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Coupling the 8mm gearbox shaft to the 4mm paddle shaft?

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I bought the Heng Long dual gearbox (150 rpm) units from Bangood. seems one side has an older motor than the other as it is more noisy and possibly not as fast. but close matched speed doesn't matter as they will be mixed, eventually.

For now I am asking for help on how to connect the shafts. Be assured that I have no real idea how best to do this.

The gearbox shaft has a flat and has a small diameter threaded tapping (if that's the term).

I bought the Paddle kit from Floataboat (visit that place with a fat wallet and no wife) and have made them up.

I'll set up everything on a board before even thinking about the hull construction. I bought the  P.S. Alexander Arbuthnot plans ($A55) which are seemingly well presented. Figuring them out will be a hefty  learning curve, methinks.  Was advised to go with that rather than the more complicated hull of the Adelaide.

Thanks in advance


Morning Mal.............

Firstly, the Float a Boat plans are well drawn and represent the respective original vessels quite well...[I have the FaB plans for the Adelaide and Oscar W]

150 RPM is a good starting speed for a 1:20 scale paddler, however if direct drive onto the paddle shaft's is intended, you many need to use full motors speed as a starting point....gearbox noise may or may not be an issue

Universal shaft couplings are relatively inexpensive and are ideal for the low rotational speed we use.......[there are 100's to choose from, although 8mm diameter will limit your selection, or dictate that you may need to bore a coupling half to suit this size] ...just [google Model shaft couplings]

Action Electronics from UK produce a series of speed controllers for twin propeller vessels, however are of course suitable for a twin motor paddle drive. These controllers provide proportional motor speed on one stick of your R/C transmitter....and naturally also provide the same in reverse for astern rotation [ Component Shop UK.......they now market the Action range]

Using one of the above controller's will eliminate any bias or difference created with the twin motor setup with 2 independent shafts and provide tank type steering.......however if you study the subject... :thinking may find this method of control not to your liking

Now saying this, no Australian paddler had independent shafts........after a number of incidents in the UK, dual shaft paddle drives were outlawed for passenger ferry work

Keep us posted with your progress ...any specific question...just ask ..........Derek............ :beer

Following your advice I find I can get a 8:4mm reducer and a 4:4 universal. If I connect those with a short 4 mm shaft (hardened steel ) it should suffice?
I think maybe the Heng Long gearboxes was not a good choice, the noise I can reduce, or ignore, but the quality of the units leaves a bit to be desired. One rotates with 6.6v at 125 rpm, steady, the other (the newer looking motor and build) varies  3 or 4 revs under no load.

Just in case, I’m looking on eBay for alternatives, either one with a left and right shaft for direct coupling, or 2 units to use as I had in mind with the ones I have. 

For instance, this one.

Do the paddles require a lot of power once under way?  And what do you suggest in rpm for this model (36” ) ?
Thing is, what parameters should I look for?

I appreciate your help


Mal......the 12 volt worm & worm wheel electric drive you show is very similar to the old windscreen motors that many members used years ago for paddle drives

The worm & worm wheel provides a very quiet and stable drive with very low current consumption.......these were not on the market 25 years ago

Having dual output shafts concludes that endfloat is taken up internally which is a only one motor assembly would be required

Using a single motor also means that your choice of an electronic [Action brand ] speed controller is less expensive.......the electronics controlling these modern day devices does not provide a reduced voltage to power the motor, but some form of wizardry in pulsing the applied current to slow the motor.....again all very stable without any jerkiness

The dual 7mm  diameter output shafts could be accommodated with a pair of universal couplings...and a massive 10kg of stall torque on the shaft

All in all, mechanically, electrically and  with a very high reliability promise due to the robust design a very good choice and @ $25.00.. a bargain  :gift                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                         

Your ESC will cope with zero RPM to full RPM without overheating or shuddering and you may find that whilst 100 RPM is fine for top speed....windage does play a part in model boats performance and it is always good to have extra reserve of blade power [150 RPM] if needed

So to answer your question on the paddle blade force to push a say 15 kg very complex to answer

However in reality you could place one finger on a 150 tonne vessel moored at the dock, and you will move the vessel

Model scale rules?......

Remember your Alexander Arbuthnot's river speed is only ~~6 to 7 knots…….so importantly your model will never be a speed boat


PS....[I have no association with Action products.......just a very satisfied customer over 20 years]

Thanks Derek, you have explained everything very well and I'm more aware now of what is required.

Since I've ordered the bits to convert the 8mm to 4mm I'll set that up on the bench and play around with the system, checking my stocks of speed controllers.

But I'm pretty sure I'll get the larger, more simplistic worm gear unit and make things easier from the start.

Thanks once again for your speedy and very clear advice.

I'll keep you posted on what I come up with.    8)



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