Deathly Hallows - Beetle - Evil K'Weevil

[Deathly Hallows]

Ladies and Gentlemen,

I am proud to announce the build thread for my first combat bot.
The text bed featherweight robot went really well and was completed to rolling powered chassis in record time. With this accomplished I can now move on to designing a combat bot and a beetle seems a good place to start. So without further a do I introduce.....

Evil K'Weevil

Who will have the following characteristics:
Two wheel drive
HDPE sub-frame
Bolt on Metal armour (type tbc)
Any way up operation
Drill engine driven combination coring and flip weapon

Been playing in OnShape and hope to have some rough designs to share by end of this week.

[Zenith]

Drill engine driven combination coring and flip weapon

This sounds very interesting. Could you explain a bit about what your plans are?

[Deathly Hallows]

A picture says a thousand words
The front face is missing (as are the wheel, internals and some sub structure), from which the weapon protrudes, positioned centrally.

Evil K'Weevil Empty Shell.png

[Deathly Hallows]

Keeping weight under 1.5Kg is going to be a lot harder than I thought. The mass calculations in the OnShape CAD very quickly highlighted that the initial design was not viable without some radical rework. So bulk heads will have to be lightened. I am still working on the idea of using those 12.7mm thick Bonzer Chopping Boards for these components, as they are such good value; but I may have to go thinner.

Bulkhead.png
The idea remains to build a sub-frame to bolt armour on to the outside and to fix the internal parts to. M5 counter sunk bolts should suffice to hold the structure together. Well back to the CAD for me...

[Deathly Hallows]

I reworked the design again. However it seems to me that the way forward is to resolve the internals first, then I can build a box they fit inside. I can rework the chassis ad infinitum without moving forward so I need some help.


Drive motors are for a 1.5KG robot so I don't need a lot of power. Would something like 12V Pololu 75:1 be enough? I was looking for something a bit more torque but find it hard to find anything under 100g seems to be a jump from these 10-30g units to 150-250g units


Hubs to fit


Wheels very dependent on matching wheels to chassis height I want big wheel just clearing floor and roof for anyway up driving.


If it was the mentioned motors I could get away with a pretty small ESC but these 20A Turnigy are cheap and light.


Want to ensure I can save some weight for weapon motor and armour

Appreciate any feedback

[Ocracoke]

The speed controllers won't work for this application if it is for the drive - the advert states they do not have reverse. I'd possibly also say the motors are too small though I'll leave that one for someone with better BW experience to call it - I had originally planned to use a similar type of motor in my Beetleweight but they are not powerful enough (though they were 6v 298:1 motors!).

[Deathly Hallows]

Damn it - must have been half asleep. <EDIT - still asleep the ESC has no reverse! >

I found these rough looking units on ebay no mention of reverse but the advised applications would require it. <here>

But these sound better on robotshop <here> a week or so till in stock but no rush. Decent torque for size and at 82g well under 100g target.

<EDIT - then the speed controller must be different - I found this one but no brake here
This one here but no BEC which I could work around using the weapon ESC or a separate BEC unit. or perhaps I should re-purpose my Sabertooth 2x12A RC for the job. But was saving that for by test bed.>

[Maxamuslead]

quick question, your beetleweight it looks like it is gonna be a ram bot why not design as much as you can, see how much it all weights then fill the rest of that budget with motors and gearboxes. nearly every bot ever made starts out over weight so you can always thin out some armour here or there or run a smaller battery

[Deathly Hallows]

Thanks for your input. It won't be a ram bot, but if drives are good that will be fine attack too. The intent is for something a little different. I want to get further into the design before sharing too much about weapon system. The weapon system, chassis and armour will require a lot of the available mass, the drive and wheels will dictate the dimensions. I've probably over complicated it but I am nearing a solution I think.

[Maxamuslead]

fair enough. just had another idea that you could use a brushless drive similar to speed 900 setup use by a load of people.

make me kinda want to design one.........

[Deathly Hallows]

Still working that design through. Getting under weight limit is killing me. Of course this is also all calculated as not drilled a hole or soldered a wire yet.

The motors, wheels and hubs look good and allow flexibility in design.
Weapon and it's motor is a problem as what I have in mind dictates chassis dimensions and will take 1/3rd the mass I predict
I will have to size the battery (LiPo) last when I see how much weight is left I have a min and max option 700mAh to 1500mAh and weights
The remainder I can spend on chassis and armour.

Here I may need to get creative. From a simple box I am moving to more complex shapes to reduce surface area. Could look really weird! Cool evil weird but weird. I think the HDPE bulkheads made from that Bonzer Board is a no go, surprising heavy but at 12.7mm it soon adds up.

I will try and generate a CAD image soon worst case next week. At the moment I have no been able to virtually assemble the parts other than the drive system.

[Deathly Hallows]

Evil K'Weevil.png
So not quite done -but this is a mock up of Evil K'Weevil.
LiPo 3S
RB-Sct-1060 geared drives (12V 730 RPM)
Rotary interchangeable weapon in drill chuck
Weapon design uses drill motor (but trying to save wight here)
Armour is an area I can work on. Balancing weight and strength.
Calculation at moment coming in at 1517g would like 50g comfort at least

[Theo]

Looks great! We need more drills in the lower weight classes, they can have a good impact on plastics and other materials. To save weight, a large MFA motor would do the trick, they're the same as drill motors but lighter. That is if you're able to modify the shaft to take drill chucks.

[Deathly Hallows]

That would be a good idea Theo. I have searched for direct to Drill chucks but have not found anything that opens wide enough for the bits I would fit so far. What I have found are two possibilities:

1 - a motor arbor looks to be used in RC planes for fitting props, this would take core cutters but not all weapons
2 - a CNC collet grip adapter and collet grip could work, but could also be heavy

I will keep looking, and if anyone has any ideas please let me know

EDIT: This may work - ER11 6mm CNC extension but the chuck would have to be heated to expand before fitting a 6mm drive shaft. Not sure how I would do that though, as my soldering iron could not manage that load. I could heat in oven to around 250'C but that's as hot as I could go.

EDIT: Arbor solution With this M10 arbor and this chuck I can use a smaller motor. But I need to find a <150g DC motor with 5mm shaft.

[Deathly Hallows]

I have been quiet as away on business and despite the OnShape having an Android App, I couldn't get to grips with it. I managed to investigate a weapon motor alternative to the drill I had planned. I also think I will have to get the weapon machined for me rather than an off the shelf option when I was using a drill. Using a motor with lower rpm and more torque but smaller in size and weight allowed me to also change the shape slightly reducing surface area so less weight in the armour too. Here's a 'naked' snap i.e without the sidewalls. I must add drive mounts and the electrics but its coming together I think.
Evil K'Weevil v0.3.png