Good luck when you get to them Kenny 
Ben @BenBBB ,
I finally connected the GoMotorWorld actuators tonight to my bench power supply. I am disappointed that at 12V it seems to be about 1/2 the speed they quoted. I have the model LA12S: 50mm stroke, 10mm/sec (https://www.aliexpress.com/item/12V-50mm-stroke-10mm-s-speed-1000N-100KG-load-Waterproof-DC-linear-actuator-with-Potentiometer-POT/32813908700.html). Very disappointing. It is no faster than the little Actuonix I have been using. I see on the vendor website, in answer to a question, that it can be run at 24VDC (and it does run twice as fast), but everything on the datasheet indicates it should be getting the specified speed at 12V. What model do you have and are you getting the speed you should?
Kenny
Hey Kenny @ktrussell,
Glad to hear you’ve got the actuators going. Bummer to hear about the speed. I bought the 60mm/s 100mm stroke, 100N version. LA12Y. Controlling them with the Actuonix board. I haven’t measured the speed. My biggest issue has been slowing the steering down! Very happy with the rate of response from them for acceleration. The skid steering parameters are just taking a bit of tuning. Certainly finding it easier to drive a straight line between waypoints if I drop the mower’s speed. Other than that all is going pretty well. Bit of Ardurover side of things tuning to finish, but it goes so I’m spending my time working on the ROS side of things with the lidar and Cartographer. (https://www.aliexpress.com/snapshot/0.html?spm=a2g0s.9042647.6.2.4cc44c4dj3PCWy&orderId=95134189358963&productId=32667654225 )
Ben, I’m glad to hear the Actuonix controller will work with those actuators. I had planned to look compare the potentiometer specs of the two and maybe give it a try. Otherwise, I was going to do a DIY controller. I might try a step up voltage regulator module to get 24V and see how that works. I don’t know if the Actuonix controller will work with 24VDC but if not, I have an H-bridge controller that will.
The aliexpress link didn’t work for me in your last post, but it you are blazing a trail for me with the LIDAR and coprocessors and such!
By the way, on tuning, I found that the tuning parameters are very different for full engine RPM and lower RPM. The hydraulics just respond so much differently. I just do all my tuning at full RPM which is what I use for cutting.
Sorry, I’ll try that link again…https://www.aliexpress.com/snapshot/0.html?orderId=95134189358963
I’d certainly be happy to try a different controller. Certainly something more robust. Not sure how long they’ll take that current.
Yeah the mower is certainly much easier to drive straight at lower rpm. Tuning at high rpm has meant slowing skid steer turn parameters right down. Got to have a look at vibration affecting the IMUs as well. Seems to be having quite an effect on odometer measurements. That’s leading to poor localisation by the SLAM software. I might just try some rubber between my control box and the frame it’s bolted to, as well as the proper sticky pad (3M) that the Cube came with.
The goal is to get the SLAM stuff working well then developing a solid path planning algorithm to get my farm mowed 
I noticed that when I have the mower blades running, I get a huge offset in the compass. I demonstrated in a video (https://youtu.be/c_8d5sy455o). The new inflight compass calibration (Testers needed for in-flight compass learning) was a huge help.
Hey Kenny,
I’ll have a look at that in flight calibration. Pain in the ass taking everything apart! Coming along slowly but steadily. Not doing much on the Pixhawk side of things. Mostly mucking about with the SLAM system. THat’s a lot more like hard work 
Still, I’d certainly benefit from more tuning time on level ground with a decent GPS view. It’s on the to do list.
Cheers
Ben
1 Like
So I have gotten my mower out again this year and picked up where I left off. I have a full Reach RS+ base station going. The steering turning is coming along but my mower still overshoots its turns a bit. I want to add SLAM to the mower and I have been following the progress of others, most of which are indoor experiments. How are your outdoor experiences and have you integrated GPS with SLAM?
@Vincent_Miceli good to hear you’ve got your mower out for more work!
I’ve been doing bits and pieces with mine as time permits. I’ve struggled a lot to get things going as I’d like with a SLAM system. The 2D Lidar (rplidarA2) is cheap but not great for an outdoor 3D slam solution.
Experimenting with a stereo camera to work around that. Does take a fair chunk of computing power. Sure keeps the TX2 working hard.
Good luck if you decide to try. Hard to find a lot of outdoor suitable help around the place.
I got the mower out and it was doing really well. I then blew up the pixhawk cube with an electrical brownout/spike when the engine died in tall grass and the starter stalled when I tried to start it again. This was the second cube I blew up because of voltage spikes. I then bought a new pixhawk 4 and added a servo power isolator and rewired everything. I now have two electrical systems, one 24 volt lead acid system for the mower and motors and a 14 volt lipo for the flight controller system. On the new version of ArduPilot I started getting AHRS fail safes when the compass occasionally when berserk. Very annoying. I ordered a new compass https://www.amazon.com/dp/B01N5QL0XC/ref=cm_sw_em_r_mt_dp_U_B2dbDbQY7NDD1 which will be here tomorrow. Hopefully I can get it working and the mower mowing for real. Very close.
1 Like
I feel your pain! On my last run, about 6 weeks ago, I let the smoke out if a little arduino nano that is s handling some auxiliary stuff. Also, the $250 GPS module stopped working. It didn’t power up on my bench power supply either but then it did power up without my changing anything-never a good feeling. I haven’t really checked it out fully.
Looking forward to a good report from you!
What compass module are/were you using? Did it work well?
I’m using this module SMAKN GY-273 HMC5883L 3 Triple Axis Compass Magnetometer Sensor Module 3V-5V https://www.amazon.com/dp/B0141UFZTU/ref=cm_sw_r_cp_apa_i_1EvbDb0E292DT. It is working well. I have some issues as I expect anyone with a big chunk of metal as his/her vehicle and with some of that metal spinning! I documented the effects of the blades spinning here: https://youtu.be/gBn3Eygo88o
I have the EKF favoring the GPS for heading.
