Quadrocopter update

I used to have a tuning rig for my quadrocopter but I forgot it at my parents place before I stopped working on it for more than a year and now the rig is gone. Now that I want to continue working on the quad I had to build a new tuning rig.

Quadrocopter tuning rig
I made a new tuning rig for the quadrocopter.
Close up on tuning rig.
A close-up on one of the arms holding the quadrocopter. A small piece of aluminum tube with an inner diameter of 8 mm is striped to the MDF. Inside a M8 threaded rod is inserted into the square bar of the quadrocopter and is secured with a M8 nut and washer.

It is a little larger and better looking than the last one and there is less friction when rotating the quad. This hopefully leads to a better tuned software. I managed to tune the angular rate mode this weekend, I think it will be flyable right now but I haven’t tested it yet due to bad weather. I’ll upload a video as soon as I have tried it outdoors.

This is what I have left to do with controller software:

  • Filter yaw gyro signal, it’s to noisy right now to use as a feedback signal for yaw control
  • Activate and tune feedback control for yaw
  • Tune pitch/roll control in angle mode
  • Activate battery voltage measurement, blink LEDs with different speed depending on battery voltage. (and install LEDs on the quad)
I also started to work on a v. 2.0 of the controller with a faster processor, more sensors, more outputs and more inputs.

Upgrading Turnigy 9x with er9x firmware

A couple of weeks ago I ordered a Turnigy 9x RC radio transmitter. This is a cheap but capable transmitter sold by HobbyKing. I’m very impressed by the quality of the hardware and the thing have more buttons, switches and channels than I’ll ever use, but I’m not really satisfied with the firmware.

Luckily there are a lot of custom firmwares for this radio and from what I’ve read, the one named er9x is currently the preferred one. Guides on how this update is done can be found on many places (for example here), this is how I did it:

I used a USBasp AVR programmer, these can be bought off eBay for a couple of dollars. Since i generally prefer PIC processors, this was nothing I had so I ordered one. But I guess you could use any programmer supported by AVRDUDE.

When you have your programmer, there is a software called eepe that is a specially made AVRDUDE frontend for programming er9x firmware. I downloaded and installed that program.

Then you need to connect your programmer to the processor, this is the hardest part, but not really that hard. First unscrew the six screws on the back of the radio. Then disconnect the cable hold the two halves of the radio together.

Disconnect
Disconnect this cable

after that you need to locate the connection points where the programmer should be connected. These are all around the processor in the lower part of the radio. NOTE: I have the v2 version of this radio, the connection points differ on the older v1 of this radio!

Connection points
These are the six connection points that needs to be connected to the programmer. Note that I have the v2 version of this radio, these could differ on older versions.

To connect the USBasp programmer I made a custom cable like this

Programming cable
The programming cable made from a 10 pole flat cable and a 2×5 connector.
AVR connector
These are the different signals in the 2×5 AVR programming connector, with the connector in the same orientation as on the image above.

Note that the leads 3, 6, 8 & 10 are cut off and not used.

I soldered the cable to the connection points and followed the instructions for eepe. When I was done, I left the soldered cable inside the radio if I want to flash it again someday.

 

The RepRap is printing!

The RepRap build is moving along I haven’t installed the heated bed yet since I need a 24 V power supply, capable of delivering 10 A, first. I found a small pack of four 200 x 200 mm mirrors at IKEA named Sörli that will be perfect for a heated build surface. But for now I will print on a cold printbed. I measured the build volume without risk of hitting anything, it’s around 180x180x100 mm, so the mirrors will be perfect!

For the first real print after installing the hotend I put kapton tape directly on the aluminum sheet. The print wouldn’t stick at all, the printer just smeared a large blob of heated plastic around. I’ve read that blue painters tape is the preferred surface when printing PLA without heated bed so I bought two different brands of tape, Tesa and Kip at the local Hornbach store.

Blue painters tape
Blue painters tape from Kip and Tesa

So far I have only used the KIP-tape and I would say it works great. I’ll come back with a comparison when I’ve tried them both. Most people recommend Scotch blue 2090 but I haven’t found a supplier for that brand here.

I ordered a 0.35 mm J-Head MK V-B hotend from www.hotends.com. Most of it was already assembled, I just needed to insert the resistor and thermistor and put some kapton tape on it, then I could mount it to the extruder. I’ve also ordered some thermal grease that I will put on the resistor and thermistor when it arrives, but for now, the printer works fine without it.

J-head MK V-B
J-head MK V-B mounted on Wades geared extruder

Here are some pictures on my first print, maybe you could guess what it is?

First print
First print, here I used honeycomb infill, which probably results in the strongest parts, but to achieve any print speed, you need something more sturdy than a Prusa Mendel because of all the small print head accelerations needed to create a honeycomb pattern. The printer was shaking like crazy!
Finished print
Finished and assembled print, the outer part is mounted with two ball bearings and can be moved by a servo.
Finised print 2
The same part from above. Servo cable neatly hidden in the aluminum tube.

When generating the g-code for the printer you can choose how much infill you like to have. This particular print have the outer 3 layers solid and the inside have a 40% rectilinear infill which saves plastic filament, print time and weight but the parts are still very strong. This infill pattern is not as demanding on the printer as the honeycomb.

Infill
This image shows how the parts look on the inside, the top print was aborted half way through.

I will soon write another post about the thing I am printing together with the STL-files and a complete BoM.