In response to Martin's call for more blogs to help see us through the isolation brought on by Covid-19 I thought I'd start this one.

For a while now I have been thinking about building a rowing boat. I like the idea and the challenge trying to build something that moves using oars and looks right. There are several videos on YouTube. I especially like the attached one.

But where to start? I have been collecting materials over the past few months but haven't started to build anything yet. The plan is to control the oars with servos and electronics, two servos on each oar. A microchip to control the servos to give the rowing motion and to allow control of speed and direction. 'Throttle' and 'rudder' inputs from the radio gear.

As for the dingy I have found the attached plan which is a possibility if I scale it down. The rower will be an Action Man (acquired from ebay for 99p!) so the dingy scale will be around 1/6 to suit the rower.

That is as far as I have got. Anyone here with experience of this sort of model? I would welcome advice from anyone who has tried this sort of thing. Is the dingy plan I found a good starting point or is there a better way? Can I simply scale the plan down to 1/6 by reducing all the dimensions pro-rata, or is there something I'm missing?

In order to be able to develop and test the electronics I decided to build a test rig for the rowing action. Each oar is connected to two servos to produce the desired movement. As a quick trial I connected one pair of servos to the receiver and tried to control the oar with two channels on one joystick on the transmitter. Not very easy to get anything like realistic movement🙄. I can see that this is going to be a long and challenging project!

It has taken a week to write the controller software, but I now have it sort of working.

I'm using a FlySky FS-RX2a receiver which outputs all control channels as a string of pulses on a single wire. That connects to the PIC based controller. Software in the controller decodes the string of pulses to extract the 'throttle' and 'rudder' commands. These are used in the rest of the software to control the rate of rowing and, eventually, the direction. So far, the software only controls the oars for rowing in a straight line. The 'throttle' input does control the rate of rowing although it does attempt to row far too fast. I know the oarsman will be Action Man, but I don't think even he would have enough stamina to maintain the rate at which it can row! There is more development needed to slow the rate of rowing, and to use the 'rudder' commands to control the direction.

The video shows the action at a reasonable rowing rate 😀

Graham93

Action man needed some surgery to make him into bionic man. The body was dismembered using a cutting disc in the Dremel. These figures are very tough, the plastic is thick and takes some cutting through.

Having got him apart, a subframe (skeleton?) was produced on which two servos are mounted. One servo rocks the body back and forth during rowing, the other turns the head.

He has a new sweater, courtesy of my dear wife, who is as mad as I am 😂.

The controller has also been updated to improve the rowing action, and to enable steering. Three transmitter channels are used, one for rowing speed, one for steering, and the final one to control the head turning. I'm using the tiny FS - Rx2a receiver which does not support telemetry back to the transmitter so there is no indication of battery charge. The controller is capable of monitoring battery voltage, but I need some means of indicating when the charge is low. Current thought is to get the rower to shake his head to the left and right as it would be more entertaining than turning a LED on, or sounding a buzzer. Anyone got any better suggestions? I'm open to ideas?

Graham93

I searched for a suitable set of plans to build the dinghy and found an excellent technical paper on the FAO website. Having never built a dinghy before, this paper gives all the dimensions and full construction details so it was ideal for me as a dinghy novice.

There are a range of different sizes from 5.2M to 8.5M in the plan. I decided to use the details for the 5.2M boat, scaled down to 1/6th scale to suit the size of the bionic rower. I also decided to build the model using the same construction techniques and materials as the full sized boats. Partly for the challenge, but mostly because it means I can just follow the instructions! The frames will be oak, left over from a recent furniture project, and the planking mahogany salvaged from old furniture.

An evening was spent with a calculator and red pen, reducing all the dimensions on the plan to 1/6th scale. The full (scale) size frame outlines were then drawn on a sheet of white faced hardboard and the transom and frames assembled by nailing the pieces to the hardboard outline and gluing all the joints. The stem was assembled in the same way, cut from oak and jointed over an outline drawn on hardboard. The softwood braces are temporary and will be removed later in the build

The joints on the full sized boat are bolted with 8mm galvanised coach bolts. I couldn't find any suitable bolts of the right scale. 1.5mm would be approximately correct, but the ones I could find were not long enough. In the end I opted for 3mm button head hex bolts. This made drilling the frame sections difficult as there was not much room for error. Once construction is complete, and visible bolt heads will have the hex socket filled with epoxy and then painted to make the bolt heads look like coach bolts.

