From The Ground Up (Advice Thread)

[psycho_fling]

depends what you are going to use the steel for ali is good as a replacement aswell????????

you can use thicker foam aswell to shock absorb and its lighter

Kevlar as far as im aware has never been used in modern robots and i believe its Pricey++++++++ stick to well know materials, polyc, hdpe, nylon, steel, ali, ti and not forgetting the ultimate WOOD!!!!!!!!!!!! (block of wood = champion)

alex

[Roland]

Kevlar sheeting is 20 pounds for a 5m^2 roll, I thought I would have a fairly thin steel sheet with a layer of kevlar underneath that and then a layer of rubber/foam underneath that.
Kevlar didn't seem that expensive, and could make up for the lighter sheet of steel, I mainly chose steel for welding purposes, but I'm looking into ali welding, I don't want to go into acid baths to remove slag just for a lighter armour that might cost more anyway, I could do a steel/ali mix, bolting the ali and welding the steel.

What are the pros and cons of using different materials?
i.e. Steel, ali, poly carb, wood etc.

Thanks as always for your answers so far!

[Moritz]

What kind of kevlar is that?

[Roland]

Kevlar 300g 2/2 Twill Aramid cloth

It would be placed between two rubber sheets and a steel plate on top or between a steel plate and rubber.
It would be used in conjuction with the metal to give support for the weaker parts of steel that would need to be reduced in thickness due to weight.

That's something like what I had in mind.

[rallikas]

Kevlar 300g 2/2 Twill Aramid cloth

It would be placed between two rubber sheets and a steel plate on top or between a steel plate and rubber.
It would be used in conjuction with the metal to give support for the weaker parts of steel that would need to be reduced in thickness due to weight.

That's something like what I had in mind.

Expensive and a pain to repair.

[Roland]

Expense isn't a problem, and no pain no gain.
I'll try it once, and see how it goes!
Currently in Yorkshireland learning to weld and cut threads.
Going out to buy metal for a workbench later and should start building the bench this week.
Slow and steady!

I still don't know The thickness of steel you guys prefer? Do you galvanize it also?

[joey_picus]

I wouldn't stay up here too long, you might catch some ghastly disease :P

I believe it depends largely what you intend on entering the robot in - for spinners, the rule is 'as thick as you can get' and for anything else 2 to 3mm thick is the minimum you should be looking at for armour, although stainless steel and Hardox are both better than mild steel. If you can reinforcing it with thick plastic behind is a good idea as that stops axes and hammers from causing too much damage (in theory...)

Ultimately though how you end up mounting the armour is almost as important as the armour itself; series 7 of the TV show provided more than a few examples of thick Hardox plates being ripped off totally unharmed because the bolts holding them to the chassis weren't strong enough.

Regarding galvanized steel, I haven't actually seen any robots with galvanised panels because it then can't be welded, but I don't know much beyond that I'm afraid.

[Roland]

I hear you can buy galvanizing spray after you've welded you apply it.
You can also grind down the weld edges to remove the Zinc so you can weld, but that's a bit more risky.

I'd be looking at building a spinner since I see it as being the most simple design for me that contains moving weaponry, I'd have it designed so it would have front interchangeable weaponry so I could still go to contest which bar the use of spinners.

I was thinking of 3mm - 4mm Checkered mild steel plates, I always liked the look of footplates on a robot.

[joey_picus]

I wouldn't do a spinner for your first attempt to be honest...if you're looking at a design with a moving weapon do a lifter or an electric crusher of some kind, spinners are:

1: Rather dangerous - one of my (now retired) fleaweights was a spinner, and the entire robot weighed 75g with the weapon assembly weighing only about 15g maximum, and it still caused me a few injuries/cuts...any weapon on a robot is dangerous but spinners are even more so and the potential for damaging yourself - even if you work as safely as possible - is still high.

2: More complex and expensive than you might think - a properly balanced spinning mass, some method of gearing down the motor you use, the motor itself, and crucially a method of switching the motor on and off that will handle the current (either a very large relay controlled by a R/C switch, or a fairly hefty speed controller) is going to cost you a fair bit and take up a lot of space inside the robot.

3: Limiting in the events you can go to - you can't run spinners at the vast majority of events that run featherweights, if you had one you'd only be able to play with it once or twice a year at an event with a 2F grade arena (which so far only Robochallenge have, although I believe the RR arena can be set up in a 2F configuration if not for cost)

4: Rather dangerous - safety is always first when building and fighting robots so this point needs making clear! :P

If you've got your heart set on a spinner this can be a bit hard to swallow, and nobody's going to stop you doing one as your first robot if you really really want to, but a lifter or crusher is, in my view, a cheaper and easier (all you really need is the weapon itself, a linear actuator and something like a Team Delta dual ended relay board and you're in business for less than 100-150 pounds and hopefully with all your fingers still attached) way of getting an active weapon for a first time builder.

EDIT: I've just seen the interchangable section which makes a lot of this post look stupid and patronising, very sorry :P but I would still build a non-spinner weapon module first and do the spinner when you've got a bit of experience from that.

[Roland]

I had a small feeling someone might bring this up, and I have put some thought into it.

I thought about building the shovel first but I realised that I would end up building two robots if I were to then build a spinner afterwords. As changing the chasis might cause a bit of a problem so it'd actually be cheaper to build the spinner first.

The plan was I'd design the robot to have a drum at the front , but I'd only apply teeth once I had finished the entirety of the bot, and even then the teeth won't be sharp, and are most likely to be blocks.

That or I'd design the robot to have the space to hold the tech needed for the spinner and build the shovel to start, then go back to it once I have more experience. One problem I found with that was that I might not be able to accurately predict size and weight of each part needed for the spinner, and the best way to work it out would be to buy the parts, which would mean I'd have the bits and bobs sitting around my workshop for sometime.

*shrug*

Without teeth the drum would just be as hazardous as having a pillar drill or grinder. Probably less so.

I'm probably totally wrong.