Sunday, December 21, 2014

WLT v262 problems

Tried to fly my v262 the other day and even at full throttle, it doesn't have enough power to take-off. Fore-Port motor is especially weak. Sprayed motors with contact cleaner and lots of black dust came out. It didn't help. Sprayed Tri-Flow inside ... still no help. Removed foam body and now quad flips over on take-off. Eventually, Fore-Port stopped turning completely.

Motors 3,4 run CW. Motors 1,2 run CCW.
Each red prop is build different and rotate opposite
each other. Same with black ones.
Brushed motor
Open in a new window and then click to Zoom-In

One brush is fair. Other is ground-down to nothing and missing (only part of wiper-arm remains).

Should I fix a $60 quad? Probably not, but I really like my v262 because it's impossible to crash it or damage it with body left on (it just floats down to earth). It was my first quad trainer. Motors aren't too expensive so I currently have some on order BG's US-Warehouse.

To repair my first v262 motor failure, I ordered 4 of these from BG USA-Warehouse at $6 each. I ordered on Saturday and got them on Tuesday  :cool:. This was with Free-Shipping via USPS.

All 4 have a large sticker on plastic bag that says "V262-16 Motor"

Smaller sticker:  SKU088984 ClockWise EVK 1028-0
Inked on motors themselves: N50-3124, 2014-10-22

Smaller sticker:  SKU088984 CounterClockWise 0925-2558
Inked on motors themselves: LV-N50-3027/34.5, 2014-06-06

Even though they are supposedly the same, I ordered 2-CW, 2-CCW ... and will replace as such. Unlike the store pic, gears are mounted towards the middle of the shaft like originals.

Repair went fine, I replace Motor #3 with a ClockWise-motor. Gears mesh-together a little loose (a fraction of a millimeter off) but there isn't really a way to easily adjust that. CW means red-positive-wire goes to + sign on motor. Once the bad motor is replaced, controller board now spins all motors at full speed (which it wasn't doing before when it detected a bad one). LEDs on 2 front red-prop-ed motors are white. LEDs on 2 rear black prop-ed motors are red/blue.

I also made a better battery mount. Battery holder is turned upside down to accept spare slightly larger (but exact matching) $5 battery from HobbyKing. Added a loose wire-tie for a little middle-support, and then a velro-strap from junk-box.

Compass holder cracked, oh puck

Flying around in the backyard today. It's confined and has plenty of obstacles, but was mostly just light flying, hovering, and  AutoTrims. Also testing GPS on cold, overcast, cloudy day with high Kp-Index of 5-6 (was mostly getting sats=7/hdop=2.2 ... pretty surprising actually. Eventually went to 8/2.0).

During a fair landing, I kinda landed on one LandingGear skid and quad flipped over upside down. It wasn't even that bad a landing and really surprised me. Anyway, as it came to rest I heard a cracking sound.

It was the compass puck. So, Prop-Guards won't save the puck. I "glued" it back together with Plastruct solvent. 


Installed new double-sided foam tape on bottom. I did a new mount with a Plastruct strap (and small single-sided foam tape cushion) and tiny metal screws.


After Compass Calibration, new Compass Offsets are -118, 9, -1 . One of those is significantly higher than before, but still well within recommended range (-150 150).

Also recalibrated the Accelerometer while I had MP running.

EDIT 2015: Ended-up changing to this mount after cracking puck. Simpler and no extra metal screws near compass. Compass Offsets are a little better now at -99, 17, 15.

Sunday, December 14, 2014

Telemetry Radio - Moved inside aircraft

Telemetry radio has been working fine attached to bottom of Nova. Therefore, I bought a 15cm SMA cable and moved radio inside Nova and the antenna comes out the side of body. It's a tight fit, but radio is in channel between PowerBoard and shell. Only thing cable is really touching is the slight edge of ESC white nylon socket.

EDIT 2015-01 : This is the my old Internal layout. It has since been changed and optimized.

EDIT 2015-05 : Since the above pic, I had moved the 915mhz radio back outside/underneath Nova. I have now tried moving it back inside again (during gimbal install). I didn't want it in old location because GPS is over there now.

This is the new location. Notice FrSky antenna moved to top of RX (still at 90 degrees to back one). If this all passes interference and RSSI testing, it stays here. I will just add a bit of foam tape to prevent vibrations between radio and case.

