It rolled!… a few meters.

Posted on April 5, 2012

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And now, in an exclusive video report just for you the special readers of this blog, we have a very rare sighting of a differential tricycle in the wild…

I’m sure you’ve never seen anything like it. It is a very dangerous beast, and if that fierce rotating luminous eye isn’t enough to put the fear of technology into you, I don’t know what is. 🙂

And in another rare exclusive footage we have collected just for you at great peril, you can see us trying to tame the beast and ride it! Inside the house, no less!

So, enough cavorting, this is the current status of the project: the Trike was able to function as a coherent vehicle for the first time, but we burned the power electronics once again. With this one, it’s the third time NJay’s power bridges release their magic smoke – which is not surprising given that they are being developed from scratch and we lack any formal testing procedure other than NJay’s methodical attitude and infinite patience. Unless an idiot riding an experimental vehicle indoors in a crammed room counts as formal testing. 😉

Anyways, the reason the bridges burned this time was because they have no current limiting whatsoever, and the stall current of these little motors at 24V is about 120 Amps if we let them get away with it – and since the mosfets are rated for about 30A… you can spot the difference, right? In our excitement to try out the new gear, we kind of forgot this fact. Of course these batteries would never reach the 240A mark, but they have enough juice to fry a handful of mosfets. I was hoping the current didn’t jump too high on a flat surface with smooth accelerations, but as soon as we put the trike outside the house the motors had to overcome very rough terrain – hence the fried mosfets. I should have known it, but I just couldn’t resist playing with the stick of joy… 🙂

Oh well, we just love soldering anyway. 😉 We’ll need around two hacking sessions to rebuild, program, and test the bridges with current-limiting firmware. So I expect to have it rolling on the road again in about 3 weeks. And next time, I promise I’ll behave. 😉

Meanwhile, I’ve implemented an exponential law to reduce the sensitivity of the joystick, because as can be seen in the video it was far too twitchy. Bit by bit, the puzzle is coming together! 😀

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