In addition to the servos which move the oars fore and aft to produce the rowing stroke, another servo is needed on each oar to raise and lower the oar into the water at the start and end of the stroke.

To hide them away these servos need to fit under the floorboards. There isn't much depth available so I bought two 'wing servos'. These are only 10mm thick and should fit in the available space. (Haven't made the floorboards yet - time will tell!)

A plywood mount was constructed from 3mm ply. This holds the servos at an angle to the horizontal so that the pushrod attached to the oar is, as far as possible, perpendicular to the output shaft of the servo. Mounting them like this should help with the oar movement, but does make it even harder to fit them under the floor. The servo mount bolts on to an oak block glued to the keel. There are two M3 nuts embedded in the underside of block for the bolts to screw into. The pushrods are simple straight lengths of bicycle spoke with an M2 thread on each end. Ball connectors are screwed on each end to accommodate the movement of the oar.

Back to some woodwork!

The plan includes several suggestions for the flooring arrangement from a minimum of a small section forward over the V shaped section of the hull through to full flooring fitted flush with the frame members. I opted for the latter, as I want to hide the servos, wiring, battery, receiver and controller under the floor. There are four 'bays' between the main frames and each bay is floored with two sections of flooring, port and starboard. The flooring is not fixed in position and can be removed for access below deck.

What to use for the flooring? A search through my timber stock turned up a couple of odd shaped lengths of wood. I don't know what it is, but it is a hardwood of some sort, and very fine grained. Several strips were cut 14mm wide on the table saw and these were then sliced into 3mm thick planking. The planking fits on floor joists cut from the same material. The joist fit into hangers glued to the main frames. Each plank was trimmed to fit against the hull wall at the outer edge, and to fit around the frames where necessary. Superglue was used to glue the planks to the floor joists with 2mm plasticard spacers used to give an even spacing across the floor. The main frames were protected with masking tape to ensure that the flooring didn't become permanently stuck to the hull. As each section of flooring was completed, the inner end of the planks were trimmed to the centreline.

The floor sections over the two lift servos need to have holes to allow the pushrods through. I wanted to be able to fit and remove these floor sections without having to disconnect the pushrods so small separate trim sections of flooring were built to fill the gap. These are held in place with magnets. (Since taking these photos, I have replaced two floor planks so that the pushrod apertures are the same size!)

Finally a small jig was made to help position pre drilled holes for the flooring nails. 336 holes 0.5mm dia were then drilled and 10mm brass pins fitted to secure the planking.

Bionic Bill needs somewhere to sit while rowing so, with his help, the position of the Thwart was determined. Bill balanced on various blocks of wood until a position was established whereby his arms would reach the oars throughout their range of movement.

The thwart was cut from 4mm oak. Cardboard templates were used to work out the shape of the ends where the thwart needs to fit round the frames of the hull. Two oak beams were also cut to provide support for the thwart. To make access to the internals of the hull easier, the thwart is not permanently fixed in place, but is held in place with magnets. Three pilot holes were drilled in the supporting beams and panel pins used to mark the corresponding locations on the thwart. These marks were then drilled out 5mm dia. to the correct depth so that magnets could be epoxied in position. The support beams were then pinned and glued in position onto the frames at each side of the hull.

This completes the dinghy construction. All that remains is to finish it inside and out, make the oars to replace the sticks that Bionic Bill has been practicing with, and to add some scale features/accessories. So, time to check the weight and waterline.

The plan for the full size dinghy states an all up weight of 700kgs. At 1/6th scale, that equates to 3.24kg. Checking the weight of the model on my digital scales, including Bionic Bill, receiver, controller, servos and battery the actual weight comes to 3.08kg. The hull still need to be finished inside and out, and some scale accessories added, but the weight should turn out about right in the end.

I also had the opportunity to test float the dinghy this week. It floats close to the correct waterline. Possibly a little light at the stern, but I can move the battery to help with that. Unfortunately, Forgot to get photos of it on the water, but there will be plenty of opportunity later.

While I'm waiting for the paint and varnish on the hull to dry, time to get on with some other details.

Having checked the waterline, some ballast towards the stern would be an advantage so I bought four 3700mAh NiMh cells to make up a battery. These will provide the extra ballast as well as having a good capacity to keep Bionic Bill rowing. I decided to make up a battery from loose cells so that I could fit them either side of the keel. The cells came with tags fitted so it was a simple task to solder them together and then insulate them with heatshrink.

