"Steel-Roller" - Dom builds a spinner


So I’m bored of try-harding Decalodon V2 for now. Since Labman FightFest in July I’ve been looking to cook up something for BBB Feb, but I’ve found myself stuck in the loop of:

Sketch out robot ideas
Pick an idea and start to make it competitive
Spend ages in CAD
Get bored of looking at the same design for weeks
Come up with some other robot idea
Start all over again

This rut is sorta bumming me out, so I need an antidote - which I’m hoping is just to stop caring, see what leftover parts I’ve got, figure out what manufacturing processes are available to me, and build a big weird robot with a big dumb weapon and a big dumb drive system. Hopefully it will mangle some other bots. Even better if it gets obliterated in the process.

I don’t really know much about building spinners but they look fun - good bit of mayhem. There’s lots of sciency stuff about spin up times, calculating KE and tooth profiles for optimal bite etc etc. Apart from the max tip speed requirement I don’t want to get involved in any of that as I’ve not got a whole lot of time - Want to just get building and I reckon if I’ve got a big bit of steel spinning fast it’ll do cool stuff when it hits the other bots.

This’ll be rough and ready (that includes any sketches and CAD), with a build diary to accompany it so I stay on track.

Ok, I gotta go to the store - I’ve got a pretty good idea of what I’m gonna build and I’ll upload a cad or something in a few days! Oh yeah and the robot is called Steel-Roller. Like a steam roller! But it rolls over steel!


Okay I’m back! CAD is not finished but solidworks is having a meltdown and I need a break.


The stats:

  • 2x 2s lipo batteries in parallel for 4s equivalent (Pinched from Decalodon)
  • Some big boi 3 inch foam wheels from a previous failed project
  • 2WD BBB Brushed 22mms cos I have loads
  • Some old Bot Bitz escs 10a
  • Two non-driven aluminium front rollers to support the weight of the bot. The arms onto which they are mounted can also rotate like suspensions because why not.
  • Outer bulkheads are 8mm hdpe.
  • Where possible I’m using stainless steel as I can get that done easily on the laser at work. Weapon is 6mm stainless, weapon bulkhead 3mm, armour 1.2mm
  • Bolted together with some mishmash of barrel nuts, nutstrip, and the Gareth ali standoff technique which impressed me a bunch in “gear down for dom”
  • Dimensions are rougly 250mm wide, 150mm long, 100mm tall (without the weapon) So it should be a big boi.

Where things are starting to get funky is weapon stats - I spent a while trying to figure this out on my own and I’m just going round in circles here. Could do with advice:

So I gather 2836 outrunner brushless is all the range but tracking any down at a high KV is a nightmare these days. I’m a fan of Overlander stuff as their products just work and spooted this:

Which is larger in size and I guess would do the job - but then it sounds like I’d need some sort of monster esc to cope with the max 55A. (They’ve all got this OPTO guff that makes thing more complicated - For real where did all the brushless motors and escs go???) The vortex boys (great build diary btw) used a hobbywing ebay thing but there’s not much in the way of stats on it and I don’t fancy cooking some escs to find out what’s going on there.

So I guess what i want to know is, what’s the deal with using a lower KV and just reducing the pulley ratio? I’ve heard it’s not recommended and the power output will be less - but will that actually affect the spin spin in a real world scenario? Really bad spin up time? Dog slow expected tip speed? Cook the motor?

Part of me is just tempted to run something like this, even with a lower KV
on a BBB Brushless esc (cos I have those kicking about as well) and seeing what happens? https://www.overlander.co.uk/rc-motors/outrunners/2836-08-1120kv-tornado-thumper-v3-brushless-outrunner-rc-motor.html

Add to this that the ever-popular fingertech beater bar set seems to use an inrunner - what’s the deal with that when everything else goes the outrunner route?

Any help would be very much appreciated! Again all I really want is a setup that isn’t really expensive and won’t just fry itself straight away.

Thank youuu :blush:

(I just realised I wrote spooted instead of spotted but I’m leaving that in there cos that’s funny as heck yo)


Very unique design for a vert. Can’t say I’m fully seeing what the benefit of the rollers would be over forks or a skid plate etc but its nice to see something that isn’t forks.

What I would say is 6mm stainless is really not going to be enough to survive at beetle levels. That will bend and warp with ease. If you are dead set on using stainless I’d say a minimum of 10mm and still treat it as a consumable. Don’t expect to get more than a fight or two without having to regrind impacting surfaces.

