Have never seen anyone post MTBF numbers for any servos, but I’m guessing it’s highly dependent on loading and duty cycle. I can tell you that using these on my Exmark mower and while moving the full linkage system, they never got warm.
Steve, you are absolutely right. The machine is rated at 10.6mph forward and as long as I am not sitting on the machine it can go as slow as it wants. Were you able to keep the manual controls with the linear servos? I am probably going to model the linkages today and if I can find a data sheet on the linear servo I will model it or better yet a cad model of the servo so I can drop it into my model of the linkages. 4 inches of throw on the servo is more than I think I need which is good. I am considering using 12-15 ft/lb springs between the servo and the linkage so the mower can still be used manually or if the servos need to be overridden.
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I went with the linear servos because they were moving the full control system minus the return/neutral springs. The servos were hooked to the original “stubs” that the steering handles bolted onto. Quickly found out that the play in the control system (normal wear at pivot points) didn’t help and there was too much slop in the system to make it track well. If a human is driving, not an issue. We quickly adapt and don’t think about it again. But any slop really complicates tuning when you are trying to hold <0.10 meters while mowing. I eventually removed all the manual steering components and have regular servos hooked directly to the control lever on the transaxles.
Initially considered using springs to retain the manual controls, but talked myself out of it during testing.
Glad I did. Really don’t see a need once the R/C system is sorted, which you will need anyway. Onward!
I also considered attempting to retain manual control but decided against it and have never looked back.
I’m aware of another mower project that will selectively remove the autopilot from any control loop and instead use microcontrollers and encoders to send manually operated switch/lever positions to the servos and relays as necessary. It’s a big project but an elegant solution to retaining manual control without the need for physically changing the control linkage.
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I took some measurements today. It looks like full reverse to neutral is about 6.6mm (0.260") and neutral to full forward is 17.07mm (0.672") for a total 23.76mm (0.932"). The HDLS-4-2-12V linear servo has way more stroke than I need which is great leaving plenty of room to extend the length of the lever on the transaxle. I too have found a lot of play at the base of the controls. Explains why I have had such a difficult time mowing straight line. I did manage to model some of the linkage today but sounds like my best course of action is to abandon the factory linkage. I will get the HDLS linear servos ordered tonight! Thank you @Swebre for the recommendation.
Now that the servo issue should be behind me, what electronics should I be looking at? Orange cube, GPS receiver, etc? I have a very clear view of the sky through 99% of my property. There are 2-40ft tall trees along the property lines but there should be enough visible sky to obtain GPS data and if there is an issue I will mow those areas the old fashioned way, send the kids out to do it or maybe it’s time to get goats!
Thank you @Swebre and @Yuri_Rage @SJohnson for your help is sorting out the servos!
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I am very happy with the Orange Cube and it has been easy to work with. It is a top choice by several of the recent mower builders. As far as GPS the ArduSimple boards are more than capable and they come at a reasonable price. I am still implementing my GPS system so I can’t share my first hand experience with the Ardusimple F9P boards. Based on the experience of other users, I am not sure I would go the RTK2Blite board again. Reportedly they work and can be implemented to work with Ardupilot, but they are temperamental to setup. I will be attempting to set mine up soon. I know @ktrussell just directly wired two full size Ardusimple boards together for YAW steering. Other people are using different systems, but I just stuck to the low cost solution.
The Cube Orange is a great bit of kit and has a proven record. But if I built another, I’d probably go with a Matek H743-Wing. It’s 1/4 the price with the same processor and flash, and exposes more UARTs with almost no downside (on a Rover) as long as it’s in a good enclosure. I have one on a smaller electric vehicle and am very happy with it.
I love ArduSimple’s products in general, but I dislike the SimpleRTK2B+Heading (daughterboard) kit. They did recently revise the config to one that works a little more intuitively, but you cannot use the autopilot’s auto configure feature, which could prove frustrating.
In my opinion, go with two of the SimpleRTK2B boards. You won’t go wrong there.
The SimpleRTK3B+Heading is impressive and works well, but the cost is quite high.
I do have firsthand experience with all three of the moving baseline configs I just mentioned and stand by the twin SimpleRTK2B solution as the most cost effective, best setup for what we intend to achieve with our mowers, with the SimpleRTK3B+Heading as a close runner up (or winner if money is no object).
I prefer the survey grade antennas (no real need for the more expensive calibrated version), but the mag mount patch antennas work almost as well.
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Jason - Have no experience with other GPSs but I’m using these with two on the rover and one at the base for RTK.
No issues at all once I figured how to wire then up (this stuff is not my background) and they have been flawless to date.
Am using a Durandal Flight Controller on my mower/tug and it has also been flawless to date. Several hundred miles logged so far pulling a weed wiper and a mower on the property. Any issues have been self-inflected and part of my learning curve. And still a bunch to learn…. That said, I bought another Durandal and it promptly bricked the first time I tried to load the latest firmware. Kenny is trying to save it. Meanwhile I am building another guidance system for a friend and am using a Cube Orange just because it seems to be popular at the moment. Onward.
