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In other news, the motionco pulleys arrived.

The 6mm bore pulleys attached to the motor shafts with no issues.

Connecting the pulleys to the thruster shafts was a different story. The shafts have an M5 thread on the end however the next smallest bore I could get was 3mm. Therefore I planned on drilling out the bore and tapping it myself. I found a spare of adjustable plumbing grips to have the same locking thread as the pulley making it a secure holding to combat the torque of drilling.

Sadly, the drilling seemed to be very problematic as all I have is a hand drill. The drill itself is good, however the issue I feel is me keeping the thing straight. This is were a pillar drill would be very useful. I do plan to get one as soon as I sort my outbuilding/workshop out. A lathe and milling machine is on the cards also.


Hi Folks, time for another update.

The bow thrusters were mounted on some 6mm MDF. This would allow me to position the motors to gain the correct tension on the belt and then finalise the position with a screw.

At the end of the last update, I was stuck with threading the pulleys which attach onto the prop shafts. I mentioned my issue on a model forum on which I am a member and Trevor kindly offered to bore and tap the pulleys for me. I got them back a few days after sending and so the motors could be installed.

The main prop shafts were oiled and finally installed in the tug. The kort-eze was then tapped back on and thus completing the main drive. The motors were ran out of water for around an hour on low speed with plenty of lubrication added. This allowed me to experiment with the various programs on the speed controllers. No pics as there wasn't much to see. 

As part of the previous process, the korts themselves were installed. They came with some resin arms which would normally connect via a rod to the servo. These weren't needed and so they were set on fire in the garden....... for a very good reason... They contain a brass sleeve in the middle which would act as a secondary securing device for the korts.

I intended from the start of the build to use pulleys for the kort system. The main kort shaft is 8mm dia and the only pulleys which I could get for this were these larger type, again from motionco.

I obviously also needed a pulley for the servo. I found them quite hard to find but I tracked down some brass servo fittings which featured a 6mm bore in the middle. This combined with some 6mm brass rod and the bore reducers which I ordered with the pulleys should give me a way to mount the pulleys.

The brass rod was forced into the bore reducer with a vice.

And finally the pulley was attached to the kort shaft.

The next stage was to build a suitable and secure mount for the servos and put the servos in the correct place to achieve the correct tension! The bottom line is I managed to do it first time, somehow! It all just seemed to work and the tensions are perfect. 

I essentially started with two bits of MDF and I secured one servo directly to it and slipped the belt on and held this under tension. I then propped up the two bits of MDF with servo attached and very carefully place the other servo on the 'frame' and again slipped the belt on. I gained the tension needed while still placing tension on the already fixed servo... when they felt right, I clamped the loose servo with my fingers and drilled directly into the MDF and secured it. The whole procedure was repeated with the two secure servos, to check the belt tension. It was perfect.

The assembly frame was cut down tom size and this picture shows the setup hanging in tension.

The servos were given a more secure mount with nuts and bolts.

The supports were screwed onto the frame.

The whole setup was then secured to the tug hull with fibreglass filler. It was allowed to harden and then the frame with servos was removed.

I am using servo-morphs again from ACTion Electronics in-line with the servos in order to control their rotation speed and maximum throws so they don't hit and bang on the prop shaft. I wanted a place to locate these close to the servos and decided to make a separate mount which sits on top of the servo frame. Some 6mm MDF was cut to shape and securing screws drilled.

I checked and re-checked the clearance to lift the shelf which servo-morphs attached. I then secured the servo-morph boxes with superglue.

The servo leads themselves were then routed and tidied up by securing them to the servo itself.

The servo-morphs were then installed in their boxes and wires routed.

The setup was then installed in the tug. The frame holding the servos goes in first, then the shelf holding the servo-morphs is installed and the two wires connected. The belts can then be slid into place. This makes for a very easy and compact setup which can easily be removed.

I then put the tug back in the bath as I couldn't resist giving the motors a run in water. I weighted the stern down and the leaking began once again. I couldn't believe it. I dried the tug off and gave the kort brackets an over coat of normal car body filler in the hope this would stem any leaks. I have yet to test the repair but the picture above shows the difference of colour in filler.

The next issue I found is that in testing, the BEC on the main board (Battery Eliminator Circuit) which pumps out 5 volts and is designed to power a radio receiver, struggled to cope with one servo alone, never mind two with a respective servo-morph. I then decided to use two separate BEC modules of which two models exist. One pumps out 5 volts, but its input voltage is limited to 12 volts. The other pumps out 6 volts, handles upto 1.5 amps and the input voltage can be anything upto 36 volts I believe. I have opted for the for latter model and they are on order. This will allow me to power the servos off a separate power bus therefore bypassing the receiver. The servo-morphs will still be connected to the receiver but only by the white or command wire. I still need a 12volt battery in which to run the lighting circuit off and may end up using that as servo power also, however the bigger model allows me to do as I please.


Time for another update, albeit a fairly small one. I've not had much time to work on the tug due to other commitments.

Picking up from the previous update, the system was tested and I began to notice small issues. The servos we very glitchy and would simply not sit still, the RX powering them simply overheated (I expected this) and I wasn't really happy with the rigidity of the setup. I contacted Dave Milbourn, the former owner of ACTion Electronics. Daves a genius and he set about thinking of a new way to atleast power the system. He also suggested I swap the servos to a more known brand such as Hitec.

Dave came up with the following electrical layout:


I had previously ordered some plastic pulleys from a robotics website, however they didn't fit on the old servos. As they were a Hitec fit to start with, they simply dropped onto the new servos. I also removed the brass collar (which had been set fire to previously) and turned the large alloy pulley upside down and secured it that way. There was a small height difference of around 4mm which was fixed by using some 4mm MDF as shims glued onto the servo frame supports.

I decided to move the servos a little closer to the main kort pulley, this also meant a new set of belts. I also made a new servo frame, using the old as a template. You can see one of the shims I spoke about in this photo.

This shows the harness Dave made.

I now have two options for power. I can run the system off a 6v BEC which is turn is powered off a 12v battery. Alternatively I can use a dedicated 6v battery which a switch harness on. The use of a powerboard in the first instance is fine, as the lighting circuit on this tug will be 12v, using 12v LED's.

Upon testing the system, it certainly feels a lot more rigid and there's hardly any glitching. The small amount there is can be attributed to incorrect trim settings on the transmitter.

All that awaits is a sea trial!


More Soon!...

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©Dan Walker