Robot Arm C

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iwonder
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Re: Robot Arm C

Post by iwonder » April 22nd, 2013, 5:42 pm

It depends on the xbee module you get... check here http://www.digi.com/xbee/

The ones that run on 2.4ghz are pretty much, from a rules standpoint, operating like bluetooth to my knowledge.
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Re: Robot Arm C

Post by jander14indoor » April 23rd, 2013, 7:53 am

Usual comment about not official, etc...

At the national tournament, we have 60 teams to judge in 6 hours, less breaks & lunch and then have to turn in the scores to avoid delaying the awards ceremony. A large goal when I and others write rules (besides a good learning challenge for the students) is how to supervise the event accurately and efficiently. A key part of that is to avoid specialty measurement devices whenever possible (unless maybe I'm looking for an excuse to buy something, and even then I try to make sure there are low tech answers). The tools to measure broadcast frequency are just not something most people will have. And while voltmeters are more common, access to all test points is problematic at best. As a result, the rules are written to depend on MANUFACTURE'S LABELLED specifications for things like voltage (batteries are generally less than label voltage) or broadcast frequency.

So, instead of challenging the event supervisor with 'knowing' your xbee TRANSMITTER is operating on 2.4 GHz, or expecting them to look up specs on the internet, just make sure the device is clearly labeled by the manufacturer, you know where it is, and you can easily point it out to the event supervisor when asked! Again, its the TRANSMITTER that has to be checked under the rules.

Oh, and frequency hopping is OK, as long as its within the allowed bands.

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Re: Robot Arm C

Post by olympiaddict » April 23rd, 2013, 5:26 pm

Yeah, the challenge I'm seeing is that a lot of the DIY solutions to wireless at least appear from product photos not to be labeled regarding frequency. The only exception to that which I've seen (and this is just my experience, I could be way off) is bluetooth modules because they say bluetooth which I would assume is sufficient in labeling the frequency to be within the 2.4GHz band.

My suggestion would be to change the rules slightly to permit a student to provide documentation from the vendor or manufacturer that states the frequency.

So regarding frequency hopping, would a robot that uses that technology be considered able to operate on at least 3 frequencies and therefore no changes would ever need to be made to it in that respect in order to compete legally? Cuz then that seems like a no-brainer to me.

I know some Xbee's allow you to set a channel mask or something along those lines which allows you to set which channels in the 2.4Ghz band it uses, but for other events, like Sumo Bots, for example, it may be impossible to remove the module, connect it to a laptop, and reprogram it all within the few minutes setup period.

Also, what advice would you have as far as the reliability of using Bluetooth or other 2.4GHz systems (they are different, right? bluetooth implies frequency hopping while you can also just have a standard 2.4GHz transmitter?) concerning problems with cell phones, wifi, etc. that I've heard about?

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Re: Robot Arm C

Post by iwonder » April 23rd, 2013, 5:56 pm

Bluetooth not only implies some kind of frequency agile capability(frequency hopping), but a very specific protocol(who says what, and when) over 2.4GHz. 2.4GHz typically refers to the ISM band that exsists for general use, and is used by wifi, Bluetooth, zigbee, etc. Cellphones almost always operate in licensed bands that cell carriers own or have agreed to use exclusively(2.4GHz being unlicensed) and they shouldn't cause a significant problem. Most high level(meaning they watch for interference and such) 2.4GHz decices(Bluetooth, wifi, zigbee, xbee, etc) are required by FCC Part 15(it's the little label on every device if you look) to not emit harmful interference, and they typically don't cause too many problems. Things like wifi and Bluetooth can handle multiple devices in the same area, much more than you'd see at a SciOly event(at least, of those watching robot arm). So you should be fine.

Personally, I'd submit a clarification asking wether or not a spec sheet from the manurfacturer stating that a device uses the 2.4GHz band is acceptable, if yes, use XBee, if no, use Bluetooth. To me wifi is way more trouble than it's worth. Of course, if I were in this position Id stop trying to go wireless and get a USB cable in there so I could get it done and practice in time ;)
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Re: Robot Arm C

Post by olympiaddict » April 23rd, 2013, 7:05 pm

Okay, yeah, I didn't expect interference to really be a problem but I had just heard stuff about that in the past so that is why I was wondering- maybe someone knows what it was I might have heard that I misunderstood.

Yeah, I'm not using wireless for Robot Arm for this year- I was more thinking about future years, and it was a question on my mind that I was just wondering about for general knowledge purposes.

thanks.

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Re: Robot Arm C

Post by iwonder » April 23rd, 2013, 9:02 pm

Ahh, got it. and I've heard stories of bluetooth interference before too, but the only actual time I've seen it was with a robot I had running off a wiimote (bluetooth to mindstorms) in a school cafeteria with 1000 or so people and probably 200 bluetooth devices. The issue there was that the computer routines I had written would only try 5 devices to find the wiimote before giving up, and obviously they never lucked out... But I can't imagine any scioly event like robot arm that would have 200 bluetooth devices in the crowd.
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Re: Robot Arm C

Post by chalker » April 24th, 2013, 7:50 am

iwonder wrote: But I can't imagine any scioly event like robot arm that would have 200 bluetooth devices in the crowd.


Really? Oftentimes at the larger tournaments you'll have hundreds of people in a gym observing various events, including robot arm. I'd think you could easily encounter the same issue you mentioned.

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Re: Robot Arm C

Post by olympiaddict » April 24th, 2013, 8:03 pm

Yeah... that's what I'm worried about.

So what advice would you have as far as a reliable way to implement wireless communication and still be able to use a controller more like a video game controller than an RC airplane controller?

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Re: Robot Arm C

Post by ohiostar » May 3rd, 2013, 3:31 pm

http://m.youtube.com/#/watch?v=0c9Lu2DwO-I

Has anyone seen this in person? It's hard to tell, did the part of the arm that raised the ball previously score at least one point? Impressive!

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Re: Robot Arm C

Post by FawnOnyx » May 4th, 2013, 6:36 am

ohiostar wrote:http://m.youtube.com/#/watch?v=0c9Lu2DwO-I

Has anyone seen this in person? It's hard to tell, did the part of the arm that raised the ball previously score at least one point? Impressive!
I think the justification for that might be that when the ball is placed in the telescoping arm, the arm scores a point for holding the ping pong ball in (above) the north zone. Then it is raised. However I still don't think it'd count because: 1. The lifting action wasn't a separate, distinct, and final action in the run (they scored another ping pong ball when lifting and placed the ball in the north zone) and 2. The lifting action didn't start at the ground elevation. Those two things were explicitly clarified in the last two FAQ's here: http://www.soinc.org/node/473

Nonetheless, that looks like an incredible arm, must've been expensive though :P
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