much time with CAD and setting the machine up that it's hard to get things done. First time never comes out right. Unless you're making a lot of parts "production" style it's always easier to make the part manually.

IMO, that's only true if you are already a real machinist and/or your CNC isn't as friendly as it could be.  I'm not a machinist and our CNC system is pretty awesome (the touch probe is a big part of the magic).  Almost everything made on our CNCs are one-off.

One of the students was ragging on me for using the CNC mill for a drill press (massive overkill), but the touch probe let me get things aligned very accurately and very quickly.

Of course, that touch probe system probably costs more than a "home user" CNC machine.

I suspect there are similar differences in a reprap and a $100k Stratasys, especially if you can throw in Solid Edge or similar professional level CAD/CAM software.

-j
62  Using Arduino / Project Guidance / Re: Help with my first quadcopter on: November 14, 2012, 05:55:46 pm
Two pieces of advice:

Google ardupilot mega before you buy any avionics.

Buy extra props.  Lots of 'em.

-j

https://sites.google.com/a/uah.edu/uahuntsville-software-safety-and-security-laboratory/home/projects/uahexcopter
63  Using Arduino / Interfacing w/ Software on the Computer / Re: assignment of port on osx on: November 12, 2012, 02:12:25 pm
Depends on the USB device.

With FTDI, it's 100% consistent.  The FTDI has a serial number in the hardware and a well written drive that makes this possible.

With the newer USB-CDC devices (e.g. arduinos that usa an Atmel chip as the USB interface), that's not possible since there is no serial number (or other unique identifier).  Technically the driver could create a device special file name based on the location in the USB tree (e.g. KeySpan on OS X does this), but Apple didn't put that functionality in their USB CDC driver.

-j
64  Using Arduino / Programming Questions / Re: Maintain Hover At Given Height on: November 09, 2012, 09:25:59 am
Google Ardupilot Mega.

They use barometric pressure for higher (more than a few feet) altitudes, and sonar near the ground.

-j
65  Community / Exhibition / Gallery / Re: Navigation Calculations for Arduino GPS on: November 08, 2012, 10:23:18 am
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Standing next to the AWS the barometric altitude read the same as the map, as did the EM-406.

Standing isn't moving.  A typical GPS does seem to settle down to a decent altitude measurement if you aren't moving, or are moving at a relatively constant speed.

Too bad barometric pressure altitude is weather dependent.  One project in my "when I get time" pile is a rocket tracker that uses an initial GPS measurement to determine MSL and uses that data to adjust baro for a more accurate altitude reading for a rocket tracker.

-j
66  Community / Exhibition / Gallery / Re: Navigation Calculations for Arduino GPS on: November 08, 2012, 07:29:17 am
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the altitude is way more accurate than position

Eh?   Altitude is position - the third dimension.

Typical commercial GPS receivers are known to provide poor altitude measurement, especially when the receiver is moving.  The satellites are nearly always low to the horizon, so the errors are a larger percentage of the actual angle being measured.

If you thought you were getting good altitude data, it either wasn't GPS (barometric pressure, etc), the receiver had special firmware, or maybe something was lying to you to make you think the altitude was good.  Or maybe it was the beer.

-j
67  Using Arduino / Networking, Protocols, and Devices / Re: xbee configuration MAC OS X on: November 06, 2012, 09:35:47 am
X-CTU runs on a windows vm under Mac OS X (I used VMware Fusion and a windows XP).

The Xbee devices I am familiar with (a very short list) can be configured via a standard terminal application by putting it into a configuration mode (send +++ is the default), then configure with AT commands.  This can be done with any terminal application on any operating system. you could probably even use the Arduino serial monitor.

I doubt you can do things like flash new firmware onto the xbee, but for changing addresses, baud rates, etc, it works just fine.  Just read the manual to find the appropriate AT commands.

-j
68  Using Arduino / Networking, Protocols, and Devices / Re: max6675+ethernet+sd card on: November 05, 2012, 02:14:09 pm
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The ethernet library has a bug that leaves the w5100 SPI enabled after the Ethernet.begin() call.

