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**Ocracoke** · 1 November 2018, 09:36

Hey there, welcome to the forum!

Specs look OK to me, perhaps a bit of a query on the drive motors as to wherever they'll have enough oomph to move this but otherwise looks fine. I will have to note that it is generally not a good idea for a first time roboteer to build a FW spinner - if they go wrong, they go wrong quickly and, as you can imagine, the consequences of that going wrong can be very hazardous. Also, not all robotic events support spinners due to their specific arena safety features - you'd have to get confirmation that you could use this.

To answer some of the questions you have:

2. I've been looking at using a round belt for the weapon drive - does anyone have any experience with these?

Not directly but if under enough tension, that should be OK. The only problem I can see is that after a few hits, the belt is going to wear out very quickly methinks but does avoid the need for a dedicated clutch.

4. Does anyone think the ball transfer units at the front are a bad idea?

Not particularly. I've used them before in The Honey Badger to help with turning. The problem with them is that they do have a tendency to fail under hard use and then it locks up. If you needed to save a bit of weight, you could replace these with some Oilon plastic feet to save a bit of weight.

**Eidg** · 1 November 2018, 10:28

@DR.Crane Your drive Motors are too week.
I am using 800W Brushless Motors for my drive, the robot is also a spinner. Next time I will go for 1200W.
Your Motor has around 10W...
I would recommend you to use multi v ribbed belts, with the pj profil.

**Maxamuslead** · 1 November 2018, 15:24

"I am totally new to anything engineering-related" so let's build a dangerous spinner with 2kg bar spinning at 2500-3000 rpm.

please just make a nice simple wedge bot. making a robot which can move well and make it through 3 mins of madness is an achievement in itself.

For drive just grab two cheap cordless drills and using the gearbox and motor. the drive for most FW. plenty of power and cheap.

**Theo** · 1 November 2018, 20:12

Basically what he said. A spinner is a very bad choice for a beginner to combat robots, moreso someone with no engineering experience. I've been doing this for nearly 2 years now, and still haven't felt confident in my abilities to make a spinner.

Plus, cordless drill motors are a fantastic option - cheap, rugged and powerful enough

**Team Gremlin** · 2 November 2018, 09:56

I disagree that a spinner for your first build should be out of the question.. I'm a carpenter and my team mate is a mechanic, we had never built anything like this before and jumped straight into a heavy weight spinner that worked a treat in battle.. aslong as it's done safely when testing etc there shouldn't be a problem.. sometimes it just comes down to the person and if they're competent or not. As for the price Â£500 seems alot for just part of a frame?.. my heavyweight cost about 1500 or so all in. All this said I'm no expert so take the advise from whoever you feel confident with..

**firefly1** · 2 November 2018, 14:40

As long as the robot is planned well enough, since when building a spinner there is much less room for error, I feel a spinner as a first build is completely doable. You will defiantly learn a LOT if you go through with this and future builds may be very different but there is nothing wrong with challenging yourself on a first build. I would happily bodge bits on one of my featherweight builds but never if i was building a spinner. Also as everyone else has said those drive motors wont do, drill motors are the cheap option that everyone uses or if you want even more of a challenge try getting your head around a brushless drive train. Also remember to factor in how your locking bar would fit before you start building it.

**Maxamuslead** · 2 November 2018, 17:50

Originally posted by Team Gremlin View Post

I disagree that a spinner for your first build should be out of the question.

The strange thing about this sport is that the lower weight classes are arguably much more dangerous than the large ones due to how much power they still have at there size. Yes, people have built spinners with no past experience in combat robotics you are a great example of that (gratz on coming third) however I would never recommend it to anyone for their first bot. making something move well and make it through a match is great. Something about walking before running

**Team Helix** · 2 November 2018, 17:56

If you are confident and safe fine. But remember there is a good chance that you will be going home in a bin bag!! Test it for every eventually you can think of.

**Ocracoke** · 2 November 2018, 18:07

I can see where you are coming from. Because of the lower weight classes and the smaller overall size, I sometimes get the impression that folks don't take account how dangerous these things can be. Doesn't matter about the weight class, if it goes wrong, it goes wrong quickly and the amount of energy in one of these things... well you get the picture.

I've had catastrophic failures happen to me like this, even with a Antweight. It was still a case of me putting it in a sealed container rather than test in the open because like heck I was OK with having a ~5g bar flying at my eye if it got loose.

Spinners are dangerous and they are dangerous for a reason. There is really nowhere safe to run them apart from an appropriate arena and they have to be built properly, hence the recommendation to build something simpler in order to gain engineering experience first before taking the next leap.

**Eventorizon** · 3 November 2018, 12:47

Welcome to the sport!

Given this rather reminds me of my first build and parts choices I figured I'd weigh in here. I'm going to try and not go too in depth, but rather than simply telling you, I feel its better to explain why so you can apply the logic to other things in the future.

First of all, yes it is generally considered a bad idea to build a spinner as your first robot, however that doesn't mean you can't provided you take the necessary precautions during the build and testing phase. I did what many said not to and built a vertical disc spinner on my first attempt -

https://www.youtube.com/watch?v=FXey3Phs3eQ

- and like it has been said, it did go home in (not quite) a bin bag, (but close).

Overview NST.jpg

Testing was done in phases, were first the motors were tested, then the weapon on one motor, then on two, all of which had the robot G-Clamped to a work bench and I went out the room and use a mirror to watch the tests through the doorway. If you also check the system fail safes before attaching the weapon mechanism, you can stand right next to it in case something goes wrong without being in any danger.

