I don't want to be a naysayer. OK, yes I do! No. Really...
But the largest assembled brain trust on the subject of EV's is the Electric Vehicle Discussion List:
http://evdl.org for info.
The subject of open source home brew controllers comes up every other month on the list, usually suggested by someone who wants to do a conversion, but doesn't want to (or doesn't have the means to) fork over the beans for a commercial controller.
In the 2 years I've been reading posts there, nobody has yet made one. The challenges are serious, when you consider the job a controller has to do and the environment it has to do it in, and the consequences of something going wrong with it while & where it's being used.
And it's not for lack of smarts. The number of
really smart people on that list is astounding. The fact that a bunch of really smart & experienced people haven't yet made an open source controller that anyone can build for less money than a commercially produced one tells me something.
Not saying it can't be done. But since I'm not an EE with time to spend on the problem, instead I continue to haunt eBay regularly watching for a bargain on the unit with the specs I'd like to have...