May 27, 2018

Upgrade of the ZMR250 with HGLRC F3V4 PRO AIO

All in one! AIO! Sounds tempting doesn't it. Well, I fell for it!

I don't get much time to fly nowadays but I got out a few weeks back and took the ZMR250 for a spin. That didn't go so well. Partly because I always forget between flights, partly because the camera is faulty. In fact, all my "modern" cameras made for FPV have had intermittent problems. Something I have never seen in the DIY cameras everyone used a few years back.

Anyway, the ZMR250 build was a bit of a quick fix of a second hand quad I got and it had a few weak points;

  • Badly soldered PDB
  • PWM configured ESCs with classic servo connectors
  • No OSD
  • Crappy antenna wiring from the VTX
  • Intermittent video feed from camera
  • F3 flight controller with no voltage or capacity monitoring

My idea was to adress a few of the issues but maybe not all. I don't have much time to spend on building, waiting for china packages and don't want to spend money on a quad that I might only fly a few times this summer. The goal was to quickly and cheaply get it working and reliable.

I have a "HGLRC F3V2 PRO AIO OSD PDB VTX" ( I think I got it all in there ) board laying around for another build I forgot what it was. Combining this with a look inside the crappy (Foxeer, now you know) camera was going to be good enough. So, two evenings one hour each and I got it together and flying. I didn't take time to document it but I wanted to share my experience with the AIO board. So here goes.

First off, link to the actual product that I bought: http://bit.ly/2JfslAW. I bought it over 6 months ago and there are new boards out now so don't buy this one. In fact, even if it was newer I can't recommend it. Keep reading to get your expectations down to earth.

The flight controller board

First off, what does the flying. The board is based off a SP Racing F3. This is actually the same board that I took out of the ZMR250 so I won't be getting any better flight experience. This is an outdated board as of writing this and already when I got it the F4 were quite common. From flying this board, I must say it is performing as expected.

I had some issues with programming flight controllers with betaflight before but this particular board works really well. It always connects, always reconnects after reboot and connecting both USB and battery does not fry the voltage regulator (as on some boards).

Power distribution

The board is speced as having a built in PDB. It does not. It has a connector where you can put an XT60. Which you should NOT! It will then rip your FC appart when you crash and your battery comes loose. However, you would want to run you power through the connectors (with a wire) to get the voltage and current sensing going, which is built into the board.

The PDB part then consist a a single solder pad for each polarity where you solder your ESC leads. I did not even attempt that since it would only make a big mess. Instead I installed a real PDB below the FC which does its job, but nothing more.

So this card will not save you any space by having builtin PDB if that's what you're looking for.


OSD


The board has built-in OSD. This is an important feature and I expected it to save me some headache. However, it turns out it is just an OSD chip placed on the board and it does not integrate with the betaflight software. This is somewhat of a bummer. Now to program the OSD you must hook it up with an FTDI. This is not really a big deal, but the port is very hard to access once the board is mounted. One point I'll give to HGLRC is that they included a cable for connecting the OSD programmer. However, you must bring your own programming chip.

The default settings are working so-so. The OSD setup seems confused about battery voltage and cell count and will constantly warn for low voltage. This is fixed by reprogramming it, which is a bit of a hassle.


VTX

The VTX works as it should. I had no suprises with the operation nor the settings of the VTX. The single button interface takes a few seconds to figure out and the single digit display on the FC makes it easy to setup.
The main weak point of the VTX is the antenna connector. It works really poorly for this application. The connector does not snap in as it should (bad quality perhaps) and the still antenna cable will easily pull it from its location. I clamped it down with a plier while fixating the connector and the first part of the antenna cable with a nice dab of hot glue.
It is also possible to disable the VTX should you not want to use it.

Manual

I found no PDF-style downloadable manual. I had to mention this as it annoys the shit out of me. I hate having to google for this kind of information every time and get most of the information from product pages that I know will disappear one day.



TL;DR

To sum up this rant. Don't buy this board. It does not have PDB and the VTX connector sucks. OSD is a pain to setup. Also it is outdated. I'm going to buy a new AIO board soon and give you a new review from the AIO world!









April 1, 2018

WLToys K989, new FPV indoor car

I saw this in an youtube ad from HobbyKing some time back and I was a bit intrigued by the features they had crammed into it. We have a few L939 fitted with FPV cameras at work but those cars are really not that fantastic. They have a stiff rear drive, bad handling and tends to flip over easily while turning.

Now, the K989 is something completely different. It is a bit bigger, I give it that but it has four wheel drive, rear and front differential and a low COG. It comes with a clumsier transmitter, but with a better feel to it.

