Given the help provided by others, I thought I’ pay it forward with my spin on the installation of the FRSky DHT 8Ch DIY transmitter in my Turnigy 9x Transmitter. Before getting into the details, I’d like to credit RCModelReviews for Bruce’s how-to video as well as RCHacker.com for details on how to update the firmware of the D4R-II (to solve the PPM framerate issue). Although this is primarily about the DHT DIY module install, it goes hand-in-hand with the D4R-II receiver – so I’ve added a bit on it. Also, there are other examples of how to add the DHT module out there (Google is your friend). Instead of doing a video, I decided to take a series of stills and annotate them as I went along. Hopefully this helps you get yours installed as well as gives you some alternate ideas to the approaches others have taken.
From a difficulty standpoint, I would classify this as a 4 out of 10. It’s less involved with playing around with circuits and soldering than it is with simply finding the right place for components and modifying the antenna mounting and glueing things together. It’s a pretty easy install. Also, I’ve referenced the D4R-II receiver as it pairs well with the DHT 8CH transmitter.
Flashing the Dr4-II receiver with the 27ms framerate fix. The link above can guide you through this. Note – you only need to do this if you plan on using more than 6 channels.
Switching over to PPM (or CPPM) mode. This is easily done in Cleanflight.
Steps:
The following shows instructions on how to do this mod. To see larger pics, click the first image. It will popup allowing you to view the full size images and scroll as you go through each step. Textual instructions are at the bottom of each image.
Tools Needed: phillips screw driver (small and med), wire cutters, hot glue gun, krazy/CA glue, small crescent wrench, pen/sharpie, LiPo and ESC (for binding/testing)
Get yourself a clean area to work. Remove the back cover of the transmitter.
The DIY FrSky DHT module has 3 connections (PPM (yellow), GND (black) and +5V (red)). They will be soldered to the connections noted here. When looking at the main board, these are the top 3 pins.
The existing Turnigy transmitter needs to be removed. Flip the back over, and note the existing antenna wire as it will have to be cut once we get the board out. Remove the 2 screws to expose the module.
Some modules are glued in. Mine just popped out. If yours is glued, use a sharp knife to cut away the glue to remove the module. Tip: You can also use the hot tip of your glue gun to melt the glue away.
Note that the antenna consists of 2 solder connections on the main board. Might be wise to note this in the event you ever have to re-connect the stock antenna.
Once the antenna wire is clipped, flip the unit over and pull the wire out.
You can now screw the back module together and snap it back in place. At this point, the case purely cosmetic and serves no functional purpose.
Remove the small screw that holds the antenna in and carefully slide the antenna out through the top. You can remove the outer cover unit (that goes between the antenna and the transmitter) as it wont be used.
Run the DHT antenna cable and connector through the hole. It’s a bit tight so you may need a tool to help get it through. Don’t push the tool on the cable – push the gold screw connector instead.
Once the cable is through, screw the new antenna on, and use a small wrench to tighten the screw to the antenna itself. This will ensure the antenna does not come loose over time.
Slide the antenna back down into the hole. It should not require much force. Slide it down far enough so the base of the brass unit cant slide down any further. This is where glue will be applied.
Hot glue the antenna base to the shell being careful not to put glue near areas where the top shell meets the bottom.
Tip: The DHT module has connection/pinout information written on the bottom. Since it will be glued bottom down, it’s a good idea to write down the connection info on top .
When placing the DHT module, take note of limitations. These 2 pads are bases for the 2 spring metal units in the top shell (next picture). Make sure you don’t place the DHT module over either of these. In my case, I placed it just below.
A view of the 2 metal spring units.
Put some hot glue on the bottom of the DHT module and glue it in place.
Placing the DHT module just below the 2 pads.
