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Forum Index : EV's : Autonomous lawn mower.
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Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Been a while since I shared a new project. I have to mow about 3 acres of my place, the rest is grazed or being revegetated. I hate mowing. I have a bad back and mowing aggravates it. We are in our 3rd once in a 50 year wet season in 3 years, and I need to mow at least once a week so I can see those bastard big Eastern Brown snakes before I step on them. I hate snakes more than I hate mowing. I've seen a few youtube videos of home made autonomous mowers. Some are electric, some use a conversional IC motor, but all use open source software with GPS to navigate the mower around the property. Sounds like fun. The plan is it will run for a few hours a day, and return to a solar charging station as needed. The whole acreage should be visited by the mower every 2 to 3 days. About 12 years ago I picked up a little electric golf buggy for $60, minus batteries. It would be good for a future project I though at the time. Last week I took off the twin DC motor drives, the rest will make a good platform for a IC powered buggy.  Bought/found some steel and built the frame. The front wheels are castors, it will be steered by the back two motors.  The motors are rated at 24v 12 amp, so next I ordered a 25amp twin drive motor controller from robotgear.com.au, arrived today. The controller has forward and reverse, and several input options, including generic RC ( Remote Control ). Found a couple 24v pancake motors, something I would have picked up at a clearing sale years ago. I tend to accumulate stuff like this. To get a 1000mm wide cutting width, I need two blades at 505mm diameter, one offset forward of the other to give a overlap without hitting each other. Bolted a 505mm piece of 40x3mm flat to one motor for a test, scary, but it spins up quickly and though not sharpened yet, its cuts grass easily. Each motor draws about 1 amp no load.  Next up I'll wire in the motor controller and use a RC unit to drive it around the yard. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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phil99 Guru  Joined: 11/02/2018 Location: AustraliaPosts: 2134 |
My autonomous lawn mower (a bit too autonomous!) with inbuilt shrub trimmer. Bonus features include:- Automatic clippings disposal. Automatic fertilizer distribution. Solar powered, via genuine green energy!  |
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Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1022 |
Cool   This one eats weeds mostly. Bettong.  Cheers Aaron Off The Grid |
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| Revlac Guru Joined: 31/12/2016 Location: AustraliaPosts: 1022 |
Yes but the Eastern Browns here can reach up to seat height. Will be watching your build with interest. Cheers Aaron Off The Grid |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Had a set back  The motor controller had arrived, and I purchased a couple new 60Ah deep cycle batteries for a good price. Rigged it all together with a remote control and wifi camera, and took it for a drive.  They motors had a lot of torque and it wanted to wheel stand, so added a big old flywheel to the front to put some weight in the nose. Fixed. Then all of a sudden one motor was slipping. It was a noisy gearbox from scratch, and I had intended to pull it apart and replace what I though would be a noisy bearing. Removed the motor and pulled the gearbox apart. Its stuffed, nylon gear is stripped.  The model number returns nothing, its a EMD GB225-3002B. Made in the UK. So looks like I'm taking a few steps backwards. The motors were rated at about 300 watts, and this was way more power than it needed. Most of the time it will be going at a nice casual walking speed. Oatley electronics used to sell a 250W geared down motor, but looks like they got out of scoota stuff. I'll keep looking. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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TassyJim Guru Joined: 07/08/2011 Location: AustraliaPosts: 6094 |
That looks like a job for a 3D printer... Jim VK7JH MMedit MMBasic Help |
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Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
That 3D printer plastic might be too soft. I made similar gears om my lathe out of aluminium, to be used in my solar tracker. Worm gear cutting on a lathe can be done if an indexing head is bolted to the cross slide and the indexer is driven from the screw cutting shaft. One is limited to the number of teeth possible by the available lathe gear ratios but it was quite a few as I remember. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yeah I tend to agree, the 3D printer option wouldn't last very long, but it did have me thinking about it. Looks like I can probably get another gear box and retrofit it for around $200. But looking into other options as well, like a chain drive. No rush. I have found a few interesting videos and web sites on the autonomous mower subject. Most of them use Ardupilot as the software, and a flight computer. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| phil99 Guru Joined: 11/02/2018 Location: AustraliaPosts: 2134 |
Perhaps a local engineering workshop can make one, if you give them the good one as a template. Worth asking about the price at least. |
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| ryanm Senior Member  Joined: 25/09/2015 Location: AustraliaPosts: 202 |
