A Wild Melontroller Appears!

Thursday, November 25th, 2010 @ 5:19 | Melon-scooter, Motor Controllers, Project Build Reports

Charles! I choose you! Use SOLDERING IRON!

After a week and a half of anticipation, Melontroller 1.0 arrives just in time for me to spend the entirety of the Thanksgiving weekend blowing it up.

I used Advanced Fucking Awesome Circuits‘ $33 per board service, and the results are epic as usual. I elected to just spring for one board this time instead of panelizing or ordering more, since I wanted to make sure the design actually worked. The above is the bottom side of the board, where the crackFETs sit.

The top side is the horrible mess of 1206 component and SOIC components.

And an Arduino.

I suppose this layout isn’t that dense at all, but playing the routing game in Eagle was still a bit mind-boggling, and some times mildly frustrating. Much of it stems from the fact that I’m trying to maintain a 2-layer board. 4-layer boards would make all of this much easier, but they are also way more expensive to manufacture. I don’t think I’m quite that hardcore yet.

While the boards were in manufacturing, I placed several consecutive Digikey orders for the components that will eventually need to fill it out.

Here’s the scene. It looks kind of like a shady back-alley surgeon’s office, except with electronics.

Mid-assembly with most of the SMT passives and all ICs mounted. Excuse the blobbing – this was done with 1mm diameter solder (bigger than the damn pins themselves) and an iron with a tip so dead that I had to regularly sand it in order for the solder to stick.

That’s some serious bonage. I think it’s time to get MITERS new soldering irons.

I whipped out the Big Guns to solder in the output FETs. It’s a 100 watt Weller iron with a single 3/8″ wide tip. Not very scientific, but it flowed some serious eutectic.

Of course, I also managed to bridge together the single gate pin with all 5 of the source pins a few times, but that’s what they make desoldering braid for.

Notice the exposed conductors on either side of the FETs. Those will also be braced with some bus wire or braid in order to strengthen the trace where it is the narrowest.

And the last components to go on are the Arduino (on headers) and buscaps. This thing has some serious buscaps. I don’t know why on earth I specified two whole Joules (3x 680uF on a 60 volt system) of buscap, but they’re almost comical looking. It’s almost to the point where I’d need a precharge circuit.

I haven’t written the software or done a load test yet, but the circuit powers up without shorting the power supply, so that’s a good first sign. Over the break, I intend to write some BLDC square wave commutation code and see if I can run the MITERS Public Etek. After that, it’s time to put sensors on Melonscooter once again and see if this thing can live up to its name.

In the mean time, in classic me-fashion, I’ve already started designing version 2 before even finishing (or in this case, starting) version 1.

It’s actually not as bad as it seems. This is the exact same circuit, but better organized and routed. First, the layout is practically identical across all three phase drivers.  Second, the pull-ups and -downs are better organized and placed right next to their respective pins. Also, the outputs now use plain board pads instead of through-holes. No particular reason for this change.

Also, even more buscap.

Alright, not really – the buscap bank had to be trimmed to a mere 1,300uF. Boo-hoo.

The most important aspect of version 1.1 is that it’s a full half inch smaller in the X dimension. This can actually get even smaller, but right now this is the limit of what I’m comfortable designing, routing, and soldering. My ultimate goal is to reduce it down to the size of the average Turnigy 100A.

But don’t let the picture mislead you – melontroller 1.0 is only a little longer than a credit card, and 1.1 is shorter than one. That’s already pretty damned small for something that should handle at least 40 to 50 amps with some airflow.

reduction to practice

I’ll just leave this here.



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    4 Responses to “A Wild Melontroller Appears!”

    1. Mike L Says:

      Is it the bard or the FETs tha you think can olny handle 50-60 amps, cuz the FETs are rated at over 200 amps.

    2. Fake-Name Says:

      For really high currents, you generally want to leave the soldermask off the power traces. That way you can flow solder/copper wire onto the traces, making them heavier.

      Particularly with the 33Each boards, which are 1oz copper.

      You know there is a companion site to 33each which is 66each.com? It’s from Advanced Circuits too, you get 30 sq inches of 1oz 4 layer board for $66 dollars. They do the single-quantity student discount on it too.

    3. mightyohm Says:

      Why not just include an Arduino in your PCB design? It should be cheaper to roll your own Arduino than to buy a Nano and stick it on top.

      Also, another cheap source for PCBs, including (occasionally) 4-layer designs: http://dorkbotpdx.org/wiki/pcb_order

    4. the chuxxor Says:

      I just have a relatively constant source of the Pro Mini boards. Plus, some times I pluck them off of one board to run something really quickly. Mostly a convenience thing.