Armortek

How is the gun stab going Steve ?

Dennis.

Hi Dennis. Not there yet. The issue is the responsiveness of the sensor. I've proved the mechanical setup, using a servo for elevation, damping with RC car shocks and mass balancing the gun. That's all quite straightforward, once the geometry is sorted.

I've tried a simple single channel MEMS gyro and although it operated in the correct sense, the sensor was unable to detect the angular rotation of the hull when going over obstacles, either in rate mode or heading hold. Most MEMS gyros are multi-channel or set up for stabilising in yaw (ie traverse) but the one I used can be rotated for use in pitch (elevation), so that's not the problem. The conclusion I draw is that angular rotation alone is not sufficient a stimulus.

I was offered a state of the art MEMS gyro, the Bavarian Demon Cortex to trial. It's much easier than the Futaba to set up and should have been a lot more capable. There was some evidence of movement of the gun but not in phase with the hull movement. As far as I can understand, this one is also based only on MEMS gyros but with improved algorithms. Bavarian Demon have been very keen to support the trial and have offered an alternative gyro, the 3SX, which they claim has an "horizon mode". I'll give it a go when it arrives but I'm not optimistic and both BD gyros are very expensive.

Which leaves what I think will be the best workable solution. All the previous gyros have been designed to stabilise RC aircraft. A new breed is emerging intended to stabilise the camera platforms of drones. These require both attitude hold and the ability to fix a point of view. These are so call 6-axis gyros, which is a misnomer. They still only stabilise in 3 dimensions but duplicate the sensors, each axis having both a MEMS gyro and accelerometer. The two sensors complement each other, the gyro detecting angular rotation and the accelerometer, G forces. They claim to be able to hold both attitude or point of view, which is much closer to the case for the gun stab. These IMUs (inertial measurement units) should be much more responsive but I have a residual concern about inertia, which remains to be tested.

Once I've cleared the 3SX trial, I'll probably order an IMU to test. The one I have in mind is relatively cheap. One word of caution though. There are some very new IMUs coming onto the market as flight controllers for drones but they will not work as they output to multiple brushless motors and the flight algorithms aren't appropriate for us. There are also some which add GPS and magnetometers which would further enhance the ability to fix a point in space.

So not yet an effective production solution but enough of a proof of concept to suggest there should be a workable solution.

All the best.

Stephen

Back to metal bashing and the Vietnam modified track guards. It's quite difficult to sort out the detail of the modified track guards because it seems that the EMEI was interpreted with some artistic licence and the guards varied in detail. I'm using the guards on Paul's tank as the pattern but even they have been modified since Vietnam.

To get a firm base in every sense, I cut out templates for the three track bins in order to establish the length of track guard supporting them. I then removed from the Armortek guards all the rest. On Paul's tank, the original track guards only remain under the bins:









I'm making the remainder of the track guards from scale thickness aluminium so retaining the steel Armortek sections also gives the track guards necessary support. I'll need to remove the outer edge as the Armortek guards are a fraction too wide.

Next step is to cut out templates in card for the front sections. I then started brazing up the parts, using Lumiweld and, with the very thin material involved, being super cautious about applying the torch:





The original Vietnam guards were welded to the front brackets but for work holding I bolted the plates to the supports for brazing, removing the bolts afterwards.

The front sections were reinforced with 2 inch steel angle iron. The originals were knocked up in a hurry in theatre and the welding, whilst functional, was not pretty. That suits my skill levels with the Lumiweld.....



I've added spot welds using fabric paint beads.



Painted up and trial fitted:









Regards.

Stephen

Hi Stephen
Interesting work as always like your alloy soldering
it looks very real.

Derek

the side fenders look great stephen, i do like the textured effect on the glacis plate, looks real. regards simon.

Great to see you back on the metal work Stephen. Having finally tried making some bits of my own I have to say that my respect for your craftsmanship has doubled. You make it look so easy!

All that earlier work on the idlers and brackets more than pays off now. With the modded track guards those details are much more visible. Great stuff.

Kevin

wow those fenders look great! I was thinking the same as Simon - the glassis plate and welds look real 1:1. Can't get much better than that. Fabulous work as usual Steven.
Bob

Thanks for all the kind comments. The glacis texture is nothing special, just a few coats of Upol Hi Build Primer and a good Dremelling with a ball cutter (sorry if that sounds painful).

Having temporarily installed the cut down centre sections of Armortek track guard, I cut the sheet for the rear Vietnam track guards and added the angle iron reinforcement



It's here, in building the track guard brackets, that I started to push my new found aluminium brazing skills to the limit. I decided to fabricate the brackets as per the originals rather than machine them, which would have been easier.

I've ended up believing that Lumiweld can be successfully used to make quite small aluminium assemblies, with one reservation, the thin sheet gave me problems, of which more below.

