My first beetleweight build - some newb questions to follow!

Afternoon all. I am new to fighting robots but not to robotics or engineering.

I have always wanted to build a fighting robot ever since robot wars but have never deemed it very accessible and life always got in the way. So, after watching a number of youtube clips and ending up on a massive binge fest or all sorts of leagues and build channels I found out about the UK scene. At first thought I would give antweight a go (and still will) but after noticing just how many beetle weight fights and events there were and that a beetleweight is probably a better class for first build I cleared my schedule and began designing.

I don't want to give too much away and will possibly do a build log after my first fight but have decided on a horizontal spinner. I think I have made about 80% of the design decisions so far and am happy with my choices (probably be full of regret and lessons after first fight) but think I need to call on the wealth of knowledge here to finalise a few things.

So.

• Is HDPE a good choice for the top and bottom plates of a spinner? I had planned on using 5mm but now doubting myself as its not something ive used before. If not, what materials are people using?
• Whats the best "link" or switch to use and whats allowed as the rules seem a bit vague.
• Is there a reason why 868 MHz and 915 MHz are not allowed for robot control?

Hey there, welcome to the forum!

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Is HDPE a good choice for the top and bottom plates of a spinner? I had planned on using 5mm but now doubting myself as its not something ive used before. If not, what materials are people using?

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So long as the internal structure of the robot is solid, there is no reason why this wouldn't work. I use 4mm polycarbonate and 3mm HDPE on one of my Beetleweights. I will however note that spinners can be quite dangerous, especially if they go wrong (which I am sure you can appreciate). Just getting a combat robot to survive in the arena for 3 minutes is a victory in of itself! :P

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Whats the best "link" or switch to use and whats allowed as the rules seem a bit vague.

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I use an XT60 link in one of my Beetleweights but I've seen folks use XT30s. So long as the link is going to support the amount of amperage that is going through the wiring and works as a link, any sort of removable is normally OK.

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Is there a reason why 868 MHz and 915 MHz are not allowed for robot control?

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I can't comment on why these specific frequencies (I don't know the reason for this) are not allowed but the 2.4GHz frequency avoids clashes quite happily, a good thing given the number of competitors that could be at any event.

Hi Ocracoke, thanks for the welcome and the help.

Im still running the calcs but it looks like I have the weight allowance to use 5-6mm HDPE or with a slightly different cutout 4mm aluminium. Ill try the HDPE first as its a bit friendlier to work with.

I have xt60 connectors and so could use them. Does it have to be able to be removed by hand? Does it have to protrude from the bot? Anyone have a pic of one in use?

I will switch to 2.4 then as there are lots of options.

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I have xt60 connectors and so could use them. Does it have to be able to be removed by hand? Does it have to protrude from the bot? Anyone have a pic of one in use?

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Yes, it must be removed by hand (no tools allowed) and yes, it can protrude from the bot though in that instance, I typically have them on the top of the robot. If you recess the connector in a little further into the robot, that will help with the loop of wire not being as exposed.

Perfect, Ive just added one to the top of my design. My keen-ness made me read the rules too quickly and I thought I needed one on the top and bottom or at the back as it can invert. Thanks again.

I have lots of the Pololu 25D gearboxes here at work so was going to use them. I had though that this would keep things simple but now I am thinking of going brushless after seeing a few build vids online and having a lot of ESC's in stock. It would help with weight as until my blades arrive I only know their theoretical weight.

Any good UK suppliers or combinations of gearbox / motor that are recommended?

Hi Blair,

Welcome to the forum! Probably not as useful if you are planning on going brushless, but Bristol Bot Builders have an excellent list of commonly used parts for Ants, Beetles and Feathers. Could possibly be of use to you?

https://bristolbotbuilders.com/parts.html

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Originally Posted by beardyblair

I have xt60 connectors and so could use them. Does it have to be able to be removed by hand? Does it have to protrude from the bot? Anyone have a pic of one in use?

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As long as it protrudes enough to be readily accessible, then you're fine. I use XT60s for the link, and for most connections except brushless motors i use for weapons, as these are generally 3 cables instead of the 2 XT60 has. here's a demo of one of my links in one of my bots, the bolt incase you're wondering is just the safety brace for the spinning part (i use something slightly less ridiculous looking now). Do note the size of the loop on this link is slightly excessive, due to my own paranoia of not wanting to force an arena martial to have to get too close to the spinning bit if at all possible.
Make sure your chosen pair of connectors aren't too loose, as connectors can vary in tightness, you don't want a pair of connectors that will come loose during a fight, it happens quite often, especially in spinners and their wild throwing everything about! a brand new pair are usually tighter than a set that's been used a few times, i tend to redo my links after they get too used and loose.

Attachment 9173

Thanks for the link Mr Manuva27, very helpful.

Hey redirect Left. Thanks for the pic for reference! During my research phase I did watch A LOT of fights and tabulated the details of types of robot and reason for losing (not winning). As you mentioned there were quite a few that lost due to the link being hit or it falling out. I want to try to ensure that does not happen to m
e.

So after a long night of CAD and filling in my spreasheet, my calcs show that I am quite tight on the weight front so may need to shed a few g's by hollowing out a few parts and going all lotus with the drill! Every time I think I have it figured out there is something else. Getting close now, almost time to cut, print, mill and turn!

