[NielsD]

Hi Guys,

I'm new to this forum, but I have been working (though a bit low-key recently) on a small remix of the Scout ESC.
I am building a 1/16th scale Leopard 1A4 from Tamiya for which I want to upgrade the gearbox to a fully independent 2-motor setup.
Since the Scout ESC is designed to support also much bigger motors than I use, I thought it would be a nice challenge to make a smaller version of this PCB.

I used the original schematics as baseline, but I changed the motor driver ICs for a different model.
The original motor driver is the VNH5019 (17.2x16mm) and I use the VNH7040 (10x7.5mm).
The Rds,on is a bit higher (40mOhm compared to 18mOhm) but since I use it for a 1/16th scale model only, I expect this to be no problem.
Designing for an acceptable thermal resistance was challenging in this small form factor though, but I think it is in good shape now, especially combined with the way the PCB will be mounted + fan and air ducting.

The control of the chip is a bit different unfortunately, so I have to update the firmware a bit as well.
The ATMEGA doesn't have enough pins to fully support the VNH7040, since the VNH7040 has a lot more control options.
This meant I had to design the control logic to be as close as possible to the way the VNH5019 is controlled by pulling control pins to fixed levels.
I now expect that the rotation direction is inverse, but the rest should be identical.
This now is the biggest risk though, and I can only fully test when I have the hardware on my desk and can do some testing and measurement.

The schematic and PCB design was made in Altium Designer.
It is finished now, but I still need to order and test it.
Because the thermal design involves quite some copper area, I hope to find an affordable place that can do the SMD assembly as well.
This will be continued shortly and I hope to post an update with the assembled PCB soon.

Regarding the fitment in the Leopard chassis, I first designed and 3D printed a housing in which the 2 motors and gearboxes fit and between which the Scout ESC Mini and a 40x40 fan could fit.
To make sure things don't get too hot, I did some airflow design, which uses ducts that will finally output any hot air from the Leopard's original exhaust ports.
This took quite some time and with a 2-year old son, hobby time is unfortunately not so abundant.

Anyway, let me know what you think.
I'll keep this thread to post any updates if I have them.

[LukeZ]

Hi Niels, I think it's a great idea and your board design looks very good. I always wished the Scout was smaller, but there never seemed to be just the perfect chip available. I can't remember if this VNH7040 was around when I was designing it.

I see it has the advanced but also confusing Multisense functionality for reading currents and other info. ST uses this in several of their motor driver chips and to the extent I looked into it I never completely figured it out (the datasheet is sorely lacking in details). I suspect this is one of the things you mentioned having to set to a fixed level. I'll be interested to see how you handled it, but really, since the chip has overcurrent/overtemp and other protections, it's probably fine not to monitor current and simply let the chip protect itself.

I'm looking forward to seeing your progress. Once you have it tested and working (I have no doubt you will succeed), I will of course be happy to include it in the list of OP designs.

[NielsD]

Thanks for your reply!

I noticed indeed that it has a bit more complex ways of measuring currents and temperature.
There is some switching involved that, for example, can output the chip's internal temperature to the analog output.
Because of the compatibility with the Scout ESC, I decided to wire it in a way that it's not able to use those features  (because if I wanted to, I needed more pins on the MCU, which were not available).
The idea is to keep using the temperature sensor as in the original design.

Because I'm quite slow with this project and I am also designing the housing and mechanics in CAD, it might still take some time to finish.
I'll keep you posted on the progress!