Brushless conversion questions

[MoparB]

OK, I am converting my Challenger to brushless motors, and it currently has a 700 BB Turbo driving each jet drive through a 2:1 belt transmission. Originally, I was just going to remove the belt drive completely and make the motors drive the shafts directly, but I have run into a couple of problems here. First of all, I would have to cut up a relatively thick plywood support inside of the hull in order to do so, due to the arrangement of the transmissions. Then there are a few other adaptations I must do from there.

What I was considering doing was going with a higher rpm brushless motor set in order to work with the belt transmissions. I had planned to use a pair of Feigao 8XL motors in order to completely replace the transmissions and drive the impellers directly. What would be a good set of motors to use to drive them through the transmissions?

Thanks in advance.

[Doozie870]

To me, it really depends how much rpms the jet drive can take before it cavitates, I think with the current 700 set up, your turning the impellor at 6-7K.

[saleens7]

most jet drives would work best between 15,000-20,000 rpms....i think you should just get rid of the gear system, or change the gear to 1:1

i would just try that with the origional motors and if you still think its slow, then i would replace them.

how many cells does each motor run on?

i would find a motor who's KV will get the jet drives to spin between 15,000rpms annd 20,000rpms with the current amout of cells if you do decide to go BL....

[saleens7]

whats the diameter of the impeller?

if its around 25-35mm, it will work well with the rpm i stated above....if its bigger, i would try to get closer to 15,000rpms just to be safe....

[SJFE]

I would play it safe. Change the gears to 1:1 and then test the bl motors. If you don't hit the right combo the first time resellem and try again. Testing prototypes is not cheap. If I added up every thing I put in the jack...I'd prolly weep openly like a women..but thats them name of the game some times.

[saleens7]

i like to refer to boats as "a hole in the water you pour your money into"

but its a very addictive and fast...umm....hole...

i agree with SJFE, play it safe, dont get the BL setup till you see how it performs with the 1:1 ratio...

[MoparB]

I am not aware of any way of changing the ratio of the transmissions. The impeller shafts do not fit the same pinion as the motors, as the impeller shafts are much thicker, and I don't know where I would find a replacement belt either.

Pretty sure impeller diameter is less than 40mm, because the 40mm drive is the gas drive, and this one has a smaller impeller than that one. If there were some way I could figure to eliminate or modifyt he transmissions, I would, and just run a couple of Revolver 700 HOs which can hit 22,000 rpm with the cells I want to run easily, or even kick it up to a Revolver 970, and keep it around 19,000, but BL seems to be the only way that I can put enough power and rpms to those drives to get them in their stride.

It's no big deal if it doesn't work out totally correctly for me, because I have more boats that would love some BL action, but I want to start with this boat first, since it truly just can't do anything else, and I have enough boats that would love those 700BB's too. :)

So either way, there is no equipment that will be "wasted". It might just end up going somewhere else. I also have RC cars too, so chances are, I might even benefit from a few mistakes.

But the way I see it, if I get the rpms going, then what could go wrong? I'm hitting as you said, about 7-8k at best through the drives. The 8L is more than a match for 700BB. It will bring the power and the rpms without even breaking a sweat.

I wonder if Umi ever finished his 4-blade impeller project. That might make a fine addition to things.