Second, looking at the parts you've listed, you aren't far off. Main issue is your drive motors, they are to small, but the 800W brushless motors are not necessary either. While that is becoming the norm, Conker 1 you see in the video ran 4x RS550 motors at 4S/14.8v, on a pair of 30A ESC's, each with a 16:1 gearbox. Run the numbers (P = V x I) and at 30A continuous, each side was using ~430W; that 215W per motor. While Brushed and Brushless wattages are not directly comparable, It gives you an idea of the power needed.
Two geared 12V drill motors will happily move a FW robot, and used to be the norm. They are cheap, easy to obtain, and even come with a clutch if you need that facility. I'd suggest getting a pair of Â£30 drills, or if you have a little more money having a look at these - https://gimsonrobotics.co.uk/categor...tary-gearmotor - If you look after them they will last years, and if the motors burn out you can easily replace them or upgrade to brushless in the future.

Next, this applies to your weapon speed, but will also help you pick your drive belt ratio - https://www.technobotsonline.com/rob...alculator.html - This calculator is very useful for getting an idea of what speeds or ratios you are going to need; i use it all the time to double check my calcs for weapon and drive setups.
For the weapon, I'm going to assume you will have a 250mm Diameter bar, and will run it on 6S/22.2V. Kv time Voltage gives us ~6000rpm. On a 1:1 ratio the tip of the weapon will be doing 175mph which is a pretty solid speed. 1.5:1 Would give 117mph at the tip. For your first machine I'd say this is a better option as it should make it more reliable and you can change it in the future if needed. While the speed limit for weapons is 250mph, most robots don't actually get close. For example Binky II tops out at 175mph, my robot Conker 3 maxes at 200mph and even the crazy drum spinners doing 12'000rpm only reach ~200 due to their small diameter.
If we apply the same logic to your drive, I'd say to aim between 12mph and 15mph. If we go with those Gimson gearboxes at 13.7:1, 125mm wheels, and on 5S at 18.5V - We can look up the No Load after gearbox speed which is 1536rpm, put in the 125mm wheels, put in our wanted 15mph, and it says we need 1.5:1. Easily done with a belt. While you will loose some speed due to load and resistance, it should still drop you into that 12-15mph range quite nicely, and have quite a lot of torque.

Last note on this giant block of text. Some may disagree but I'd advise using Timing Belts on both your weapon and drive. At FW class, 5mm pitch belts are the norm, and most people tend to use HTD profile heavy duty belts. I'd say use a 9mm wide belt for your drive, and probably the same on your weapon as it will be protected by the frame of your robot and the reach of your weapon. We use 9mm on Binky's 3.6kg disc, and have only snapped a belt once; and that was due to the grub screws in the weapon pulley coming loose and eating the belt. You can use this calculator - https://www.technobotsonline.com/tim...alculator.html - to get your centre points, no tensioners required. Just look up the available belt lengths and tooth counts and you can pick the right belts and pulleys to get that 1.5:1 ratio on your weapon and drive.

I could easily keep going but I won't, that's a lot to digest, but hopefully this should give you resources and knowledge you can apply now and in the future. Happy building!

**Dr. Crane** · 3 November 2018, 17:27

Thank you everyone for the feedback!

In all honesty, I originally wanted to build an axe bot but the idea of working with high pressure CO2 frightened me more than a spinner!

The plan for testing the spinner was to clamp the bot, put it in a shed and film it with an old phone, does this seem okay?

Thanks very much for the feedback on the drive motors - pity I already bought two but hey ho. This will no doubt require a change to my bulkhead design as I plan on bolting them to the bulkheads and using square â€˜clampsâ€™ per my design.

The main reason I switched to a round belt is because I couldnâ€™t find an aluminium pulley supplier for timing belts that would customise the bore to order - as I mentioned I donâ€™t have access to a pillar drill to bore them myself. Is anyone aware of such a supplier? The motor shaft is 6mm and the weapon shaft is 20mm. I was looking at using bore reducers but again I couldnâ€™t find any with reasonable specs.

i totally take into account all of the comments regarding safety and I do understand the risks involved. Ideally I would like to create a more simple bot for my first go, however with the lack of available facilities to fabricate and machine parts myself I canâ€™t keep the cost down. Therefore I would rather make something vaguely competitive if I have to go all-in.

Thanks again!

**Maxamuslead** · 3 November 2018, 20:01

To build a axe bot at fw use a 350w scooter they are cheap and simple and fun as all hell to drive

**Theo** · 3 November 2018, 20:32

Axes are really fun, especially in featherweights.
But your plan for the shed is really smart; never test a robot in the same room you're in. We've had a few incidents here and there of people powering up heavyweight spinners up close without realising the dangers.

**R9000** · 4 November 2018, 17:41

For your pinion pulley, you can use BeltingOnline. They will modify the bore for you for a little extra cost, but be warned; this can make the order take a lot longer (even longer than they say on the website). Same applies for getting them to put a grubscrew in it. For your weapon pulley, you'll want to get one specially made, most likely. This is because it's usually best to have a smooth, flat pulley with no teeth. Not only does this mean your brushless weapon motor won't stall out as easily when starting the weapon, it protects everything downstream of the weapon from shock when you hit something. So yeah, having teeth on your weapon pulley (though a bit counter-intuitive) isn't usually the best thing. What's more, a custom pulley can have all the mounting holes for your weapon in it, and a bore sized specifically to fit whatever bearing or bushing you want to use. You could talk to your machinist about getting that made, but there are some people in the community who could make one for you too.

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