the weight balance looks fine, batteries on one end and the thingaps and heavy gearboxes on the other,

looking fine nick
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Since I can't finish Jolt this weekend, I'm doing extra development on Subliminal. Here is the template I need to have lasercut:





The yellow area is the shape of UMHW sandwich while the red area is the extra part the metal layers have for the wedge hinges. the top & bottom panels have the same outline & holes but without the internal cut-outs.
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I built one of the 7.2V battery packs tonight - its definitely the strongest pack I have made to date. I used the smaller braid to make very flexible links and the smaller size also allowed very fast soldering and kept the cells cooler. I strengtheded the pack with 22mm high pressure waterpipe and heaps of hot-melt glue before finishing it with 3 layers of heatshrink.

If I can complete the other pack and make the electronics mounting plate tomorrow, Subliminal's wiring will be finished ahead of Jolt's
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Subliminal is coming along in leaps & bounds! I finished the second battery pack, updated the drawings and cut out a MDF template for the UMHW sandwich pieces. It isn't as good as a laser cut job, but i nailed the important dimensions.

Although the battery packs came out a little heavier than predicted, I still have 10.1 Kg for the frame & armour. Now I have the sandwich piece made of MDF, I should be able to weigh it and calculate the approximate weight of the piece in UMHW - I think...

Next up is the electronics panel and the base plate. Once they are done, I can think about getting the whole thing running for a test drive at the next Marayong competition.
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Using some web research and dodgy math, I worked out the approximate weight of the UMHW fram parts. I had the weight of the MDF template, from there I multiplied the weight by the ratio of the density between MDF and UMHW and then multiplied again by the ratio of template to chassis thickness . Sounds confusing? The UMHW should weigh around 1.3Kg, which is quite a bit for plastic but still leaves 8.1 Kg for armour.

I made the electronics panel from 3mm polycarb and I am now having trouble deciding the best way to mount the receiver and gyro securely. Cable ties won't work here, so a strap clamp might be best.

I had a new idea for screwing the frame together; I was going to use self-tapper screws which grip really well in UMHW but eventually wear the plastic out if they are removed frequently. The alternative is to use threaded metal inserts called 'nutserts' in the UMHW - I have a huge pile of these left over from an old project, so it costs nothing to try.
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Brainstorming time:

I need a way to securely mount several small, low power eletronics packages that provides some shock mounting, cable retention, light weight, easy assembly, etc, etc. It also has to fit in a small space. Sounds impossible, right?

Then I remembered a packing technique for expensive electronics; the gear is wrapped in plastic like freezer bags and placed in a box which is then half filled with expanding urethane foam. the foam starts as a liquid and literally foams up to many times its volume before hardening. More plastic is laid over the inside of the boxe and then more foam fills up the remainer of the box. When you unpack it, you get a 2 part mould of the product inside a very tough foam shell.

The foam is available in spray cans as 'void filler' for building repairs. I figure that I can assemble the radio, gyro and mixer, stick them to a flat plate with all the wiring in place, put a freezer bag over everything, put a mould container over that, and pour in the foam.

When the foam sets I should have a block with tigh-fitting pockets for the electronics moulded in the bottom. it would be easy to include some mounting points inside the mould or just sandwich it into the frame.

I can see some problems here: the foam can be messy, cables could be trapped in the foam, foam could leak into the electronics during the moulding process - Can anyone see more potential problems / solutions? Keep in mind that Subliminal is really tightly packed and I can't fit a conventional plastic box.
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They used to have a system like that at a place I worked, but it was a big system used for packing shipping boxes.

It had two big pressurised 44-gallon drums of the chemicals that were connected via hoses to a spray-gun. You wrapped the thing you wanted to ship in plastic, then sat it in the box and sprayed expanding foam around it, then closed the lid while it expanded.

The warehouse/shipping guys really liked it over the conventional plastic-peanuts (that get everywhere), until one day after a few too many ale's down the pub at lunchtime, they came back a wee bit intoxicated and proceeded to attack each other with the spray gun and ended up both looking like the michelin man..

