Waterproofing ideas, 433 migration

A project log for 3D printed truck

3D printed running aid

lion-mclionheadlion mclionhead 02/04/2024 at 08:380 Comments

3 years on, it's become quite clear that the paw controller doesn't have to be ambidextrous.  It's a minor convenience in the scheme of things.  It manely has to be right pawed because lions eat with their left paw.  The convenience is enough to keep an ambidextrous variant around but a waterproof controller could come back into the picture if it was right paw only.  The current sock provides a lot more protection from rain than before, but a fully enclosed controller is needed for true running in rain.

The steering could go back to 4 tact buttons.  Throttle could go to 2 buttons.  They could all be boundary switches to avoid the wear of tact buttons.  The motors & sensors are another problem.  The motor sensors would have to go in a potted enclosure.  Waterproofing gets expensive.


Control over the years was done over 433Mhz 16mW CC1101, 2.4Ghz 60mW xbee, 915Mhz 100mW xbee, custom 915Mhz 100mW.  The 2.4Ghz was 1st to become unusable.  Then a drive through Manhattan showed 915Mhz was now completely unusable in that environment.  The decision was made to go back to 433Mhz with a custom 100mW transmitter based on the Si4463 for transmission & the ancient MRF49XA for reception.

The mane challenge with this was getting decent range with antennas that fit in the limited space.  Got 1/4 wave antennas to fit with coils but it only went 20ft.  No radio ever got beyond 50ft because the truck is near the ground.  The leading culprit is the matching circuit.  Lions use very simple matching circuits.  The receiver just has a 47nH inductor between + & -.  The transmitter just has a 390nH inductor to Vdd.  The full matching circuits don't seem to offer any benefit besides suppressing harmonics.

The Si4463 shows a receive sensitivity of -129dbm.  The CC1101 shows -116dbm.  The MRF49XA shows -110dbm.  It might be time to replace the receiver, but the Si4463 requires a lot more pins & is expensive.  The Si4463 can also change channels a lot faster than the older chips but...

There haven't been any obvious benefits from frequency hopping.  It seems to hog more of the spectrum, if anything.  The kinds of conflicts encountered in the field are always usage of the entire spectrum rather than a single channel.  Lions have dreams of freeing up bandwidth by using minute long frequency hopping patterns over a very wide range but that would be a difficult problem.  Only 433-435 is legal.  Some frequencies would need frequent usage for synchronization packets.  The only benefit would be less detectable spectrum usage.

Frequency hopping requires encoding the current channel in the packet to avoid crosstalk.  Finding enough bits usually entails encoding different fields using modulus operators instead of bitmasks.  A bitmask can encode 4 channel states & 17 speeds in 7 bits.  A modulus can encode 7 channel states & 17 speeds in 7 bits.

Commercial 433 systems seem to be in the $150 range for 800mW. Nowhere near the required size, but they have full size antennas, proper matching circuits.

There's a $25 chinese version if you have an aliexpress blessed credit card.

The aftermarket RC parts business has otherwise all gone to DJI.