LCSC Components | My thoughts

Last week, I got surprisingly early my ordered parts from LCSC. I should probably mention, that Im not affiliated with LCSC in any way. I just want to share my opinion with a shop that I didn't use before.

As you may have already seen in one of my recent posts, I'm assembling a huge amount of DIY FrSky compatible receivers. Some of the parts are quite expensive (about 2.5€ each) in reasonable quantities from my usual suppliers Mouser and Digikey. This time I wanted to try one of the more trusted chinese suppliers. I have some experience with parts from Aliexpress (especially rf ones) and most of them where not worth the cost saving. This time however I ordered as already mentioned from LCSC. No hugely critical components just resistors, capacitors, some ICs (and a reel of 5000 resistors just for kicks ~5€). In total I spend about 80€ including shipping cost to Germany. The cost savings in my case are about 65% compared to the same amount of parts from my already trusted suppliers. Maybe I just had luck, but the next day the order was already marked as shipped. I have not paid any extra fees for express shipping or anything like that so that was quite impressive. Again probably having luck, my order arrived only 2 weeks after the payment at my destination. I expected the parcel to be delivered to the local customs office because of the value. Over here in Germany it's quite common to pay the customs afterwards, so you should consider that already during the shopping. In my case, I pre-calculated the possible amount that they could have charged me. But still the cost saving was so high, that I thought, it's worth a try. I can't tell at the moment how the parts will perform and whether they are out of spec or not but I will give an update to that for sure. All I can say at this point is, that they arrived in a pretty well packed box and individually labeled.

DIV8RT development updates

As mentioned in a previous Post about my Receiver design, I have ordered a large amount of components to assemble a lot more units. Assembling this many boards takes a lot of time. If you don't organize your workplace and every process that it's going to need to build the device prior to the assembly it will almost certainly take a lot longer. I always sort and position most of the tools and parts used during assembly with about an arm length on my desk. There is nothing is more inconvenient and annoying than having to search for stuff while dealing with fragile electronics.

There are some more changes since the last post. First of all the receivers enclosure has changed to a 3d printed one as the old one was too fragile during the extensive testing that I have done. Also the overall volume has been reduced to shorten printing times and make it more useful in small airplanes.

The next change was more an addition. The antennas are now secured with some special electronic grade silicone. This prevents the antennas from being ripped of the connector or PCB. I got the silicone from Aliexpress for about 2Euro, so no large investment for a lot more security.

And finally I changed the pinout of the auxiliary Telemetry Port to match FrSky without having to build a special cable. This was as easy as routing the pins to the matching locations on the second revision of my PCB-Layout.

This project has already been one of the most time consuming things that I have ever done in my rare spare time and that is also why it takes so long to do updates or even get new features made. However I did a lot of software work to get the vario finally running the way it should. The most time went into a bug in the Processor itself. The barometric sensor had every now and then jumping values in the order of a couple kilometers. After many tests I decided to look at the data on the I2C lanes... Sometimes the processor decides to transfer an extra byte or even a zero byte. After quite some time someone pointed me to the errata sheet from ST, where this bug was already listed with a possible workaround. The workaround is to use I2C only with DMA except for single byte transfers... For me, who has never really used DMA before, there was a steep learning curve. But after stepping into many common pitfalls and general misunderstandings I got it working. Now the sensor was responding as expected.

Another really wanted feature was a automatic gain control of the amplifier stage. The problem without these few lines of code where missing packets and even complete signal losses on short distances (about 2-3m) due to overloads in the receivers input stage. Disabling the receivers amplifier during bind and high signal periods in combination with some window comparison did the trick. Now the antennas can almost touch each other without overloading. 

A huge software project for the future will be adding D16 LBT and a custom bootloader to update the firmware via the transmitter and therefore building a custom .frk file converting script. At the time I'm writing this, the first part of the d16 development is almost done. I'm already able to bind and receive channel values. I now need to look into failsave values, telemetry and lbt functionality. Last mentioned has to my knowledge not been reverse engineered entirely so some nice stuff to investigate and learn. So far the D16 protocol implementation has been a nice journey, because midelic and jry on RCGroups.com have done most of the hard work and I only have to implement it into my existing software.

Saito radial engine repair

As almost every RC fan I'm fascinated by model engines. Most of them are however quite expensive to buy new or even used.

By the end of 2017 I got hold of a very cheap but broken Saito radial engine. With the experience that I have built over the years of flying gas and nitro engines I was very convinced that I would be able to get also this engine back up and running. I only did a few rough calculations if for the given price it was even possible to repair without paying more than I would have for a good running used one...
Immediately after the parcel arrived I wrote a list with all the broken and missing parts. The engine has already been disassembled by the previous owner, but he did a wonderful job packaging and marking all the parts. That made my job a lot easier...

The damage was quite substantial as the previous owner had an unplanned 'landing' at the airfield. With broken Cylinder, Rocker arm brackets and ripped screws there was a lot to be done. Luckily I was able to drill some of the broken screws out and save some more parts that I would have otherwise had to buy new. Also the crankshaft and the matching bearings where in good condition. Here just a few impressions. There where a lot more parts damaged but I think they illustrate it the best...

The whole cleaning and inspection took 2 days in total and afterwards I placed an order for the missing parts. Unfortunately the shop I ordered them from had to order them from Japan (Saito is a Japan company) so the delivery could have taken over 3 Month. Again having luck the parcel arrived by the middle of February. I also could have ordered the parts at a local German hobby shop but they would have cost more than twice as much. 

The day the parts arrived I started sorting and assembling of the parts. Unfortunately one of the cylinders had a large leak at the exhaust valve. I decided to try to grind it in using some abrasive cleaning solvent. However it did not work at all. Maybe if I would have ground it a lot longer than I already did. After that I bought a proper valve grinding kit for a few Euros. This grinding paste was way more on the coarse side and made fast work of the leak. Another night of valve grinding and screwing parts together later I had 2 cylinders in place with decent compression. The third cylinder got assembled in the following morning. The engine got to me with a Keleo customs exhaust. It was in really bad shape too. Having no exhaust but a ready to run engine I took a flip without a muffler.
It fired up at the third try and ran pretty smooth afterwards. 

With that result I was really happy having invested in the broken parts only the muffler being an open issue. Two weeks later I tried to get the muffler back into shape. Propane torch, huge clamps and a vise later I finally got it, so that it would fit the engine again. It's certainly not a thing of beauty anymore but the sound will not be affected by that. And as it will be screwed under a hood it won't be seen too.

Hopefully the repairs will last a long time and I will find a suitable airframe in the future.