Garmin GPS 18x: Low-cost High-quality GPS Receiver for DigiTrak Autopilot of TruTrak

Garmin GPS 18x receiving unit

Four years ago, with friend Mel's help we installed the DigiTrak autopilot made by TruTrak in our Zenith 601HDS, N314LB. The autopilot requires GPS NMEA 0183 input. To save cost, we supplied that input with the already-installed Garmin GPSMAP 195.

In the DigiTrak installation manual, TruTrak advises against that choice since the 2-second update cycle of the GPSMAP 195 is not quite fast enough for the autopilot and may result in wandering flight during turns. That problem did indeed occur, as well as occasional meandering in straight-and-level flight.

Recently, the GPSMAP 195 battery needed for retention of user options failed. A replacement battery that nominally should last 10 years failed after eight weeks. Ditto for a second replacement battery. Clearly, it was time to eliminate the GPSMAP 195. Indeed, except for the autopilot, the GPSMAP 195 was no longer needed since the combination of Garmin GDL 39 and iPad installed a year ago produces much better graphics and lots of important data.

But how could we supply the autopilot with the required GPS NMEA 0183 input? A call to TruTrak provided the answer: with a Garmin GPS 18 or the more recent GPS 18x. These are tiny receiving units that can be installed on the glare shield.  There are several versions of this amazingly small and powerful GPS unit: USB, with just that connector; PC, with serial connector for the NMEA 0183 output and a cigarette lighter plug for 12/24V power input; and LVC, with just wires.

We were about to order the LVC version when our son Martin pointed out that all versions require 5V input except for the PC case, which accepts 8-30V. Since we did not want to get into the 5V supply business, the PC version was the logical choice.

 It would have been a big mistake to cut off the plug of the PC version and hook up the wires directly to 12V, since the plug converts 8-30V input into 5V and thus must be kept. This forced connection of the 12V wires to the plug. 

Here is our solution. We disassembled the plug to extract the metal tip of the "+" connection. Next we drilled a small hole into the tip, inserted the connecting wire, and soldered it in place. For the "-" connection, soldering the connecting wire to one of the spring clamps was not possible, since they are chrome-plated. Instead, we drilled a small hole into one of the clamps and attached the connecting wire with a small screw. Here is the result.
GPS 18x power plug with connecting wires
Connection to the female serial plug providing the NMEA 0183 output was simpler. We added a male serial connector and soldered the wire for the output to the #2 pin.

Installation in the plane was time-consuming but not difficult. The GPS unit has on top the name "Garmin" in white letters. The canopy reflected that name right in the middle of the field of view. We eliminated that annoying image by applying a black coating over the name with a sharpie. At the top of this post is a picture of the GPS unit on the glare shield.

 The test flight was a delight. The GPS 18x acquires satellites within at most 45 seconds. In flight, the one-second update cycle is perfect for the autopilot and results in smooth turns as well as straight-and-level flight without any meandering. And all this for under $75!

 A word of caution: Garmin also offers a GPS 18x version with a five times per second update rate. If you go for this fancier version for some application, make sure the equipment receiving the signal has sufficient baud rate to process the flow of data.

Comments

Post a Comment

Popular posts from this blog

Testing Rotax 912/914 Generator and Voltage Regulator/Rectifier

Image
Our original installation of the Rotax 912/914 r egulator/ r ectifier. 24 years later, the two brown wires on the left were replaced by yellow wires of a new stator, see photo below. The Rotax 912/914 electrical system may fail unexpectedly. I t happened to us once at a really inconvenient time : S ee Rotax Goes South As We Go West . Most likely the electrical failure is caused by the voltage regulator/rectifier.  To ver ify this , we now carry in the plane a small multimeter that measures AC/DC voltage and resistance and use the checklist below. The checklist assumes a standard installation as described in the Rotax installation manual Section 24-00-00, without additional external generator, and that the voltage is not in the normal range. Testing Electrical System Beyond Regulator/Rectifier It is possible, though quite unlikely, that the electrical failure is caused by something other than the generator and regulator/rectifier. There is an almost infinite variety of poss
Read more

Rotax 912 Engine: 2,400 Hours in 28 Years (achieved in 2023)

Image
Rotax 912 engine The  Rotax 912 engine  in o ur plane, a Zenith 601HDS, has reached an important milestone. Over the past 28 years, it has run 2,400 hrs without major repairs. Zenith 601HDL, N314LB It's appropriate to reflect about this performance and muse how this is possible. After all, when we bought the engine, in 1994, the suggested TBO was 1,200 hrs.  Since then TBO has gone up, first to 1,600 hrs, and more recently to 2,000 hrs. Of course, those increases apply to later engines, not to our early model. Let's see how the engine performs after all this time. Performance after 2,400 hrs Compression is 76-80 lbs/sq.in. on all cylinders. Oil consumption is less than 1/2 qt per 25 hours.  During each oil change, we cut open the filter and look for metal. There is almost none, just one or two tiny specks. Essentially, the engine shows no sign of wear. The engine performs well up to the legal limit of 14,000 ft MSL for flight without oxygen. When flying
Read more

uAvionix TailBeacon: Installation and Testing

Image
TailBeacon of uAvionix mounted on rudder of Zenith 601HDS The uAvionix TailBeacon is a low-cost device that satisfies the ADS-B Out requirement kicking in on January 1, 2020.  The TailBeacon piggybacks on any Mode C or S transponder, and thus avoids purchase of a much more expensive ADS-B transponder.  There are two TailBeacon versions: the TailBeacon TSO for certificated aircraft and the less expensive  TailBeacon  EXP for experimental aircraft.  We bought the EXP version for our Zenith 601HDS, N314LB. uAvionix also offers an alternate ADS-B Out module: the  SkyBeacon .  It uses similar technology, but is installed in a different part of the airplane. Details on this below. T here are two versions: TSO and EXP.   This post covers why we selected the TailBeacon and how we installed, tested, and evaluated it using the  FAA ADS-B Performance Report. It's easy to adapt the process for installation of the SkyBeacon. ADS-B Out Requirement Starting on January 1, 2020,
Read more