The twins do end up weighing quite a lot, 3kg is pretty normal. But with 2W18's and wemo's it will still hammer along, you are at 1:1 thrust to weight. I too think bungee is safer on grass fields, although I have had reports that the retracts are ok on short grass, my experience has been I need huge power when dealing with grass and rotation and small wheels!

I would stick with 2W18's, the 1W30 setup pulls stupid amps and requires big batteries, its ok for a single but for a twin you would need to carry 5000mah 4s packs to get any sort of run time.