Flux [featherweight]

A while back at a friends house I came across one of these old fashioned tonka toys - a chunky steel thing which surely wouldn't be allowed anywhere near a child these days.

http://lh6.ggpht.com/_3v3udRbjClg/TK...0/SDC12230.JPG

Clearly I wasn't about to take one to a sandpit but it was the first time I'd seen rubber tracks at an almost-perfect scale for a featherweight. Here it is by my beetle for comparison.

http://lh4.ggpht.com/_3v3udRbjClg/TK...0/SDC12235.JPG

And so, after finding two of these monster-toys on eBay and spending silly amounts of money on various other components here's where I am:

http://lh3.ggpht.com/_3v3udRbjClg/TK...0/SDC12238.JPG

The observant among you will notice it's essentially a larger version of my beetleweight. I actually started planning and compiling parts for this one long before fractal but the beetle was much easier (and cheaper) to build. I was at one point hoping to finish this machine by September but instead have decided to take it slowly but surely, as is usually the route to more successful designs.

http://lh5.ggpht.com/_3v3udRbjClg/TK...0/SDC12239.JPG

Instead of the four powered axles on the beetle this will only have two, with two dead axles at the front. One of the most complex elements of this design is likely to be track tensioning, something that I really don't want to be rushed on - there will most probably be two additional suspension arms per side.

http://lh3.ggpht.com/_3v3udRbjClg/TK...0/SDC12241.JPG

Here's a shot to give you an idea of the arm/weapon actuator. It's a combination of an MFA como drill motor and homemade gearbox (although the standard motor will likely be swapped out for another 540 sized one). The overall reduction is 831:1 (the three stages being 11:1 > 40:1 > 9:17). Hopefully it will be pretty damn hard to back-drive given the worm stage.

http://lh3.ggpht.com/_3v3udRbjClg/TK...0/SDC12242.JPG

The drive gearboxes are the new-style 26:1 reduction banebots ones with 540 style motors fitted. The motors are 9.6v hobby-racing style motors to be run off a 14.8v battery. The wheel diameter over the track is approx 74mm (which compared to the body height of 38mm should give decent clearance). You'll notice the toothed drive-hub for transmitting power to the track, this took a lot of maths and patience to get right!

http://lh6.ggpht.com/_3v3udRbjClg/TK...0/SDC12244.JPG

Here's a size-comparison with the beetle. It's pretty compact for a featherweight, and I've still yet to build to the new 13.8kg rules, thus I'm going for a mostly steel and hardox welded construction (inc. all hardox scoop). Having got the hang of welding this should be fun - when I've got the time and money to finish it all!

I love it already

Thats really cool...

So just out of interest how do you make the weapon actuator/ what parts are needed?

http://lh3.ggpht.com/_3v3udRbjClg/TK...0/SDC12241.JPG

The first stage is quite simply one of these http://www.technobotsonline.com/re-540- ... -11-1.html which is an easy way to get the motor speed down to a reasonable rate for the worm stage (which isn't well suited to the ~10,000rpms of the motor). With the como drills range the ratios ‰ 11:1 usually have larger MOD spur gears than 50:1 and above, hopefully better able to take the torque.
Then the worm stage is comprised of one of each:
http://uk.rs-online.com/web/search/sear ... &R=5216963
http://uk.rs-online.com/web/search/sear ... &R=5216890
for a reduction of 40:1. Worms allow a great reduction in a small space, at the price of lots of friction. You can see in the above picture roughly how I'll be housing this, of course with lots of bearings and additional shafts
The final stage is simply a chain stage (9T sprocket to 17T sprocket) which will be rigged on the side of the housing, I may get some bigger sprockets though as I'm dubious that 6mm chain will stand up to shocks on the arm.

This set-up, using the standard motor and ignoring inefficiencies would provide ~22rpm no load output at 14.8v with ~10kg/m stall torque. The motor I'll probably be using is rated at approx 40% greater rpm at ~3 times the stall torque (with an awful lot more current and heat!) http://www.robotmarketplace.com/product ... P5737.html

Nice, thanks a lot. The robot is looking amazing right now

Looks awsome Ewan. Always wanted to make a tracked robot but never found any decent tracks the right size, and making metal ones is a lot of effort. Also when they get damaged its going to be expensive to keep replacing them.