Verified 3DRobotics 915mhz Telemetry radio settings. ECC is on. While slower through-put, official docs say it is recommended and supposedly it has better distance range. Yes, you can change settings on the slave radio from MissionPlanner (without removing it from quad).

Monday, December 8, 2014

Repairing GPS & Compass Modules and Cables

I cleaned away black tarnish and corrosion from pins of PicoBlade socket on the BS-126 GPS-Module (HK Nova stock one). The blade-pins appeared to be made from a solid/non-plated metal. Tarnish and pitting (causing the poor electrical connection) was pretty deep and hard to remove, but I managed. I carefully scraped with a small/dull hobby-razor knife, used a special file for cleaning/ burnishing relay-contacts, and cleaned with "CRC QD Plastic Safe Liquid Contact Cleaner". As usual, this was all done under extreme magnification and lots of light. I got all surfaces of blade-pins nice and shiny again (and able to conduct electricity). 

I ordered parts to build a new GPS-Module cable and they arrived in a few days. Wires appear to be 30 gauge with thin flexible silicone-type insulation. Pins were much better than original ones and didn't have any strange plating on them. Crimps also looked fine. I carefully removed the Dupont (RC Type) pins from included single-position plugs and installed new pins/wires in a good 4-pin-position black Dupont plug from spare-parts box. Connection seems to be 100% now and not susceptible to drop-outs during basic flexing of cable or vibrations. During back-yard testing, I was getting a fast GPS-3D-Lock and good sats/hdop numbers. I'm calling it fixed.

New GPS-Module cable installed. Pic is good enough to see pin-outs.

I replaced the foam tape to be similar as shown above. I used 4-5 layers to make it as high as possible. The ceramic antenna on top is just barely touching the top plastic body cover (when fully installed) and seems to get the best reception this way (for this entry-level GPS Module that means just "acceptable").

Never again will I assume a connection is good, just because connectors are securely fastened (not on this model-aircraft anyway).

Upon inspection of Compass-Module, found the same problems. Luckily I ordered some extra parts to build more cables. New cable will end-up being about 1.0 inch shorter (but still reaches with length to spare). Like before, still had to carefully clean tarnish and corrosion from cheap imitation PicoBlade sockets themselves, soldered to the boards at both ends. Then, I installed the new cable.

New Magnetometer (Compass) cable
As you can see from the above pic, the pin-outs (for the stock Nova compass) are:
Update 2015-01: I have not had a single problem with GPS-Module or Compass since replacing these cables and cleaning away corrosion and tarnish (from the modules themselves).

Monday, December 1, 2014

No GPS (again)

Drove down to field to fly. Clear sky day, winds 10mph, Kp-Index is 2 (good). I flew my smaller v262 quad and then got the Nova out.

I couldn't get a GPS-3D-Lock at all. DroidPlanner was reporting sats=0/hdop=100 after 15 minutes on flight line. Tried power-cycling and even a new battery.

Apparently, with GeoFence turned on ... if you have no GPS-3D-Lock you can't Arm at all or even fly in manual (I couldn't Arm in Stabilize either). You can't change settings like that with DroidPlanner-1. Without my laptop at field (to turn it off) ... no flying for me today. I packed it up and drove home.

In MP/Terminal/test/gps it gave me the response "ublox ok". ScottFlys (from RCGroups forum) helped me and pointed-out that my Logs revealed the GPS-Module seemed to be communicating with APM-FC but there was no satellite data. GPS Status codes were all "1" (trying to acquire sat data) after many minutes. It was acting like maybe the ceramic gps-antenna was bad or broken.

I considered turning-off GeoFence for now in case problem re-surfaces while at field. However, instead I will just fix problem. As long as I have a minimal GPS-Lock, it will still Arm. On second-thought, just turn GeoFence off while trouble-shooting GPS problems (on less variable).

BeStar BS-126 with ubx-g6010-st U-Blox chip

Upon opening the Nova, I found everything looking visually ok. The GPS-Module's blue-led was flashing (so it was getting power). The gps-module cable was plugged in all the way on both sides (the Molex PicoBlade side at gps-module and RC-Plug side at FC). I removed cable and did a rudimentary continuity test (using only exposed outer contacts) with my ohm meter ... all 4 wires passed. It's a simple cable... GND-TX-RX-VCC.

