Team Triforce Featherweight drum

[TechAUmNu]

Finally got round to taking a video of the drum testing.

This is at 10500RPM, 60A motor current (can go to 90A), limited to 80% duty cycle by the erpm limit of the focbox. Spindown time is 53s.

[dotDominic]

Ouch - that sounds brutal. What a beast! :0

[TechAUmNu]

Been working on a new design to solve our drive problems. When we got back we tried driving around again after fixing the front wheels and snapped both drive belts! So new plan is for 2 wheel drive on a wide chassis.

This is the current idea, with a full 4mm hardox welded chassis.

[TechAUmNu]

Finished welding the frame, everything else is staying the same so should be quick to finish!
JPEG_20190512_145123.jpgJPEG_20190512_165533.jpg

[Eidg]

Fine looking Bot really nice, but the weldings...

[TechAUmNu]

Haha yeah the top panel welds are pretty awful, but its just extra bits added on to clear the motors. I can clean it up later on.
20190512_144336.jpg20190512_142607.jpg20190512_144348.jpg
The interior welds are much better and more just to tack it in place before I did the welds on the bottom and edges.
It was my first time using 7018 which is a right pain to restart.

[TechAUmNu]

Got the wheel shafts a bit shorter so they now fit. Checked everything fits. The drum mounts nicely, although I forgot a bit to put the locking bar so will need to cut up the old frame and bolt something on.

Getting close on the weight now!
20190515_195211.jpg20190515_195126.jpg20190515_200129.jpg

[McMullet]

That is a frightening amount of drum! Looks great.

[TechAUmNu]

Back from Bolton now. Was a lot of fun The drum seems to be working great, although after the last rumble it's not spinning freely anymore so might have damaged a bearing on the huge hit it got.
The recurring theme of this bot, the drive didn't work very well. In the first fight it sucked one of the bolts holding the drive motor and punched it through the belt jamming one side. The other side didn't have the belt tensioned enough, so it started slipping and completely stripped all the teeth off half the belt.

I got the bolt out of the belt and flipped the one that had stripped over. Then spent a while trying to make the bolt holes for the wheels further back to increase the belt tension. I think this helped a lot as it was working a lot better for the second rumble, although I still lost one side quite quickly and was just spinning on the spot or being used as a battering ram.

For the first rumble the drum was limited to about 10k rpm and sounded quite nice, but starting it spinning was a pain and it took about 20s to get it spinning the right direction. So for the second rumble I decided to change to duty cycle mode on the vesc and turn up the speed to the max. The drum started spinning perfectly at the start of the fight and after a short time was making a nice death hum at 245mph (13000rpm). Although it must have been taking a LOT of current to keep it there as it very quickly started slowing down again. I think the vesc was overheating or the batteries were drooping in voltage enough to trigger the low voltage cutoff on the vesc. So I will need to do some testing before the next event to figure out how to make it spin at max speed for longer.

Once I got it out of the fight the smell was awful, most likely the grease on the bearings burning with the high rpm. Once I take the drum apart tonight I will see what the damage was from the big hit. I might need to be adding more preload to the taper roller bearings if they are damaged. Another drum hit the tooth and took a big chip out the leading edge.

Overall it was a really awesome experience and a much more laid back event than Insomnia. The new frame suffered no serious damage, just a few nibbles from Drumblebee on the back. So next thing is to change the terrible T5 belts out for some spur gears and MUCH bigger wheels!!

20190707_171903.jpg20190707_122937.jpg20190706_180650.jpg20190707_160338.jpg

[Ocracoke]

It was great seeing your creations in the flesh! Triforce in particular looked amazing. The drum on your Featherweight was definitely scary to hear in the melees

[TechAUmNu]

Been doing some reading on continuous current of the focbox, looks like they are almost certainly overheating with the 60A motor current. So I will need to add a chunk of aluminium to the bottom of the one for the drum and change the thermal pad for something a bit less rubbish.

As for the bad drive reliability, I have ordered some MOD1 spur gears, 12T and 80T, which still lets it go 19mph, but with almost twice the torque. Going to increase the wheel size from 70mm to 85mm so it gets stuck on the floor less. I am fed up trying to get belts to work right, they are very finicky and an easy target.

[Scarrosaki]

that drum made a beast of a sound, but I think the real winner was the table for not collapsing

was great to see Elevate and Triforce!

[TechAUmNu]

Just took apart the drum, the motor looks a bit burned lol. I think when it got hit the drum moved slightly and the magnets hit the stator.

[Eidg]

@TechAUmNu
How much grounde clearence does the robot has?

[TechAUmNu]

I think it had about 10-15mm before I am changing the size of the wheels, should have about 30mm after.

So this is why the drum broke:
20190710_185058.jpg20190710_174141.jpg

I am replacing the tiny 10mm aluminium shaft with a 20mm titanium one. Also going to take the motor out of the drum for now and run it with a 15mm htd5 belt instead. It will still be the same speed, maybe slightly wider and with bigger bearings.
20190710_221909.jpg