8 Cell Predator Rigger

[j.m.]

Hey guys,

I'm wanting to run my predator on 8 cells. With my current motor, a 540 7L, and 8 GP3300's. I ran this through FECalc, and it said I came up with an x427 drawing 25 amps cont. at 40mph. I have a graupner K40 I turned down to 29mm i'd like to use. A 430 gave 44 mph and 35 amps cont, so i'm thinking the 429 will give me nice long runtimes and reasonable speed.

So here's my question>
Will a 29mm prop even be able to move a predator with 8 cells??

[Scott T]

I ran that motor with 8 GP2200 cells in a 22" sport hydro, and it went really well on an X637. Run time was OK.

With a rigger and GP3300s, a 435 should still give good run time, and hook up a lot better than a 29mm prop.

[Simon.O.]

Cutting a K40 down to 29 is an interesting concept.
I would imagine that the blade shape is very different from the original.
I have read that the K series although stated as X4 are less that that and are more like a X2. This being the effective pitch of 1.2 vs 1.4.

Please do not take this as a slight on your ideas, I am well known for trying different stuff and will always encourage it when I see something that has some merit.

The setup you have specified should get the rigger up and honking on a genuine 427. I can't say if the prop you have will do the job, but you can tell me soon.

My small rigger which was loosly based on the predator has had over a dozen brushed motors and batteries from 6 to 8 nimh but now with BL and Lipo I still trial different combos.
My favourite is 8S on 2 Lipo to a 632 prop.
For insane fun I can put a 432 on there and drop a 3S lipo in.
Seriously not reccomended.

Let us know what you go with.

[j.m.]

Yeah, definitely. First I need to get my hardware mounted to the hull... Transferring a rudder I made from another hull to this one.

[Scott T]

I've also run a rigger with an 8S motor on 2S with a 632 - good combo.

The 7L is a different animal though, I think you'll be disappointed with the speed with any prop under 35mm. I was actually running a 640 originally (on 8 cells), but had problems keeping the boat on the water! The 637 worked well.

This was all on a non-cooled Barra 80 BTW. So it's not a hot set up.

Cheers,
Scott

[j.m.]

Im on a cheapo 60 amp esc though... So I'd like to keep the amp draw to 45 max.

[Simon.O.]

If you are absolutly commited to the 8 cell Nimh then a 60A esc is not going to net you a lot of power.
1.1v / cell x 8 = 8.8 loaded volts x 45 A = 396 W
This will spin a 432 and if you can get the rpm up enough (with the right motor)you may see 40mph

This is data that I have. Some of it is based on FECalc and some of it is water time.

There are a lot of variables.
Some things that will deffo help. A good prop. When I went from non-metal to metal props my eyes were opened.
Nimh has its place but again when I eventually went to lipo because it was easier and cheaper than Nimh then my boats woke up a lot.

The 7L motor with 8 Ni cells is not the best combo for a rigger.

[j.m.]

I know... It's just what I have. Eventually I will buy some lipos and a lipo charger. :)