New Build/CAD Advice request.

So, there is a new series of Robot Wars on TV.
Which means there are probably going to be a few posts like this one, because I think 'I can do that' is part of the appeal.

But, you know what?

I think I can do that.

I think I can build something competitive. I think there are a lot of people trying new, interesting and wacky ideas that don't actually work that well. I think if I don't try and be clever, if all I try and do is avoid making textbook mistakes and build something simple that actually does work - I think there is a lot of mileage in that. Lots of drive power, lots of hard steel at oblique angles so spinners can't get a firm 'bite' on me. Probably an axe/pick of some kind as the active weapon. In my mind I have something like the bastard child of Chaos 2 and Thor.


Core build objectives would be:

• Should be legal in all national/international events. If I'm building a war robot, I want to be able to use it.
• To Finish First One Must First Finish. Build for durability, reliability and repairability rather than out-and-out power/performance. Lots of robots seem to be losing fights because people can't get them back into fighting order in a couple of hours.
• KISS. Where possible, try and build with off the shelf parts that just work right out of the box. Don't try and be clever, just try and avoid doing anything stupid. Stick to proven concepts that I know work.
• Target budget £1k. If I can't afford to build it then I can never compete. If I can bring it in for not too much money then it's achievable.

Some of which are more realistic than others, but if that's what I aim for then hopefully I won't end up too far off the mark. Unsurprisingly, lots of ideas rattling around in my head.


I think the next stage is design. Spend some time with CAD, get the ideas into a coherent form and see how it all fits together. Try and get a firm idea what exactly I am trying to build and how. Try and work out how best to package lots of electric drive motors, an axe thing, and all the ancillary hardware into a robust box. How much said box weighs, and therefore how much weight I can use for the drive-line and axe systems. Figure out how the axe is going to work. Figure out just what 'and all the ancillary hardware' actually is.


Which takes me to the question/purpose behind this post.

Where is the best place to find out component specifications that I can plug into a CAD package?
Things like electric motor size, power/torque output and cost. Wheel sizes, battery pack sizes, what control hardware I need, etc, etc, etc?

Thanks.

Twin weapons rarely work. I'd stick to a single weapon especially for a first machine.

"Should be legal in all national/international events. If I'm building a war robot, I want to be able to use it."

Stick to FRA rules for the time being. These will see you good throughout Europe. There are some differences state side but I wouldn't worry about those for just now.

"Target budget £1k."

Doable but keep in mind most competitive machines in robots wars cost three times this at least. No machine in the final has cost less than this. Live events are a different kettle of fish.

"Where is the best place to find out component specifications that I can plug into a CAD package?"

From the manufacturer. Ask them for a data sheet. Should give you all the specs you need.

"Things like electric motor size, power/torque output and cost. Wheel sizes, battery pack sizes, what control hardware I need, etc, etc, etc?"

I'd recommend reading the various other threads on the forum. There are so many variables in this question I couldn't possibly begin to start answering it.

I don't think Lostdreamer was aiming for twin weapons. I think they just meant it might look like a combination between Chaos 2 and Thor.

Thank you both for your quick replies.

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Originally Posted by typhoon_driver

Stick to FRA rules for the time being. These will see you good throughout Europe. There are some differences state side but I wouldn't worry about those for just now.

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That seems sensible.

As I understand it this means that things like massive kinetic energy weapons a la Carbide arn't suitable. The smaller arenas simply can't contain them. One of the reasons for thinking along the 'armoured axebot' lines.

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"Target budget £1k."

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Doable but keep in mind most competitive machines in robots wars cost three times this at least. No machine in the final has cost less than this. Live events are a different kettle of fish.

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Hence asking people who know more than me! :proud: To try and get a feel for what is sensible/doable and what isn't.
People on the show do keep saying about how they built theirs for only a few hundred, but I don't know how much of that is having lost track of how much they did actually spend when you added every up, how much is kinda circumstantial - "Yeah, we used these handy jet engines from a old fighter plane we just happened to have laying around...didn't cost us a penny!" and how much of that is that, yeah - you really can build something that will get you through the door for a few hundred quid. Split that with a teammate, and it's potentially quite an adventure for the cost of a weekend in a B&B. Even if you don't win.

