miniature transmission

[The_Paso_Kid]

I've been looking at these miniature IC engines for sale on eBay, Banggood, and other websites. I was thinking about possibly using one to power a radio control boat but would need a transmission with F-N-R capabilities to tie into such a motor. closest thing I have found so far is a rather large gearbox for a go-cart, which is far too large for my purposes. Any suggestions. Thanks.

 

[Tim Hooper]

As far as I know, the only RC boats that are capable of reversing are electric powered, where the motor is controlled by a dedicated electronic speed control (ESC).

I'm not a marine modeller, it's true, but the only IC-powered boats I've seen have forward thrust only, albeit with a throttle control.

Tim

 

[dnalot]

The answer to your problem is a variable pitch propellor.



Web site Controllable Pitch Propeller microcosm-engine.com

I have built a number of full size boats with variable pitch props and they work great. Set your engine RPM to a speed your engine likes then control speed and direction with the variable prop.

Mark T

 

[Sprocket]

I don't have a way to draw this for you but think of two discs at 90 degrees to one another, one is powered, the other is on the drive shaft. The one on the drive shaft has to be on splines so it can slide along the drive shaft. When the driven disc is on one side of center it's forward, the other side is reverse, a gap in the middle is neutral.
It's continuously variable both forward and reverse. Depends on friction to drive it.
I hope that makes sense. It's been rattling around in my head for a long time.
Doug

 

[Gedeon Spilett]

I did a friction drive on a similar principle for a little diesel shunting loco powered by a mini 4 stroke engine with spark ignition (1.5cm3), no, not a true diesel I confess...
this variable drive works a treat; and may certainly work on a boat, with changes, as the general arrangement is very different.
the system is visible at the end of the video.
I do have blue prints for my model, but I'm not a pro of drawings...

 

[The_Paso_Kid]

The answer to your problem is a variable pitch propellor.



Web site Controllable Pitch Propeller microcosm-engine.com

I have built a number of full size boats with variable pitch props and they work great. Set your engine RPM to a speed your engine likes then control speed and direction with the variable prop.

Mark T

Thanks for the info. I had seen these on eBay. However my grandfather was leaning more towards a sidewheel paddle boat design. This would work great for a steam engine that does not have throttle or reverse capabilities.

 

[The_Paso_Kid]

I did a friction drive on a similar principle for a little diesel shunting loco powered by a mini 4 stroke engine with spark ignition (1.5cm3), no, not a true diesel I confess...
this variable drive works a treat; and may certainly work on a boat, with changes, as the general arrangement is very different.
the system is visible at the end of the video.
I do have blue prints for my model, but I'm not a pro of drawings...




View attachment 137009

Very interesting design. It looks like you have a rubber o-ring making contact with the spinning disk. The reduction gearing is a great idea as well. My grandfather was thinking about a paddlewheel boat so the RPM's have to be fairly low. Thanks again.

 

[timo_gross]

I am confused if you want a model of a steam boat, why not put a steam engine in it? It would have a reversing gear and a steam boiler and a gas burner.
Off you go.
If you cannot agree if steam or internal combustion. Just make two.

Back to problem .... other maybe a little weird options: ( not to be taken too serious, but for a DoNothingBoat maybe still fun to make)

• Drive a hydraulic pump that provides power for a hydraulic motor. The direction can be changed with some valve.
• Make a generator and drive the propeller with the generated electricity
• Drive an air compressor with the combustion engine, with the compressed air you drive a steam engine (steam engines can be reversed)
• Could you use an old school flat belt? like in this animation.
  • Instead of pushing the belt left and right you can drive two belts on the motor side. Then you have two belt tensioners (model servo) and depending which belt you tension it runs forward or reverse. Got the idea from here
• I read there are systems for real boats. The motor drives a chain sprocket and a gear (always) then on the propeller (if you like paddle wheel) side there is a clutch.
  • if the clutch is neutral, the propeller does not do anything
  • if the clutch couples with the gear on the propeller shaft the propeller rotates the oposite direction of the motor
  • if the clutch couples with the chain sprocket the propeller rotates in the same direction as the motor.
    • chain can be replaced by a timing belt or you just make the same thing with two gears and one gear
  • as clutch you could use a similar system as on the loco model shown above ( closing the loop )

