Attitude Adjuster (Beetleweight)

[Roboteernat]

if using conbolt drills, go slow and use lots of coolant. i was able to drill through 3.2mm Hardox with some cobolt drill bits from Toolstation - about £3-5 each 5mm-7 about

[scott]

Lots of progress since the last update. I've been accepted for the Euros with Attitude Adjuster, so that gives a good deadline to work towards.

I cut some weapon bulkheads, using the tried and tested technique of the table saw and the mitre saw. I used a 20mm forstner bit to cut out some holes, and measure the distances this time instead of laser cutting a template.

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The biggest game changer is learning how to use the 3d printer at the hacker space. It only uses PLA, but that should be enough for what I want to use it for. I started with a battery holder for the 3S lipo.

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Then I made a holder for the electronics at the back of the robot, so they don't get in the way of the weapon. I also made a couple of armour mounts. I put in some threaded brass inserts using a soldering iron. I also put some brass inserts in the chassis to hold the weapon bulkheads on, and to hold the top armour.

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Today I finally got around to finalising the design for the axe and cutting some titanium! I used my Dremel to cut it initially, then finished with a hacksaw, and drilled with a cobalt bit. Going slow with lots of lubricant made it super easy, and there were some fun sparks. I now have an axe head.

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I weighed the robot chassis for the first time, the bolts and brackets must weigh more than I thought!

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Also considering going brushless. I tried the axe for the first time with a 300rpm gearmotor and was disappointed with the power. It was slow and couldn't self-right. I picked up some brushless DYS BE1806 motors that have already been converted with 1000rpm gearboxes, and I'm considering transplanting the 300rpm gearbox onto one of them. I also have a 500rpm motor as a last resort. I also picked up some cheap Afro ESCs on ebay and flashed them with SimonK.

When testing my flashing, disaster struck! I accidentally plugged an Afro in the wrong way, and promptly blew it up. The battery also doesn't seem too healthy (feels a bit swollen :/) so I'm planning to not use it again in case I burn my house down, and have ordered a replacement. I will now not do anything with a lipo unless I use the wiring harness that has a fuse and removable link.

Finally, been doing a lot of soldering. Added connections to all my ESCs so that I can't plug them in backwards. I also need to make my wiring loom A LOT smaller. There is not a lot of room for the wiring in there. I have about a month until the Euros and not much free time in September, so I will have to try and make time when I can!

[scott]

Small update for today. Spent a few hours making the axe, so now I have a weapon. It has an aluminium shaft, aluminium supports for the axe head, 2mm titanium axe head and a 3d printed spacer between the head and the supports. I saw in the FRA rules there's a section requiring a tether, does anyone know if that's something I will need to implement in my beetleweight? If so, what should be tethered, just the axe shaft? What do other people use for tethers?

Also, it is still satisfying when the robot looks like the renders

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[Ocracoke]

I don't recall tethers being a thing at the BW level, best check with the event organisers. Certainly at the UWE Beetle Brawl in February, I can't remember seeing any but then again, I don't recall there being that many axebots around.

[RogueTwoRobots]

If I remember rightly, tethers are more for Grade 3 arenas and lower (aka non-spinner) so the tether is to prevent the axe head, or part of the shaft, flying away if it breaks off and potentially breaching any wall or netting. As far as I know it's not required in spinner-capable arenas as a flying axe head will have much less danger potential than the amount of shrapnel that gets pinged about. To my knowledge there aren't any active/regular beetle arenas that aren't suitable for spinners, so you should be fine. If in doubt, contact the organiser for any events you're planning to attend.

[scott]

Thanks Michael and Jamie, looks like the best idea would be to double check with the event organiser.

[scott]

Another quick update - finally put the axe together. I swapped out the 300rpm brushed motor for a 500rpm brushed motor and was pleased with the torque, as it can self-right, but not so much with the speed. I'm going to experiment with putting the gearbox from the 300rpm motor onto one of my DYS BE1806 brushless motors to see how that works when geared down ~3:1 by the belt. I should also make a tensioner, as the belt is a little bit slack, though that could be good for protecting the motor.

I put the robot together but was having issues with the snap ring staying on the Fingertech hub, I think I might've bent them. I've ordered some replacement 7/16" snap rings that will be arriving later this week. The axe hub and pulley also work themselves lose, so I will put some blue threadlocker on them when that too arrives later this week.

I did a quick weigh, and it comes in at ~1250g. That means I have ~250g for the wedge + mounts, wheelguards, foam wheels, drive ESCs, various nuts and bolts, and final weapon motor mount.

Still quite a bit on my to-do list:
* Cutting the titanium wedge
* Making the mounts
* Making wheelguards
* Cutting the top covers
* Adding a fuse and power LED (I have both of these, they just need fitted)
* Making a cradle
* Making a weapon locking bar
* Putting the wheels on and making it move
* Loctiting all the bolts
* (If I have time) Making the hammer more potent
* (If I have time) Making spares, e.g. top covers, wedge, hammer, etc
* Anything else I've missed! (Anybody notice anything?)