Another option might be the industrial-style velcro. I dont mean the wimpy fish-hook and carpet style stuff.. its available in stronger versions where the hook side is a solid plastic dual-pronged barb, and the fuzzy side is strong nylon loops.

One of the Gyrocopter guys used to use it to stick things all over his Gyro. Map cases, Oil bottles, radio's you name it. a few square inches of the heavy duty stuff would easily hold you to the ceiling, yet it still provides a little bit of "give" to provide some shock resistance.

The IBC's and radio etc in Scoopy Doo are mounted using pockets carved out of a very low-density foam similair to what you describe. The foam is cut to shape, stuffed in in layers, then spaces cut out to hold the receiver, gyro etc. Works Fine so far..
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Velcro would be good for all sorts of bot applications, I have never seen a good way to hold it down to a metal surface. Most options use glue backing and I have never seen it work well, even when I tried various industrial adhesives. looping it through a cutout seems the strongest way to hold it down, but that's not possible for this setup

I like the foam option as it should mould around the connectors and stop them popping out, something the velcro won't do so well.

You mentioned that the packing boxes were closed before the foam had finished expanding - what happened if the box was over filled? I figure that moulding into a (mostly) closed container will force the foam into the contours of the parts better but if there is too much pressure the parts might not release afterwards. Even then, the foam could be cut off and tried again...

Since I have a can of the foam from last year, I will cut out some test shapes from mdf, find a mould container and just try it
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I might have missed something but have to ask, why are u putting a gyro in a wedgebot?
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just to improve on nicks execellent driving

as for the weight thing nick the density of uhmw is 0.9kg/m^2 or something like that... i just find the volume of a part (taking dimensions in mm) and multiply it by the density...

excel and the volume function on rhino work wonders.. sounds like someone needs rhino cad (i think you asked for it before :s currently putting it in the robots case as we speak)
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The gyro is there 'cause I want to see how it goes with the rest of the drive system - its not so useful if the bot gets inverted so I might drop it once Subliminal gets closer to finished - perhapes my driving will be even more excellent by then

I think someone mentioned an advanced gyro that could account for being inverted - or was that wichful thinking?

The volume of this part is hard to calculate with out smart software like Rhino - I found that MDF has a density around 0.8 and from there it was easy but probably none too accurate.
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i use velcro in some of my bots i use a smal piece of 3 m ali with the edges rounded to clamp it down i use rivets or nuts and bolts through the ali the velcro then into the body of the bot to atach it so far the batteries in the cheese havent moved and they are both just held in with velcro overlapped the whole lenght of the batteries.the ibc's are also held in with velcro in the cheese ans t2m when it has an ibc fitted

I have to say I like the idea behind this bot a lot.

I think I will have to try something along these lines, but only with junk I find of course. Or something noone else would every want to place in a combat robot

@ Prong: I will show you around the insides - you will get lots of ideas as while the materials are "high tech" they don't have to be and the concept is really LOW tech. Strangely enough I got it from a story about undercover gun making, where this guy had made a pistol firing a 12 gauge shotgun shell. He used just hand tools and a laminated metal and plastic frame - I have wanted to use the technique ever since.

The electronics mounting has sorted itself out along the KISS principle. The IMX mixer is larger than the radio and has mounting holes at each corner. If its mounted on standoffs, the radio will sandwich neatly underneath, between layers of foam. A light plastic shroud will drop over the whole thing and the job is done. I will mount the gyro seperately in case it is dropped from the final design.
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Here is the latest development on Sunliminal:


The Battery packs are not expected to get all that hot but I put heat saver rings on anyway, with an extra thick one between the calls to make the join stiffer, The whole thing will be sandwiched in foam anyway but extra precautions never hurt:






Here is the overhard view with the MDF template, aluminium base and polycarb electronics panel in place. The IMX is now sitting over the radio. All the power wiring is done and the controllers are active when I turn the power on.





A closer view whowing the wheel well and IMX/radio bundle. One thing I totally forgot was the invert switch - it can be attached to the polycarb near the IMX.

Question : What do people use for invert switches? I heard that mercury tilt switches were bad, so I was thinking about a reed switch and a magnet on a hinge.

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