TPU Stack v1 design

In this post, I will cover the design process of the TPU Stack, from parts selection to the assembly.

Part Selection

As this stack is intended for big quad, the main stack will use the 30×30mm standard mounting pattern. Using bigger board will also make the final integration easier.

4 in 1 ESC

There is a lot of great BLHeli_32 4 in 1 ESC nowadays, but it turns out few matched all my criteria:

Big heatsink on MOSFET. Mandatory, heat dissipation will be critical in a sealed enclosure.
FC connector on the other side of the heatsink. Mandatory in order to keep all the wiring nicely inside.
BLHeli telemetry support. Mandatory. I consider it safer than direct ADC measurement for battery voltage.
Dedicated shunt resistor for each ESC. Optionnal, that’s for a futur project that may use this stack. Also allow precise current limiting on each ESC, safer.
6S, 40A mininum rating.

My choice went to the T-Motor F45A 4in1. It fulfill all of my requirement, and it is marketed as a highly reliable ESC by a well-know manufacturer, T-Motor.

Flight controller

The main requirement for the flight controller was to have an onboard Vtx with decent cooling capabilities. This only criteria drastically reduced the number of options, as this kind of board is more of a niche than a popular setup. I end up picking the KK-F4 from LDARC:

All the I/O use connector instead of solder pad.
The Vtx won’t be exposed, as there is a heatsink for that purpose.
Design and layout seem good quality.

Misc

Some other parts are needed :

Motor connectors: Amass MT30 are perfect for this application.
Filtering capacitor: The F45A comes with 2 10×16mm low ESR capacitor, they will be integrated.
Rx: I’m a FrSky user, so a R-XSR must fit inside.

Design

After modeling all the parts, I started to move them around to find the optimal disposition in order to get the most compact but still buildable stack. I end up with the following layout (yes, the pink cylinders are the capacitor):

The next step was to build around the enclosure, which is composed of two parts. The bottom holds all the component, and a top cover closes the stack once finished. The top also features an integrated cap for the USB connector of the flight controller. I managed to keep the total height of the stack at 20mm, so it can be used in low profile builds.

3D print

I printed both parts in Sainsmart TPU, my go-to material for drone stuff. I couldn’t avoid supports, which are a bit touchy with this filament. But they came out pretty well on my Ender3.

Build

The final assembly is a tedious process, as there not much space to work with the solder iron. First, capacitors and MT30 connectors are placed in their slot. I used glue on the MT30 to secure them. Then the ESC (with wires already soldered on)is inserted. After that, it’s just about soldering everything: motor, wires, battery lead and capacitors.

Next, the flight controller can be put in place with the Rx placed inbetween the boards. Camera wires as well as the antennas go through holes in the top cover, so they are connected at the last moment when the top cover is set in place.