1 Like
Hi, guys.
I just wanted to let you know that this thread has been the single-most-helpful source of tuning information I have found to date. Not so much as a source for actual settings, of course, but as a means of better understanding the PID tuning process, values, and relationship between high and low-level systems in AP.
Thanks!
I’m building a platform to stripe a field. I haven’t yet decided if I’m going to use a mower or paint, but for guidance tuning, it’s not relevant. The goal is to make geographically repeatable 800+ foot long parallel lines; grass grows, mow/paint the lines. Grass grows some more, mow/paint the exact same lines again.
The platform is an electric wheelchair base with a Pixhawk and RoboClaw 2x30 for the motors. GPS is uBlox M8T with an internet NTRIP feed for correction. I also have a 42" ZTR to play with if the project swerves in that direction. To that end the hydro control discussions are also helpful!
If you guys know of a good starting point for RTK implementation information, I sure would like to hear it! I don’t know WTH I’m doing there…
I’m just getting started, and have a long way to go I’m sure. I’ve been watching this thread in particular since it started, as this idea has been swirling around in my head. Now that I’ve got a platform actually running (sloppy) missions, I just wanted to take a moment to thank you guys for all of your help thus far, whether you knew you were helping or not!
3 Likes
I am so glad to hear that these conversations have been helpful. Since you are trying to paint / mow very straight lines I think you will run into serious challenges, some of which I have already run into. Mowing a grassy field or rural lawn is a very forgiving endeavor that doesn’t necessarily require centimeter accuracy or repeatability. With standard magnetometers and GPS RTK units you will probably achieve something close to straight but not straight enough to make most people happy with the result. I am currently exploring using https://www.ardusimple.com/ products that have the latest and greatest GPS RTK modules and can also provide an accurate heading that isn’t influenced by metal objects and electrical fields in the environment. This might result in a much straighter line that is more reproduceable, but maybe still not enough for painted lines. I am also researching Visual Odometry and SLAM to use a camera to get accuracy needed for really straight lines and patterns.
That being said, you might still have hope depending on the size and design of your rover. A slower, more stable rover on level and consistent surface will yield better results than a fast moving zero turn mover over uneven ground. I explored the idea of using tracks instead of wheels since they are less likely to be pulled off course by small bumps, dips, and naturally want to drive straighter.
I also wonder if something even simpler could yield a better result. This might be crazy and not viable on a grassy field, but what about a line following robot? It would require lines to be painted first, but the maintenance could be automatic, assuming the original lines are still visible to some degree.
There are also beacon based location systems. These require a few beacons to be placed on the field before the mission but could provide very accurate and reproducible paths.
PS: I don’t think these guys are in production yet, but they give me real hope and a target to shot for https://www.mowbotix.com/videos/
Yea, it’s a journey!
I’m not sure how RTK will work out; if it’s accurate enough. Line following is out, as the lines are painted/mowed only once per year, every year, for an event. They just happen to be in the same exact layout each time. The whole point of this project is to save the day or so it takes to get 3-4 guys out in fields with 300’ tapes and flags to lay out the lines. Then this guy goes back and scalps the grass on those lines with a mower. “Meat-odometry” if you will. Lasers might be an option, though the field is roley and line of sight would probably take about 15’ of altitude to be seen from rover level at the other end.
What about multiple waypoints along the lines? A waypoint every 50’ for instance would be 16 or so points to try to hold the line?
I think I’m just going to have to take it out there and run it to see how it does. For now, I’m planning to get the PIDs and pivot turning as tuned as I can, and give it a go to see how it works.
It’s all a little in the air right now (but it’s not, because it’s a rover 
)
Aaron, I look forward to seeing how your mower turns out. I 100% agree with @Vincent_Miceli that it is very difficult to get perfectly straight travel in all conditions, but hey, give it a try. I also agree on some Ublox F9P board as the way to go for the RTK. I am using its predecessor but have 2 F9P boards that I am about to experiment with.
On using multiple waypoints in a line, that should not be necessary. The navigation tries to get the rover back on the line between the previous and current waypoint, rather than heading to the current waypoint from where ever it is. There are parameters that govern how hard it works to do that. This wiki from @rmackay9 is very helpful to me in understanding the navigation algorithm: http://ardupilot.org/dev/docs/rover-L1.html.
@ktrussell Thanks for the clarification on how nav works between points. It makes perfect sense that the rover is always trying to intercept the line.
I haven’t had a chance to try the rover “in the wild” yet. I’m hoping I can actually get it out to the field in the next week or so to do some real testing of the PID parameters.
If I can’t get the rover to travel in a perfectly straight line, I think I have an idea that will compensate for whatever drift occurs, provided I can keep the oscillation to a minimum:
Imagine that I’m painting a line with a gun attached to the rover. It will paint the actual path the rover takes between way-points, waviness and all. But, if I were to move the gun to a “trailer” attached to the rover, say about 5 feet behind, the trailer’s oscillation would be significantly less than the actual path the rover takes. It might just be enough to get good results! But if it does work, it’s going to cause another issue: Is there a way to prevent the rover from performing a pivot of more than 90 degrees? Pulling a trailer with a zero turn rover is just asking for a jackknife situation.
1 Like
You could disable pivot turns completely and insert additional waypoints to guide your rover as it turns around. You might have to have it swing widely to make a gentle turn. It might be tedious to build the mission. Mission Planner has several parameters that govern how a vehicle turns at the end of each pass in a survey. You may be able to get it to generate what you need. I’m not sure.