Designing bot to fit inside cube

[Roboteernat]

Hi All.
Been on here for while (2+ yr)
Im building a mini version of my robot wars bot (Short Circuit series 6) and was wondering how you guys design them, parts layouts, to fit inside the size restrictions.
I have built a mock of the bot using 3d printed chasis and card, but it seems small compared to other ants, ive seen drawings on 5mm square paper, and cad models on solidworks/sketchup, but i was wondering how you design them.
I have sketchup designs of the parts, and placed them together, but build a bot chasis visually to fit inside the square i cant fathom, esp as the larger dimensions are accross the diagonals of the cube.

Additionally, what is the concensus on speed controllers for the bots? I have dimension engineering Rx5 RC bassed on reading up on them, but there are others now and was just curious, not much has been mentioned about them on the forums for a while.

I am using 2x12mm gearmotors 300RPM, and have some hobbyking brushless motor and speedcontroller for weapons. I have the pololu wheels of various sizes and a 350ma lipo (name cant remember).

maybe i should continue just sticking together with card and see how i can get it to fit together

Thanks for any advice.

Nat

[BeligerAnt]

Sounds like you're pretty much there!
It's up to you whether you use CAD or cardboard, it all comes down to trial and error - there are no hard and fast rules. I usually do my designs on paper in 2D (cos I'm old skool ) but nothing beats a cardboard mock-up to really understand how it goes together and whether it fits in the cube!
However you choose to design it, best to design to a 100mm cube, then if you manage to build to 1mm overall tolerance you will still fit in the 4" (101.6mm) cube

If you want to design a maximum-length chassis to fit across the cube at an angle then you will need some geometry to figure out the actual length, or draw a 1:1 side view and overlay a 100mm square or a 5mm grid to figure out how it should fit.

As to component layout, it's whatever fits! Think laterally - can the battery go below the motors? can speed controllers be stacked one on top of the other?
Best to keep the receiver away from the motors, especially brushless ones.

Really the best advice is to get something built and try it out. Most people don't consider their robot "right first time", after several iterations it might get to "good enough" (or is that just me? )

[Remote-Controlled Dave]

Hi dude, Short Circuit was a great low-tech heavy, shame it got cut in half!

I think the best way to see if your bot goes in the cube is to build a cube! I've been building ants for years now and I am still consistantly amazed what people can fit inside the 4" dimensions. CADs and technology are all brilliant tools, but I have known people build a bot that CAD says should fit in the cube only for it not to when it was built. A cardboard mock up is a great way of giving you an idea for dimensions and layout. I wouldn't worry about it seeming small either, antweights run a large gambit of sizes.

Good luck with it all! Hope to see it at an event sometime soon.

[joey_picus]

Hiya Nat, I do remember Short Circuit and thought it looked pretty good at the time shame Supernova had to happen...

Personally, not being in any way an engineer I have a tendency to design from an artistic or hopeful viewpoint and then worry about how to fit it into the cube, which has been an issue in the past! As a rule of thumb though, I find that ~140mm is the maximum dimension it is possible to have between any two edges and still fit into the cube, and what I generally do is design to a width that is close to, or slightly smaller than (~90mm is probably advisable having rewatched your fight and noticed it had side bars!), 100mm and then check the robot against a 4" square drawn on some paper as I'm building it, which gives you most of the accuracy of a cube without having to actually build or purchase one. Then again, what I also have a tendency to do is buy or come into possession of a load of components and only then consider how to make them into a robot, so take all that with several tablespoons of your preferred low-sodium flavouring...

As for speed controllers, the standard these days (I think!) is Peter Waller's custom built boards, which come in many varieties and have never once let me down (along with the best customer service possible since he's at nearly every antweight event XD). That link doesn't have the prices, but this post does. I did use a Sabertooth 2x5A for my first robot and had no issues with it, but the Waller boards are far lighter and actually somewhat easier to use as you don't need to fiddle with terminal blocks!

Hope that ramble helps in some way, and the best of luck building it - I'd love to see a replica Short Circuit fighting in the ants

ADDENDUM: 350ma is a little bit on the large side for antweight lipos - I've run a 2wd spinner with quite a big motor and had a 180mah 2S battery last a few matches, so if you find yourself struggling to fit the parts in size and weight you can probably reduce the battery size quite a bit with no problems.

[Roboteernat]

Thanks for all the messages,
Once i bought the sabertooth, i had few issues with the FTS so had to get replacemet from the USA, but was thinking as using it as a 'starting point. I always had the throught of writing my own picaxe / arduino code to control it and make it as small as possible.

I am working on a cardboard version of it to start with, then have carbon fibre at the ready with alu plate to build it.

The 350maH battery was bought as it was small and light, http://www.hobbyking.com/hobbyking/stor ... _20C_.html is the one, thought it was nice size bassed on i think i will be having a spinner on it, and 21g, (cant remember on what site i saw the battery listings)

the RX is a 3 channel 5g reciever for my turnigy 2.4 tx. so far i have 3d printed a base for it, but found issues so looking at other options, and the link to the rx31? small 2.4 rx has given me the idea to build my own again, and as TB6612 is popular i have purchased some to try and build a 'plug-in' controller to fit my RX, simular to the links of the option boards, (insert guys name here - sorry) but specific for my rx.
I also was thinking of having a swithed output as apposed to a servo output for controlling on/off devices using a smal mosfet, so at the extremes of stick travek you can turn on/off device...

anyway thats an idea, i will see ho the card goes and will make a start on the PCB

Thanks

Nat