I've found with beetles it's easy to go over the weight limit so it's a good idea to weigh all the electronics first before cutting the armour to size :)

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Originally Posted by COAESystems

I've found with beetles it's easy to go over the weight limit so it's a good idea to weigh all the electronics first before cutting the armour to size :)

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Yeah, spent some time today updating my spreadsheet as I get further into the CAD design. Trying to account for every nut, bolt, washer, wire, shim, spacer and belt. Electrics wise I think I have all my weights. I have done a bit of weight saving by cutting pockets into some of the internal areas and non-critical frame sections. I have entered the material properties into CAD and am at about 180g for the top and bottom frame parts and 190g for the main chassis.

Weapon wise I have sent off to have the blade (and spares) cut. Once I have these weights I will then be in a position to finalise a few of the other parts and decide if I will have to print them of if I can mill them on the 5-axis.

To save a bit of weight and combine a lot of the circuitry I have worked with my business partner today and come up with a main board that will house a number of the safety features and handle power management and regulation. She normally spends her time making flight controllers and complicated control systems for our UAV's and other robotic projects. This has got her interest though as one of our company goals was to enter robot wars. This is hopefully the first step towards that goal. Whatever she finalises on will be over specced, redundant and as light as possible. Ill show all after the first fight.

Im really enjoying this so far and already have a few ideas for another beetlewight or two.

Made major progress today. After "finalising" the main design I fired up the 3 axis and went to work cutting the main parts out of HDPE. I usually cut alloys or carbon so today was a treat, HDPE is like butter. It took a few test pieces to set up my speeds and feeds and with the correct tooling it was a breeze.

So the good news is that my calculations worked and I was within 4g of expected weights. Bonus.

I have also printed out prototypes of all the main parts so I will hopefully be able to do a mock build of the chassis tomorrow. Still waiting on the new gearboxes (I decided to go brushless), blade, belts and some minor electrics. But all in all things are going well... famous last words.

Ive also started to design an antweight and have another two sketched out on paper. I will probably start a build thread to document this.

I know I asked it before, so who would I need to speak to about using 868Mhz? It only really hit the UAV hobby market last year but they are citizen allowed frequencies so is this something that could be added to the rules? Who governs this at FRA?

You'd want to e-mail Kane at the FRA (contact info can be found on the site) but I've personally struggled to get in contact with the FRA directly and even then, I don't think they would add frequencies "on the fly" so to speak, they would consider it for the next year's build rules if a good case is put forwards for it.

All parts have now arrived and I have weighed everything and finalised my spreadsheet. The good news is that I am 100g underweight so I intend to move up to a slightly more powerfull motor. 40% extra torque for just 22g extra weight. My chosen battery had 30% higher capacity than required to take into concideration room temprature, cycling and degridation over charges so it will be fine for the additional power consumption.

The 3 blades I had cut on the waterjet arrived and they look very menacing. Therefore I will be designing and then ordering up some Lexan on Monday to make a test box or ant arena/test box. I will not be firing it up until I have something to contain it!

I intend on building it with the parts I havecurrently as I want to check the weapon and drive systems. I also really want to test the chassis for strength and durability. I have a list of changes for V2 already but wish to iron out as much as possible prior to cutting more parts.

I also have a lot of software to write to get things going now and have a few features in mind that I have not came accross so far during my research. I will write about that at a later date. I will try to get things together and tested this week to ensure Im on track for my first event in Edinburgh next month.

Well things escalated quickly here. V1 was built and all parts played well together, elctrics were tested and my ideas seemed to work. However there were space issues in the main compartment and some changes I wished to make to strengthen up the overall build so V2 was designed, cut and built. Our 2 custom PCB's then arrived and were right on the money for size and weight, these were fitted and the programing began. It was at this point that we began weapons testing. That was well, interesting!

The motor I had chosen was up to the task but the external printed gear was not. And to get the required gearing in the space we had available everything became a compromise. A V3 was designed but the calcs proved it to not be the best way forward so nothing was built.

So at this point I was happy with the weapon system, drive system, electrics, batteries and main chassis. The issue was purely weapon motor and gearing. So I mocked up a few systems and began testing. I used one of our UAV (drone) thrust stand controllers to test each motor and gear combination to work out spin up time, amps and monitor heat. I then designed V4, this included a heat sink and a metal gear on the motor side. I have included a larger bearing to hold the motor axle as I also noticed the smaller bearing was not up to the task due to the tension the belt was under.

So with less than 6 days to my first competition its now time to re machine the chassis and hope that tests go well! Wish me luck!

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Wish me luck!

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Good luck! Sounds like you've got a good handle on things for your first build and look forward to seeing it at Edinburgh. I haven't done a scratch built beetle for about four years and mine is currently 90% CAD, 10% physical bot so got to get the finger out!

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Originally Posted by Ocracoke

Yes, it must be removed by hand (no tools allowed)

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Sorry about hijacking this old thread. Just to check (which I unfortunately believe is the case from rereading the rules and this thread) Whyachi-style switches are not acceptable under FRA rules, the only acceptable way to power on/off a robot is a removable link that does not require tools to active/deactivate, but could be hidden beneath a panel that is toollessly accessible i.e. a latch or velcro?

Yes, that is correct. The panel that covers it, if you fit one, has to be toolessly removable as is the link itself.

Thanks, you've been super helpful today.

links at beetleweight levels tend to be an XT60 connector with a wire loop. At featherweight levels its more an XT90, although some do use xt60.