last but not least, there is a ready made solution to your problem



So now I stop that, otherwise my brain cannot stop. I will watch that last youtube now. As I see it it all boils down to making a clutch or some belt fork. Clutches, but a RC car model with fuel motor must have a clutch or not? Then it is only a matter of putting two of the clutches into the model. One for forward, the othe one for reverse. - done

Greetings Timo

 

[animal12]

The O=ring drive is pretty much as the transmission on a lot of the snowblowers out there not counting the Hondas . I would love to see how the Hondas work but no one will let me take theirs apart to find out .
animal

 

[Steamchick]

Hi Animal, Timo,
I had a "problem" when I made a Stuart Sun engine... 180degree single acting twin steam engine - and decided to fit it into a boat. The engine (designed for continuous running, and used for "high speed torpedo boat models" more than 50 years ago) needed a transmission to change from Forward - Neutral - Reverse. So I made a relatively simple twin-disc and friction drive. This drive also was incorporated to drive the boiler feed pump, and change screw speed from the 300~2000rpm of the engine to something more useful for the boat. With a bit of trial and error, I developed this arrangement.

In this view you can see the RC servo, that drives a rod (with springs) that pushes the "collector" wheel from a central "neutral" position to either Drive wheel (a single steel bobbin driven from the engine). It didn't work with steel on steel, but worked well with an O-ring. Until the paint on the drive wheels got wet with steam condensation. So I knurled the faces of the drive wheels, when everything worked well. But the engine (4 1/2 lbs) was too heavy for the hull, so I changed it for a Stuart Star engine (2 lbs) and now the trim is good! The gearing (toothed belt drive) was changed to suit the "half-sized" engine, that runs faster, but develops the same sort of speed as with the Sun engine. The collector wheel - with toothed belt drive to the main-shaft, rotates on a bearing concentric with the main-shaft.
A few other photos show me tinkering, and the boat.
This drive does not permit speed variation, but on the pond, the boat was very manoeuvrable with forward-reverse working as planned.


Incidentally, the exhaust from the engine passes through a concentric tube condenser (using pond water as the heat sink) and returns it to the boiler via the flat collection tank and a feed pump driven off the "bobbin" shaft. I arranged the single acting feed-pump to have approx. 3 1/2turns to "Pump" and a single turn to "prime" as the pressure difference on the piston for the 2 strikes was significantly different (Atmos vs. Boiler 20psi), so would cause the engine to "slow-down and speed-up" as it pumps. It is nearly smooth with the "eccentric" drive, so the boat speed variation is not observable.
I have no drawings, as I wiped the black-board after making bits. But I'll draw it if anyone needs drawings.
Also: I suggest anyone who is interested should have a look at Torotrak transmission. =>
Torotrak Infinitely Variable Transmission -- articles & patents (rexresearch.com)
It inspired my simple FWD/N/Rev arrangement.
K2

 

[Gedeon Spilett]

nice steam launch, Steamchick !
if the disks on the bobbin were a little bit larger and the central wheel with the o ring made movable in the front-rear direction to change the radius rolling on the disk, the speed could be changed...
but it is obviously annoying to modify a perfectly functioning set up !

