Re: paper: How to Get Multiple Cameras on Robot
 

Easy if you use USB webcams like we did with a laptop on the robot.
You can easily put 2 webcams on a laptop, sometimes 3 (depends really on the number of root hubs in the laptop, most netbooks have 3 USB ports but only 2 root hubs).

If you use a MultiTT USB hub you can usually get to 3.

We can confirm that putting a laptop within the rule restrictions is allowed and has passed inspection at 3 competitions.

It's quite cost effective as well. Consider how much 3 of those Axis cameras would cost versus the $25 webcams.

You can get 1080P webcams now. Think about what you could do what that sort of resolution. Think about what you could do with 45-50 frames a second from some webcams at 640x480.

Re: paper: How to Get Multiple Cameras on Robot
 

This whitepaper is documenting how to attach a second camera and add it to the driverstation display. In this game, likely as a POV camera for ball hunting. As described in the whitepaper, this takes about 30 minutes or less of programming, and no particular expertise.

So I fail to see how adding an entire laptop with USB cameras is a more economical solution to this problem. (Axis cameras are about $125, by the way. Is that a $200 laptop?) And then there's the complication of the custom code on your laptop and interfacing that to the code on the driverstation to display the video from the cameras.

So, while a secondary laptop for image processing is a nifty idea, I don't think it has any relevance whatsoever to this (rather good) whitepaper.

Re: paper: How to Get Multiple Cameras on Robot
 

We had a slight problem with this at the Colorado regional. The tutorial was excellent and we got the second camera up in like you said 30 mins.

BUT...

We could not get our ping times on the field low enough to support both cameras together. At the worst we saw pings of 160ms, and at best we saw 30-40ms. The threshold value to be "satisfactory" is 20ms, told to us by the FIRST field staff is where you will not have comm issues. When we operated with one camera we saw 6-8ms with the old axis and 10-20ms with the new axis camera. Together they were 30-40 so that was a no go.

Anyone got any ideas on how to get ping times down with two cameras? we were at the lowest resolution 7fps on both and 75 compression. I couldn't think of anything else. We also found that switching cables and locations helped significantly but not good enough...

we just guessed the field network cannot handle all the video stream we want to put through...

Re: paper: How to Get Multiple Cameras on Robot
 

Dialing down the camera settings should have been good enough. Perhaps your Driver Station computer is being overtaxed by trying to display the images. You can check its CPU usage in the Task Manager.

Re: paper: How to Get Multiple Cameras on Robot
 

3 Axis cameras at $125 each would be $375. I originally wrote:
"Consider how much 3 of those Axis cameras would cost versus the $25 webcams."

However, now that you've stated you've been getting them for $125 each can you tell us how? Last year when we bought them they were at least $150 each.

If you really want to send the video back to the driver's station from a webcam(s) attached to a robot mounted laptop there are quite a few ways to achieve that. Including but not limited to installing VideoLAN and streaming it from the laptop on the robot to the laptop at the driver's station.

Here's an example of how to do it in Linux (which is what the students had on our robot laptop) and even rebroadcast that to the Internet:
http://www.wikihow.com/Stream-Your-Webcam

BTW, this example uses UDP, not TCP, which might actually come in handy if you do start dropping packets.
This method gives you fine control over both ends of the streaming, including the compression methods, transmission protocols, and the communications stacks themselves (for example you can reduce the MTU, you can increase the receive window, etc).

There's no problem with the whitepaper at all it is great work. There is just more than one way to do this and there shouldn't be any problem with mentioning that considering the title of the topic in question is: "How to Get Multiple Cameras on Robot". Consider for archival sake what will happen if someone searches for that later when this topic is less recent.

Sorry if I've ruffled anyone's feathers wasn't my intent.

Re: paper: How to Get Multiple Cameras on Robot
 

A few other things about VideoLAN that might be relevant to using it like this:

Here's a way to overlay something on the video (like the privacy filter on the Axis cameras):
http://www.recipester.org/Recipe:Ove...yer_3 3186770

Here's a way to 'float' the video without the frames in an overlay.
http://vollnixx.wordpress.com/2011/1...rlay-with-vlc/

If you dig around in VideoLAN you'll also find that you can basically control all it's functions remotely from devices that can't even run VideoLAN itself. For example it can run a telnet server you can connect to and issue it directions.

Re: paper: How to Get Multiple Cameras on Robot
 

What kind of lag can be seen when adding a second camera? Is there a significant difference in your first camera when the second one is added? Is it a good idea to add a second camera, or will it tax the control system too much?

Re: paper: How to Get Multiple Cameras on Robot
 

Assuming that you are only using the 2nd camera to display on the DS, the only thing it stresses is the driver station computer. Based on my experience, the classmate can't handle two cameras without degradation. By default, everything degrades equally (both camera's and robot communication). The easiest solution is to use a more capable laptop.