I have bought three Cobra 4130/12 motors as the Turnigy motors that I purchased are not really suitable for the type of mounts that I have. The Cobra Motors are nearly 50mm (2") diameter and 61mm long.
I have also bought three 50mm props and three 120Amp brushless speed controllers and I have three 5000mAH 14.4Volt Lithium batteries for this beast!
The Specifications - 4 Cell Lipo battery at around 14.8 Volts should produce about 1000 watts for each motor, that should be enough!
| Cobra 4130/12 Motor Specifications | |
|---|---|
| Stator Diameter | 41.0 mm (1.614 in) |
| Stator Thickness | 30.0 mm (1.181 in) |
| Number of Stator Slots | 12 |
| Number of Magnet Poles | 14 |
| Motor Wind | 12 Turn Delta |
| Motor Kv Value | 540 RPM per Volt |
| No Load Current (Io) | 1.85 Amps @ 20 Volts |
| Motor Resistance (Rm) per Phase | 0.029 Ohms |
| Motor Resistance (Rm) Phase to Phase | 0.019 Ohms |
| Maximum Continuous Current | 65 Amps |
| Max Continuous Power (5-cell Li-Po) | 1200 Watts |
| Max Continuous Power (6-cell Li-Po) | 1440 Watts |
| Max Continuous Power (8-cell Li-Po) | 1920 Watts |
| Motor Weight | 398 grams (14.04 oz.) |
| Outside Diameter | 49.8 mm (1.961 in.) |
| Shaft Diameter | 6.00 mm (0.236 in.) |
| Motor Body Length | 61.8 mm (2.433 in.) |
| Overall Shaft Length | 84.5 mm (3.327 in.) |
| Motor Timing | 5-10 degrees |
| PWM Frequency | 8 KHz |
These Motors are only 540 rpm per volt, compared to the Elco at 1100 rpm per volt, as the propellers for the Schnellboot have a pitch of 2-1 compared to the Elco pitch of 1-1 and they are larger diameter props, this means that for every revolution the propeler pushes the boat more than twice as far (excluding losses) as the Elco (Higgins/Huckins) propellers.
I bought these 1/35th scale cast propellers from G-Factor (E-Bay) the top three are for a 35th scale S-Boot and the bottom three are for the 35th scale Elco. note that the Schnellboot outside props are counter rotating and the middle one has no spike because it sits in front of the main rudder support.
The Elco props are all the same.
These are all solid cast brass, the quality looks really good - However - I do need some 20th scale versions!
It is 2021, I have finally designed some 20th scale Schnellboot propellers that I am happy with, see the sbootshaft page, I had three attempts with designs, all made by Shapeways in brass and the latest ones I have had made are also available in Nylon with a natural finish (and a chemically polished finish, which is not bad but takes off a bit of material). I have three of the nylon props to try on the boat as I think they will be great, they seem tough enough and they are really inexpensive compared to the brass or bronze option, 3D printing seems to give a much better result than trying to cast propellers, much more accurate.