The K989 is a real joy to drive, especially considering the price point compared to the alternatives in similar size and performance. I gave it two essential initial improvements, which owner should consider.

Improved front bumper


The stock "bumper" is just a piece of foam. It is good considering it will protect the chassis from damage on front impact. However, the front wheels and suspensions are not protected at all. And spare parts are still a bit hard to come by, at least if you can't stand monthly shipping delay from China. So, protecting the suspension is quite essential.

I made a new bumper which covers the front wheels, place right behind the edge of the body shell. It turned out it was quite important as I broke the first version after only a few minutes. So I improved the design a bit and printed it in ABS instead of PLA and I haven't managed to break it since.

The bumper model can be found on thingiverse.

K989 broken bumper

Lubricating the differentials

The diffs aren't that great. My specimen had a read diff that felt really bad out of the box, but the front was ok. I had to take a peek in the diffs to see if they were ok, which they were. But they needed oil. I gave them some 800cst silicone oil to work with. I didn't fill the diffs with oil as I suspected they would leak it out on the floor anyway. And they are leaky. But with at least some oil to work with, even the rear diff came to life and feels smooth now.

Oiling the diffs are probably the most important thing to do right away, they are dry on delivery and the planet gears are not of the best quality. To prevent the diff from eating itself you should probably lube it up right away.



FPV Mount

Mounting an FPV module on the car is quite easy. The stock receiver/ESC module is flat, positioned in the front of the chassis and makes for a perfect placement of a camera. The windscreen of the cover needs to be cut of course.

A colleague mounted the camera module simply with a rubber band and some hot glue. But I couldn't settle with that and I made a mount to 3D-print of course. The mount also holds a voltage regulator and I draw power from the main lead of the battery, since the battery is connected using the balance lead to the car itself.



WLToys K989 FPV mount

January 27, 2018

Very last order from banggood?

A few issues have come up lately that has made me thinking I might just have made my last order from banggood. So what's going on?

Well first off I order less stuff now than I did a few years back. Simply because I'm not spending as much time on the RC hobby anymore. I have ordered other stuff than hobby stuff a few times, like lamps and electronics but the impact of quality is higher on items like that and I tend not to order household products from China.

Second, I've had a few bad experiences lately. Tracking is working less well than before and a few packages never arrived. When packages don't arrive, banggood customer services have started becoming a bit more complicated to deal with (despite my VIP status and my order history!). Worst of all, I got one of my last orders re-sent only to arrive without all the items I ordered.

And third. And this is the most important one. Sweden is changing its policy regarding postal packages from China. The swedish post will introduce a fixed fee for ALL packages passing customs from China via the postal service. The fee will be about 14€. I think this is a good thing. The shipments (especially since Wish started their business) have increased tremendously from China and it is because of a few reasons.

  1. People order cheap Chinese crap products, often without QA and valid certifications. Many are illegal to use in Sweden/Europe.
  2. No VAT is paid on most of the orders.
  3. No shipping is paid, since China subsidizes shipping and the trade agreement between Sweden and China causes the Swedish post to pay the shipping in Sweden.
  4. Most Chinese shops ships each ordered item separately. This is probably due to a subsidiary system behind the internet portals.
So. The Swedish post ships 140 000 parcels from China every day. Many containing small products worth a few euros. The Swedish post pays for the shipping. And local and domestic shops are met with unfair competition since the online shops do not pay VAT, do not meet certification requirements and do not pay for shipping.

It was fun while it lasted, but now that they take care of the problem I must say it was about time.

The only negative part about this is that many times when I order stuff from China it is because I cannot find them in Europe or Sweden. Simple things like screws and transistors have become less available to others than corporations ordering large quantities. But that's still a minor problem in the bigger picture.

December 30, 2017

Wall mounts for my RC cars

I designed (if you can call it that) and printed simple wall mounts for my RC cars this weekend.


This is how 5 of the prints turned out. My printer needs a lot of love to print. But when it prints it prints well. I had not given it enough love apparently. But when I took the time I got it back to friendly operation again.



And then this was the result. Simple wall mounts to hang the car by the tire. Turned out I actually only needed the middle screw hole.


The mounts in "action" with the cars dangling by the front tire. Haters gonna say it's bad for something in the suspension obviously.


The hanger is available on thingiverse for the ones that would want to print their own: http://bit.ly/2zQLxML



Final flight of the F-35

Last time I flew it I broke its nose. That was two years ago. After the nose was broken off, it might have been ugly, but it flew well.

And today was the day to fly it for the last time. Since I do not expect to fly this plane any more and it is ugly and taking up precious space, it was time to get rid of it. With a few final flights.

To spice things up I had 4S batteries prepared. ESC and motor is speced at 2-3S.

