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• Disassembling Losi Rally 1:24 car

  Frode Lillerud • 08/20/2016 at 20:47 • 0 comments

  Today I started on disassembling the stock Losi 1/24 Rally car. One of the nice things when picking this car as the base for my robot is that it is designed to be hackable. RC people like to (or are perhaps forced to) work on their cars. Replacing broken parts and upgrading to better parts is part of the experience for RC-people. So that is good news for me, since it makes modifying the car so much easier.

  Here is a picture of the stock car, where just the body has been removed.
  

  Removing the protective insider cover as well makes the electronics visible as well.

  I'm replacing all the electronics, the motor, steering servo and parts of the frame. The electronics will be replaced with my own custom Teensy-based PCB, the motor will be changed to one which is slower and with more torque. The stock servo for steering uses five wires, so that will be replaced with one that has three pins.

  Gutting out all the parts I don't need I end up with this;

  I've bought a new base plate, made from delrin, from a spanish seller (jamachucka) on Ebay. It gives me plenty of room to work with, and with delrin it is easy to drill new mountingholes.

  Here is the new baseplate mounted. I've bough a replacement servo from Losi (LOSB0814) which has three-wire setup, and a servo-saver.

  Lastly I've connected it up to my custom PCB. You can see it running the test-program for the steering in this video.
  

• PCB, revision 1

  Frode Lillerud • 08/18/2016 at 19:57 • 0 comments

  As mentioned the PCB is where I've put most of my time so far. Doing an iteration of schematics in KiCad, pcb layout in KiCad, order from China, wait, solder and test, takes so much time that I don't want to put it off until it's too late. The first revision was designed and soldered a few weeks ago, and I've tested most of the features.

  In this first version I've got a fairly big PCB. It's about 90mmx63mm, and just barely fits under the body of the car.

  
  

  It has a Teensy 3.2 mounted on female headers in the center of the board. Surrounding is a WiFi module, a Bluetooth module, various headers for motor, steering servo, driveshaft encoder and IR-sensors. Additionally I've put on a few components for monitoring power consumption, and a gyro/accelerometer/compass combo.

  Why both Bluetooth and WiFi? Well, because I haven't tried either the ESP8266 (WiFi) or HM-11 (Bluetooth) modules before, and I wanted to give both a go. In the next revision I'll probably keep just one of them. Haven't decided on which one yet, though. The ESP8266 would allow me to host a webserver on the car, which would be cool. On the downside it is really powerhungry, and will probably need to be flashed with a custom firmware. HM-11 on the other hand would give me just a simple wireless serial connection, which is easier to work with and is more in line with what I really need. So for now I'm leaning towards keeping the BT module, but I'll have to do a bit more testing before I make up my mind.

  The IR sensors I use (GP2Y0E02B) are really small, and use I2C. Since they all use the same I2C address I have to use a multiplexer for flipping between each of them when querying for distance. That is done by a TCA9548APWR I2C mux. I used it on the car I built last year, and haven't had any problems with it. For the next revision I plan on changing it to a TCA9548ARGER, which is basically the same chip, but in a package which is about half the size.

  For my IMU (Inertial Motion Unit) I've got a combo of the MPU-6050 and a HMC5883. Most likely I'll use the sourcecode from FreeIMU. I've done a brief test of the MPU-6050, and it seems to work just fine.

• Status so far

  Frode Lillerud • 08/06/2016 at 21:18 • 0 comments

  Let's see, what is the current status...

  On the mechanical side I've bought a Losi 1/24 Micro Rally car. It'll serve as the base platform for which I'll build the car. I'll have to disassemble most of the car, remove all the electronics and replace a great deal of the hardware, like motor and servo. I want to make the end-result still look neat and sexy, and not like a hacked together piece of cr*p, so if I can, i want to hide all my modifications under the original chassis of the car.

  On the electronics side is where I've put all my effort so far. Since attending the previous competition in May 2016, I've been doing research and worked on the custom circuitboard for this next car.

  As the "brain" of my car I'm using a Teensy. It fits into a socket on my custom PCB. I use IR sensors for detecting the walls on the racing track. The previous car had three. This one has potientially eight.

  Propulsion will be done by a brushless motor, powered by a 7.4V LiPo and an Electronic Speed Control from HobbyKing. Steering will be handled by a small servo.

  In addition to sensors and actuators for motion, I'm also including a few extra features on my PCB for future use. I've added an onboard IMU for motion detection, a current sensor for monitoring power consumption, bluetooth / wifi for debugging and configuration changes, and a few other minor things.

  But, right, I was talking about the current status.

  The first revision of the custom PCB has been drawn in KiCad, and created in China. I've soldered almost all of it, and am in the process of verifying that all the features work as intended. Most do, but some minor problems have been identified. I'll come back to the PCB in a later post.

  Lastly, there is the software side. The code for the car will be written in Arduino-C. I've got some code from the previous cars, but will probably rewrite most of it this time around. One new key feature to implement is a PID-controller for improved navigation.

  From here on out I've got about three months to get the car ready. I'll focus on the electronics in the beginning (since it takes a while to receive and test new boards), then move over to doing the mechanics, and lastly focus on the software.

• Initial commit

  Frode Lillerud • 08/06/2016 at 20:57 • 0 comments

  Ok, so, this is a project I've been working on for a little while already, but there still remains a ton of work. I want to document the project from here on out, and hopefully it'll be interresting to follow along, maybe it'll spark some discussions, and force me to be more structured.

  The project is an autonomous model car which will race around a racetrack on its own, using only onboard sensors and computing power. The end goal is to compete in a competition for autonomous racing cars in Sweden in November (2016), and in Estonia in December.

  I've attended a few competitons in Sweden already, but with other robots (we call the cars for robots) than this one. Those entries have been so-so. Last year my car died in the second heat. This time around I want to put a lot more effort into the robot, and hopefully learn a lot along the way.

  There are a few rules for the competition which I need to adhere to. Though not a complete list, here are the most important ones.

  • The car needs to be totatlly autonomous during the race. No remote control allowed.
  • It can be max 20cm x 15cm x 15cm
  • It has to have standard IR sensor used to start the car (www.startmodule.com)
  • It cannot harm or jam the other racing cars
  • Complete the most laps in a certain amount of time to win.

  The project requires some mechanical skills (which is probably my weakest part), some electronic skills (which is what I find most fun to work with), and some programming skills (I'm a developer by day, so that should cover that part).

  Hopefully you'll find the project interrestng to follow1

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