Bolts - Featherweight Flail Bot

Extreme Robots is in Colchester in September, close enough to me (within 100 miles), that I can justify making it the teams first event.
So because PC Plod won't be ready for heavyweight competition, The Scrappers are making an invertable wooden wedge, driven by Argos drills to enter into the featherweight division. The goal being to keep it as cheap as possible, whilst still being effective.
Due to a lack of experience and time, we've decided to go with two chain flails attached to the back of the bot as our main weapon. We're also considering adding some spikes facing up the wedge, allowing us to hold others on top of the robot (should they drive up it) and drive them around.

Some questions before the build officially begins:
1) What is an average size guide for featherweight bots?
2) Which type of sheet metal and what thickness would you recommend we cover the wood with for armour?
3) Are the spikes on the wedge worth it? Would they help control other bots, or just get in the way when running upside down?

I've just built a flail bot and the idea was a bit not great. It kept beaching itself on the chains. I'm not sure if more ground clearance would help though. Ended up taking a random metal box lol. Most feathers are about 50cm x 50cm give or take.

Looks like I'll have to do a lot of testing to find a way around the beaching issue if it arises. Hopefully it won't be much of an issue, the wheels I'm using should be big enough to keep it moving, even with something underneath it.
Considering the lack of an active weapon, hopefully I'll be able to go a bit bigger, maybe 50cm x 70cm total.

Thanks for the info and the warning.

Yeah no worries.

It's something I wanted to stick with but it kept beaching itself. I watched Nuts on youtube and it has a ton of ground clearance, so when the chains go all over the place it just sort of rides over them and keeps going. I think if you had like 150mm wheels and a 60mm body etc. It'd be fine. As it was I had a 90mm body and 120mm wheels lol.

Drive circuit for Bolts has been roughly put together and tested. Now to build the chassis around it.
Attachment 6666

omg you even use the same electrics and motors as me thats so weird! be careful that you have a failsafing receiver, i got stung with that..

Well, this must be some pretty good beginner equipment if we're both using it. Thanks for the warning.

So, we're having a little trouble with how to attach the wheels.
We're using the new Argos drill motors and some cheap wheels from Homebase.

The motors have a M5 reverse thread internal and a M10 external thread (we think).
Attachment 6677
The wheels have a 13mm bore, not threaded.
Attachment 6678
Any recommendations on how to attach the wheel to the motor?
If anyone has any links to correct size bolts or other parts to help, they will be really appreciated.

Unfortunately, drill gearboxes have a 3/8 UNF external thread. I don't know why they went with a weird imperial measurement, but they did. Your best bet is to find some 3/8 UNF nuts on eBay and melt them into your wheels. Go look up Ellis of Ranglebox's YouTube channel, there's a very good video there detailing how to do it.

Thanks for the quick help, off to eBay I go.

Parts ordered and on their way. Here's a preview of what it should look like once the wheels are attached.
Attachment 6686
Once the parts arrive, we'll heat press the nuts into the wheels, attach then to the motors and fix them in place with lock nuts.
Then we'll be able to give Bolts a first test drive before we start shaping the top to make the wedge.

So, because we're getting closer to having Bolts in driving condition, we'll very soon be in the place where the wedge is in place and it's technically "battle ready" (in the sense that it could enter an arena and last 3 seconds), I'm looking at what to add to the outside of the wood as an extra layer of armour.
In another build diary, I remember reading something about 10mm HDPE being pretty good against most axe/hammer bots. Would this be enough, or would we be better spending the extra cash and weight on metal armour? If so, which metals and how thick do you recommend?

10mm HDPE will hold out most hammers and axes in the featherweight class. For heavies, 30mm ain't enough.

If you go metal armor in the featherclass. The least I can advice is 3.2mm hardox 450, and if you can afford it (weight or money), thicker. If money is a problem, you can try thicker in normal steel.
If weight is an issue, I can advice HDPE, or else , with enough funds, titanium.

So what thickness of HDPE is enough for heavies, if 30mm isn't?

Thanks for the info.
Chances are we'll go with HDPE this time for money reasons. Hopefully, if this design performs well, it'll be worth the investment into Hardox for the next version.

No idea how thick is thick enough.
But if I find a way to form a 30mm shell in 1 piece, that will be an experiment worth the trouble.

Quote:

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Originally Posted by maddox10

No idea how thick is thick enough.
But if I find a way to form a 30mm shell in 1 piece, that will be an experiment worth the trouble.

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Vacuum bags around a cast mould perhaps? Kinda like mixing wet lay ups with resin casting

The top panel is hinged at the back with gate hinges. The back should hopefully be avoiding most of the damage and the metal will help strengthen the wood, whilst making it easier to access the internals.
Now we finally have a good idea what the wooden top panel looks like.
Attachment 6702
Bolts currently weighs in at 8.2kg, meaning we still have 5.4kg to play with.
I know for a fact we still have to shape and attach the side panels. Then order the 10mm HDPE to make the added armour and shape the wedge into the point.
If we still have the weight left over, we're hoping to get an aluminium front wedge piece machined (we don't have the equipment to do it ourselves) to strengthen the front.