For what it is worth there isn’t really anything wrong with low kv low reduction. Just make sure you’re not massively underpowering your motor. If something is say sub 500kv then chances are its for 6-12s voltage ranges so it’s going to be a bit of a wet fish on 3s for example.

Check out the Surpass range of motors, heck just scroll through the first page of aliexpress search results to be inundated with 28mm motors and budget ESCs.

Fingertech likely works with an inrunner because it’s a lot easier to mount as you can clamp it, face mount it etc and not have to worry about wire eating which is good when you’re selling it as a product. You don’t want to give people rope to hang themselves with.


Thanks Harry :slightly_smiling_face:

There’s not really much of an advantage for the rollers other than I thought it would be fun and I have too much 25mm ali tubing lying around. :stuck_out_tongue_winking_eye:

Yeah I’m kind of expecting the stainless to get chewed up and I only really want 1 event out of this build. Didn’t realise 6mm would be so likely to get mangled tho - 10mm will defo put me over the weight limit. Hardox would be ideal but I’m not sure if I can get that cut in time, and pestering a waterjet place to quote me on small beetleweight parts often ends up in just being ghosted.

Thanks for the advice regarding the motor setup - that’s a big help. I am always a bit wary of aliexpress escs just lying about specification, and even just bad quality control on stuff like motors. But I’ll have think.


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How big is the weapon? I’ve got some old Bonbonbonbon spinners that I’d be happy to send your way if you’re in need of something quick, can supply STEPs if you think about 120mm diameter is what you’re looking for?


Thanks for the offer strang! The weapon is 150mm diam - so I would need to change somethings but it could work. I’ll see if I get into the feb brawl and have a go at contacting Emsea or similar first - I keep forgetting it’s a lottery selection process! But I’ll get back to you on that :slight_smile:

Honestly I’d take that in a heartbeat. Nothing is committed to metal (or plastic) yet so I’d tweak the chassis to accommodate. You’ll have a much better time and can spin it that little bit faster before you hit tip speed limits!


Also have some TCD weapons I’d happily give ya Dom if you want a bit bigger? - 165mm effective diameter/6mm raex 500.

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Thanks for the offer but Henry’s gonna help out with a spinner :slightly_smiling_face:

Yeah thought that was the case, but thought I’d offer the option anyway. Look forward to seeing it develop :grin:

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I love the look of this thing, proper old school vert vibes, like Nightmare or something!

I’d love to see Decalodon return, but first priority is always to make the bot that makes you happy

Hi Dominic,
Let me know if you want me to ask around a few people I know for water jet cutting.
Also, if you need anything in Aluminium CNC machined, let me know I can do that, PM me if thats possible on this forum.
Cheers, John.

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Thanks again everyone for the kind offers for help - I have settled on a more-or-less finalised design which will use pretty much entirely lasercut and 3d printed parts to reduce the build time. Strang is sending my way a really nasty weapon bar which I’m excited about. I think the only bits to be made “traditionally” will be the outer side hdpe bulkheads which I’ll do with a jigsaw, and the ali rollers themselves:

The Robot is right on the weight limit (Solidworks, which is almost always wrong, is estimating about 1300g which does not include wires and bolts.) I’ve fought tooth and nail with the weight limit to try and get a servo powered self-righter in there, but if it ends up overweight I can remove that.

Components are as they were before. Going for the overlander 2836/08 1120KV with BBB Brushless drive esc combo for weapon. 4s lipo on these big wheels and weird weight distribution will hopefully result in some pretty hyperactive driving.

Ordering parts this eve and I’m going to start actually building stuff during lunchbreak tomorrow. POM is only 3 weeks away so it’s going to be close - just have to forget all my inhibitions and not be too precious about things for once!


With very little time left I opted to skip competing at BBB Feb and put some more time into this build. Have been out of the loop for a few months but now getting back to it, and I had enough bits and bobs done to put together this prototype - Armour is mostly cheap leftover PLA and lasercut stainless. Looks OK.

Have run through a few further CAD iterations to deal with some problems in the prototype. Although the new model looks similar, most parts have been changed, so I’m pretty much starting over again with regards to this build. Had the time to put some actual effort into the Srimech design now, which I think is a much sleeker solution and creates more space internally for wiring.

We’re right on the limit with regards to weight again (Solidworks estimates about 1380g without wires and bolts. Surprisingly it was accurate with weight calcs last time). An easy fix will be to switch the ali rollers out for plastic ones if it goes over 1.5, although that would be a bit of a bummer. So we’ll see how it weighs in at the end.