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[Ocracoke]

Looks good. I might suggest some top padding/extra armour over the battery area as that top armour looks fairly thin to me.

If you need to get some weight reduction in, I'd possibly look at the axe arm with a few smallish holes in it.

[scott]

Not a bad idea, it's 3mm polycarb but with some scary looking saws around then I might see if I can double the thickness around there, or put a little but of 1mm titanium under the polycarb to protect the battery. I have access to a manual mill, so if necessary I could mill some chunks out of the axe arm, it's 1/2" 6082 aluminium for sturdiness.

[scott]

Small update on progress from this weekend. I 3d printed a new weapon motor mount and combined ESC container and rear armour mount in some snazzy red PLA. I drilled out the top armour so now I can mount it. I also spent a few hours on Friday sculpting the wheelguards out of 5mm HDPE using a vice and a heatgun. Weight-wise, it's sitting at 1360g without the wedge, wedge mounts/bolts, drive ESCs and one wheel. I've also used a couple of 3d printed armour mounts, hoping they hold up.

The main bit of construction left is the wedge, and drilling out the mounts for that. I'm aware I've also put the weapon motor in harm's way, so might add a little bit of polycarb to protect it. I need to also add the fuse and the power LED, and the weapon locking bar/sharp edge covers. Also wondering what spare parts I should bring, I was thinking about spare wedge if I have time and maybe a spare top panel, as well as a spare ESC, motors and wheel hubs?

I got the axe running at the hackerspace, so we had fun making little dents in bits of wood. I don't think it will cause that much damage, but it can self-right the robot using the 500rpm motor. I also tried running the wheels using the brushless gearmotors I have and the power and torque of the 1000rpm gearbox immediately caused one of the wheel hubs to loosen. Oops. I have purchased some threadlocker, and will transplant some 500rpm gearboxes that I have onto the brushless motors to make them a bit more controllable.

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[scott]

After an hour and a half and 3 dremel cut off wheels I have two wedges. The sheet of titanium I have was the right size to make two wedges out of if I cut it lengthwise. Luckily I laser cut a template wedge out of acrylic, I discovered that I hadn’t updated the holes on the wedge to reflect the latest size of the robot and distance between the bulkheads. Need to drill out a bunch of holes, but shouldn’t be too much work. I need to make 4 aluminium brackets for the wedge, as the ones I made before are wonky. If I ran out of time and 3D printed them out if PLA would they hold up in combat? How does PLA generally hold up at a beetleweight scale?
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[scott]

Drilled the holes in the wedge. Unfortunately the 3d printed mounts didn't work out. I printed them with 100% infill which was a mistake, as when I melted the brass inserts into the mounts the plastic had nowhere to expand to and the mounts ended up warping. I'll go back to my original plan of aluminium. This meant the holes didn't line up. I feel I may have to make them slightly bigger anyway, we'll see.

I took the protective coating off the polycarb top panels for the first time, it looks weird without the translucent white! I have some vinyl wrap I can put on if I have time, but that is literally the lowest priority job at the moment. Due to the constant re-designing of the internals there is now quite a bit of wasted space inside, which is disappointing.

More pressing is the weight - without the drive ESCs, wedge bolts, removable link, fuse, power LED and one drive wheel it weighs in at 1482g. Hopefully I'll save some weight by going back to aluminium wedge mounts, but it's still going to be a little bit over. I think I completely underestimated the weight of the nuts and bolts and wiring. Oops. Planning my weight saving holes already!

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[Ocracoke]

Looks very good! I wouldn't worry so much about the internals at the moment and focus on the weight problem. Do you know if it is the axe arm and head that is the main weight culprit here? It could do with a few weight saving holes in it by the looks of it.

[scott]

Thanks for the suggestion Michael, will look at that tonight. The axe shaft is down as 80g in my spreadsheet so I think some holes could help. The supports holding the axe head to the shaft are also bigger than I intended. My main issue is probably nuts and bolts and wires - I don’t think I took account of them in my design and they are possibly contributing to the mystery extra ~130g.

In other news I made a carrying cradle out of some wood I found lying around, so that will keep the wheels off the ground when it is in the pit. I mounted the wedge, using my dremel with a carbide cutting bit to “adjust” some of the holes I put in the wrong place. I also replaced the 500rpm brushed motor with one of the brushless motors with a 300rpm gearbox on it, and it was scary! However it shook itself apart after a few “good hits” on a block of wood, so more work required. It also jumps a bit.

Finally, any recommendations for sharpening my wedge? I have access to a bench grinder, will that do the job? I did the axe using a sharpening stone, but it took ages and I think it might be too small.

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[Ocracoke]

Ah, good point about the cradle. I have some old wood from a AW arena build that I can use for that. Yeah, in building my Middleweight, I figured that the 230+ bolts in it would contribute to the weight. It turned out to be more than I expected as well. Once there is a bit less weight swinging, the jumping might be alleviated.

Won't the Dremel do for for sharpening the wedge (remember, you need to have a cover for sharps protection)? I'll probably end up doing that with Shu! when I tidy up the new arm.