Hi Everyone,
Every now and again an opportunity comes along, by this I mean idly scrolling through eBay and making impulse buying decisions, long story short I happened across a very nicely presented example of a Deans Marine DUKW, now I have seen several of these come and go over the years, (not something I keep an eye out for honest) all have been ok examples, some better than others, but on the whole not what I was looking for in terms of build quality / price.
This one however got my attention, nicely put together, the running gear was made of all the stupidly hard to find these days Robbe axles and many of the terrible original white metal / cast fittings had been put to one side and done properly in Brass, on top of which, there was a servo controlled 3 speed gearbox, a separate MFA geared motor for the propeller drive, remote working lights and a servo operated rear winch, in working order.
In short it is a beautiful model and I am very happy with it, but man is it huge, you never really appreciate just how big something like this is until it is on the work bench in front of you, with no room to move, they are also tremendously heavy models having a thick GRP hull, which I am sure is robust, it is just very unwieldy.
But as anyone who is already familiar with my posts knows when I buy something off eBay, it doesn’t remain un-tinkered with for long and the first thing I wanted to address was the land speed; which was a little fast and a bit all or nothing for my liking, powered by a Graupner Speed 600, I also wanted to swap out the motive power for one of my trusty Mabuchi 555 motors, high torque and low drain, I have these in most of my models.
So, if speed is the issue, can’t you just put the existing 3 speed transmission into a lower gear? I hear you ask, very good point, I have looked over the gearbox, (which is buried underneath a mountain of thick grease) if it is shifting, which I am not convinced by, then it is having little noticeable effect on the overall speed of the model, I could degrease the entire thing so I can properly access the internals, so as to ascertain if they are working correctly or not, but for me it is going to be more fun making something that bolts on to the existing gearbox and is going to be a lot less work in the short term, than dismantling the entire drivetrain, which is a project for another day.
I already kind of knew what I was going to make, it was just a matter of rummaging around in the ShedShop until I found a suitable pile of parts, I already had the motor, (as I was also swapping out the unknown age 7.2v buggy stick packs that came with the model, for something out of my Lipo collection) which was going to be running at a higher voltage and therefore be going faster, I also wanted plenty of torque, so that this large model can pull itself out of the club lake, I initially elected to couple the motor to a Chinese 3:1 planetary gearbox, which after an initial trial mock-up in the model required the use of another set of gears to allow the motor to be installed alongside the existing transmission, as the rear of the motor was otherwise fouling the inner rear wheel arch.
I did very briefly toy with the notion of notching the wheel arch, but in hindsight, I am glad this is how it remained, a very brief brush with madness.
To construct the coupling gear box I elected to use the same methods I had been in my 3D printed jet drive project, namely, 3D printed panels that hold the bearings in place separated with standoffs, it makes for a robust and quick to assemble package; so one quick design and printing session later I had the parts on the bench, put it all together, went to trial install it and it didn’t fit, motor was now fouling on the front wheel arch! (It was also fouling on the transmission tunnel that gives space for the driveshafts underneath the hull to take drive to the rear axle from the transmission)
On closer inspection it was not by much and by cutting down the output shaft of the Chinese gearbox, using shorter standoffs and taking a hack saw to the 3D printed parts, I gained enough distance to clear everything.
The new gearbox now fits, but is not in a suitable condition to be tested with anymore, so I tweaked the design and printed new parts for the first revision, (at the same time I also decided to throw in another gear reduction, no idea why now though) with the first revision box assembled and successfully bench tested, I managed to successfully install it into the DUKW, put it on the ShedShop floor for a test annnd…. Was immediately underwhelmed, it moved sure, it could probably climb 60 slopes, but man was it slow, a little too much gear ratio me thinks and the simplest way to resolve that was to remove the Chinese box from the equation.
With the new setup reinstalled, once more a floor test was performed and although much more sprightly, not quite there yet, it was at this point I remembered I was still using the old 7.2v stick packs, once swapped over the speed was much more pleasing, now it is not going to be called fast anytime soon, but for such a large model, it is a good rate to drive in and out of the lake, which if I’m honest, is what the land drive is going to be used for most of the time.
I can’t wait to be able to get down the lake once all of this craziness is behind us and give the DUKW her first voyage under my ownership, but until then, I hope you all remain happy and healthy tinkering in our respective sheds.
If anyone is interested, the gear ratio finally used is here:
https://geargenerator.com/%23225,500,75,5,1,3,722.5,4,1,13,3.25,4,20,0,0,0,0,0,0,0,30,7.5,4,20,0,0,0,0,0,1,1,17,4.25,4,20,0,0,0,0,0,2,0,30,7.5,4,20,0,0,0,0,0,0,1,3,226The parts as they stand are:
Alex
Author
Topic: eBay Deans Marine DUKW (Read 1950 times)