[ros-users] [Discourse.ros.org] [ROS Projects] Tractobots, my attempts at field robots

Kyler Laird ros.discourse at gmail.com
Thu Mar 30 18:57:28 UTC 2017

Thanks for the help, xqms!  I'll try to respond to your points in order...

One of the best parts about my new kill switch system is that I can program it.  Yes, I originally made it so that there was a heartbeat and if the switch was hit, the heartbeat stopped and the tractor was killed.  I switched away from that to only transmit a kill signal for a couple reasons.  The main one is that I wanted to save the battery.  I don't know how long it'll last if I'm transmitting all of the time but I sure don't want to run out of battery at the end of a day and be tempted to bypass the kill switch.  I also plan to have several kill switches operating several robots which could be miles apart.  I want kill switches to be able to move in and out of range without killing tractors.  I do consider having one heartbeat switch that stays in the field with the tractor (and is connected to a power source like the command center) and then have other switches that send signals only when activated.  I like keeping it simple for now, though.

I do not use a localization filter.  I work directly from the GNSS data, which is plenty accurate for me.  I would love to fuse an IMU, though, so I can get higher refresh rates and lower latency.  Yes, "direct tf transforms" sounds like my current need.

Yes, I get course and pitch from the receivers.  Here's the data I get about the base line to the second antenna:
1.     Latitude-projection of base-line, m
2.     Longitude-projection of base-line, m
3.     Height-projection of base-line, m
4.     Base-line length (Rover-to-Base distance), m
5.     Base-line course (angle between base-line vector and North direction), degrees
6.     Base-line pitch (angle between base-line vector and horizontal), degrees

Right now I'm using nvector for all of my calculations.  I think about switching to UTM but I'm a little concerned about conversion errors, especially in fields which are over a mile in one dimension.  I suppose that if I calculate my lines in nvector and then convert them to UTM, I should be OK.

Alright, modeling the robot in URDF seems to be the place to start.  I've tried it a few times and not gotten far.  I'm sure it's something I can do.  I will give it a shot.

The next steps overwhelm me right now.  Good to know I'm on the right path, though.

Thank you!

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