But fair play for doing it.

Yeah it's looking great. Nice work with the wheels as well. Whenever I see a tracked robot it always makes me want to make one, although I probably couldn't do a decent attempt.

But I'd love to stick some on my grabby-robot when I rebuild it, something meaty like on this Aussie bot:
http://www.robowars.org/forum/album_pic.php?pic_id=1516

Anyway, will love to see it in action when it's done :)

Is this thing still being made?

Over summer hopefully, university takes up all of my time at the moment.

My Easter holidays have begun and so has the race to get this machine finished for the Yeovil Robochallenge event. Here's how it looks today (apologies for poor quality, I'll use my camera instead of my phone next time!):

https://lh3.googleusercontent.com/-W...2021.06.35.jpg

https://lh5.googleusercontent.com/-r...2021.08.48.jpg

So the set-up will be two slightly modified 9.6V GR01's for drive (built into the chassis rails), a 14.8V 4000mah Li-po for power and a Scorpion XXL (in a heat-sunk & fan cooled enclosure) as the speed controller. The weapon/scoop is powered by a GR01 slaved to a worm reduction stage (hence at 90 degrees to the weapon shaft) and then slaved again by chain to the shaft, a total reduction of approx 1200:1 from the motor. I've had the worm-stage housing laser-cut from aluminium which isn't in this picture.

The end result should look pretty similar to my beetleweight:

https://lh6.googleusercontent.com/-L...0/SDC12215.JPG

Tomorrow I'll start cutting up the 4mm Hardox which will make up most of the exterior, then begin welding the scoop, front axles and side arms together. Lots to do!

Looks good, be nice to see something different and tracked!

Nice Scorpion Enclosure.

you got a source of spares for those tracks?

Cheers PJ, can't actually remember there being a tracked feather before (probably for a good reason!)

I've got two pairs Dave and probably getting another pair soon, they're pretty tough rubber but I expect they'll fail one way or another so worth having spares.

Finished cutting all the main bits today, nice weather for it:

https://lh4.googleusercontent.com/-k...0/SDC12444.JPG

https://lh6.googleusercontent.com/-Q...0/SDC12445.JPG

The pile of cut bits pictured weighs 5800g, with another 1000g not pictured, this machine will be a majority Hardox by the looks of it!
The weight tally so far is: Tracks 390g, Battery 380g, Wheels 680g, Front shafts 200g, Speed controller 180g, Weapon motor 510g, Drive motors + side rails + weapon shaft 2010g, Total: 4350g leaving 2400g for the weapon transmission, speed controller and accessories.

Lots more grinding and drilling to come tomorrow plus assembling the lifter gearbox.

Looking great Ewan, tracked bots always seem to get the roboteer juices flowing! Would love to see it in the flesh and fighting, but I won't be at the Yeovil event unfortunately. So make sure to get some videos :wink:

Quote:

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Originally Posted by ewan

I've got two pairs Dave and probably getting another pair soon

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Do you have a link to where you get these? Or is it just a case of scouring eBay for those Tonka trucks? Carcinus will probably need re-done after the champs and I think it could possibly suit tracks. Failing that, I quite fancy building an off-road FW-size machine at some point.

I'll be at yeovil and I am looking forward to seeing this in action :)

Cheers guys, I hope it does the beetleweight justice, I'm pretty happy with how that one's running.

Looking forward to seeing your axed machine as well Dave, the most recent pictures look awesome (and are making me reconsider the top armour..).

For the tracks Jamie, eBay'ing 'Tonka Bulldozers' (and making sure you get the big 'Mighty' models made around 30-40 years ago) is your best bet (and the only source for the ones I've got so far). Of course watch out for the quality, it's a safe bet the ones which are rusting on the body have been in a climate for rubber degradation too.

Have just spent £35 on drill bits for two holes (14mm). Damn you Hardox

I learned the hard way that cobalt-enriched HSS ain't the way to drill hardox. The cutting edge chips. TiN coated stuff ain't up to snuff either.

Plain HSS, loads of cutting oil and the slowest speed possible, easy does it. If I have the option, I drill it with my mill, 60 rpm is plenty slow.
Otherwise, heating the drilling spot cherry red, and drill it when cooled seems to help, sometimes. It ruins the strenght localy tough.

