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Compact DC Servo Driver

A breadboard friendly VNH7040 breakout board to power all sorts of DC motor related tasks up to 36V and 35A.

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Which one is cheaper, literally just 4 MOSFET's or a fancy $5 chip with 4 MOTSET's in it? Alright, using a VNH7040 isn't the cheapest, but for a compact driver to power a couple of wheelchair motors I recently bought, this chip seems perfect! With fault detection, integrated current sensing, and low level controls, you just need to hook this up to a Teensy and get whrrring!
I went with a 2 layer board with 2 oz. copper instead of a 4 layer board to push down costs and I've panelized my design and bought 150 boards for just $30 from JLCPCB! No way will I drop the $750 on 150 VNH7040's, but a 10 pack isn't too bad.
I've decided to put capacitors on the outputs in order to absorb the current spikes and pass less AC. But, I'm guessing these will blow up from all the switching events, and can be replaced with TVS diodes to protect the motor and PCB from transients.
I've included KiCAD files since I want you to make these yourself.

I've used XT30 connectors since I really love the friction fit. I've made the form factor breadboard friendly and compact so that you can maximize your density, but also have one exposed column on the breadboard for your wire connections. I could have added data pin resistors, but on this revision, you need to put resistors at the inputs to protect your MCU.

kicad_pcb - 358.75 kB - 01/03/2021 at 02:28

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sch - 11.47 kB - 01/03/2021 at 02:28

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  • Assembled and Inspected and Re-worked

    Sina Roughani02/07/2021 at 18:44 0 comments

    I'm starting to hate ST for using this package. Sure, the logic inputs separate from the power pins is a nice touch, but using 0.5mm spacing was terrible. In a legged package, the bending and deformation of the legs through rework or drops means they have a higher propensity to short together. If it were 0.5mm spacing in a QFN or DFN package, they could avoid this. It should have been 0.65mm though. Why am I complaining about 0.15mm? Well, now that I have professional inspection lighting, here's the results of assembly a few weeks ago.

    Some turned out like this

    Perfect in every way, just like myself.

    And then some turned out like this, actual garbage like myself.

    The misalignment couldn't be corrected even after rework.

    Sure, a swim in the isopropyl bath can clean the flux off, but how do you realign a 0.2mm spacing which has been reduced to 0.1mm? The IPC standards which I don't generally agree with say this is now good for about 10V, and I'd agree with that. But, I'll run it higher because it's not going in a plane, train, or automobile.

    Let's take a dip

    And after their little bath, they just vibing.

    I did an electrical test and surprisingly, none had short circuits.

    I'm not willing to trust $10k robots to these though, so I'm going to bin them and put the best in my PUMA robot.

    Here's the "Hello Whirl" for the drivers.

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