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I think they just meant it might look like a combination between Chaos 2 and Thor.

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That's what I am thinking of at the moment, yes.
Form wise, something quite close to Thor. Lots of diagonal plates and an axe/pick type weapon.
But taking a lot of concept ideas from Chaos 2 and basically trying to build a 100kg bulldoser. Aim to have an advantage in speed and traction and just keep battering other robots around the ring.

I'm not thinking of building some form of uber weapon system that can tears my opponents apart and give me a quick victory. I'm thinking of building something quick enough to be able to relibly close with my opponents and tough enough that three minutes later I can take a judges decision due to having spent the entire match driving at them flat out and hitting them with an axe.

I'm a skilled motorcycle mechanic,

I've come into this all blind, yeah i know how RC equipment works. I know how to build stuff, but there is a ton of stuff you overlook. So far i think i have spent dozens of hours touring the forum.

I have 2 prebuilt shells that i purchased from 2 very good members on the forum, to save me fabrication time.

Neither Shell lends itself to any one design so i have taken the best of both and merged. I currently have 4 different drive trains planned to try out.

Once i have hit it with a sledge hammer and dropped it rom 6 foot numerous times and it won't die, then i will consider it battle ready.

The rest is going to come from learning fixing and reading... Whilst CAD and fancy skills are fantastic i do think that it can limit you in otherways such as quick repairs.

I agree there is no subsitute for practice, experience and getting my hands dirty. One of the reasons for posting here, to try and get feedback from people who have been there and done that.

But i'm good with trying to create a design to work to. I can mock things up in CAD all day to see how to fit everything together and try and make a working concept. All it will cost me is loads of evenings starting at my computer and some cups of tea. Both of these are pretty much sunk costs, but tea is cheap and daydreaming about robots and how to put it all together isn't exactly a boring thing to do, so i'm good with that plan.

The other next obvious step is to actually get out and see a live show. I'll miss the next couple for various reasons, but there is an Extreme Robots event on the 6th/7th of May I might aim for.

Anyways, after a while window shopping on the internet I already have another stupid newbie question.
The Ampflow A28-400 seems to be a popular motor choice if the Robot Wars website is to be believed. 3+kw @24v. Nice.
Oh, and almost 600A peak current, presumably at stall. Which is probably gonna happen. Lots. Being pushed around by other robots, driving into things, etc. Matches seem to involve a lot of shoving matches and getting stuck on stuff.

That's a lot of power draw. Especially once you allow for several of them. If it isn't a rude question, what sort of battery configurations are common?

Big lipo's.

Stall , not happening a lot as long the drive stays whole. (and is geared sensibly)
You can't get that power to the floor with the weight and tyres we use.

As a school we have a tight budget - Expulsion was built with £1000 but then we were given the £500 by the BBC. It was difficult. Our steel was cut for a fraction of the cost it should have been (£320). Two main things that stand out.

Don't underestimate the cost of little things. Heavy duty cables, crimps, fuses, nuts, bolts, removable link, chains, gears, sprockets. All adds up.

Put it this way. This is £100 worth of stuff: 2 Chains, 2 Sprockets, fuses and fuse holder, 1m Cable red and black, nuts and bolts, Cable ties, Bearings.

Then factor in the fact you need spares of every component. I would go on eBay and add every single little component to your basket then look at the figure.

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Originally Posted by maddox10

Stall , not happening a lot as long the drive stays whole. (and is geared sensibly)
You can't get that power to the floor with the weight and tyres we use.

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Ahha.

That makes some sense.

Hence seeing people swapping out so many fried motors etc on TV. It's not just people running them overvoltage and outside spec. If a wheel jams then you DO get stall currents, which DO fry the electrics.

Would I be correct in assuming people deliberately don't insert a big fuse to protect the motors in the event of a jam because then you are actually introducing failure mechanisms?

But it also means that I don't necessarily need to find 300A worth of control hardware, batteries etc for something like a cordless drill motor.

