Revron (Ant) Build and Iteration Diary

Revron (Ant) Build and Iteration Diary

Preamble

In February 2023 I attended my first Antweight event, SCAR 2 in Sheffield. I entered with a fairly simple 4WD pusher called Shoveron.


(shoveron before)

I had a great time, met some great people, learned a lot and even managed to win a fight. One thing that surprised me as a newcomer is just how effective some of the spinners were and by the end of the trip home I’d convinced myself for the next event it’d be fun to build one.


(shoveron after fighting Icebreaker jr and learning what a well designed spinner can do)

A bit of research later and I set a few targets for my build

  1. 4WD
  2. Vertical spinner, ideally a drisk
  3. Use more durable materials
  4. Go positive W:L for the next event
  5. Separate armour from chassis

Revron V1.0


(Revron pre SCAR 3)

For the first iteration I took a lot of design inspiration from the US beetleweight scene and robots like Lynx and Ablation (the peterbar kits).

For the electronics I used 2 x N20 BBB 1k RPM motors for direct drive at the rear, Rx and ESC’s were handled by a malenki nano and for the weapon i opted for the BE1806 and BBB brushless esc. The battery was a 350MaH 2s pack which in hindsight was overkill and a bit of a waste of weight. I wanted to start out with pretty well know reliable components so I could spend a bit more time on the mechanical design without having to worry about respecifying parts that it would depend upon.

On the mechanical side I decided against tyres and tried out a full cleat system using laser cut stainless spikes attached to printed pulleys and with 1mm thick o-rings acting as belts between the rear wheels and the fronts for 4wd. The chassis construction consisted of a polycarbonate printed pocket for the motors and electronics to be housed. 1mm CNC’s polycarbonate sheet was used for the top and bottom panels as well as the front armour. The side armour was machined from 4mm HDPE and was attached to the chassis using 6 Aluminium standoffs and aluminium bolts. One of the standoffs also doubled up as the axle for the front wheels. The drisk was made from two laser cut pieces of 304 stainless one directly mounted to the motor and the other attached through a polycarbonate spacer. Finally the motor was supported both sides by 4mm HDPE uprights and I turned down the prop mount to allow for a flanged bearing to be used on the rotating side.

SCAR 3

I managed to finish the build just before SCAR 3 and in testing a few issues had become apparent that were fixed the night before. Firstly the front wheels would sometimes bind, this was remedied by a small amount of grease on the standoffs. Secondly the cleated drive did not provide the traction expected. It turns out Ants don’t carry enough weight to make this as effective as it is for US beetles so I swapped out the rear cleats for few O-rings and hoped for the best.

SCAR 3 went well with the weapon working better than expected. Revron won all three qualifiers with a few nice roofshots and made it into the round of 16. It was knocked out in the round of 16 by a very well driven GNC. Revron took very little damage throughout the event and overall I was happy with a lot of the design choices I’d made regarding the chassis construction, armour package and weapon.

The loss to GNC showed some of the areas that needed improvement. Mainly traction, drive speed and my driving ability.

Images of early build


(First chassis test assembly)


(First drive motor tests using borrowed shoveron parts)


(Final printed prototype with all internal components before commiting to machining and laser cutting)

Thanks for reading and I’ll update this post with the series of updates I made over 2023 as I get chance,
Jordan

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Big fan of your design style and how your ants look like the larger bots! Looking forward to seeing more of the builds. Was awesome to see you do beetles.

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Cheers Joe,

I’ve got a few new Ants in the works for this year and I’m hopeful that when I work through the snags on the beetle I’ll get the reliability improved!

Very cool. Agree with joe - impressively beetle-like in construction for an ant - really nice to see that construction style scaled right down

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Revron update package 1

Components upgrades

Problem number one to fix was drive speed. Revron is, even for an Antweight, pretty tiny and as such runs pretty tiny wheels. 19mm OD cleats up front and for the first version 20mm o-rings on the back. This coupled with 1000rpm motors meant many other bots were much quicker and it was easily outmanoeuvred by most control bots. To fix this I had two options;

1- Fit bigger wheels and as a result scale up the bot to deal with this
2- Find motors quicker than 1000rpm

I really didn’t want to alter the size of the bot as I was pretty pleased with the form factor so I set about shopping around. Eventually I came across Turnabots spicy N10’s and bought some of the 1200rpm and the 2200rpm motors to try out. I also picked up a couple of their batteries which were slightly smaller than the turnigy nano’s i’d been using up to that point. I decided to run the 2200rpms after some brief testing.