Graham93

The dinghy is built inverted on a building jig. The plans include full details for construction of a jig based on 4x2 and 6x1 timber. Rather that scale all the timber dimensions down to 1/6th scale and build the jig out of timber sections I decided to take a shortcut and build the jig from salvaged chipboard panels. This simply involved cutting the panels to size on the table saw and screwing them together using chipboard screws. Much quicker and stronger for a temporary construction.

Once the jig was assembled, the frames were attached and a couple of battens nailed across the top of the frames to hold them steady.

One consideration having built this solid boxed-in jig is that once the dinghy is complete it will be necessary to remove it from the jig. Many of the fixings will no longer be accessible as they will be covered by the hull. This would not have been an issue if the jig had been constructed from timber sections rather than chipboard panels. I have tried to ensure that once the dinghy is complete, enough screws will still be accessible to allow removal of the dinghy from the jig, but time will tell if I got that right 🤞🤞.

The Hog runs along the centre of the dinghy from the stem to the transom. It is bolted to the stem, frames and transom.

Once the Hog was in place the hull was strong enough to allow the sides of the frames to be chamfered so that the planking will lay flat across the frame edges. Notches were then cut into the corner of the frames to allow the chines to be bolted on. Drilling the long bolt holes through the chines and frames while sighting the drill by eye proved to be very tricky. I think they came out OK, but won't be able to see how well the bolt heads are centred in the frame members until I remove the hull from the building jig.

With the chines in place, time for more chamfering, this time the hog and chines were chamfered so that the floor planking will lay flat across them.

The planking will be 3mm mahogany. Four planks 24mm wide are needed for each side. Fortunately, the mahogany boards I have are 1" thick so I just needed to slice thin strips off the board edge. The first two planks (the sheerplanks) were nailed and glued across the frames, one on each side of the hull. I'm using 12mm brass nails which are only 0.5mm dia. Knocking these in through the mahogany, and into the oak without them bending proved to be a challenge. Eventually, I found that pre-drilling with a 0.4mm drill made the task viable.

With the sheerplanks in place, 26 intermediate frames were cut and fitted between the main frames. The plan specifies that the intermediate frames should be bolted to the chines. I decided that this would not be practical at this scale as recessing the M3 nuts into the chine sections would weaken the chines significantly. It would also be a very tedious task. I had some nice brass gimp pins available, so these were used instead. It wasn't possible to hammer these in from inside the hull as there wasn't enough room to swing the hammer so they were driven home using a C clamp.

The sides of the dinghy are planked with four mahogany planks on each side These are 3mm thick and 24mm wide. Fortunately I had suitable timber to allow each plank to run the full length of the boat, so no jointing was necessary.

Each plank was butted against the previous one and a torch used from inside the hull to show any gaps. Once the gaps had been removed by careful planning and sanding, the plank was glued and pinned into place. Each plank required 57 pins, three into each of the frames.

Once fitted, the final planks on each side were chamfered to match the chamfer on the chine in readiness for fitting the floorboards. The chamfer was not carried all the way to the front, as the floorboards at the front of the hull butt onto the side planks rather than lay over them.

(photos in reverse order - I will get the hang of this eventually!)

Bill the bionic rower hasn't been able to get to the barbers for the past 6 weeks during lockdown 🤣😂🤣

The keel was cut in two pieces from oak. The rear section (deadwood?) was shaped to fit the curve of the bottom of the hull. Both pieces were glued and bolted to the hog.

Oak battens were then fitted between the keel and chine to support the bottom planking. Notches were cut into the frames for the battens. A straight edge was used between the hog and chine to determine the depth of the notch in each frame such that the battens are set at the right level to support and attach to the bottom planking. The forward half of each batten is made from two thinner laminates to enable the batten to bend sufficiently to follow the curve of the hull. The battens are glued and pinned to the frames. The two laminates in each batten are also glued along their length. Waterway notches were cut into the battens at several points along their bottom face. Finally the forward section of the battens was flared into the stem to give a smooth support for the subsequent planking.