Model Boat Mayhem

Technical, Techniques, Hints, and Tips => Tutorials & "How To’s" ... => Topic started by: GG on August 01, 2019, 04:39:08 pm

Title: Row-Ver - Working oar mechanism
Post by: GG on August 01, 2019, 04:39:08 pm
Part 1

Models driven by oars or paddles are nothing new but still something of a rarity.  Possibly this is due to to the use of complex mechanisms and/or electronics when attempting to create a realistic rowing or paddling action.  The aim of this model was just to create the illusion of rowing without demanding any more than the basic skills and tools that most modelers should have.

My previous experience with such models started a long time ago with the Graupner "Tina" kit.  This was a typical highly engineered German product with the oars driven by a single electric motor using a worm gear, springs and levers.  To be truthful, it never worked well since steering was by lifting a still rotating oar clear of the water.  So any rocking of the model from side to side made it's progress something of a random event.

Some time later and the idea to build a canoe based model, with independent paddlers on either side occurred.  The linkage to turn the motors rotary motion in to a paddling action was taken from Peter Holland's book "Amazing Models".  It worked well and I have seen a few models built to this plan (Waddler - Model Boats Oct 2016).  But, the idea of a rowing boat RC model wouldn't go away and numerous "back of the envelope" sketches were made until a potentially workable idea appeared.  This was to use a geared motor, pulleys and suitable belt/band to drive  metal shaft.  Using rudder tiller arms, the rotation of the shaft could be transferred to the inner ends of the oars.  To keep the oar blades vertical at all times, screws passing through slots in the oars would be used to secure them to the hull sides.

As with all apparently good ideas, some sort of proof of viability was needed before starting to build a model.  This took the form a simple test rig with a single oar and was made from scrap lumber found in my workshop.  This quickly taught me a few important things.  Firstly, the mechanism needed to needed to be "loose" but secure to accommodate the angles that the oars moved through. A suitable maximum speed of about 60 strokes per minute looked reasonable, any more and the rower could be called in for a drugs test!  This was achieved using a RE385 motor geared down in the ratio of 50:1, a MFA 950 D501 motor/gearbox combination using a six cell Nimh battery comfortably gave this speed.  By using different holes in the tiler arm, it was easy to adjust the motion of the blade.  Finally, clear the workbench of loose items otherwise the rotating oar will throw them all over the place!

Mrs Guest, who really ought to know better by now, was highly amused when she popped into the workshop and saw my test rig thrashing about in a manic fashion.  But, it worked so a suitable model was designed for to carry a double oared version.

Glynn Guest 
Title: Re: Row-Ver
Post by: GG on August 01, 2019, 04:57:07 pm
Part 2

A simple dinghy style was chosen, the type built at full size from sheet of plywood.   Liteply and plywood something around 1.5 to 2 mm in thickness was used for the two hull sides along with 1/4 inch (6 mm) balsa for the transom and midships bulkhead.

Two strips were to be fitted along the insides of the top edges of the hull sides and these were made from balsa.  To make life easier later, I cut these strips a little longer than the sides and only glued them to the sides between the between the transom and bulkhead positions.

The transom and bulkhead were then glued and pinned to the hull sides taking care to keep things square whist the glue was fully set.

Title: Re: Row-Ver
Post by: GG on August 01, 2019, 05:17:41 pm
Part 3

The bows were formed by pulling the sides together.  Before they would meet, the excess balsa strip had to be cut back and the ends chamfering to produce a neat joint

Not gluing these strips to the hull sides ahead of the bulkhead allows the required bending to be made more easily and places less stress on the structure.  Now glue could be placed between the strips and sides, then the bows pulled and glued together.  Some clips were used to keep the sides in place but care was taken not to "dish" the sides inwards which would look awful.

A simple glued joint at the bows has always seemed to me to be a potential weak spot. It was reinforced with a strip of glue soaked fabric pressed across the inside of this joint.  So far, and with numerous accidents to support this idea, this reinforcement has never failed me.

