Servers by jDrones

Newbie putting a rover BOM together

Registered today after a few days of reading, yes, my head is spinning, as I am new to all of it.
I understand electronics and software; however, I never had or ealt with an RC controlled vehicle, not with any autonomous vehicle.

I live on 10 acres, with 5 acres needing to be mowed. While I like the place, I do not like mowing, which I consider a waste of my time… :slight_smile: so many things I want and need to do; mowing just does not fit the bill ATM.

So I read a few blogs on building an autonomous lawnmower; more specifically the MrMower blog. And here I am, wanting to build one of these.

I can weld and solder, hence, building the mechanics of it is not seen as a difficult task. However, the ‘controlling’ side of things is where I am kindly seeking input, which would help me to come up with a BOM I can order in confidence; meaning I have the right parts that work with ArduPilot and a system that works on a Linux Mint machine.

From what I gather, there are three main systems:

  1. A fixed GPS station to provide a defined reference to increase the accuracy of received GPS SAT signals.
  2. the autonomous rover with all its electronic bits
  3. some mission control and route planner software

MrMower had this block diagram:


… which agrees with me from a functional perspective.
The only thing missing are the three cutting deck motors, and linear drive rod thingy to adjust the height of the deck.

What components do I have to buy to get this system going?
My philosophy here is, while there is a limit to the budget, I’d like to buy brand gear simply to eliminate any compatibility issues, which would be hard for me to track down, given my current inexperience with these systems.

  • I have the batteries (a left over from a solar PV project) 8 LiFePO$ cells 3.2V @ 400Ah.
  • I have ordered two wheelchair motors,
  • a Sabertooth 2x60,
  • the Mauch 24/5V converter, and the Mauch I/V meter.
  • have the Linux PC and/or laptop

(…this was the easy part)

I also need (and I am hoping for your input WRT brand and place to buy):

  • a Pixhawk 4 FC (there are so many variants that I am not sure, which one exactly to buy)
  • telemetry radios; 300m LOS will be fine; since I am in Australia it needs to operate on 433MHz
  • RC transmitter and receiver; here I am not sure, firstly how many channels (given the block diagram) do I need.
    • I figure start/stop for the deck motors is one channel;
    • higher/lower the deck another.
    • The drive motors may be one channel;
    • so is left/right
    • I am really lost on this one; locked at a bunch, but have no knowledge to make even an educated guess on what to chose. all I know it has to be a ‘stick’ controller.
  • then there is that PPM encoder, which translates a number of RC channels into a single stream (of sort) for the Pixhawk to decode (I guess)
  • I just realised the block diagram does not show the Pixhawk 4 power board; since an image is connected to the Pixhawk 4 and other things.

I had a look at ArduSimple, but do not know what to buy. I reckon the ground/base GPS station can do with Survey performance antenna?!

As for the mission planner type software; I could run the MissionPlanner in a MicrosoftVM on Linux, or chose GroundControl instead. Have no experience with either.

Any hints/input appreciated. Thank you.

Hi @Max_G,

I think you’re on the right track, your parts list seems appropriate. I’m not sure the Sabertooth 2X60 is necessary, I’ve used a 2X32 in the past but blew it up (probably through incorrect wiring, not because it wasn’t capable for the job) and replaced it with a 2X60.

I’d get one of the nicer Mauch BECs if you can. There are a few offerings on the Mauch website, some BECs can only source 5V @ 3A, if you’re planning on having a companion computer you might want the nicer 10A version. I’m running up against the limits of the 3A version currently.

You only need the PPM encoder if you don’t have a modern RC receiver/transmitter pair. I bought a cheap one off Amazon a few years back and didn’t think to check for compatibility with the Pixhawk, hence why I also had to purchase the PPM encoder. They’re cheap though, so if you’ve already purchased one it’s no big deal. Otherwise read this topic to make an educated decision.

If you buy one of the starter kits from ArduSimple it will probably work fine. Make sure the radios you choose are appropriate for your application. I think the one I’ve linked to there was what I purchased a few years ago.

Hope this helps,

Drew

Thanks, appreciate your response (didn’t want to bug you directly) :slight_smile:

I will look a bit closer at the Sabertooth specs and what it means in cost to decide.

I understand you’ve improved a few things along the way, and while I have read some 75 posts of yours, I may have missed updates on improvements.

Could you please elaborate (or point me to the relevant MrMower post) what the Pixhawk power board is being used for; the same with the RaspberryPi.?

I haven’t bought anything other than the motors, the Mauch stuff is in the cart; thanks for suggesting to get a bigger 24/5V converter. :slight_smile:

These starter kits have two uBlox F9P boards; one for the rover the other (this is a question) for the GPS base station?! If the latter is the case, then I probably buy the boards and RTKs plus ‘survey performance’ antenna separately.

And yes, it did help :slight_smile:

On flat, grassy terrain my wheelchair motors pull about ~5A @ 24V collectively. My robot weighs about 300lb. You can use that as a data point to size your motor controller. On more hilly or uneven terrain they will probably consume more, but I’d be surprised if it’s more than the Sabertooth 2X32 can handle. I believe that’s 32A per channel, not total. You might be able to get away with a 2X15. Your call.

The Mauch BEC (functionally the same thing as the “Pixhawk 4 power board” in your picture) supplies the 5V that I use for the Pixhawk and peripherals (telemetry radio, RC receiver, GNSS, wheel encoders, etc.) in addition to the ArduSimple rover module. The Mauch BEC and I/V sensors are pretty confusing to wire up, and the documentation on the website is not always clear. There are lots of ways to power the system, all you really need is a pretty clean and reliable 5V that can source all the current you need.

You’re correct about the ArduSimple boards. If you buy the kit, one will be identified “rover” and the other “base”. They’re configured out of the box for one to survey-in it’s location and then broadcast it to the rover. You can change the settings with U-Center, U-Blox’s GNSS configurator software.

If you decide to purchase the survey performance antenna, let me know how it turns out, I’ve toyed with buying a pair myself to see if they give better robustness or accuracy, but haven’t got around to it. Make sure you buy a pair, I’m told that using different antennas can make it harder to keep an RTK fix.

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Looks like all the reading is doing my head in, and mixing up things…

“in your picture” had me puzzled. I thought this is from your blog; but it seems it is from somewhere else.
Out of interest, what software did you use to draw the block diagram?

Thanks for the current data; I have ordered the 2x32A Sabertooth… and after some reading and input from the ArduSimple people, I most likely settle on their simpleRTK2B long range kit.

All I have too find now is a genuine Pixhawk 4 board.
[edit1] ordered one from Holybro[/edit]

And I think I get it now: the Mauch modules are equivalent to the Pixhawk power board.

I think you will find that it needs to operate on 915 Mhz in Australia?

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What a can of worms :nauseated_face:

Quickly read up on it, and you seem to be right. Thanks! :slight_smile:

I checked this out; the picture source is from DeepSouthRobotics

I also managed to sort out the communication part building a rover: how to remote control it

Servers by jDrones