Problem two was traction and this one proved a little bit trickier to solve. The cleats hadn’t worked as expected so I could either try and refine my cleat setup or move over to tyres. I started by testing new cleat designs, I designed and tested cleats made using arduino header pins, sewing pins, perforation wheels used for marking out fabric, sharpened versions of my original laser cut cleats and ultimately they all performed poorly. At this point I decided a rather big redesign was needed and I set about finding some suitable tyres.

I’d previously cast my own silicone tyres form shoveron however the whole process was fiddly and a little unreliable. I’m sure with more time I could have improved it but ultimately I decided there were probably better off the shelf options. After a fair bit of searching and chatting to a few people about options my uncle mentioned that he thought scalextric stuff might be about the right size. He was right and Ultimately I ended up settling on the Scalextric F1 tyres, they’re cheap, have incredibly high grip and can be easily mounted to a printed hub.

False starts and silver lining

With my new components ordered and in the post I set about redesigning Revron in CAD. This version had tyres all round, I moved the motors forward and ran a spur gear system to drive the front with belts to the rears. I also moved a standoff to in front of the front wheel to allow for modular armour packages that wrap around the standoff and slide in from the side. I also realized that with the weight saved by the new battery I should just be able to run an additional disk which seemed like it could be fun!


(Pic of V2.0 CAD)


(Assembly of one drive side for V2.0)


(Semi-assembled V2.0 alongside V1.0 and a Pnematic ant… Ignore that for now)

For those of you familiar with the bot the above CAD and pics will look pretty unfamiliar. This is because while V2.0 looked good in CAD it didn’t really work. I had some real issues getting it to handle and drive as expected. The extra gearset had a bit of backlash and the tyres were so grippy the belts on the 4wd had a tendency to slip before the bot would turn. Despite a lot of time spent tweaking and reprinting parts I just couldn’t get it to drive in a way I was happy with.

At this point I’d spent a lot of time developing but hadn’t really go much to show for it and SCAR 4 was starting to get a bit close. I decided that maybe it’d be best to only use the grippier tyres at the back and keep the cleats upfront. This would at least allow for a bit of extra pushing power but not at the expense of the speed of turning. That decided I went back to my original CAD, made some quick alterations spent some time I didn’t have messing with elastic bands and forks and built a couple of the V1.1 instead of V2.0.

At the time I was a little gutted to abandon V2.0 however much of the learning from it would be incredibly important for the beetle even if I didn’t know it yet.


(Finished CAD with fork setup)


(Weight check)


(PLA test chassis)


(Fully exploded view of final parts)

SCAR 4

SCAR 4 went very well with Revron winning 5 straight matches and proving to be an incredibly destructive bot. The new speed massively improved weapon bite which seemed to be the main contributing factor in the damage it was causing. It also “helped” Petrifeye win the most destroyed award separating the top and bottom half of the robot in pretty spectacular fashion in a great fight in the round of 8. The run ended after a pretty back and forth fight with Iceberg where their slightly longer weapon reach caught the side of my weapon motor and sent me out of the arena.

Unfortunately due to previous damage All Star had to forefit the playoff fight which gave Revron a third place finish. I also picked up a best engineered award which given all the time spent experimenting with the drive on this bot and working on its previous short comings I was really pleased with.


(Revron looking a bit battered after a good day of fights and earning some silverware)

In retrospect

While SCAR 4 had definitely been a success for the bot competition always shows areas for improvement and this event was no exception. In the box I couldn’t have asked for much more however in the pits was a different story. The bot is slow and fiddly to work on due to the sheer number of tiny parts, it also made keeping track of spares very difficult. A secondary problem was my use of directly threading into polycarbonate. After a few rounds of removing panels for battery changes the threads were starting to strip out and I realised the chassis was probably only going to be good for this event.

Sheffield roboteers events

This version of the robot also competed at a couple of the Sheffield roboteers events with mixed success. During the first event I accidentally swapped 2 motor phases during a weapon motor replacement and subsequently sent myself out of the arena multiple times before I realised the issue.

The second event I managed 7 straight wins before losing out in the final to an extremely well drive Paranoia to finish second.

For The next round of upgrades I set myself the following goals.

1-Reduce unique part count
2-Improve service life
3-Maintain performance

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