To create a larger gluing area when fixing the hull bottom, some lengths of balsa strip were glued along the inside edge at the bottom of the hull sides.  Only when the glue had fully set was these balsa strips sanded flush using a sanding block that was long enough to reach across from one side to the other.

 Glynn Guest

Title: Re: Row-Ver
Post by: GG on August 01, 2019, 05:32:06 pm
Part 4

A slightly over-sized pieced of plywood was cut to fit on the bottom of the hull and was glued into place.  A few suitable weights kept the glued surfaces together.  When dry, the excess was trimmed away and the corners lightly sanded.

Two extra bulkheads were fitted now, one in the bows and one between the transom and midships bulkhead.  Being an "open" hull, these two extra bulkheads will offer some help should the model ever start to ship water when sailing.  The aft one also formed the compartment for the receiver and rudder servo.

It might be a sign of paranoia, but at this stage in a models construction I always try to run small beds of glue along all internal joints and smooth them off with a fingertip.  This makes sure there are no gaps/cracks at any joints and adds a little extra strength.  It may be totally unnecessary but it makes me happy and my models do not fall to pieces.

A scrap piece of balsa was added to the hull bottom between the transom and bulkhead.  This doubler created extra support for the rudder tube.
Title: Re: Row-Ver
Post by: GG on August 01, 2019, 05:52:28 pm
Part 5

The support arms for the shaft that rotates the tiller arms and hence transmits the motion to the oars, have to be both strong and stiff.  A couple of hardwood strips which has been laying for some time in my "too good to discard" box at last found a use.

The arms must allow the shaft to rotate freely without being too loose.  An old knitting needle was being used for the shaft which was made from aluminium with a smooth hard plastic surface.  In previous models I've found at modest speeds and loads that these shafts with rotate freely in holes drilled through hardwoods.

The size of these arms and optimum position of the holes was found whist running the test rig.  But as a precaution the arms were a little oversize with a couple of extra holes to allow for any changes that sailing trials might reveal.

The two arms were glued together with a spacer block of wood between them.  This block had to create a gap for the pulley that was to fit on the shaft later.  When the glue had set, the arms were glued to the rear of the midships bulkhead taking care to keep it central and upright.

Glynn Guest
Title: Re: Row-Ver
Post by: Tug Fanatic on August 02, 2019, 10:07:34 am
A nice simple way of achieving something unusual.


Does it look good in action?
Title: Re: Row-Ver
Post by: GG on August 02, 2019, 10:56:09 am
Part 6

The oars were made by using some half round beading from my local hardware store.  They were assembled with some 3 mm thick wood strip between them.  This allowed me to create two slots in each oar, one at the bottom end for the blade (made from 3 mm thick plywood) and the other higher up for a securing screw to fit through.

A wire rod was glued into the top of each oar to connect with the tiller arms.  I used a large paper clip which had been straightened out, more than strong enough for the job and easy to bend and trim for any adjustments that might be needed.

The test rig had shown that the oars needed to move smoothly on the hull edge where they were secured with screws.  This combination of rotation and up-down oar motion required something more accommodating than a flat surface.  The answer was to use some short lengths of half-round beading for the oars to sit on.  This converted a a noisy and jerky action to something, if not perfect, at least a little quieter and smoother. These bearing block were stuck to the hull sides with some balsa support pieces below them.

Glynn Guest
Title: Re: Row-Ver
Post by: GG on August 02, 2019, 11:28:26 am
Part 7

The motor and its integral gearbox (MFA 950 D 501) was screwed to a balsa block which had been glued ahead of the bulkhead.  The block being built up to match the pulleys and belt used on the prototype.

My pulleys offered a further slight speed reduction and used an "O" ring to connect them.  Unlike many elastic bands, "O" rings do not relax under tension and perish in sunlight.  The key to success is to fit them with just enough tension to avoid slipping under load.  An alternative would be a toothed belt and matching pulleys.

You might have noticed that the midships bulkhead had to be trimmed to clear the tiller arms when they rotated.  Just enough material was removed to do this and the support arms remained secure.

