Hi Steve,
Basically you need everything to be able to run a brushless equivalent of the 900 motors.
I'm guessing the 24V comes from SLA batteries, which are not very good at delivering high current for a longer period of time...
If the 24V come from quality NiMH cellpacks (20-24 cells per motor), you could use those, until you can afford lipo's.
I'd recommend two of these:
http://www.ebay.de/itm/D2VN-New-Aeolian-C4250-06-KV800-Outrunner-Brushless-Motor-for-RC-Airplane-Aircra-/131015174601?pt=RC_Modellbau&hash=item1e811ce9c9I'm running one of these in my MAS (110 cm 3-4Kg) on 4S lipo (14,8V, two packs in parallel for long runtimes) turning a Ø60 mm two blade prop with coarse pitch.
To get an idea of the speed, see this video, made last summer on the river Weser in Germany:
Turn up the sound (really) high to hear the running noise:
http://www.youtube.com/watch?v=-igDcvLySEMCurrently I'm using this ESC:
http://www.himodel.com/electric/HiModel_ICE_100A_2-6S_Water-cooled_Brushless_Navy_ESC_ICE-100A.htmlThis ESC works flawless in my single motor application, but getting two to sync needs two receiver channels and a computer transmitter with elaborate mixer options, according to my buddy, who runs two of these ESC's in his boat.
If your Action 97 mixer can handle two brushless ESC's that should work too, but you need two ESC's with identical neutral points to get them to work.
I chose the ICE ESC because I'm using them in my fast electrics and the price is reasonable.
There are not many alternatives in this price segment that have reverse, Graupner has a few, but these are currently out of stock:
http://www.graupner.de/de/products/fe157a63-1203-43c8-866d-64197ac67366/7258/product.aspxWith the two 4800mAh (budget) Lipo's wired in parallel, mixed running, meaning 80% at a brisk walking pace, with the occasional 200m speed run, gives me more than two hours of continuous running, the average ampdraw is 4,5A/h
Let me know if you need more info.
Regards, Jan.