In making the brackets, I learnt a couple of lessons worth passing on. If you want to assemble small pieces, it's really important to follow the advice to keep the brazing rod away from the flame, using the heat from the parts to soften it. The abrading rod is then used to distribute the brazing alloy into exactly the right place, in the right quantity. It's tempting to cheat by putting the rod near the flame but this invariably results in a poor join, incomplete removal of oxidation and generally too much alloy flooding the joint area:



I got the second tip from a Utoob vid, a very simple method of work holding. Just rest the base part on a fire brick, and use the corner of a strip of steel bar or section to rest on the smaller part to be brazed on. The weight of the bar holds the work true but the minimal contact reduces heat loss. I used that method to join the two sections of bracket and add the mounting for the exhaust boxes without the whole lot coming adrift:





The whole lot did come adrift when I attempted to sweat the brackets onto the track guards themselves. There's something I haven't mastered yet about heating thin sheet. It seems, perversely, to absorb the heat without noticeable effect (until a hole appears). Having tinned the surfaces and temporarily bolted the brackets to the guards to ensure correct alignment, I thought it would be easy to heat from underneath and sweat the components together. Wrong. I nearly burnt a hole in the sheet, despite moving the flame, the tinning remained obstinately hard but the bracket chose to collapse. Pause for swearing.

The brackets were spot welded to the steel sheet on the real one, so I want to avoid using bolts which would be the obvious alternative. I've opted however to call it quits while I'm ahead with the brazing and drill and tap the brackets and sheet and use a blind bolt from below to join them, with some epoxy for good measure. It won't be seen from above.





I've sourced the Lumiweld here:

http://www.lb-restoration.co.uk/cgi-bin ... 01450.1725

Onwards and upwards.

Stephen

Stephen,
Great result. Your perseverance has paid off again. Thanks for sharing the highs and lows of the process. I have learned something new!
regards
Fabrice

The production retaining clasps for the tow ropes were easily ripped off, so the Vietnam track guards adopted the simple expedient of a welded piece of angle iron to retain the end fitting:



When you then realise you put it in the wrong place, you can enjoy cutting if off and brazing it on all over again. In order to protect the other assemblies, I use hefty chunks of steel bar as heat sinks and they double up for work holding:



I chose to solder up the other tow rope fittings on the rear brackets in brass, using resistance soldering:






A coat of etch prime and then base coat:








Next the centre sections. I'll need to join the Armortek steel section of track guard and the aluminium replacements with flush fittings. Allan Bowers has come up with PEM Spotfast SF fasteners by Penn Engineering, which look just the job - if a retail source can be found:

http://www.pemnet.com/fastening_product ... sheet.html

Penn also do a range of MicroPEM fasteners which might be very useful for some of our smaller parts, particularly where you might want to avoid soldering:

http://www.pemnet.com/fastening_products/micro.html

Thanks Allan.

Regards

Stephen

Primed and painted the centre sections in base coat. The Vietnam track guard retained the original sections in the centre where the bins were fitted but the 2" angle iron edge reinforcement was continued along the full length.





I've now got a join to make between the three sections, where the 1mm aluminium sits over the 1mm steel of the Armortek guards. Unable to braze dissimilar metals, I'm going to use these, as a trial:







They are Spotfast self-clinching fasteners, which I've sourced from Zygology in Thame. Despite being an industry wide distributor, they've been very helpful, have sent samples and have agreed to supply to a minimum order of 100. I've ordered some to try.

Regards.

Stephen

Ciao Stephen.
Sometimes, I think it is useless to do every time the compliments to you ... then I see the study, skill and perseverance with which you realize your small masterpieces ... and here I am, back to get my compliments!
Unfortunately, every time I do not know what else to say!

Indeed - it is like following an exciting TV series. Only much better! And so much to learn!
Thanks,
/Chris

Me too, I'm also interested to see what turns up next - I've no idea except to say that I'm ready to try new things, some of which even work. So thanks for your curiosity to follow this mad journey and your kind comments. Much appreciated.

One thing has worked a treat. After a false start with Spotfast fasteners which were marginally too thin, I've struck gold. The sheets I'm joining (aluminium and steel) are both nominally 1mm. The appropriate thickness of fastener has a tolerance of 0.08mm on each sheet so the SF-5-1.0-ZI should have worked. It didn't. The fastener depends on forming the metal of the two plates as it penetrates under pressure (from in my case an arbor press).

Zygology were marvellous in understanding the issue and suggesting two possible causes, insufficient down force or sheets oversize. They quickly sent some samples of the next size up (nominal 1.2mm), which did the trick. The technique is very simple, drill 5mm in the top sheet, 4mm in the bottom one, position the fastener in the top hole, apply pressure from an arbor press and the job is done. The join is stronger than the surrounding material, the fastener is flush to the bottom and only slightly raised on top (I'm sure this is due to the limit on the pressure a hand tool can apply). The results are pretty good although I'll probably use a thin layer of filler to tidy up my rather poor attempt at grinding the tops flush.













All the best.

Stephen

Stephen,
As always, a very elegant solution to a given problem.
Engineering bonus: your "racing" Cent will go even faster due to reduced parasitic drag.
The late Howard Hughes would be very pleased .
regards, Fabrice