Adjusting the mechanism to produce the desired rowing action was a matter of ensuring that both oars movement were identical.  The size of the circle that the oar blade makes can be altered by the position of the tiller arm on the rotating shaft, closer to the end, the larger the circle.  Moving where the wire rod fits through the tiller arm will change this motion.  Bending this wire will also change things!

The aim should be a smooth movement with the rudder blade just sweeping to a depth just below the bottom of the hull.

Glynn Guest

[/size][size=78%]  [/size]
Title: Re: Row-Ver
Post by: GG on August 02, 2019, 12:30:25 pm
Part 8

Figuring that this model was hardly going to move at a high speed, it seemed obvious that a large rudder was needed to produce an acceptable turning circle.  Rather than a commercial item, one was made up from aluminium sheet, rod and matching tube. The balsa doubler in the rear compartment gave good support when the tube was installed.

The servo was mounted to one side of the rudder tube.  No great forces were expected when operating the rudder so it was only secured to a balsa strip glued to the rear of the bulkhead. Any movement of the servo body being prevented by gluing a balsa strip to the hull bottom along side the servo.  A simple wire link connected the servo and tiller arms.

Before a trial float to establish the positions of the RC items for the correct trim could be made, the outer surfaces of the hull were sealed.  I wanted to retain the "plywood" appearance of a simple dinghy and so used three coats of a clear sealant.

Knowing that the propulsive power of the oars would be limited, I didn't want to add any extra weight to get a level trim.  Luckily the model would sit perfectly on the water with the receiver on the opposite side to the rudder servo, the battery pack slotted behind the midships bulkhead and the ESC adjacent to the motor on the other side.  And yes! I couldn't resist operating the model even though it was on our small garden pond.  At least it proved the model would move ahead and astern with some suggestion the rudder worked.

To hide the RC gear and rowing mechanism, some plywood covers were made to cover them.  The front and rear compartments just had covers that slid into place but the others were secured with screws into balsa strips glued to the hull sides.

In this form the model was given a proper "shake down" run on the local canal.  Perfect weather, just enough wind to ripple the waters surface a little but not mask any problems.  The oars proved capable of driving the model along, in both directions, at a speed that was a good match for the scale size.  The rudder response was good to, again in both directions.  But the most important thing was, despite creating a different noise to most other models, nothing failed!

Glynn Guest

Title: Re: Row-Ver
Post by: GG on August 02, 2019, 01:51:10 pm
Part 9

The idea of using a toy doll or figure to man this model had reoccurred many times whist building this model.  The problem was that unless the figure was very loosely articulated then it would place an unwelcome extra load on the rowing mechanism.  As the model could never claim to be an accurate scale model, a "humanoid" shape was felt to be OK.

The figure was based around a rectangular plywood back which was secured to the seat with a hinge.  Across the top edge of the back a hardwood strip was glued for the arm securing screws.  The arms were made from plywood with generously sized holes at each end.  The upper ones for the screws into the hardwood strip, the lower holes for the wire rods fitting between the tiller arms and top end of the oars.  Some experimentation was needed to get the right arm length to create a suitable rowing action.

To bulk out the body and arms some expanded polystyrene was glued to them and then carved and sanded to shape.  The final touch being a ball of the same stuff to make the head.  A couple of coats of pink emulsion paint, left over from a daughters bedroom decoration, and some clothes suggested with oil paints and the figure didn't look too awful.

Glynn Guest
Title: Re: Row-Ver
Post by: GG on August 02, 2019, 02:22:29 pm
Part 10

Back to the canal and it was found that the addition of the rowing figure had not changed the trim.  So, the final sailing tests could be made.  With no propwash over the rudder it was clearly not going to be as effective as in a conventional model.  But, its large size compensated somewhat and turns down to around 4 m (13-14 feet) in diameter were possible. One thing noticed was that if the oars were stopped out of the water after applying full rudder, then the model could turn even tighter as it drifted to a stop.  This has become a handy feature to use when caught in a tight spot. Sailing astern is much the same with the rudder still being able to steer the model.

