I got the RPLidar A1M8-R6 with firmware 1.29, and at first, it was just plastic spinning around, and none of the libraries worked.
But I got it working on Windows, as a sanity check, so it wasn’t broken. So I started again on getting it working on the Raspberry Pi Zero W.
Tried the Adafruit python libs, but v1.29 had some insurmountable issue, and I couldn’t downgrade to v1.27.
So needed to compile the Slamtec SDK.
A helpful post pointed out how to fix the compile error and I was able to compile.
I soldered on some extra wires to the motor + and -, to power the motor separately.
Wasn’t getting any luck, but it turned out to be the MicroUSB cable (The OTG cable was ok). After swapping it out, I was able to run the simple_grabber app and confirm that data was coming out.
pi@raspberrypi:~/rplidar_sdk/output/Linux/Release $ ./simple_grabber --channel --serial /dev/ttyUSB0 115200
theta: 59.23 Dist: 00160.00
theta: 59.50 Dist: 00161.00
theta: 59.77 Dist: 00162.00
theta: 59.98 Dist: 00164.00
theta: 60.29 Dist: 00165.00
theta: 61.11 Dist: 00168.00
I debugged the Adafruit v1.29 issue too. So now I’m able to get the data in python, which will probably be nicer to work with, as I haven’t done proper C++ in like 20 years. But this Slamtec code would be the cleanest example to work with.
So I added in some C socket code and recompiled, so now the demo app takes a TCP connection and starts dumping data.
./ultra_simple --channel --serial /dev/ttyUSB0 115200It was actually A LOT faster than the python libraries. But I started getting ECONNREFUSED errors, which I thought might be because the Pi Zero W only has a single CPU, and the Python WSGI worker engine was eventlet, which only handles 1 worker, for flask-socketio, and running a socket server, client, and socket-io, on a single CPU, was creating some sort of resource contention. But I couldn’t solve it.
I found a C++ python-wrapped project but it was compiled for 64 bit, and the software, SWIG, which I needed to recompile for 32 bit, seemed a bit complicated.
So, back to Python.
Actually, back to javascript, to get some visuals in a browser. The Adafruit example is for pygame, but we’re over a network, so that won’t work. Rendering Matplotlib graphs is going to be too slow. Need to stream data, and render it on the front end.
Detour #1: NPM
Ok… so, need to install Node.js to install this one, which for Raspberry Pi Zero W, is ARM6.
This is the most recent ARM6 nodejs tarball:
wget https://nodejs.org/dist/latest-v11.x/node-v11.15.0-linux-armv6l.tar.gz tar xzvf node-v11.15.0-linux-armv6l.tar.gz cd node-v11.15.0-linux-armv6l sudo cp -R * /usr/local/ sudo ldconfig npm install --global yarn sudo npm install --global yarn npm install rplidar npm ERR! serialport@4.0.1 install: `node-pre-gyp install --fallback-to-build` Ok... never mind javascript for now.
Detour #2: Dash/Plotly
Let’s try this python code. https://github.com/Hyun-je/pyrplidar
Ok well it looks like it works maybe, but where is s/he getting that nice plot from? Not in the code. I want the plot.
So, theta and distance are just polar coordinates. So I need to plot polar coordinates.
PolarToCartesian.
Convert a polar coordinate (r,θ) to cartesian (x,y): x = r cos(θ), y = r sin(θ)
Ok that is easy, right? So here’s a javascript library with a polar coordinate plotter
So, plan is, set up a flask route, read RPLidar data, publish to a front end, which plots it in javascript
Ok after some googling, Dash / Plotly looks like a decent option.
Found this code. Cool project! And though this guy used a different Lidar, it’s pretty much what I’m trying to do, and he’s using plotly.
pip3 install pandas
pip3 install dash
k let's try...
ValueError: numpy.ndarray size changed, may indicate binary incompatibility. Expected 48 from C header, got 40 from PyObject
ok
pip3 install --upgrade numpy
(if your numpy version is < 1.20.0)
ok now bad marshal data (unknown type code)
sheesh, what garbage.
Posting issue to their github and going back to the plan.Reply from Plotly devs: pip3 won’t work, will need to try conda install, for ARM6
Ok let’s see if we can install plotly again….
Going to try miniconda – they have a arm6 file here…
Damn. 2014. Python 2. Nope. Ok Plotly is not an option for RPi Zero W. I could swap to another RPi, but I don’t think the 1A output of the power bank can handle it, plus camera, plus lidar motor, and laser. (I am using the 2.1A output for the servos).
Solution #1: D3.js
Ok, Just noting this link, as it looks useful for the lidar robot, later.
So, let’s install socket io and websockets
pip3 install flask_socketio
pip3 install simple-websocket
pip3 install flask-executor(looking at this link) for flask and socket-io, and this link for d3 polar chart
app isn’t starting though, since adding socket-io So, hmm. Ok, this issue. Right, needs 0.0.0.0.
socketio.run(app, debug=True, host='0.0.0.0')Back to it…
K. Let’s carry on with Flask/d3.js though.
I think if we’re doing threading, I need to use a WSGI server.
pip install waitress
ok that won’t work with flask-socketio. Needs gevent or eventlet.
“eventlet is the best performant option, with support for long-polling and WebSocket transports.”
apparently needs redis for message queueing…
pip install eventlet pip install redis Ok, and we need gunicorn, because eventlet is just for workers... pip3 install gunicorn gunicorn --worker-class eventlet -w 1 module:app k, that throws an error. I need to downgrade eventlet, or do some complicated thing. pip install eventlet==0.30.2 gunicorn --bind 0.0.0.0 --worker-class eventlet -w 1 kmp8servo:app (my service is called kmp8servo.py) ok so do i need redis? sudo apt-get install redis ok it's already running now, at /usr/bin/redis-server 127.0.0.1:6379 no, i don't really need redis. Could use sqlite, too. But let's use it anyway. Ok amazing, gunicorn works. It's running on port 8000 Ok, after some work, socket-io is also working. Received #0: Connected Received #1: I'm connected! Received #2: Server generated event Received #3: Server generated event Received #4: Server generated event Received #5: Server generated event Received #6: Server generated event Received #7: Server generated event
So, I’m going to go with d3.js instead of P5js, just cause it’s got a zillion more users, and there’s plenty of polar coordinate code to look at, too.
Got it drawing the polar background… but I gotta change the scale a bit. The code uses a linear scale from 0 to 1, so I need to get my distances down to something between 0 and 1. Also need radians, instead of the degrees that the lidar is putting out.
ok finally. what an ordeal.
But now we still need to get python lidar code working though, or switch back to the C socket code I got working.
Ok, well, so I added D3 update code with transitions, and the javascript looks great.
But the C Slamtec SDK, and the Python RP Lidar wrappers are a source of pain.
I had the C sockets working briefly, but it stopped working, seemingly while I added more Python code between each socket read. I got frustrated and gave up.
The Adafruit library, with the fixes I made, seem to work now, but it’s in a very precarious state, where looking at it funny causes a bad descriptor field, or checksum error.
But I managed to get the brain turning on, with the lidar. I’m using Redis to track the variables, using the memory.py code from this K9 repo. Thanks.
I will come back to trying to fix the remaining python library issues, but for now, the robot is running, so, on to the next.