I re-connected it (didn't really do anything to it) and GPS-3D-Locked in seconds after powering Nova on. I was getting sats=11 and hdop=1.3 very easily. However, if I wiggle the wires and connectors it goes to sat=0/hdop=100 again. Appears to be a good old-fashioned intermittent bad connector or wire. I'm thinking on the RX or TX lines since the GPS-Module is getting power the whole time (it's blue-led is always flashing).

Inside APM FC
Let's start at the beginning. I opened the FC and checked the 4 gps header pins. All clean and shiny metal. Their solders to PCB also look ok (not great, but acceptable). All these examinations are under heavy magnification with lots of light.

Cable: RC-Plug/Dupont (FC side)
After documenting the whole cable's pin-outs, I carefully backed-out the pins and examined the crimps under magnification. They looked fine. I didn't see any corrosion or tarnishing (contact points were shiny). I couldn't really find anything wrong so I just adjusted (very slightly bent contacts) the pin-sockets in this end of the cable to be tighter and cleaned with contact cleaner. Pins do appear to be fairly low-quality metal but ok.

Cable: Molex PicoBlade (BeStar BS-126 GPS-Module side)

First thing I notice is that the white nylon plug is poorly made/moulded and not a genuine Molex part. It is also missing the Molex patent marks. I carefully backed-out the pins. Second thing I notice is that the pin-sockets are very low quality clones. They are obviously not genuine Molex parts either. They also appear to also be poorly Chrome-Plated ? Since when are contacts chrome plated? Shouldn't it be something like gold or even tin ? There is also a black tarnish inside them where the contact points actually touch the socket's pins (appears to be a bad "un-like metals" reaction). Surprised it was making any contact at all. Looks like I have found the root problem.

Zoom-in the see spots of black tarnish on pin blades.
It's the same on other side of pins.
BeStar BS-126 GPS-Module (PicoBlade socket)
Found similar black tarnish on both sides of pin "blades". But only on the 4 pins that the cable uses (so it's obviously a unlike metals reaction). Comparing to some new genuine Molex PicoBlade sockets (direct from DigiKey), it's obviously a cheap clone. The pin's actual shape is a little different and you can let the blade-pin's composition metal is not the same as the genuine part.


I have ordered parts to make a new cable. I will try to clean (poorly cloned) PicoBlade socket's blade-pins on GPS-Module and salvage it.


I only have about 8 flight-sessions on my Nova. During that time I have experienced 2 complete failures of the GPS-Module (to find ANY satellites) and 2 attempted fly-aways during GPS dependent RTLs. At the time, I chalked them up to sun-spots, CME, and/or poor Kp-Index (general GPS glitches). One I even thought might have been me flipping the wrong switch (and/or incorrect FrSky radio switch programming) while trying to invoke FailSafe condition. Due to the intermittent nature of this problem, it's taken a while ... but it looks like I have finally found the root cause of those failures.

GPS Module Trouble-Shooting:
Here are some notes. I will flesh-out these notes if I ever have to do more GPS-Module TS or decide to replace/upgrade mine completely.
  • Test GPS-Module outside (on a clear-to-partly-cloudy day) so it's ceramic antenna has a clear view of sky (and satellites). One less variable to worry about.
  • Give it at least 30 minutes to acquire a signal before you give up.
  • Verify cables and pins are good with a multi-meter (voltage and ohms)
  • I think GPS works on radio frequencies 1.2ghz and 1.5ghz . Nothing else should be running on those frequencies or you will get interference.
GPS Module's Blue-Led: Means GPS-Module is getting power and I think (maybe) also initialized and ready/working. Can't go much further without this.
GPS Module's Red-Led: This led is mirrored by Nova's external Green-LED. Flashing for "trying to obtain a GPS 3D-Fix" and solid for a proper 3D-Fix.
You can connect Nova's stock uBlox GPS-Module directly to laptop with an Arduino FTDI-to-USB adapter. Use uBlox's u-Center for Windows software. This will verify GPS-Module is good without any help from Flight-Controller. uBlox GPS-Module must have APM config file loaded (only needs to be done once ... unless it gets corrupted somehow).
If you ever connect VCC power to GPS-Module backwards (reverse polarity) you have likely fried it completely. You might try removing the battery (or is it a super-capacitor) or otherwise master-reset it's memory.
To estimate what GPS you should be getting: