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  #31   Spotlight this post!  
Unread 10-12-2017, 06:17 PM
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Re: Electrical Board or Distributed System?

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Originally Posted by That1GuySteve22 View Post
I would advise you to stick with one main electrical board and one main pneumatic board. Keeping all of your main pieces (PDP, Rio, PCM, etc.) together allows you to build a board (or two if you're using pneumatics) outside of the robot and place it in when ready.
Why a seperate "pneumatic board"? Also, if you have a seperate board, where do you put it?

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Originally Posted by That1GuySteve22 View Post
ALSO words of wisdom (from experience), always use CAN-jumpers!!!
And yes, what are "CAN-jumpers"?
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Unread 10-12-2017, 08:11 PM
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Re: Electrical Board or Distributed System?

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Originally Posted by firecrafty View Post
Why a seperate "pneumatic board"? Also, if you have a seperate board, where do you put it?
This isn't an "every year" thing, but we did a separate pneumatic board for 2016 Stronghold. It turns out that with the 2015-19? control system, you only need to run two power wires and two CAN wires from the main board to the pneumatic board if you're willing to provide your own terminating resistor. (Looking forward to see if the CANifier will similarly simplify any feedback). In our case for 2016, we had some space forward for controls, and some space aft for controls, but neither was big enough for everything to fit neatly. As all of our pneumatic cylinders were towards the rear, that's where we put the PCM, compressor, tanks, and other pneumatic items. The RIO, radio, and motor controllers went forward.

Edit: When thinking post-2015 (Recycle Rush) about building a tetherbot, this is also the idea that emerged - make the fixed part of the robot work all or mostly on pneumatics to minimize the current running from the battery to the remote hull. In our design, we even put an SRX on the remote part of the robot just to act as a sensor reception point, not to actually drive a motor.
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Unread 10-12-2017, 10:15 PM
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Re: Electrical Board or Distributed System?

Quote:
Originally Posted by Al Skierkiewicz View Post
Greg,
The 2017 radio has a built in shield on the bottom/mounting side. No additional shielding is needed. When I suggest high and clear I am trying to get teams to mount the radio where the antennas are at their greatest efficiency and maximum sensitivity to the field antennas. When the radio is buried inside the robot, surrounding metal will produce reflections and likely detunes the internal antennas. On a moving object like a robot, the variables of reflections, antenna issues etc. are likely to cause problems that are both unusual and impossible to replicate. I am speaking from a broadcast and ham radio background. Knowing the issues teams report (lag, loss of connection, odd behavior) it is possible that placement and surrounding metal are likely. Again, noise introduced by the robot systems is yet another unpredictable variable. I don't think it is much of a problem as many teams seem to think.
Reading this it occurred to me that my handheld scanner would lose reception when I picked it up quickly (~800mhz range ). 2.4ghz is a really short bandwidth. A radio system in the UHF or high VHF band may handle more jostling. The drawback is a slightly longer antenna.
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Unread 10-13-2017, 08:40 AM
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Re: Electrical Board or Distributed System?

Tom,
It is unusual for a radio to lose reception when handled. If your scanner has a collapsible antenna, it may need to be replaced. The signal drop likely is caused by intermittent antenna contacts.
As the frequency rises the wavelength does get shorter. A simple 1/4 wave antenna is 234/frequency in MHz. So at 2.5 GHz the antenna would be a little over one inch long. At 5 GHz, (the frequency First uses on the field) a 1/4 wave is just over a 1/2 inch long. This plays into an old amateur radio rule of thumb, objects less than 10 wavelengths away from antenna start to degrade the performance. So metallic objects within 5 inches of the radio can cause issues with the antennas. The modulation and error correction used for WiFi helps with getting connectivity under harsh conditions so even objects located near the radio can be overcome. Teams should keep this simple rule in mind when designing radio mounting. Give the radio a chance and it will perform for you.
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Unread 10-13-2017, 10:09 AM
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Re: Electrical Board or Distributed System?

Quote:
Originally Posted by Al Skierkiewicz View Post
At 5 GHz, (the frequency First uses on the field) a 1/4 wave is just over a 1/2 inch long. This plays into an old amateur radio rule of thumb, objects less than 10 wavelengths away from antenna start to degrade the performance. So metallic objects within 520 inches of the radio can cause issues with the antennas.
Fixed that. (Doing the math I get between 23 and 24 inches.) Of course, the closer something of a given size/conductivity is to the radio, the more interference it is likely to cause.
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Last edited by GeeTwo : 10-13-2017 at 10:14 AM.
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Unread 10-13-2017, 04:44 PM
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Re: Electrical Board or Distributed System?

