My local electric RC shop says:
Sounds like a great project.
For this sort of model I'd suggest that you need to be around 100
watts/pound minimum. If it were me I'd go for more like 150w/P and as you've
got a couple of good battery packs already, lets look at 150.
3.5kg = 7.7pounds
6S = 22.2V
150W x 7.7 = 1155W
1155 / 22.2 = 52Amps
So that gives us plenty of choices.
I'd look at a Z4025/10. This will run on either 5 or 6 cells easily and as
it will burst up to 1300W - we are easily in the money.
The new Titan speed controllers can now handle up to 6S so a Titan 80 OPTO
is your best bet there.
We also have a new product in today from Hyperion that looks great - An SBEC to save you having to run a separate receiver battery.
As for mounting, the basic motor mount would probably be your best bet and
at $29 they can save you a lot of work.
Does anyone have any thoughts on this?