Saturday, June 11, 2022

Lander Update - 06/2022

I have been doing a bad job of updating progress. I had intended on once per week initially, but life.

Lately I have been focusing on finishing up avionics and firmware, and getting moving on some of the other significant mechanical work I have head of me. I finished assembling the TVC actuators and have tested them. I also built up a portion of the ground station terminal I will be using to operate and work with the vehicle.

Current CAD state of the vehicle -- I have not worked on this portion much lately. I have recently determined how I plan on mounting the COPVs, although the CAD below is missing the bottom support bucket and strap. Those will be hose clamps seated onto a rubber or TPU cup. I also bought a TIG welder for the garage, so I can get cracking on work without having to visit the machine shop space.

All avionics boots up and works fairly well. Some weird bugs to fix in the peripheral board firmware. The backup IMU I got on ebay is behaving weirdly, and the analog multiplexer does not seem to be multiplexing as I expect. But I have reason to believe neither of these is a PCB issue, either device or firmware level. I'm able to drive all the relays, but there is a weird timing bug where when everything boots up, the relay board sinks power into the IO expander and fires itself for 250ms prior to Teensy poweron. Not really fixable via pullups, I'm going to take a closer look at the register map to see if there is a persistent fix. These annoyances always crop up lol. Parsing 2x GPS packets seems to work fine.

Linear Actuators! I've finally finished building them up, and testing out the drive board software. I had to update the firmware on  a linux system, so that required me using a raspberry pi, and I felt like I should just build a ground station computer while I'm at it. Anyway, the bandwidth already is quite good. I plan on  trimming the stroke once I have a design figured out for the thrust structure/gimbal plate and the mounting points for the engine/chassis side.

I also designed a smaller, cheaper, and hopefully more stable linear actuator that I might use for the throttle valve actuator. It uses a 22mm carbon tube as the effector. It also has some 3D printed parts that I'll need to sus out in PETG. Most other components are laser cut stainless steel. I still dislike the mounting situation..

Here is the prototypical grounds station in a pelican case. The portable monitor is used from ebay for $80 and is a super great deal. Basically an XPS15 screen you can just bolt down anywhere. I designed 3D printable adhesive bolt down brackets for it, with heat threaded inserts. Worked out quite well. The bottom of the case has a bunch of extra hardware you can tap into while out in the field. I will print some standoffs and laser cut an aluminum recess plate for the keyboard + other stuff to go onto. Work in progress!

I still need a good antenna solution...

I also made some custom battery packs for the valve power supply. These will be dedicated to firing valves, and have all the right electrical isolation to separate systems.

The look sketchy, but I've done worse...

Still so much work to do.
  • Finish up small issues with avionics 
  • Get the ground station network piping figured out and update FSW, and start writing ground procedures for polarity testing.
  • Finish welding the feedheads and hydro test the tanks! Finally! Please!
  • Take what I learned and apply it to the lox tank, mount that to the airframe
  • Mount my COPV
  • Hold a design review w some of my friends for the P&ID plumbing diagrams for all fluid systems
    •  This will also help me figure out much more to spend on components.. I have most of the regs/valves and a bunch of fittings. but no tubing lol
  • Design and build the throttle valve
  • Finish thrust structure and gimbal plate design
  • FSW and GNC Sim work (Julia Lang?)
  • Engine design!!!!
  • Countless other things I have on my white board

Here's a great picture I took the other week.

Saturday, March 26, 2022

Lander Update 03/26

I spent a lot of time in February working on the lander, but most of March hurried by as work got busy and I decided to take a break. I need to kick back into gear again, as I had the ultimate goal of getting the  vehicle ready for cold flow and maybe static fire (stretch) at the end of the year.

The goal for march is/was to do the following:

  • finish all avionics boards and firmware (got close, just some firmware to go)
  • get tank mounted and get ready for hydro test (close, tank is mounted but still needs some welds, and I still need some pump parts for the test)
  • finish each of the TVC actuator prototypes (close.. parts are in a good state, just need to machine some stuff)

Here are some progress pics from the last update...

The " Everything Else Board" is finished. Here are a couple pictures at the beginning of assembly, and then a final one where it's finished. I also made a new mezz board for the top of the flight computer, since PCBs are super cheap now, and I had a couple things I wanted to make better.

The Teensy 4.1 is the prime mover and shaker here. It reads from 2 GPS receivers, 1 backup IMU, commands an IO expander to drive the relays, reads an ADC port through an 16 channel multiplexer, and communicates with the flight computer over SPI to do tell it about that information, and to receive valve timing commands.
You can see the full Flight Computer Sled assembly in concert below.  Check out the snazzy silk screen on the flight computer. The XBee is just for fun, and for cheap debugging
The Avionics Bae box with the sled mounted

I also finished designing, ordering, assembling, and testing the power board. It powers all the digital logic, and also distributes an isolated battery power to the relay board to power all the valves. The logic power rails are 12V, 5V, and 24V. It kind of just powered on perfectly, and has noissues so far, which tends to be rare. But I kept the design pretty KISS anyway.