Based on experience, when buying heatshrink it is easy to buy the wrong size.🙄 The cells I bought have a diameter of 23mm. This equates to a circumference of 23 x pi or approx 72mm. Heatshrink is sold flat and in specified widths. 40mm heatshrink gives a tube with a circumference of 80mm, and so is suitable for these cells. If I had bought 30mm heatshrink, thinking it was big enough for a 23mm dia cell, I would have been disappointed.

I had several ideas for how to hide the on/off switch for the dinghy. In the end I've settled on using a latching relay, actuated by two magnetic reed switches. The two switches will be hidden below the floorboards and actuated with a loose magnet which I will need to keep safe somewhere. Bringing the magnet close to one of the reed switches for an instant powers one of the relay coils an turns the power on. Bringing the magnet close to the other reed switch powers the second coil in the relay and turns the power off. Reed switches are quite delicate so I will be encapsulating these in plastic tubes before fitting them in the dinghy.

The outside of the hull was painted with a white gloss rattle can over the previously applied grey primer. The name, ordered on-line as a self adhesive vinyl decal, was applied to the transom and then several spray coats of silk lacquer were applied to seal the decal and finish the outer hull.

A mooring bitt was carved and bolted to the fore deck. All the hex recesses in the visible fixing bolts were filled with epoxy and the heads then painted with gunmetal grey to give them the appearance of coach bolt heads.

All the remaining bare timber was given two coats of thinned epoxy resin rubbing down between coats where access was possible. Once fully hardened, this was then over coated with brush applied satin yacht varnish to take the shine off the surface. This finish has brought out the colour and grain of the exposed timbers which is what I was aiming for.

Finally all the brass components were cleaned and polished and dip coated with metal lacquer.

Between coats of paint/epoxy/varnish I was able to complete development of the rowing controller. Development of this started in September 2019 and has taken until this week to complete. I estimate I have spent 500 hours working on the software, mostly in the evenings while sat in front of the TV with nothing worth watching. The software was developed on a windows laptop and is then loaded into the controller. Work on constructing the dinghy did not start until April, when I had Bionic Bill rowing in a test rig in order to prove the concept. I didn't want to start on the woodwork until I was confident there was a reasonable chance of success with the software.

The block diagram shows the basic approach. There are 6 servos in all, two for each oar, one to rock the body back and forth during rowing, and one to turn the head. The receiver is a miniature FlySky FS-R2A unit which provides the received channel settings in a PPM format down a single wire. This is fed into the controller where it is decoded to provide remote control of the rowing action.

The controller is based on a PIC 16f microprocessor. The software is written in assembler code. The power and capability of these modern microchips is staggering. When I left Uni and started work in 1973, I worked on programming a PDP 11/20 minicomputer to control a metal turning lathe. That minicomputer was the size of a coffee table, weighed 50Kgs+ and cost £10,000 (in 1973!) It had less functionality, power and performance than the microchip used in this rower, which is the size of a fingernail, weighs 2g and cost less than £4.

Three channels are used from the received signal, Ch1 for steering (rudder), Ch3 for speed (throttle) and Ch4 for the head turning. Three more channels from the transmitter, Ch2, Ch5, and Ch6 are also decoded and provided as spare outputs from the controller with standard PWM format (1-2mS).

The controller generates the rowing action by producing standard PWM control signals to the two pairs of servos attached to each oar. By generating PWM control signals for the servos that sweep through the range from 1mSec to 2mSec, the oars can be made to move through a predefined cycle to simulate rowing. The rate at which a servo is swept from one end of it's travel to the other determines the speed of rowing. This sweep rate is controlled by the Ch3 (throttle) input from the transmitter. Similarly, the range of movement of each oar is adjusted based in input from the Transmitter Ch1 (rudder). For example, pushing the transmitter stick to the right, to request a turn to starboard, results in the stroke length of the starboard oar being reduced and the action of the Port oar produces the requested turn. With maximum turn requested, the starboard oar stops all movement.

As the rowing speed increases, so does the oar stroke length. To improve the realism of the action, the servo installed inside Bionic Bill also starts to rock the body back and forth. This helps keep his hands on the oars.

The receiver used does not have any capability to send telemetry back to the transmitter, so it is not possible to get the battery charge status displayed. Not wanting to find bionic Bill stranded in the middle of the lake, the controller monitors the battery voltage and when the charge level drops below a threshold, Bill starts shaking his head from side to side as though to say 'enough, no more - bring me back in!' 😆 I hope this proves to be reliable in practice. When not indicating that the battery is running low, the head can be turned at will using the transmitter joystick.

