![emot-4.jpg](https://modelboatblog.tedatum.com/wp-content/gallery/jmotors/emot-4.jpg "The shaft is a rather small 1/8\\" diameter. There are splines to help hold whatever is installed on the shaft.")
Engine Room
Information about the propulsion system for the Dauntless.
Motor Mount Ideas
I have a machine shop and engineering project for the Dauntless boat project.
I have done a fair amount of research on the motor mount of scale model boats that use electric motors. One thing that totally astonishes me is the casual use of cheap universal or “ball” joint between the motor and the drive shaft. What is typically displayed in the Dumas (boat kit manufacture) and other brands is a fairly noticeable angle between the motor and the drive shaft. Many times a crude plastic “dog-bone” connector is in use between the yokes.
Of course I have seen a lot of very good installs. The racers usually have found out the secret to best running is with straight shaft alignment. The modeler shouldn’t always follow prototype with a waterline level engine mount fastened to an angled drive shaft. Even if there are quality parts available to do it.
This is not a problem for an automobile and other low RPM drive-shafts that have no slop roller bearings built into the cross and yoke design. In my experience and opinion, slop is one heck of a problem for very high speed drives like are used in fast running model boats. I am talking 5000 to 10,000+ RPM. Would anyone build and run a dragster with the bearings removed from the U-Joint? Model boat builders seem to do it all the time. This is where a lot of the vibration noise is coming from.
I have installed hundreds of powerful motor and pump systems in commercial central plant HVAC system with a precision drive coupling between the pump and the motor. There are especially trained technicians with very expensive test equipment who do the alignment job correctly. For highest efficiency and lowest wear and noise (power loss) the two shafts and the coupling must be perfectly aligned. I believe no less care should be taken with the high RPM model boat drive line.
Yes, the quality model u-joints are made for a small angle but it is probably not wise to run anything more than a few 1000 RPM for short periods with that set-up.
So my design goal is to build a motor mount system with coupling and engine room drive shaft alignment built in. This includes the HQ stuffing tube mount through the hull. The prop end mount will have to be carefully designed if the boat design requires an exceptionally long drive shaft. I may even use ball bearings on the shaft and stuffing tube if I can figure a way to do it. However, I have read that BB’s are somewhat overkill as flanged Oilite bearings work great and are easy to replace.
A lot of time getting this part of the build right will pay big dividends when running out on the pond. I have read a lot of stories where the motor was installed (for the first time) the night before the big outing with a couple of straps to hull blocks and the u-joint expected to take care of all the alignment.
That’s not for me.
Johnson Motors
I am not sure if these motors are keepers yet. Well, I will keep them but not sure if they will get installed in this project. The specifications seem good (see below) but the motors, well… they seem so small. I did find some two inch diameter motors but I don’t think they are as plentiful as these Johnson brand motors. The price for the two Johnson’s was about $7.00 each. I have seen a conflicting price on the larger motors but all I see now is about $10.00. At that price it is worth experimenting .
I purchased these Johnson 9167AK from a seller on Ebay. There are quite a few sellers with this motor so it must be widely available. I didn’t see it listed under this number on the Johnson Motor web site. I assume it may be some kind of overstock for someone needing a small motor of these specification.
Johnson Electric 12VDC Motor (6 to 18V) – Model 9167AK
Extreme Torque of 2.2 in-lbs
Super Grip Serrated Shaft
This motor is quite a bit larger than most hobby types. It’s suitable for any model or experimental use where high shaft power and torque are needed. Please note that there are a couple of different Johnson model 9167 motors. The 9167AK is the biggest one with the highest power.
Runs very smoothly over the range of 3VDC to 18VDC.
Light load Medium Load Heavy Load
3VDC: 1,400 RPM 850 RPM n/a
6VDC: 3,150 RPM 2,100 RPM 750 RPM
12VDC: 6,560 RPM 4,900 RPM 3,400 RPM
18VDC: 9,800 RPM 7,350 RPM 5,100 RPM
At 12VDC the motor has very impressive torque.
Starting torque is 2570 gm-cm = 36 oz-in = 2.2 inch-pounds, at 14 amps.
Operating torque at medium load is 440 gm-cm = 6.1 oz-in at 2.8 amps.
As the load is increased, the torque and current will increase correspondingly. Please check that the case temperature stays below about 100 deg C, in order to maintain long life.
On a dynamometer, the motor was able to generate a continuous 31 watts of mechanical shaft power, with a peak value of 46 watts (temperature limited). A typical small hobby motor can only produce 2-3 watts and a medium-size motor about 10-12 watts, usually not continuously.
Overall length is 3-1/2″ including terminals and shaft.
The body is 2-5/8″ long, 1-1/2″ diameter. Or 65 mm by 38 mm if you prefer metric.
The shaft is 3/4″ long. It’s 1/8″ (.125″) dia with a .130″ serrated end section that grips tightly to a suitable hub, pulley or shaft coupler.
The heavy duty self-aligning front and rear bearings are lifetime lubricated oilite bronze.
The brushes are low-friction and long-life graphite carbon, NOT just copper spring arms as in many small motors.
The armature is 5 pole and the spin is reversible by reversing the power wires.