Check the 24V monolithic RECOM converter. I asked for samples and they sent me 3! These are to supply the Ubiquit Rocket M modem that lets the flight computer talk to the ground.

Here is everything mounted up besides the batteries. I made the harnesses for everything, and everything powers up. What an exciting moment! Glad I didn't release any magic smoke.

I'm pretty happy with the solution. Hopefully things continue to keep working... Next step is to finish the firmware, make a couple more harnesses, and then test out all the other functionality. I also want to get the flight computer talking to my simulated ground station.. Then I could feasibly start remotely pushing new softwares loads. I could even hook the USB interface of the FC up to the Teensy and upload new firmware remotely...

Here is what some of the harnessing looks like so far... it will get cleaned up.

On to tank stuff...

If you had followed along on tank progress, the previous mounting solution was super janky. This one works a charm. I designed some 2 dof sketches for the main mounts, got them laser cut with sendcutsent, and the TIG welded them. I then fit the tank with the bent sheet metal brackets I fabricated earlier, and it works a charm. I'm so glad I decided to use laser cut metal instead of 1" steel tube which was very hard to cut properly.

I also welded the cross bracket for the avionics box.

Next steps here are to tig weld the feedhead and diffuser to the top of the tank, and then buy the rest of the parts needed for hydro test.

TVC... I have been meaning to finish these actuators for a long time, but machining gets so expensive. I decided to test two methods: Joey B and a Chinese Machine Shop. Joe is a great human and was down to help me make some parts. I sent him my files and we got started on his new Tormach P440. I am new to CNC machining, so I learned a lot and realized. Damn it's definitely hard to get down. As far as the overseas machine shop goes.. the communication was very difficult, as it was all over email rather than wechat, so we'll see if they ever arrive.

The parts came out super beautifully. We stumbled on a couple things along the way, as we learned how to make these kinds of parts, and it was a great learning experience!

The homies

Tuesday, January 18, 2022

Lander Avionics, out with the old...

 I started working on the avionics for the lander over a year ago. I started off with a professional embedded approach, where I employed STM32F446 devices with their own supporting circuitry and used a traditional firmware development approach. It was a stacked sandwich set of boards where one micro did all the sensing related tasks: GPS, IMU, analog channels... and the other micro did all the actuation sets of tasks: interface with the valve driver, UART ports for the throttle valve motor controller and TVC actuator controllers. I realized this was silly.. first of all I split things up into two boards with two sets of firmware. Second, I was using a microcontroller that I wasn't super familiar with and writing firmware for ended up being a colossal pain in the ass. Most of the toolchains/tools I used for doing development were pretty much a nightmare to get started with and I realized that If I abstracted some of the systems to a  USB interface with the flight computer and the others to a Teensy, I could probably write the firmware for it in a couple days tops.

Regardless, I'll share what this old system looked like.. as it at least didn't look too ugly.


Sunday, January 9, 2022

Lander Update 01/09

I haven't gotten a chance to do a lot of work lately with holidays and work deadlines.. But I have been putting some thought into a couple things. I redesigned the tank mounting hardware. Pay no mind to the interlapping components, there are a couple bends that will fix the issue.

The bent sheet metal component will get tig welded to the tank, with smallish heat affected zone. Then the whole assembly will bolt down to the 1inch steel square tube welded to the chassis. This will allow for simpler tank integration. had issues with how tight the bends are, so I did them myself. This was my first time playing around with an industrial sheet metal bender, here is  how they turned out:

I also have been working on the "everything else board" which connects over SPI to the flight computer and does all GPS reception, reads all analog channels, and does all the expansion/timing for the flight computer to command the relay board and therefore all of the solenoid valves / things that are activated via relay. This will also include ignitors, etc. I also added some interfaces for switches and an extra IMU: the Aceinna OpenIMU platform. The main controller is a Teensy 4.1 microcontroller. I had designed this beautiful stacked avionics system before.. with two STM32F4s because I thought that was the most professional approach. It turns out that the best approach is the one that uses the tools you're good at using and the one that will finish the job the quickest and yield the same results. So... Teensy! This will cut down dev time by a lot.

I guess I'm also learning a lot about design philosophy in this project too.

I am still designing this board, but he're what it looks like. The main cable harnesses for all ADC inputs are mildly chunky since they need a drive voltage, ground line, and then return ADC line for the mux. Since some devices need to get driven by 12V and some by 5V, there are some complications involved with routing. Similarly, all get fed through a mux that heads to an ADC who has a maximum 3v3 rating (Teensy).. so I need custom dividers for each line. I added a common divider at the end, and give each port the option to add more inline R1 resistance to bring voltage down further. 

I also have been working on my printers. I added octoprint, and now have web interfaces for each of them to start prints. Only a mild convenience at this point, since I don't have a webcam and I didn't connect them to a port on my router.