Away it went. My friend gave it a perfect toss and the power of 4S made it fly perfectly. It was fantastic. For about 10 seconds, then I misjudged the distance to a tree and the plane was converted to garbage.

Collected remains of the F-35

December 17, 2017

Futaba replacement?

Well hello there dear old blog! It's been a while now. I haven't forgotten about you, I just haven't done much on the bench lately.

BUT. I did get myself a radio on the HobbyKing sale maybe a month back. Being a Futaba fanboy, I never expected that I would ever in my life buy a Flysky system. But now I have, I got myself a Turnigy Evolution. I've been looking at alternatives to the bulky Futaba, at least for the leasure flying I do at the office and now that it was on sale I ordered the Evolution at 35€, incluing a receiver.


60€ radio to the left, 600€ radio to the right


Ok. So, there's a small price difference between the 14SG and the Evolution. Don't get me wrong. The 14SG is a flawless radio, at least by the time it was launched. It has never ever glitched in the transmission and the telemetry was a great addition and quite unique in the price range before the Taranis arrived. I really love that radio.

But for flying quads, especially indoors I need two major features.

  • 6 channels
  • Voltage telemetry
And the Evolution has that. Yes, it has telemetry. And the receivers are dirty cheap. And the radio was dirt cheap. In fact, I think I can outfit most of my rotor crafts with receivers for the price of one single Futaba receiver. 

But how bad can it be? I'll get back on that if I have issues with it.

I will not forget to mention there are alternatives to the Evolution out there as well. One of them is the TBS Tango. It's a purpose built radio for quad racing and has some nice features in therms of programming. It is quite expensive, and comes without a transmitter. Which makes it ridicously expensive.

And coming up is a multi protocol radio called iRangeX iRX-IR8M. It looks like a knockoff of the TBS Tango and comes with multiple radio circuits built-in. I won't order one until there are some decent reviews online. My guess is that it will have a bit better gimbals than the Evolution and a poor feature set in the software. It's mostly the form factor, the basic telemetry and the multi protocol feature that will push this product.

October 14, 2017

"Fixed" the z-slop issue on my Fabrikator 2

So. I've finally worked out an extremely simple solution to the Z-slop issues I've had with my Fabrikator II.

The problem with the Z-axis is a combination of two issues with the printer.

  • The Z-backlash prevention mechanism is poorly designed
  • The Z-axis does not run smoothly and has to be forcefully pulled down by the Z-axis rod
The obvious solution would be to address those issues. And I have tried, but can't get the Z-axis to run smoothly enough.

What happens because of this is the there is a 0.2-0.4 mm slop in the Z-axis when it descends and then starts climbing again. This happens when the print starts (home, lift, descend to first position) and whenever a lift is done during the print. As an effect the printer will print 2 or 3 layers at the same height, causing the printer to print badly and the model to be of incorrect height.

So far I've only printed parts in the printer where the effects of this issue is not problematic. Which is quite limiting.

After a bit of googling gcode I realized I can solve the issue at the print start with only a bit of fiddling with the pre start gcode snippet. By default in Cura it looks something like this:

G28 ;Home
G1 Z15.0 F6000 ;Move the platform down 15mm
;Prime the extruder
G92 E0
G1 F200 E3
G92 E0

One of the important parts to notice here is the "move down" which on this printer is actually a "lift" part. It is when the printer comes down from this movement and starts moving up again that the problem will occur and the printer will put down multiple layers at the same height. So we can remove that line.

But the homing process will still have the same problem. The last movement of the homeing process is the Z-axis descending until the endstop swith is triggered. After this, the first 0.2-0.4mm of any up movement by the Z-axis stepper and rod will not result in movement of the print head. To counter this the entire build must offset to move the entire model up and prevent this initial slop.

This turned out easier than I expected. By using the G92 an axis position can be adjusted. This will introduce the offset needed and will effectively cause an initial lift of the given value. So I added this command as the last initial command before the print. The resulting Start Gcode now looks like this.

G28 ;Home
;G1 Z15.0 F6000 ;Move the platform down 15mm
;Prime the extruder
G92 E0
G1 F200 E3
G92 E0
;Set the Z-position with offset to counter fab2 z-backlash issue
G92 Z-0.2


This will cause my prints to turn out good and not need any further adjustments. The solution has two drawbacks.

  • The initial movement of the print head will traverse the bed at 0 height. This can cause issues, but might also wipe the nozzle. Which is not always a good thing if it happens at a less preferable location.
  • The print cannot contain any lifts. Prints that would benefit from lifts can still not be printer with this printer.
So. This solves my issue short term. But I should probably try to solve the mechanical issues as well to avoid this hack.