 

[Steamchick]

Hi Gideon. I had considered that option, but it required more space than the boat has. And instead of that complexity, a variable pitch screw option would have done a better job. I don't think my option is the best, but I made it work, and needed some sort of drive directional change with a suitable shaft to drive the boiler feed pump. This fitted nicely.
Next time I will set the engine crank in-line with a variable pitch screw, then have a belt driven aux shaft for the water pump. It just makes sense, and less weight. (Though I could have made the twin-disc bobbin from aluminium?).
K2

 

[Steamchick]

Just spotted the photo of the firing end of the boiler - shows how I used an electric fire element inside the boiler firetube to give more power to the boiler from the radiant heat off the element, which is in the gas flame. You can see it glowing orange. Only a small increase, but every little helps!
K2

 

[timo_gross]

Hello,

another idea I came across when googling for transmission and gears. A spur gear differential can invert the rotation of the input shaft, if the cage is stopped.
If the cage can rotate freely it the output shaft will only rotate due to friction of the gears.

Getting side tracked once again, I made one small example just to see if I understood correct. Due to the spur gears I was able to make the gears without special cutter. Purchased or salvaged gears would probably do the trick too.
If I am correct a planetary gear will also work, but the differential does not need a ring gear, so it is easier to make I guess.
Two of the differentials go in parallel and the two input shafts are driven all the time. Two brakes stop either the left or right cage (big gear on the picture) and then the respective output shaft starts turning.

I hope that is of use or sparks some idea.

Greetings Timo

p.s. now I am rotating that contraption, serves as fidget

 

[timo_gross]

Now while playing around it comes to mind that this might as well be used as a easy normal clutch. Open the brake, shift in reverse, apply brake again?

 

[ddmckee54]

Timo:

I think most gas powered RC cars use a centrifugal clutch which engages above a certain RPM. That way you can start your car at idle and it won't try to run over you. Here's a video on how they work.
How they work

Don

 

[Steamchick]

Timo, The Torotrak variator drives one part of a planetary gear arrangement:

Consider "input" at green (planets) : the Torotrak variator then adds the variable rotation of the variator output to the centre of the planetary gears (Sun). The output - Red - then rotates as the algebraic sum of the planets reacting on the sun gear.
It also works with an input at yellow, using the variator output through green to run the "reaction" green planets around the sun gear so the red reacts to the algebraic sum of the 2 rotations.
Effectively it couples 2 parts of the planetary gears, so when it drives one shaft for "forward", the whole drive goes forward, and when it "reverses" the drive the output reverses. But when in "the middle" it drives 2 parts at "equal" speeds so the output is zero - I.E. Stopped. Hence it is a constant engaged drive that can change from forward to reverse, and accomplish healthy gear ratios infinitely between the limits. I may make one "one day" when I reach that great workshop in the sky?
K2

 

[timo_gross]

Timo:

I think most gas powered RC cars use a centrifugal clutch which engages above a certain RPM. That way you can start your car at idle and it won't try to run over you. Here's a video on how they work.
How they work

Don

Hello,

makes sense, when trying to find something on the typical Chinese sales platorm they looked like there was no outside control of the clutch.
From the video it seems not be too overly complicated to make one. But the orignial question was also how to implement a reversing function.
Slow down to idle shift a geartrain and speed up again?

 

[Steamchick]

Hi Timo, I would guess that is appropriate, like driving a car, except to stop a boat you need to go from forward to reverse while still moving, so maybe a coupling to the engine throttle from the gear shifter would "over-ride" whatever is set as the throttle position, so it does drop to low revs as the gear shifter changes from forward to reverse. Logically, we can work anything we want, but "mechanically" it becomes a little more difficult!
K2

 

[timo_gross]

Timo, The Torotrak variator drives one part of a planetary gear arrangement: Effectively it couples 2 parts of the planetary gears, so when it drives one part forward, the whole drive goes forward, and when it reverses the drive the output reverses. But when in "the middle" it drives 2 parts at "equal" speeds so the output is zero - I.E. Stopped. Hence it is a constant engaged drive that can change from forward to reverse, and accomplish healthy gear ratios infinitely between the limits. I may make one "one day" when I reach that great workshop in the sky?
K2

The Torotrak seems very complicated to make. ( building a scale model of a modern double clutch gearbox? ) For the model boat you might get away with a rubber O-ring on the "torotrak-model". Would be interesting to see one made.