Well here goes
Being one of an elite group not usually catered for by manufacturers, I decided that I would try and build my own left handed, model boat transmitter.
On opening the case of a fairly new 2.4 gig. transmitter I almost gave up at the sight of so many wandering wires. My grand-daughters bowl of spaghetti had nothing on this!
The first necessary task was to carefully label the leads running to the trim tabs with the colour of the central lead running to the potentiometer it served and note which leads went to the various switches and ‘pots’.
Then unscrewing the tabs, joysticks and switches I untangled the leads and laid them out to discover where they all went and if it would be possible to alter them to suit my intended controls.
I have always preferred a wheel for steering and a slide ‘pot’ for speed control which meant that the joystick for these would certainly have to be changed but that I might be able to get away with a joystick for the gun controls.
With a wheel it is so much easier to control a boat, just use the spoke that points in the same direction that the boat is heading. The left side moves in the direction the boat should go when travelling right to left and vice versa. Up and down control the same direction when the boat is moving away or towards you.
Measuring the size of the printed circuit board (There was no way I was going to alter that, my expertise does not extend that far but I did grow up with valves and ‘pots’ etc. since my father was a radio and TV engineer so I was not completely lost.) and laying out the approximate positions of the controls determined the size of the box I would need to house the new arrangement. A hunt through the electronics suppliers catalogue showed that there was a high impact, ABS instrument case that was reasonably near the size I was after. (Jaycar HB5972 size 225 x 165 x 40 mm.)
The wheel was the most difficult part I had to make up. It started from one I had previously made from a Sanwa transmitter joystick control and this was still adjusted by a manual trim mechanism. The electronic trims on the new transmitter are far to slow and have insufficient movement for model boat work especially steering, where a straight line can often be controlled from a manual trim alone, to compensate for wind and tide.
The first thing to change was the ‘pot’ since it was only 5k. and it needed to be at least 10k. even if I could not obtain a 12k. ‘pot’ to match the new Tx. ones. Of course the shafts of the ones from the new Tx. were fluted metric and the Sanwa used imperial shafts with a flat side so a new pot had to be obtained from overseas via the net. The new one although with a flat side, was of course metric with a different shaft diameter but I was able to combine the brass fixing ring from the Sanwa with the plastic ring from the new Tx. so that it fitted the rest of the mounting.
The next task was to extend the trim tab and turn it 90 degrees so that it would protrude from the front of the new case. This was done with a short length of 3 mm. brass rod, flattened on one side to assist glueing to the trim tab and bending it, after heating, to the required angle. It was fixed with 5 minute epoxy.
The wheel was constructed from a piece of 19 mm. aluminium rod, drilled 5 mm. at one end to take a piece of brass rod to allow the aluminium to be held in an electric drill chuck and the end shaped. Holes were drilled on opposite sides of the aluminium to take brass spokes turned out of 8 mm. rod. The Sanwa joystick included a piece of plastic that fitted over the fluted shaft and this was screwed with 10 BA brass countersunk bolts from the scrap box, into tapped holes in the aluminium. (you can possibly see a piece of 3 mm. perspex between the black plastic and the underside of the aluminium which was from the previous arrangement and so well glued to the black plastic that it was left on.)
The whole assembly is screwed to a shaped piece of perspex glued to inside of the front case. A 20 mm. hole was cut for the middle of the wheel and a curved slot for the trim lever. The spokes are a tight fit in the holes of the wheel centre and can be removed to allow the wheel to be fully removed.
The construction is not as rigid as I would like but should stand up to fair use. If there is a problem I would make a separate the bearing for the wheel and have a loose connection to the ‘pot.
In order to have the speed control slide ‘pot’ operate over its full length, a 5k. one was chosen and a 3.3k. fixed resistor soldered onto each end to bring the total load nearer to the 12k. of the original ‘pot’. The slide ‘pot’ was fixed with 3 mm. screws to the new case after cutting a slot in the plastic for the shaft.
As can be seen in the photo of the inside of the case, quite a few parts had to be sanded off with a coarse wheel in a mini drill to make level surfaces for the ‘pots’ etc. to fit snugly.
The new Tx. used four 1.5 volt batteries and I changed these to five 1.2 volt rechargeable NiMh. in a battery box glued and fixed with a brass strap to the rear case. Access is by a hole cut in the case and covered with a piece of 1.5 mm. perspex held in place with four 3 mm. screws. To allow the front and rear cases to be separated, a plug and socket were installed in the line.
The printed circuit board was fixed to the front case with five countersunk head brass bolts held in place by 3 mm. thick perspex blocks glued to the front case. Small rubber washers to reduce the strain on the PC board. This arrangement gives a much cleaner look to the front of the case and I wish there was an easy way to replace the rest of the screws that appear on the front and back of the case. The battery status indicator lights were fixed in a similar manner to the top of the case so they are flush with the case surface.
The gun on my corvette is rotated by a servo with an ACTion electronics ‘Servomorph’ to extend the travel, and microswitches, operated by a mini servo, control elevation. These need a ratchet limited movement in one plane and a self centering movement in the other. One set of ‘pots’ on the Tx. joystick had this arrangement and only needed one ‘pot’ to be reversed to the other side to fit into the corner of the new case. This was just a matter of unscrewing two opposite sides and changing them and the yoke that holds the stick, over. A hole was cut in the case and the joystick screwed in place with small brass countersunk bolts tapped into the plastic of the joystick frame. Since the stick was slightly too long and got in the way of my finger on the wheel spoke, I shortened it by turning it down in the drill chuck.
The fifth channel is used to operate another microswitch for the horn and the lever was replaced with a momentary push button located at the side of the top end of the speed control slider ‘pot’ which is just the right location for my thumb to rest on.
The rate of travel switch is not really needed but it and the range test – trainer switches were mounted on the top of the case. Slightly more difficult was the sliding On – Off switch mounted on the PC board. Not wanting to unsolder it and perhaps damage the board, I dismantled it from the top and soldered wires to each point and ran them to a double pole mini switch mounted on the top panel.
The aerial appeared to have a fixed connection to the board but after considerable thought of how to securely fix the aerial to the case without breaking the wire I found it was just a push fit connection and I was able to attach the aerial to the top of the case with four small bolts and nuts.
I tried to operate the Tx. without the electronic trims but the controls were unstable. For model boat work they are not really needed so they are taped to the inside of the front case. It still looks a bit like a bowl of spaghetti and I wish I could eliminate them.
The channel reversing switches have been left where they were and are not used. If you cannot connect the servos etc. correctly, the battery box could be moved up and the hole and cover extended to give access to them without dismantling the case.
Author
Topic: Left handed, model boat transmitter (Read 3484 times)