TW-715 Project

Page 7: Installing the Electronics




There is a reason I left the electronics until the very end on this model.  There is a tremendous amount going on here.  The above picture shows my first attempt at connecting everything together, and even this is a simplified version for reasons I'll discuss shortly.  As a baseline, here is the channel breakdown:

If you were reading closely you may have noticed that I was intending to run the entire system at 7.4V from a UBEC.  When I hooked everything up the steering wheel didn't work, and I eventually discovered that my servo reverser only functioned at up to 6V.  My next plan was to run almost the entire system off the 7.4V UBEC but run the steering wheel servo only from the 6V BEC in the ESC.  This would have been quite painful to wire.  While experimenting, I discovered that an external UBEC wasn't really necessary.  The Hobbywing 1080 ESC has a maximum of 6A of output which was plenty without any brown out problems, so I just eliminated the UBEC from the circuit entirely.  Later I got a higher voltage servo reverser allowing me to switch the internal BEC back to 7.4V.  The instrument panel includes a battery charge indicator, so that meant I had to split power directly off the battery with a JST connector to power the panel.  Luckily it is capable of 2s or 3s voltage so I have battery options.  I also eventually realized that my temporary EcoPower 120T steering servo had plenty of torque so there was no reason to spend an additional $100 on the Black Label.


   

The lighting system and instrument panel were a big surprise because they were not documented at all on the web site or promotional material.  The PCB shown on the left is a splitter for Channels 1-3 with  additional outputs to an external lighting board and an instrument panel.  That instrument panel is shown on the right.  The speedometer, tachometer, and the area between are all part of a single rectangular panel.  Let's start with the center area.  That "N" in the center is indicating that the transmission is in neutral and it will change to 1 for Low and 2 for High.  The upper portion of that area is currently blank but it has green arrows for when the left or right turn signals are flashing.  The tachometer is on the right and it indicates throttle position.  The ring around the outside of the tach indicates battery charge.  The red and yellow arcs shown indicate semi-low battery.  Additional green arcs would be present for a more full battery.  The speedometer on the left doesn't really indicate speed, but it parallels the tach when the transmission is in gear.  It is smart enough not to show anything on the speedo when the transmission is in neutral.  The speedo does not indicate any more speed in high gear than in low gear even though it has all the necessary information to do so.  The additional panel in the center of the dash is a clock and the three buttons beneath it are for setting the time.  There is a button cell battery in the clock PCB so it remembers the time even without a battery in the model.


   

This model doesn't use individual 3mm or 5mm LEDs for lighting, instead everything uses chip mounted LEDs.  On the left you can see the backs of the boards for the headlights.  The turn signals each consist of 5 LEDs that move sequentially to indicate turn direction.  It's pretty cool.


   

There are 5 chip LEDs for each tail light as shown.  The two on top are red and are used for tail lights, brake lights, and reverse flashers.  The three on the bottom are amber and are used for turn signals.  The amber seems to show up OK through the red painted lens.  The wires can be completely hidden behind the plastic tail panel and then under the bed deck.




I procrastinated doing the diff lock cables until the very end, but it turned out not to be all that difficult.  Again, there was absolutely nothing about how to do this in the basic instruction videos.  There was a separate video just for rigging the cables, but it was only in Chinese.  This photo shows how the cable shrouds terminate and how the cables clamp to the actuation mechanism.  There are spring cartridges in series with each cable that help to reduce the load on the servo when the locks are engaged.


   

These pictures show the best I was able to do to consolidate and hide all the wiring.  The piles of servo connections are inside that bundle of electrical tape. That wire running over the top of the engine is the battery cable.  I ran out of bandwidth in my brain to do any more work on routing.

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©2022 Eric Albrecht