And yup, lot's of window shopping ebay doing a back-of-an-envelope pricing etc. I'm building a rapidly growing spreadsheet with lists of how much all sorts of things cost. I think it is possible, but I also think that typhoon_driver was bang on the money when he said right at the start it would be borderline competetive. That cost constraint means I can't bring the same levels of performance / power to the party that a lot of other people do. I would be basically building a target.

It's nice to know that Explulsion was built for a similar budget. And it's nice to know that £1.5k target budget actually does include a lot of the little stuff like fixings and wiring that it's so easy to cost at nothing because 'I just had it laying about'.

If I am creative in my sourcing of parts and start shopping at my local scrapyard rather than ebay, it should be possible. Canibalising mobility scooters seems to be popular for example. I'd be be making way more work for myself than I would like and in danger of missing my 'KISS and use off the shelf bits' objective but I guess that is secondary to the 'can I do it at all?' issue.

So now I have another silly question. Said spreadsheet is giving me an idea of how much some of my costs will add up. It's also making it clear how quickly weight is going to add up. So, err, exactly how big length/width/height are many of the robots? How much can I realistically expect the shell to weigh?

Why do I feel I'm seen as a newbee by you, Lostdreamer?

It's still Robot wars, not Barbie Bumpercars.


With a good drivetrain stall is rare.
Only mechanical failure wil do that. Shattered magnets due shockdamage is the most common atm.
A good second is jammed gears/chain after huge impacts.

Battledamage is battledamage.

With a load of fuses everywere you just going to protect the fiddly bits untill the disk goes trough those after the fuse did do the protecting.

I rather fry a £250motor than lose a battle because a £ 0.3 fuse went early.

Oh, of course, not to forget, electronic components getting ripped off the PCB is another common failure in our machines.
Again, purely mechanical, due the G-loading during the impacts.
Most spectacular are big LiPo's with a good charge in them. Short those and you have a nice smokescreen going. if the short happens in the cells, or before any fuse, (in the few cm of wire comming out of the pack), your £0.3 fuse could survive.

But that's me.

For the rest. Cannibalising scooter motors is a way to go.
But it's a lot easier to buy the now common MY1020 scootermotors (in any powerflavor you wish) from Ebay or simular sites.

If you want cheap power, look at older startermotors.(difficult to control tough)

Weight of a heavyweight shell.
The bodyshell of Bullfrog is 1000mm long, 500m wide and 180mm high. Weight, around 25 kg, all Hardox 450 3.2mm thick.
The drives have own armor, and each drive is 14.8kg.

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Originally Posted by maddox10

Why do I feel I'm seen as a newbee by you, Lostdreamer?

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Oh hell no.

And I never ment to even imply that.

The problem is, I very much AM.

I think part of the appeal is that you look at these things and go 'I want a go at that!'.

...but I havn't a clue what I am doing. So i'm asking a whole load of stupid questions as I try to understand what is actually involved. Because I don't know, and asking here and chatting to people seemed as good a first step as any. All I know so far is what I've seen on TV and, well, real life and TV are not known to be on the best of speaking terms.

I'd like to try and avoid making any obvious mistakes, which only adds to the number of stupid questions as I try to work out what they are and how to avoid them. So yeah, I'm doing stupid things like looking at $100 dollar cordless drill motors and going:

'Ok, that looks like a starting point. 300A peak current? Won't I be flat out for most of the match? How the hell do I power that?!'
to which the answer is 'You won't be drawing peak current.'
Which leads to 'Ok, so why are people still blowing motors? Can't you just put a fuse inline so you ain't replacing £500 components every fight?'
To which the answer is 'It's more complicated than that.'
Which I suspected. But it's nice to have a bit more info on how.



I clearly don't have the budget to compete with many of the massive kinetic energy weapons etc out there currently. And I can't anyway if I want to use it somewhere other than robot wars.

But maybe I don't have to. Most fights don't last for 5 mins. Maybe If I can make something that can take being thrown around the area like a rag doll for five mins and spend the whole five mins going flat out for the other guy I can take the judges decision at the end of it.

So there will be a lot of questions about what breaks and why because the concept I am trying to figure out at the moment isn't focusing on breaking the other competitors in half. It's working out how I stop that happening to me.

I'm sorry I'm not doing the best job of explaining myself.