For my team we had a combination of both. Majority of our motor controllers were mounted on a piece of polycarbonate that acted as our belly pan. We did mount one Talon SRX on the back side of our gear arm (basically a claw) so we could make it an easy subassembly, plus we did not want to stretch an SRX ribbon cable that far of a length. On our climber since that was removable, we mounted the Sparks directly to that so when we switched it to our practice robot, we didn't use up 2 more motor controllers. Partially for the reason for the partially distributed is that we also started to run out of room on our electronics board.
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Unread 10-14-2017, 04:06 PM
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Re: Electrical Board or Distributed System?

> " And yes, what are "CAN-jumpers"? "

Are they thinking the Can Connectors?
http://www.ctr-electronics.com/can-c...or-5-pack.html
We used these last year, they are pretty handy to segment sections, along with Power Poles, etc.

My ~20 year old hand scanner, I referenced, has a Rubber Duckie. It has taken some lumps. Usually it won't drop out. When it did, it was on the 800+ mhz frequencies.
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Unread 11-26-2017, 01:27 PM
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Re: Electrical Board or Distributed System?

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Originally Posted by timytamy View Post
For our team, we've found a nice balance between the two.

Firstly, we try to have a traditional spider layout w/ banked motor controllers for the drive train eg

The key thing is that the path from battery to all the drive motors is as short as possible. This means we usually end up with a layout similar to the above, except with only four-to-six motor controllers in the banks.
Sorry to ask, but what CAD program is this?
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Unread 11-26-2017, 01:35 PM
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Re: Electrical Board or Distributed System?

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Originally Posted by ttnn58 View Post
- inspectors like it all together
Ohh, the old LRI-a-roo...
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Unread 11-26-2017, 01:59 PM
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Re: Electrical Board or Distributed System?

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Originally Posted by Jospeh0 View Post
Sorry to ask, but what CAD program is this?
I believe that model was made in SolidWorks as a full 3d model. That picture looks like a top down view.
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Unread 11-27-2017, 08:18 AM
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Re: Electrical Board or Distributed System?

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Originally Posted by GeeTwo View Post
Fixed that. (Doing the math I get between 23 and 24 inches.) Of course, the closer something of a given size/conductivity is to the radio, the more interference it is likely to cause.
Gus,
??? 10 x 0.5 is 5 inches. The 1/4 wavelength equation is 234/freq in MHz with the result in feet. 234/5000MHz= .0468 ft. or 0.5 inch.

Everyone, please check my original post for edit in 6. above.
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Unread 11-27-2017, 09:44 AM
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Re: Electrical Board or Distributed System?

Quote:
Originally Posted by Al Skierkiewicz View Post
Gus,
??? 10 x 0.5 is 5 inches. The 1/4 wavelength equation is 234/freq in MHz with the result in feet. 234/5000MHz= .0468 ft. or 0.5 inch.

Everyone, please check my original post for edit in 6. above.
Al,
Your calculation of 1/4 wavelength was OK, it was scaling up to 10 wavelengths that was the issue. 40 x 0.5" = 20", not 5".

Gus
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Unread 11-27-2017, 11:21 AM
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Re: Electrical Board or Distributed System?

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Originally Posted by GeeTwo View Post
Al,
Your calculation of 1/4 wavelength was OK, it was scaling up to 10 wavelengths that was the issue. 40 x 0.5" = 20", not 5".

Gus
Gus,

Maybe Al was talking about antenna length rather than wavelength? For an "electromagnetically short" antenna (like a 1/4 wave antenna) far-field effects begin around 2 wavelengths away from the radiating source, so 10x *antenna length* would be pretty close.

Best,
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Unread 11-30-2017, 03:20 PM
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Re: Electrical Board or Distributed System?

Sorry Gus, You are correct. I have to stop working on two things at once. This was a wireless mic week as we have to move our mics to new frequencies starting next year. We were meeting with Shure earlier this week and looking at their new products. They have some embedded 1/8 wave antennas in some transmitters.
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