I have been looking around for a while, and I am still in need of some clarification regarding my upcoming project of making an ArduRover RTK mower.
As far as I can read, it’s pretty important to go straight for an RTK mower.
I think I read somewhere that RTK alone is not quite enough to go straight. I will need some proper motor driving, as well.
So my question for now is if DC brushed geared motors with dual quadrature encoders connected directly to Pixhawk will work along with RTK? And then simple PWM motor drivers to drive the motors, but with no encoders connected to this.
Another suggestion is to make sure your left and right wheels turn at the same RPM. In order to do this, you have to measure RPM of both wheels and if you find a difference, you can tune the servo output parameters (min, max, trim)
our slope mower with RTK is nice and straight with 2x Brushless DC motors
Biggest impact on non-straightness is the length of the grass.
A single large cutting blade generates a significant steering torque, hitting a long patch kicks the mower off course momentarily. Return mow stripe gets the same, but in the opposite direction leaving a grass island between the stripes.
If possible - 2 blades spinning the opposite direction sorts this.
I got the old DC motor controller working, which has encoder inputs. I’m running the DC motors now with closed loop, and the wheels are completely synced and has max torque at lowest RPM. I’m very happy with that result.
I’m right in thinking that brushless motors are easier to go straight with, since the speed is controlled by the ESC, right?
But that’s a good point to keep in mind!
Mower runs at 0.7m/s or 2.5 kph or 1.5 mph aka - slow but steady.
I’d prefer it working at the speed in the video, but its a robot - it works long hours without complaint. Strangely - i accidently found some more speed oday by slowing the mission down to 70% - which found another 20% on its normal 100%. Not sure whats going on, but faster was better.
encoder inputs - i assume hall sensors. We’re using VESC’s without any feedback - which is working well enough. RTK with a good local correction is important. RTK_FIXED not RTK_FLOAT.
It is probably overkill with the encoders on the motors I use regarding navigation, but it gives the motors full torque at the lowest RPM, which is great for me, since the motors aren’t geared right.
I will be using a moving baseline and a ground station with a F9P, so I hope I will have everything I need for good navigation.
What’s the difference between fixed and floating RTK?
1-2cm vs 1-3m accuracy.
fixed means the RTK algorythm has come to a solution. Floating = no solution yet found
RTK magic happens when your GPS gets fixed status. The quality of your hardware and configuration determine how long you keep it. Trees, buildings, configuration and comms issues will all mess with your accuracy.
Yuri’s minfix lua script we use to HOLD the mower when gps_status drops below 6 (RTK_FIXED) and starts once returned. Keeps the mower out of the gardens !
