Team Darklight - Featherweight Axe/Hammer diary

[qbnut]

So having completed my first proper (as in, to spec) build, the Beetleweight "Knight Of Ni" (http://www.fightingrobots.co.uk/thre...t-beetleweight) - then finding a lack of actual events it could be taken to coupled with wanting a bigger challenge - I've started work on a successor in the form of a new Featherweight Axe/Hammer robot. It's inspired by a mixture of other Robot designs, with Beta being an obvious influence.

The goal is to be done with the build by 14th April in time for i60, assuming that RoboChallenge runs their regular Featherweight event then and it's ready to be entered.

It's been in design the last few months, and is shaping up quite nicely. Some small things are still to be decided upon, but it's mostly there:

TeamDarklightFWAxe_3DRender1.jpg TeamDarklightFWAxe_3DRender2.jpg

The majority of the major parts have now arrived, so it's just assembly time now. I've built a prototype frame with assistance from my Dad (he has a rather large workshop in which the build will be done), just so that I can check the measurements in the 3D model match up with components in the real world. I've proven it does - having placed the Motors, ESCs, batteries, etc up to the prototype which was made from measurements taken from the 3D model, it all fits properly

TeamDarklightFWAxe_PrototypeFrame.jpg

Current spec:

2x Gimson GR-EP-45 12-18V Motors 13.7:1 (drive)
1x 555-based 12V Motor w/10:1 gearbox (current weapon power, subject to change)
A123 cell based battery packs (split into 2x packs run in parallel; 4/5 cell TBD)
3x Tz85A ESCs, brushed modded myself (drive and weapon)
OrangeRx R615X Receiver
80mm dia. castor-style wheels with custom mountings
20mm Alum frame
TBDmm steel armour all round (exact material TBD)

Updates are likely to be irregular, but will try to follow as the build progresses

[daveimi]

Looks nice how are you mounting the hammer.

[Andy]

Really nice looking, love the prototype too, good luck!

[qbnut]

I haven't modelled it yet, but the axe mounting should be into a pair of bearings mounted in the bulkheads, the motor mounted to that probably directly given its already geared down. How that will handle the shock impacts though I don't yet know

[RobotExtreme]

Hi,

The design looks very nice!

However i do not recommend using A123 cells instead the "normal" LiPo, even being an hammer bot.

Galactus used for 3 years A123 cells on full competition and i always used to not listen good advises about change to LiPo cells, on last 2 years i changed to LiPo and i can fully say, ITS A GREAT difference.

If you have any chance to use LiPo, use them!

About the thickness of armour, if you plan to use 20mm on entire robot..this will easily overweight even machining a lot of pockets.

Guilherme

[qbnut]

I've switched from 20mm to 10mm back to 20mm whilst designing it! I'll probably thin it out in places where it doesn't need to be quite so thick.

[qbnut]

This weeks progress...

The robot got a bit of a chassis and armour redesign, such that it can be built as a monocoque, with only the necessary bulkheads for the axe mounting and drive motors. This is in order to keep the weight down by not having to have a box frame to which everything would be mounted. Current thinking is 4/5mm steel will be used for the armour.

Also some refinements made to the panelling solution such that they can be manufactured (and fixed!) easier, with fewer cuts, bends and welds required.

Robot1.12-3d-1.png

A further prototype has also been made based on the revised 3d model, and is shaping up well (apologies for the blurry image, it wasn't from my own camera!). It gives us a very good idea of what we will need to work on. 3d models are nice and all (and have definitely helped get us this far), but there's nothing like seeing it in the flesh to see if it's actually going to work!

received_10155021364397853.jpeg

Next thing to do is check for the fit of all the components more accurately, and to do some math to see what it will actually weigh in final materials, including all the other hardware (motors, ESCs, batteries, etc). I'm awaiting new scales at the moment so I don't know yet what everything weighs and what I have left to play with. I very much suspect I will be drilling holes out of the bulkheads to make the target

[qbnut]

Today I checked the fit for everything, and it's good, all fits with a bit of leeway. Also the scales arrived, and everything weighed, it comes in at just over 12kg With the weight of fixings, wiring, etc, included, we should be confortably under the limit.

Next thing is welding up the main chassis for real which may have to be next week given how pressed for time this week will be!

[qbnut]

Progress has slightly slowed due to cold and flu, but should be getting back on track soon.

This week we got the first parts of the outer frame constructed. Ran out of welding rods though so only tacked, seam welding to be done so haven't quite finished it yet.

IMG_20170212_144919.jpg

[daveimi]

That's really nice.

[qbnut]

Progress is being made, albeit slowly! Many bulkheads cut, holes tapped, and a lot of the robots structure is in place.

The weapon testing showed that the current design has a very underpowered weapon, as the robot won't self right with the current setup. So taking inspiration from other Featherweight axes I'll reengineer this to use a hefty brushed scooter motor and chain/sprocket setup.

I would like to give brushless a try as I think that would give it extra kick, but using big brushless setups is beyond my working knowledge just yet. I'll be off now to do some more research

[Maxamuslead]

I shall keep an eye on this thread as I am to working on a hammer bot (still in CAD still, soon (TM) it shall be put in Cardboard)
Are you still planning to use a Drill motor and gearbox for the weapon ? I am planning to use a 250-350 watt scooter motor

[qbnut]

No a drill motor is too small and underpowered even with heavy gearing.

It's likely I too will go with a 250-ish watt motor as it seems to be the go to for electric axes in Feathers.

[Maxamuslead]

Had a feeling that would be the case, how does it fit in your weight budget as a they are around 4-6 lb
(https://www.electricscooterparts.com/motors24volt.html)

[daveimi]

I find brushless motors struggle with start up torque. I have a feeling this is why people have stuck with the scooter motors in the brushless/lipo era, as they make most of their torque from zero RPM upwards.