With Bill rowing on the test rig it became clear that there were many settings which would likely need to be adjusted to the start and end points of each servo movement in order to obtain a realistic rowing action and to have it balanced between port and starboard oars. Initially all these settings were values stored in the program on the laptop which could be changed and then re-loaded into the controller however I did not see this as a realistic option at the lakeside. Reluctantly I decided to develop a programming card, similar in concept to the units available for some ESCs, which allows adjustment of the parameters. This took as long to develop as the rest of the controller, but now it is working, I think the effort will prove to have been worthwhile.

The oars are simply constructed using lengths of Ramin for the shafts and Mahogany pieces for the blades. My timber of choice for the shafts would have been Ash, but I didn't have any available so I used the Ramin I found in my wood stock. Ramin used to be a common timber at wood merchants and DIY stores, being the timber of choice for dowels and mouldings on account of it being straight grained and knot free. It is now CITES listed as endangered and it is difficult to find for sale. Mouldings etc are now usually made from pine or something similar and are generally of poor quality compared with those that used to be available.

To reinforce the glued joint between the shafts and blades I skinned the blades with epoxy resin and fibreglass cloth. The brass collars that connect the oars to the rowlocks (described in an earlier post) were slid into place and glued/pinned to the oars.

One issue which gave me a challenge with regard to the oars was how to stow them so that I can transport the dinghy to the lake. With the oars in place the dinghy is 1M long and 1M wide which makes it awkward to transport. I needed a simple means of being able to stow the oars for transport, and to quickly set them in place for rowing. Releasing the oars from the rowlocks did not give enough freedom of movement to stow them. The pushrods which connect to the up/down servos prevented the oars being swung round far enough to stow them. The solution was to attach the pushrods to the oars with a small brass angle bracket which is locked in place with a 3mm button head bolt. Loosening this bolt allows the oars to swing round sufficiently to stow them onboard. The oars are reinforced with a brass tube for the bolt to pass through.

The oars attach to the rowlocks with a screwed pin that passes through the tube at the top of the brass collar fitted to each oar. The pin is threaded 2mm and screws into the rowlock arm. To prevent the pin working loose while rowing, a 1mm brass wire was formed to clip over the top of the rowlock once the pin has been hand tightened in place.

As it has just stopped raining, I took a quick video of the completed dinghy with Bionic Bill rowing, turning, and rowing in reverse (just for you Robbob 😉)

As Bionic Bill is hoping to go fishing tomorrow, he has loaded up the dinghy with some of his tackle. 😁

(I've been making bits and pieces to go in the dinghy over the past few months.)

The anchor is made from plasticard. The chain links are copper wire. The rope was 'aged' using woodstain.

The boathook is brass, turned on the lathe to a taper. The shaft was hand carved from an offcut of the timber used for the dinghy flooring.

The fishing rod is made from the smallest diameter garden cane I could find in the shed. The loops are bent from thin stainless steel wire and bound to the cane with black thread. Thin cork sheet was glued to the cane to form the handle. The reel was fabricated from plasticard and painted. It is wound with real fishing line. The float is a short length of plastic rod painted black and red. The weights are lead shot.

The landing net frame is painted brass rod. It is fitted to a handle carved from oak. The netting was found in my wife's fabric drawer.😊

The paddle is carved from an oddment of timber, I think it might be beech.

My favorite item is the bucket. It is made from a 2" plantpot. Black plasticard was added round the top to produce the rim. The handle is made from a length of copper wire from an electric cable which was painted to look like galvanised steel. The grip is part of the original black insulation which I left in place.

Bionic Bill went on a fishing trip this morning. He didn't catch any fish👎

It works!!! With little adjustment Bill was off round the lake. He spent over an hour rowing up and down the lake and there was still plenty of power left in the battery. Not sure if his arms will ever recover though 🙄.

It is such a relief, and a surprise, that it worked first time. I was expecting it to take several attempts modifying and adjusting things before it would work reasonably. There are a few things that need some attention, but they are minor. One oar is slightly lower than the other, so needs the trim adjusting, and I think it might look better with a longer stroke length. Yesterday I modified the controller to stretch the servo signal to the head turn servo so that there is more rotation. That has worked in one direction, but there is a software fault when he turns the other way which makes it look like he has a stiff neck 😉. Other than that, and the lack of lunch on-board, it went well.

There was much interest from fellow modelers at the lakeside and from the public. Many stopped (at a distance) to ask about the model and how it worked.

Phil from Buxton MBC took lots of video footage so I hope we will have a much better video available before long.

Phil from Buxton MBC made a video of Bionic Bill’s first outing and has posted it in the media area of this website. I’ve copied the link here to keep it attached to the blog.

Many thanks from me to Phil for the excellent video.