Oh, and a Drilldoctor is convenient to resharpen the drillbits.

I can't even afford Cobalt at 14mm, it's a pretty non-standard size so I'm all HSS- the lowest speed of the pillar drill is 500rpm so I'll have to hope that that plus loads of spray coolant will do it! (almost through one hole with three bits, eight more coming..)

I fear you're going to use up some drillbits.

Sounds like we had a similar day yesterday, I managed to ruin 5 bits, but I wasn't working on Hardox.....

You using a pillar drill or hand drill? A good amount of pressure helps...

Quote:

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the lowest speed of the pillar drill is 500rpm

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Oh well, laser/water-jetting next time for sure!

lasercutters don't like painted materials. Waterjet is more tolerant in that respect.

You just need to keep the drill bit sharp. We drill quite alot of hardox with standard HSS drill bits, usually going too fast (takes too long to keep slowing the pillar drill down).
Mouldy wastes the tips of a few drill bit's but not too many :). Just re-sharpen and carry on.
Just dont let them rub , keep loads of pressure on.

Maybe when you actually build a robot grant you'll get the opertunity to wear out a drill lol

It's been a pretty depressing day for the build, mostly because of a rookie welding error:

https://lh4.googleusercontent.com/-C...018.07.23.jpg#

As you can probably make out the front and rear panels have turned into bananas, distorted from the welding heat. I should've braced them horizontally to prevent this but was too consumed with making the welds half decent (to notice the gradual bending).

Not wanting to rush it or run with a banana 'bot I'm going to have to pull out of the Yeovil event to give this the extra time it really needs, including getting all the panels laser cut to a somewhat more refined design.

At least all the rest of the build has come on well, including the weapon gearbox:

https://lh4.googleusercontent.com/-D...2018.05.59.jpg

So it shouldn't be too long until it's finished...

you can probably flatten them down with a hammer

Not exactly, it's 4mm Hardox and the section is like this:

https://lh6.googleusercontent.com/-I...ld-section.jpg

Which you mightn't have seen from the previous picture actually, was a bad angle

owwwww...... yeah don't look that bad in pic ...... really big hammer lol

i know you could probably bend it bk with a hammer if it was mild or stainless steel but never really used hardox so don't really know how easy it would be to hammer bk

Why the 2 beads on the inside of the curve?

And forget hammering. You need a serious press for that.

A half hour to cut new panels and weld them up, no bother

It's made from three strip sections welded together hence the degree of distortion as the welds run along the whole length. CAD'ing up a version for laser cutting now which will involve some slotting and perpendicular support to stop it happening again, don't really want to half-ass it given the money that's gone into it so far.

Pity about the hardox.

If you heat it up that much, it will lose toughness and hardness. I fear the 2 panels are now a good grade of mild steel, and can be hammered back in shape.

Unless the welding is rubbish, and the lack of heat imput didn't ruin the qualities.

In any case, I see several options to get the stuff in shape. Unfortunatly, long distance doesn't work.

Ah, I was following the logic that I should get as much penetration as possible to ensure the welds were as strong as the Hardox itself, but that seems redundant if I'm weakening it in the process. Am I best off doing short welds at a couple of points along each length then do you reckon? That with some support brackets behind shouldn't create so much heat

Found this which goes into detail on the issue http://www.acme.pwr.wroc.pl/repository/218/online.pdf

Looks like I'll be relying on some behind-bracketing to provide the structural strength and positioning instead of long welds and so minimise heat damage to the exposed areas.

Not welding it at all.

If you need an angled shape, bend it with a d10 radius at minimum. Still need a serious press.

Or if welded, keep the heat at a minimum, cool everything down with heatsinks and wet rags.



In my case, I do weld hardox. But only with TIG, highest amp setting and highest speed as possible, with 1.4571 welding wire, adding serious supports and clamps to retain the shape, and getting rid of the heat as fast as I can. Excess Argon, backing gas, and so on.

Ewan- try a local engineering firm, they should be able to just whack it in a press and bend it without to much trouble, just make sure you tell them it will spring back a fair bit so they'll have to over bend it... or ask Ed Wallace really nicely... i used his press and gilotine to do 540's front end on some parts... others i just scored with a grinder and welded em back up once id bent them by hand :)