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Nothing wrong with the Sparkfun boards at all. They are functionally almost identical to the SimpleRTK2B boards with a very slightly higher price tag. I will add that ArduSimple has EXCELLENT, GPS focused customer support.
The Durandal is also an attractive option with a bit smaller community of users surrounding it than either CubePilot or Matek.
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@Vincent_Miceli I am happy to make a cover for the WingXine servo but I do not have a WingXine to model from. If you or anyone else has a WingXine they want to donate (can be in non working condition) I am happy to create a cover.
@Yuri_Rage I am getting ready to connect and activate my Ardusimple simpleRTK2B+heading, including the Ardusimple radio attached on top of the daughter board to receive the RTCM correction signals from the base station… I am just asking for guidance to help me start out with the best information on how to do this. I was looking at the Arudusimple website and the information there indicated that the boards had to be plugged in through the telemetry 1 port. Unfortunately I am already using that port for my main telemetry radio linking back to my computer. Can I just move the main radio link over to telemetry 2, and do I have to change some configuration parameters?
Telem1 and 2 are pretty interchangeable. I think that should work. I think they are SERIAL1 and 2, respectively on the Cube (off the top of my head).
@SJohnson, this is a nice looking installation. These kind of pictures encourage me to work on my rig.
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I have the servos @Swebre suggested on order and per @Yuri_Rage’s suggestion I ordered the Matek H743-Wing and am ordering 3 simpleRTK2B receivers. I have been reading through this thread (again) along with several others and have learned a lot albeit just scratching the surface. I was watching one of @ktrussell videos about gps last night which was helpful in understanding how the rover/moving base receivers work but I am struggling to determine how get the base station data to the moving base. I have seen suggestions for the MavLink and Xbee. Is there a benefit to using one over the other? There are a few objects that will make line of sight impossible. Can multiple antennas be used to distribute the signal around the property?
If anyone has a schematic of a complete system for a rover (flight controller, servos, GPS, transceivers, etc) that uses GPS-yaw they are will to share or a link to a resource that would be much appreciated. If one does not exist I am happy to post one for my setup once I am pretty sure I have it working and right.
The easiest way to get RTCM3 to the moving base is through Mission Planner. Connect your fixed base to the USB port of the computer, and MP takes care of the rest.
If there’s a public NTRIP station nearby, you can skip the fixed base and use that, as well (also in Mission Planner).
Skip XBee, in my opinion.
I like mRo’s 915MHz radios for a simple telemetry link to Mission Planner. It’s good to a few hundred meters and handles some minor obstructions reasonably.
Again, there is no one-size-fits-all solution to what you’re doing, so you’ll likely not find a comprehensive diagram. The Wiki is excellent for moving base config. I simply don’t have the time to create schematics, diagrams, and models of my one-off mower.
Jason here is a link to a post written by @ktrussell when he was helping me decide how to inject my RTCM correction signal from my base station.
There are 2 choices. You either run the corrections through your computer and Mission Planner or you send them via radio from your base station to a matching radio connected to the GPS unit. I went the radio to radio link avoiding the need to always have my computer hooked up for it to work.
The other method is probably easier and is what most people use.
Hey Jason - I use a fixed base GPSplugged into my PC in the shop running MP and sending corrections over a telemetry link using two cheap mRo 100mw SIK radios (same as Yuri) but with a good antenna on the rover and on the roof of the shop. Rover can wander all over the 100 acres without loosing telemetry (~2600’ max). Signal gets weak but stays active. I’d try those radios first. Any issues, there are several 900mw radios out there but they are pricey. Antennas, good coax and elevation are key to range.
I have successfully used many methods for RTCM3 injection. The easiest by far is just a radio link through Mission Planner.
I’ve used, in no particular order:
- 915MHz radios via MP
- A WiFi connection through an ESP32 (both with and without MP)
- Both of the above methods via a fixed base station with a Raspberry Pi WiFi repeater (TCP connection to MP)
- ESP-Now (ESP32 specific 2.4GHz protocol), directly to the module
- NTRIP through MP
I’m also familiar with but have not used a LoRa configuration similar to the way I used the ESP32s.
And, at present, an SIYI HM30 unit that provides video+telemetry+redundant RC, using Mission Planner and a local NTRIP station.
All worked equally well with respect to reliability (within their spec’d ranges). The SIYI HM30 unit provides the best range I’ve seen so far at an increased pricetag and some added complexity. I also really liked the ESP-Now method, but it may be a bit range limited for some applications.
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I have used long range RFD 900+ radios through Mission Planner for years and they work great. I am in process of converting the setup this year because it became annoying to have to run Mission Planner just to mow the lawn. The new setup will use the RFD 900 for direct base station to rover gps corrections. I have simplified my rover gps setup as well by installing a Septentrio with heading. In testing it doesn’t seem to locate any satellites while indoors where the F9Ps would locate dozens quickly. Outdoors, the Septentrio finds satellites quickly and starts reporting heading immediately. I haven’t tested RTK yet, hopefully this week. I will add a second short range telemetry radio to the mower for testing, ardupilot updates, and log downloads.
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