There could be hardware issues as well.  Which version of the ethernet shield do you have?  An early version may have a bug.

The W5100 is not a well behaved SPI device in that MISO does not go into a high impedance state when CS is deselected.  There is a separate enable input that is required to cause MISO to go hi-Z.  In a stroke of anti-genius, Wiznet made the two pins opposite logic (one active high, the other active low) so you can't just tie them together to get correct output.

IIRC very early versions of the ethernet shield tied the enable input active, so that effectively you could never send the W5100 MISO into hi-Z, so you could never connect a second peripheral to the SPI bus.  Later versions added a transistor to act as an inverter and activate CS and enable pins with a single input line, making the shield compatible with other SPI devices.

-j
69  Community / Exhibition / Gallery / Re: Arduino Powered Dust Collector Remote on: October 29, 2012, 05:17:02 pm
I decided to tap the tool power inside the tool, not at the panel.  Used an AC optosiolator (wired in parallel with the motor) into the arduino.  The DC power control (I used an SSR instead of a relay) and microcontroller live in a box on the DC.

I also left extra inputs - you won't regret it. smiley

I added some ESD diodes, since I was running a pair of wires down 15' of hose that moves air at 1100CFM - could be some static, eh?

It's been running for a few years (the arduino-based circuit runs 24x7) with no problems at all.

cool project!

-j
70  Using Arduino / Project Guidance / Re: Wireless Rocket Motor Testing on: October 29, 2012, 04:44:40 pm
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I thought he just wanted to trigger an ignition sequence.

Nope, looks like he's building a test stand:

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load cell provides an analog voltage signal into Arduino, Arduino sends signal to PC via wireless chip, PC records voltage and converts it into thrust.

-j
71  Community / Exhibition / Gallery / Re: Arduino Powered Dust Collector Remote on: October 29, 2012, 11:54:49 am
Cool.  I thought about doing one of these, but realized it was a) still manual operation, and b) kinda silly to worry about wireless control of a machine that is already connected by a 4" diameter hose.

I designed an AC sense circuit that automatically turns on the DC whenever the table saw is on, and lets it run for a couple of minutes after the saw is powered down.

I'm keeping an eye out for powered gates so I can make it 100% automatic (I don't have enough DC to not use blast gates).

-j
72  Using Arduino / Project Guidance / Re: Wireless Rocket Motor Testing on: October 29, 2012, 11:49:36 am
Look at your data bandwidth  - you may very well find that you will fail to record important events because the wireless data speed will not allow you to sample fast enough.

-j
73  Using Arduino / Networking, Protocols, and Devices / Re: safe to use an RS232 "Y" splitter to connect one comport to two recipients? on: October 27, 2012, 11:48:11 am
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was thinking to split the serial-out of the equipment with a simple "Y" adapter, so that one branch goes directly to the computer and the other branch goes to a serial-to-parallel converter for the printer.  Would this work, or will I fry something?

The RS232 spec calls for one TX connected to one RX.  So multiple receivers don't meet spec.

In practice, it'll probably work, but maybe not at high speeds.

I doubt anything will fry, as long as no more than one TX is driving.

-j
74  Using Arduino / Motors, Mechanics, and Power / Re: Reading a RC Airplane Receiver on: October 25, 2012, 09:31:58 am
Have you looked at the Ardupilot project?

The Ardupilot Mega already does this.  It uses a separate ATmega328 (i.e. and arduino processor) to decode RC receiver outputs.

The design team decided to use a separate processor for this decoding.  IIRC the reason was to increase accuracy and offload computation to make more resources available for the rest of the flight code.

-j
75  Using Arduino / Project Guidance / Re: Obtaining Magnetic Declination on: October 21, 2012, 12:01:06 am
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You only have 2k of data space in the uno so no chance.

Wrong.  You have 32kb of program flash and the PROGMEM macro, so if your program will fit in the 30k left, no problem.

-j
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