We've been test driving Bolts around a little and noticed something I hadn't expected.
Bolts often struggles to turn. Forwards and backwards works fine, and turning works fine when held in the air with no weight on the wheels, it just struggles to actually turn while driving.
I'm thinking this is because the centre of mass is too far forward, meaning all the weight is too far in front of the motors and wheels.

Am I thinking along the right lines? And what should I do to fix it?

Our first thought was to stick a ball bearing in the front to reduce the friction and push needed to move the front. Would this work? And is there a better way to fix it?

As your turning you have effectively a wedge trying to stick into the ground on the front edge of the wedge. try just smoothing over slightly the edge of the wedge so that as you turn, they ride over the ground.
You may find driving forwards also gets the front stuck at places, but as its a v shape it helps it ride over

Thanks, I'll give it a smooth over and see how much that helps

The HDPE finally arrived. Now it's gotta be cut to shape and fixed to Bolts.
Planning to cut it with a fine toothed jigsaw, but I'm not sure how to fix it to the wood underneath, any advice?
Attachment 6770

In response to the previously mentioned lack of drive when turning, we have a couple of solutions we're considering.

1) Add a ball bearing style roller to the underside of the wedge, reducing friction and allowing easier turning.
2) Double the width of the wheels by bolting two wheels together, increasing grip and contact area on the wheels.

I think widening the wheels might help quite a bit. Adding a roller might lift your wedge too far up off the floor.

Are you attaching HDPE over your wood? Why not just make the entire chassis out of HDPE?

We're attaching the HDPE over the wood for a couple of reasons.
Firstly, we've got the extra weight to spare, so we thought why not.

Secondly, extra armour never hurts, especially when we don't have to worry about an active weapon, we want to keep maintenance costs down considering it's our first competing robot.

Thirdly, Bolts may often be lent out to young family members who want to get involved, so we think it's best it can survive multiple matches with as little damage as possible, so they get more enjoyment out of it

Fourth, we didn't think about the HDPE until after we built the wooden chassis.

The current plan for the front wedge on Bolts is to get it machined out of aluminium. This should create a strong front, whilst also saving a little on weight.
Any recommendations for which type of aluminium to go for will be greatly appreciated.
Attachment 6771

7075 is the toughest I believe, but I'd make it out of tool steel or hardox.

yeah get a steel edge (HARDOX my suggestion). It would keep a sharper edge over aluminium and be should be resistant against damage

Tool Steel and Hardox would both take us above the 13.6kg weight limit. The 7075 should hold up, it's solid all the way through and shouldn't be taking full on hits from spinners.

Perhaps a steel edge could be done. I'll have to check the maths on that.

If anyone on here has the capabilities to machine 7075 aluminium and has the time and is willing. Please do take a look at the Sketchup files, the DXF file and the included photo with measurements HERE and PM me a quote. I am also sending off for quotes from a couple of local companies, so apologies if I don't reply particularly quickly.
Attachment 6772

you can export sketchup files as DXF file (which you will need to do at some point) using plugins



:EDIT,

Is the scaling right on that model ? as this it next to my bot which is 1:1 scale in sketchupAttachment 6773

Quote:

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Originally Posted by Maxamuslead

you can export sketchup files as DXF file (which you will need to do at some point) using plugins

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Thanks, I'll update the file type and download link.

EDIT: Done

So... It's been far too long since I've updated this. With one simple reason, progress has been slowed down due to personal life.

However, with it being so close to the event, I thought it was time to give you an update. So, in a quick summary:
1) Upgraded to a FeatherTwo ESC
2) Upgraded to LiPo batteries
3) We've ditched the flails. This one was a tough call for me, I really wanted to do flail weapons to stop us being another boring wedge. However, we've decided that our completely over the top armour thickness takes precedent, and we don't have the weight to do both.
4) The front wedge is no longer metal, but solid wood covered in HPDE, again weight issues. This is what happens when you don't plan on a computer and just decide to make it up as you go along.

But looking beyond the 9th September, to the future of Bolts. Here's a few possibilities we've been looking into.
1) Taking away the wood layer, to a HDPE chassis only. This would free up the weight to add some of the things we've had to drop this time.
2) Learning some pneumatics to design and implement a Wheely Big Cheese style flipper into the wedge. Hoping to talk to a few of the teams at the event who use pneumatics as I learn better seeing after seeing a physical example than just reading references online.
3) I really want those flails back, so I might built a smaller, more square bodied robot, that would better suit the flail weapon type.

Most of all, we're just looking forward to our first event, learning from the experience and talking to other competitors. Even though we're almost certainly coming home in a bag from what I saw of insomnia over the weekend.