Solder the 3 wires from the DHT module to the PPM, GND and +5V on the main board as noted earlier. The order is PPM (yellow), GND (black) and +5V (red) – they are the first 3 pins from top to bottom. Tip: This is the order of pins that I have on my 9x. It’s always wise to search around to see if others have the same connections (as board revisions may change this at some point)
Next you will need to decide where to place the binding button/LED unit. There are 2-3 places where it can be put (see links at top). Tip: The LED and button have a lot of height to them – you will need to add spaces to the board to ensure the don’t stick out too high (more on that later).
In order to drill the two holes, you need to know the center spacing. Others have used templates etc. I found my calipers came in handy here. Measuring center-to-center is about 7.75mm. See next slide.
Once you have the measurement on your caliper, tighten the locknut. You can use the sharp points of the caliper to mark the drilling spots. Next…
In my case, I chose the top of the front shell. Once you figure out where center is, press down firmly on the caliper to mark the 2 center holes. Tip: take a measurement of the full length and width of the LED/button module as there is limited space back there and you will want to ensure you don’t set the holes to far forward or back. I found that center (front to back) worked well, but also had to play around with it a bit to get a nice fit.
Showing the 2 marked holes ready for drilling.
Tip: Take a small phillips screwdriver and mark the holes a little larger. This will help keep the drill bit centered.
Select the appropriate bit and drill the 2 holes. You will want a bit that is slightly larger than the button / LED.
As noted earlier, the LED/button module requires spacing so the LED and push button don’t poke out of the top too far.
Spacers: A used Apple iTunes card does the trick. Have a look at both sides of the LED/button module. There is space to add spacers on either side of the main board. After slicing up the iTunes card, I stacked and glued 4 pieces to each side. This provides the perfect height so the button and LED just barely poke through the top of the shell.
Before gluing the spacers on, do a test fit by placing the module near the shell to ensure the height works. Once done, glue the spacers to the module edges. Krazy glue works well.
Clean up the holes and do some test fitting of the LED/button module to ensure there are no snags when pressing the bind button. Once you are good use hot glue to set it in place. Start with a bit and test the push button a number of times as the module can easily shift while the glue dries.
The next step is to find a place and mount the mode switch. The location for mounting is depending on your plans for using this switch. In my case, I am leaving it the same way (#2 position) and mounting it inside the case (as I don’t need to access it). I found an impression to the right that is a perfect spot.
Before applying glue, make sure that the switch can toggle all 3 positions. Once ready, drop a small bit of hot glue under the base to hold it in place. Test the toggle action of the 3 modes again. Once happy, put more glue around the base. Tip: To avoid the switch flipping modes if you drop the TX, put some glue from the top of the toggle switch to the case. This will ensure it stays where it was set.
Do a quick check to ensure that none of the internal components touch the switch and ensure there is no chance of other connections arching against the metal.
Drop glue around the rest of the switch base to hold it in place.
It’s also a good idea to glue down some of the longer wires to ensure they don’t get in the way of screw channels etc.
Check your connections again and ensure everything is mounted correctly. Before closing the case, be sure to plug the white connector that connects the back unit to the mainboard of the TX. Next step is to bind and test the TX/RX. When closing it up, I suggest only using a few screws to keep in closed. Once binding and testing is done, then the rest can be done.
Binding is straight forward. On the transmitter,hold down the bind button and turn the power on. Release the bind button. The red LED on the transmitter will be flashing. Then, hold down the reset button on the receiver using a small screwdriver, then apply power from your ESC. The LED will flash indicating binding has been completed. Turn power off on the receiver and transmitter. Then, turn the transmitter on, then apply power to the receiver. The green LED on the receiver should now be on. Plug a servo into one of the receiver channels to test the connection. If the servo does not move, you don’t get desert tonight! Note: you can download instructions from the FrSky site.
I decided to go with the FrSky D4R-II as this and the DHT are popular combos. I used PPM (CPPM). To use PPM, bridge the signal connectors on channels 3 & 4 (pictured) with the provided jumper that came with the RX.
Hook the receiver up to your flight controller. Pin 1 on the FrSky to Pin 1 on the controller (Flip32+ in my case). Follow instructions to get it working in PPM.
This is easily done on the Cleanflight configuration page.
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