Have a gander at this mob Gizmo. Lots of suitable small motors. https://www.motiondynamics.com.au/ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Thanks ryanm, looks like they have a suitable gearbox for a reasonable price. There is a local bearing mob that I'll check out tomorrow, I seam to remember they had some worm drive gearboxes on a shelf last time I was in there. If no luck I'll order the one from motiondynamics. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Placed order with Motion Dynamics. I did check out a local supplier, they had the same gearboxes in stock, but at more than double the price  Just wait for it to arrive, more research in the meantime. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Making some progress on the lawn mower. Its mostly been R&D so far. I bought a Ardusimple SimpleRTK2B board, a RTK enabled board based on the u-blox F9P chip. Not cheap, about $400. After a few weeks of brain strain, not having a clue what I was doing, I finally managed to work out a GPS system accurate enough for a lawn mower. Fortunately I have a free NTRIP server within 15km of my location. Its a government run service, you just need a username and password, and a internet connection, to receive a RTK correction data stream. I'm using a ESP32 board with Wifi, to connect to the NTRIP service over my NBN connection. This data is sent via a serial pin to the SimpleRTK2B board to process and come up with a "solution". Depending on the number of satellites and cloud cover, it manages a "Float" solution with a accuracy of 20cm, or a "FIX" with less than 2cm.  The GSP antenna will be mounted on the mower as low as possible, between the two drive wheels. This is so if one wheel goes up or down over a rock or something, the GPS aerial is still roughly in the same position, and the mower wont be inclined to think its gone off course. I'm using a little arduino compass board to get bearing. This will be mounted on a mast about 1 meter above the mower deck. This is to get it as far away from the motors as possible, magnetic fields and all that. I'll put the wifi aerial on the mast as well. Finally I'll have a Raspberry Pi 3 as the web interface and data storage. This will use its own wifi channel. I'm using a Pi for this as I have one spare and I'm very comfortable with writing MySQL/PHP code on that platform. The Pi will store all the waypoints, log data, and have the web interface to manually drive the rover, progress updates, change waypoint info, etc. The ESP 32 will request the next waypoint from the Pi, then use its compass to turn to face the next waypoint, then travel in a straight line until it reaches the way point. Once there, its reports back to the Pi ( for logs and updated map ), and requests the next waypoint. I've started on the driving code. The ESP32 will do all this stuff, its more than capable. Mostly just a bunch of functions, like turn to X degrees on the compass, motor drive, veer left or right, watchdogs, etc. Glenn. The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Interesting project, way out of my league though  I thought a 2cm accuracy was military grade but then, the surveyors require something similar for their work. May that mower treat all grass blades equal |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Yeah that sort of accuracy for civilian use can only be achieved with a near by base station. I'm lucky, there is a free base station service about 15km away. Anything under 40km away is good enough. If I was any further away from a free base station, I would need to set up my own base station, which isnt hard to do, its the same board, but configured differently. So I would need 2 SimpleRTK2B boards instead of the one. The disadvantage of using the government free base station is the rover needs to be connected to the internet to get the RTK correction data. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| ryanm Senior Member Joined: 25/09/2015 Location: AustraliaPosts: 202 |
Any updates on the mower Gizmo? I'm sure I'm not the only one keen to see how it turned out. |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Its a slow project :) I found the NTRIP servers connection wasn't as steady as I would like, so opted for the local base station and rover option. I ordered another Ardusimple RTK2B module ($$$) and configured it as a base station. I'm using a pair of HC-12 modules to let the base station and rover communicate. Its working, and gets a solid fix. I'm now working on the code to make the rover navigate and move. This are functions to do things like. Get compass reading. Calculate direction to next way point. Rotate until compass faces new direction. Move forward, check wheel turns. Following a line between old and new waypoints. If off to one side, make little changes to one motor speed. etc etc Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
OK, about time I updated this thread. Lots of changes. Built a little rover using a pair of windscreen motors to drive the wheels. Got the ESP32 code to a point where I could give it a list of waypoints and it would drive from one to the other. But I did have a issue where it would move in a curve instead of a straight line. I knew what was going on, and how to fix it, but I decided to go down a different path, unfortunately.  Bought a flight computer ( $170 ) and installing Ardurover firmware, using Mission Planner on the laptop to program missions, etc. This is a common solution and a lot of the rover/mower builders go down this path. Problem is, it was a hell of a learning curve. Very complicated, hundreds of settings to play with, documentation a bit useless. But after 6 weeks, its now working, fingers crossed. In hindsight, I should have stuck with the ESP32 and my own code, it was so close, and it would have been easy to add features as I needed them. I may still do this, see how things go. Moved the smarts to the bigger rover. The worm drives were terrible, 10 amps just to free wheel. Bought a pair or gear reduction scoota motors and some bike sprockets and chain. Much better.  Next I'll mount the cutting deck and see how it goes cutting grass. I have a question. Which way should it go, drive wheels at the back or front? I can see merits for putting the drive at the front, including a longer wheel base and the caster wheels have less authority when they hib a bump. Any thoughts? Glenn Edited 2024-04-15 15:07 by Gizmo The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
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| Murphy's friend Guru Joined: 04/10/2019 Location: AustraliaPosts: 648 |
Interesting project Glenn. Regarding drive choice, assuming the cutter is as wide than the wheel track then rear wheel drive would mean the wheels run on mowed grass. It might make a difference if the grass is wet. Just some idle thought. |
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