Long term project 51" mono proposal

[Old School]

Thankyou, I was concerned that just a 1/4" stubshaft would severely limit prop selection.

[Old School]

I have taken the plunge and purchased the 51" cat hull and will need to wait a few weeks for delivery. A search online has failed to find a 5mm motor shaft to 1/4" flex drive collett, so it seems if I go with a 1/4" flex then I need to use a motor with an 8 mm shaft. I have seen a 40 series with a 6mm shaft designed for helicopter use and a collett is available. Thus if an 8 mm motor shaft is needed then options are a high end TP Power motor (4070) or a 56 series motor.

Is a 1/4" flex essential given the size of the hull (51" X 14.5") or would a quality twin 3/16" flex be adequate please? Two 4082 motors with 45mm props will get the boat into the 60 plus mile per hour range with 6s so I think a 40 series set up should be adequate. I assume the factory uses 3/16" shafts (two piece I believe). This will be a long term project but I feel will be worth the wait.

[rol243]

you can get collets for 8mm motor shaft to either 3/16 shaft or 1/4 inch shaft sizes, maybe the good quality Aeromarine or CC Racing 3/16 flexshafts would be suitable as its not like you building a twin outrigger hydro that asks for long shafts, the cat hulls normally have there motors positioned approx 1/3 rd in from the transom so your shafts would only be about 17 inches long. so its 50 / 50 on shaft size as the price difference if going to 1/4 inch flex is approx $20 plus abit more for strut size difference but not alot i would say. just remember its a big hull and your going to run big powerfull motors.
edit; cc racing flexshafts = 3/16 = $34 and 1/4 = $35. so its $2 more not $20.

[Old School]

Yes, that is what I was thinking, 1/4" is a more sensible option.

[MarkF]

If your only going to run a 4070 on 6s, I would go with 187 or 3/16 cable. You don't need 1/4 shaft for that power system. You only need 1/4 shafts if your going to run big 5860 motors size and gas size props.

Mark

[rol243]

so Mark what is the point for those larger 40 series motors to have 8 mm rotor shafts ?

[MarkF]

I don't know. Mine has a 5mm shaft but just because another one has an 8mm doesn't mean you need a 1/4 cable. I will be running a 4070 1570kv on 6s in a rigger and I would never put a big 1/4 cable in the boat. And I plan on this boat being an 80 mph boat. My 100mph cat used 3/16 too.

Mark

[Old School]

Mark,
just to clarify, the motor I was looking at the TP Power 4070 (40mm X 100mm) has a nominal 3850 watts with a burst of 7500 watts. Compare to a TPP with a 5 mm shaft, the 4050 (40mm X 83mm), the nominal power is 2350 watts and a burst of 5000 watts. The 4070 is a greatly more powerful motor and perhaps needs the 8 mm shaft.

Compare to a Leopard 4092 with a nominal 2600 watts and a burst 4200 watts.

[MarkF]

I don't care how many watts a 4050 to 4070 motor is capable of. I would not use a 1/4 shaft. Period. You will just add drag and more amp draw to the motor unnecessarily.

Mark

[Old School]

Thankyou Mark, as my first "big" boat I am relying on information from those who have done it before and will be guided accordingly. The engineer in me implies the 8 mm shaft on the 4070 is there for a reason otherwise they would have stuck with the common 5 mm shaft.

[rol243]

looks ok to use 3/16 flexshafts with your hull and motor combos but make sure you use a good quality set of shafts like the two brands mentioned also think if your going counter clockwise rotations be sure to use a left and a right direction wound flex shafts not 2 of the same windings.

[Old School]

Many thanks. Definitely going with counter rotating props. I believe that cats spin inwards. With 3/16" flexshafts the issue will be finding a stinger setup big enough. OSE does some nice 3/16" "smart drive" units. I have seen 1/4" drive units the same as on the big Genesis and these looked suitable assuming I was using 1/4" shafts.

[lars_01]

"IF" you think you need 1/4 flex! http://mbp-rc.de/collet-clutches-5-x-63-SZK https://www.offshoreelectrics.com/pr...?prod=mbp-1000

[Old School]

Many thanks, have bookmarked the links.

[MarkF]

The 8mm shaft is so it doesn't break or bend as easy in a crash as a 5mm shaft would. But after racing boats for 25 years, I have never broke or bent a 5mm shaft. The shaft size has nothing to do with your cable choice. People asked for 8mm shafts because they were going to abuse the motor past it's limits and felt an 8mm shaft would hold true while being pushed past the motors limits. I would never use a 1/4 cable on a 4070 motor but hey what do I know.

Mark