It’s about time for another update on our progress towards getting you your Quadshots!
Foam Molding: First and Second Shots
As we said in our last update, the foam ‘first shots’ (first test parts out of the molds) were originally scheduled to be completed February 20th, but the mold tooling company encountered some delays and took almost two extra weeks. On March 3rd (Jeff’s last full day in China) the molds had made it to the molding company and been mounted into the molding machine, and Jeff went to see the first shots get made:
First shots are all about finding and fixing the issues that inevitably crop up, and for us it seems that most issues relate to the placement of the ‘gates,’ or inlet nozzles where the foam beads are injected into the molds. Gate placement is more art than science, and poor gate placement means either the parts won’t fill completely full of foam, or that they require cramming a lot of beads in - which results in a heavy part.
Here’s a first shot of the port wing, and you can see that the center part of the leading edge (where it would wrap around the electronics box) didn’t fill, resulting in a missing chunk of wing:
Also, this gate needs to be recessed so that flash (extra material) doesn’t block the end of the spar channel:
And here’s something that needs a design tweak: the foam near the pylon landing foot gets too thin, causing the beads to sometimes fail to knit together over the plastic skeleton:
Note that all the parts that you have seen so far are made out of Expanded Polyolefin (EPO) foam, not Expanded Polypropylene (EPP). EPO is also commonly used in RC aircraft and is better for first shots because it molds with a much shinier, smoother finish, which allows you to see small surface flaws in the molds. Also, EPO beads can be molded without any preparation, and don’t require any post-curing - as soon as they pop out of the machine, they’re done. On the other hand, EPP beads have to be steamed for 24 hours prior to molding to pre-expand them and then allowed to cure for another 12 hours afterwards. The molding company had planned on making some first shots from EPP, but their power was turned off in the middle of the night, ruining the beads they had pre-expanding.
Despite the gate placement issues, they were able to make us five or so complete EPO foam sets, which Jeff brought back to the US. Chris assembled one set into a complete vehicle:
We can’t tell you how exciting it is to finally have a fully-molded Quadshot! We can’t wait for all of you to have yours too :-)
As Jeff flew back to the US, the mold tools went back to the tooling company, where they added some gates, moved others, and fixed some places where the cavity shape was not correct. Jeff also added a slight swell to the pylon near the foot to give the foam enough room. After about a week they were done with the changes, and the molding company made a set of new shots:
The gates are in better places now, so they didn’t have to stuff the molds full of beads to get the parts to fill, which means these parts are about 20% lighter than the first shots.
The molding company also made some shots from EPP in this second round:
As you can see, they did not come out well - EPP is more finicky about the mold and gate setup, and more susceptible to deforming after it is removed from the molds.
Switching to EPO
This brings us to an important announcement, which is that after consulting with the molding company, testing both EPP and EPO, and discussing amongst ourselves we have decided to use EPO as the construction material instead of EPP.
We are changing to EPO for a variety of reasons. We initially selected EPP for its resilience – EPP foam doesn’t ‘crush’ when squeezed, for example – but we have learned that EPO has many advantages that we feel make it the better overall material:
- As you can see in the photos, EPO has a much better surface finish than even perfectly molded EPP, meaning a glossier, more aerodynamic (and prettier!) Quadshot.
- EPO does not ‘relax’ and deform like EPP can when exposed to the elevated temperatures common in car trunks and shipping containers.
- EPP is molded at a higher temperature than EPO, so the plastic skeletons are more susceptible to being deformed by the foam beads pushing past them in the molding process.
- EPO is compatible with a wider range of glues and paints, both of which are important to building, repairing, and hacking the Quadshot.
- EPO is stiffer at the same density – meaning that the airframe will react faster to quick changes in direction.
Another important benefit is that EPO will allow us to deliver your Quadshots more quickly - from what we have seen, each mold tooling revision requires between one and two weeks, and getting EPP to mold correctly would likely take multiple further revisions. With EPO, we only need to do one revision to adjust the elevon hinge thickness before we can start production. Lastly, because EPO does not require any pre-expansion or post-curing, the molding company will take less time to manufacture all of the foam sets.
If you have any questions or comments about all of this, please post them in our forum!
The first production run of the brand new Inertial Measurement Units (IMUs) that will provide sensor data to your Quadshots is complete. The assembly was carried out by our electronics assembly partners, Dallas Electronics, Santa Cruz. Here they are all assembled and tested and waiting for their new homes on Lisas:
They have the super-awesome, brand new InvenSense IMU-6000 on them, which combines 3 accelerometers and 3 gyroscopes into a single chip. The chip can run its measurements through an internal Kalman filter to provide low-noise output, or give you the raw measurements at higher rates.
We received all of the PCBs for the LED boards (the square ones on top) and the LED driver boards (skinny ones below):
Quadshots get four LED boards, each with two LEDs on it (either a pair of red or green, or one blue and one white). The driver board takes input from Lisa or Lia and drives all the LEDs with a small FET, which lets us command them to blink on and off, or even fade in and out. We’ll be assembling all these boards ourselves.
The prototype Lia boards are both assembled:
They can’t fly until Piotr and Pranay finish the Lisa/M v2 and Aspirin v2.1 software, but once those are done the Lia software should not take long. We’ll kick off production as soon as we’ve test-flown a Quadshot with a Lia and Aspirin v2.1.
Since this has turned into such a long update, we’d like to reward those of you actually still reading - so tell us what color you think the production Lia PCBs should be, and we’ll make the color combo that gets the most votes! Vote for green, matte green, black, matte black, red, blue, orangey-tan, or white boards; and black, yellow, red, or white silkscreened text in the comments!
We’ve been testing many different lithium-polymer batteries, and found that performance doesn’t always correspond to price - for example, the worst (orange) and best (bright green) packs cost almost the same!
We’ve narrowed the potential suppliers down to two and will order them soon.
Motors and Motor Controllers and Propellers, oh my!
Our supplier has finished making all the motors and motor controllers (one of our biggest expenditures yet!), and they are all heading to our cargo company to meet up with the rest of the components, including thousands of propellers, hundreds of radio transmitters, receivers, elevon horns, servo linkages, motor clips, LEDs, and other goodies. Once the foam sets are finished, everything will get loaded into a shipping container for a two-or-three-week hop across the Pacific to us, so that we can start getting them to you! We can’t wait, and we know you can’t either - so THANK YOU again for your patience with us as we pull all the pieces together :-)
As always, we hope you’ll join in on the forum at http://forum.thequadshot.com, or chat with us on the IRC channel #quadshot on the freenode network - if you have a question just look for Piotr’s handle, ‘esden’ (if you don’t have an IRC client set up you can use a web client too).
Pranay, Chris, Jeff, and Piotr