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I had the ibc set up in Vertex to hold the big solonoide in for failsafeing i found that it also got hot and drew heaaps of current if i didnt run it at full stick but that might have been something to do with the solonoide giveing back emf with the pwm from the controler .

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OK, I did some more testing and the results are that the current draw is a curve that peaks at around 50% motor speed. input current starts out at 3A (slightly more than the motors are drawing when they just start turning), climbs steadily to 24A (or more), then ramps down to 8A at full speed. I measured the battery voltage and it starts & finishes at almost 15V with a drop down to 13V when the current peaks. I would say that the current curve VS speed rules out contol glitches - it's much more likely to be FET switching problems. Too bad I don't have an oscilloscope I sent off detailed results to the Robot power guys and I hope its fixable.
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Too bad I don't have an oscilloscope

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quick answer is to try a bigass inductor from jaycar on one of the motor lines.
about $5
those inductor boards are only good for 12A i dont think your thingaps going to be running at that current level lol.

PlanB would be to up the PWM frequency
if you have a spare IBC and want to try it i can get the brain transplant running up to 20KHz
i also have an old scope that may be quick enough to see whats going on.

Whats the max current you can pull from your batteries?
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Mechanical engineers build weapons, civil engineers build targets

The batteries are SC2400 Nicad sub-C cells, which are supposed to be good for short 100A bursts. I can put in a CP3600 pack for testing just as easily.

Just for testing, could I make a test inductor? I think there are some phat ferrite torroids floating around in the workshop that I could wind for 100 uH. Would they really help though? The current drawn by the motors is looking entirely reasonable for the Thingaps - it's the Controller that is dissapating excess power. As a first step, I can substitute a set of TWR15 motors as an easier test than using inductors.
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UK 2016 Gladiator champion

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The current drawn by the motors is looking entirely reasonable for the Thingaps - it's the Controller that is dissapating excess power.

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the reason i see is that because the motors have such a low inductance your controller basically sees it as a dead short so it pulls full power then nothing.

Adding some inductance resists the change in current flow so your going to be putting out much lower "pulses" of current (the ripple is what you are trying to reduce)

you can either up the PWM frequency or add inductance.

I dont know if your average DMM will be giving you accurate readings btw you may be seeing some fairly nasty ailiasing i thinks.

(IE you are seeing massive surges on the input lines that when averaged out are quite small) then the freewheel current in the motor acts to smooth the reading for when you measure that current.)

Try hacking up a lowpass filter.
use a sense resistor (.1ohms or some such)
measure the voltage drop across it, put say a 5k resistor in line to one of your multi meter leads and stick a bigass cap across both leads.
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Mechanical engineers build weapons, civil engineers build targets

Thanks guys, it seems the low inductance of the Thingaps really is the problem. I used substituted the TWR gearmotors and the total current draw equalled the draw at the motors right across the speed range.

Those Jaycar inductors are the right price, but they are a bit big to cram into Subliminal. I might try winding my own on some inductor cores from old switch-mode supplies as I would rather have smaller size & higher weight.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Good luck with the Thin Gaps Nick, I'm interested to see how well they will perform with fixed gearboxes and larger controller. Minotaur never got much of a chance to show off... Glad to have helped out.
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I am starting to remember why I hated AC circuit design . From several inductor design calculators I tried, it looks like a large iron powder toroid and around 60 turns of 3mm sq. or 12 AWG wire will be needed to provide 200uH and carry 20A. I can get some smaller 470uH / 5A inductors from Jaycar and wire them up in parallel to get close to the right values or I can wind several layers of 1.25mm wire onto a single larger core - decisions, decisions.

Looking at the CAD, I will have to go with a stack of the smaller LF-1278 inductors from Jaycar as there is no room for a single large diameter inductor, even these small ones will be a nuisance as they are about 2/3 the size of the motor when stacked up .
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UK 2016 Gladiator champion

could you put the windings on the out side of the motor can and use that as the inductor core to save weight ..it might afect the internal magnetic flux though ..but might not iff the magnetic field is only induced in the outer can

Thanks Andrew, that's not such a bad idea as the can is quite thick - almost 3mm. Unfortunately, I made the chassis almost the same thickness as the motor diameter so there isn't enough room for a coil and insulation. There would barely be 1mm space for the wire.

I got 3 test inductors from Jaycar earlier on and will wire them in parallel to get the current rating up to 15A. That drops the inductance down to 156uH but it may be enough to do the trick. If it isn't I can strip the toroids and wind on more wire - the pre-wound inductors were cheaper than buying the bare cores so I am still ahead
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Wow! The inductor is a magic current killing bullet! After I wired the inductors up and wrapped them with many layers of rubber tape, I tried it out with just one Thingap wired in. The no-load current never got over 3.5 amps and nothing got more than faintly warm after three minutes. The Sidewinder input current was just a few hundred mA more than the motor at all speeds. I wonder that this was never mentioned on any forums before - I know that not many people use Thingaps, but some smart builders like Radicus have had them for ages. Thanks again Arron and Jake, I should have remembered about the low inductance.




The three inductors ready to solder.




All wrapped up 'n good to go.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

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Thanks again Arron and Jake

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Wasnt it Andrew who first pointed it out

Oh yeah and thanks everyone for helping Nick be able to own us with two robots! hehe