It always seems to attract more than its fair share of attention from spectators when sailed.  If you build one then be prepared for lots of questions, including the proverbial "has it got a motor?".  The only downside might be the light weight, mine was 1.1 kg (40 oz), and shallow draught which makes it susceptible to drifting with the wind.  On the other hand this light weight makes launching and recovery a "piece of cake".

Not perhaps as clever as other rowing models but this design offers a simple and relatively cheap way to enter this area of our hobby.  There is also the potential to personalize your model with a different hull style and appearance.  More ambitious might be to try using two or more rowers in a longer hull but some means of synchronizing the oars might be the problem.

If you try doing your own thing, then lets hear about it. As for me I'm happy to gently row around the lake.  Very relaxing provided other modelers and to be totally honest- myself too, remember the oars sticking out of each side...!

Glynn Guest

Title: Re: Row-Ver
Post by: RST on August 02, 2019, 09:17:58 pm
Thats a superb write-up.  You've made it look easy!
....May I ask though?  At any point did you consider using continuous rotation servos?  I've had an idea to try pretty much exactly what you did but a tad smaller with a pair of them and some servo slows.  I guess this would be "louder", but would allow easy independent control of oars via a mixer rather than using a rudder, the man's pelvis would have to wabble either side also.  I'll probably try anyway, nothing gained, but you've given me the motivation to start it now!


Title: Re: Row-Ver
Post by: Tug Fanatic on August 03, 2019, 09:03:43 am
I would have thought that any two independently controlled geared motors would work but rowing only looks good when the oars are synchronised. Two oars waving around independently out of sync & probably at different speed will look awful (to me anyway).

Does this need as much power as the motor fitted or rather is it the gearing that you wanted? 20 -30 rpm would seem to be about the realistic row rate.
Given the very low speed of the model & no propwash just how large a rudder is under there?
Title: Re: Row-Ver
Post by: GG on August 03, 2019, 10:47:26 am
Thanks both of you (at least I know two people have read it and made intelligent comments too!)

RST - The model is some 24 inches long and I'm not sure that the "continuous rotation servos" would work as well as the geared motor that I knew would.  Also, I wanted to keep things as simple and cheap as possible (plus all the stuff needed was to hand) but the idea of this thread was to encourage people to try a rowing boat model.  Even better if they experiment and come up with different and maybe better ways to do it.

Tug Fanatic - From the previous canoe model (Waddler - Model Boats Oct 2016) I knew that this motor-gearbox combination would work.  There is a fair load created by the rowing mechanism and a smaller motor might not have any reserve of power to cope with any debris/weeds or other stuff the oars might encounter.  It seems safer to have a little too much power/speed than is needed and use the ESC to get the desired performance. 

As for the rudder size, I was in two minds about posting the drafts of the plans but here they are.  The size can be worked out by talking the length of the hull sides as 24 inches.  This rudder is OK for general sailing but if you have to have "turning on the spot" then it's the complication of independent oars or at least stopping the inner oar I'm afraid.

Glynn Guest
Title: Re: Row-Ver
Post by: Tug Fanatic on August 03, 2019, 11:33:05 am
Thank you Glynn

Apart from the model being interesting & thought provoking I am also interested to see what, I guess, you would submit to a magazine for publication (with larger plans!). It is obviously a lot of work if you don't know that they will publish it. Drawing up the plans would tax me somewhat.
Title: Re: Row-Ver
Post by: rcboater1 on August 17, 2019, 04:19:13 am
I would have thought that any two independently controlled geared motors would work but rowing only looks good when the oars are synchronised. Two oars waving around independently out of sync & probably at different speed will look awful (to me anyway).

I agree — if the oars are out of sync, they would look terrible to the eye-  no one rows like that!

I love this simple design- I have been playing around with similar small geared motors and O-ring belts with paddle wheelers- there are a lot of common components.   It also occurs to me that if you don’t like the spade style “hidden” rudder, you could use a sailing dinghy-style transom mounted rudder and tiller.  There are lots of full scale small boats with this layout.  ( You would need a second figure manning the tiller— maybe the Mrs.??)
Title: Re: Row-Ver
Post by: LJ Crew on August 17, 2019, 08:07:52 am
But I always used to row like that %)