Bar Spinner structural advice?

[Flag Captured]

I'm very sorry about posting all these help threads, I'm almost there now with my design so there shouldn't be any more after this!

Basically, I'm building a horizontal bar spinner, much like how NST's and Last Rites' are - I've never built a spinner before, so I wondered if anyone has any advice or knowledge from past experience for what sort of materials would be best to hold the thing together?
The plan I had was to use a 4kg (ish) mild steel bar (not entirely sure of the size yet, but it'll be quite large I think, hopefully interchangeable so I can go for thicker teeth to tear panels off, or thinner blades for more localised damage) on a bike axle so that I can get the bearings/ratchet system and the gears on it all in one go and it's cheap which is good because I've practically maxed out my budget... Not sure what RPM it'll be going either, I think I've figured it out to be going about 6000 RPM with the gearing and motors I'll be using. Hopefully anyway, my calculations are always wrong...

For the bulkheads, I was thinking 3mm Box section as a frame, or something along those lines but I'm not entirely sure how that'll hold up when the bar hits something to be honest. I'm using this motor as well, on 6s if that helps! http://www.hobbyking.com/hobbyking/s...0KV_2665W.html

Thanks in advance for any help, hopefully I'll be better at all this once I've been in a few fights!

[maddox10]

Mild steel blade... In an arena with hardox and titanium armors. Will be a short thick chuncky one that will degrade rapidly.

Bike axle. The most sturdy ones I know of are M14 treaded rods with add on inner races for the 3 piece ballbearings. Rather long too. I fear that will sheer off. And 6000 rpm on the blade. I believe the bearings of a bikewheel ain't made for that kind of speeds.
Because if a26" bikewheel runs 6000 rpm... 750 km/h

[Flag Captured]

Hmm... I see your point. I want something made of tool steel ideally but that might be rather expensive, and I have access to Mild steel relatively cheaply so I thought I'd give that a go. Maybe not the best idea though, thinking about it...

What sort of bearings/axle would be needed for something like this, do you think, and would it be rather costly?

[daveimi]

Have a look through the NST build thread and pinch ideas...works for me

[maddox10]

Yesterday I picked up the 2 Creusabro 4800 disks I had lasercut. 1 for a feather, 1 for a raptor. Pricetag €180. Not cheap, but should be in the same "quality range" as the Christian Disks.

I plan to use a 20mm silversteel "dead" axle and 3 very well lubricated bronze bushings.

[typhoon_driver]

I would advise using a 20mm silver steel shaft and some bearings either end machined into bulkheads. Make the length of the shaft as short as it needs to be. I've discussed with Mario the merits of bushings, he is a fan, I'm not. I'm not going to comment further on that one.

Material wise, NST uses ali (around the 10mm mark if I remember right) however a steel construction or even a well designed thick nylon bulkhead could work well.

I would recommend against mild steel but if you are set on it then make the teeth from tool steel or similar, key them to the bar and bolt on. Easy enough to get a hold of a thick piece of Hardox which will do the job well, contact JL steel services who will be able to plasma cut your design for you (you will need to tidy it up with a grinder or mill).

[Max]

I made a rubbish bar which was from about 8mm mild steel, it worked but didn't do much damage but I think that was due to the motor. I hardened the tip using hardening mig welding which actually a seemed to work quite well, it didn't blunt too much in its one fight. It could work as a cheap solution but wouldn't be the best- you could always use something already made of tool steel like a lathe tool or centre punch.

[Mouldy]

a lathe tool or centre punch will crack instantly... too hard/brittle

I second what gary sais- bearings are what ive always used and ive never had a problem, there also much more suitable for high speeds. If you can get one 20mm bearing either side that would be ideal.

NST has bearings in two bearing holders that clamp to the bar, probably the best way of doing it as you get a lot of "meat" around the bearing. He also kept the shaft as short as possible for maximum strength.

[Liftoff]

I should think bronze bushes would work fine as well...if oiled would work even better. Most turbocharger bearings are bronze, that's a high speed application, and engine cranks are held in bushes as well, that's a high impact application.
Even the motors themselves are supported in bronze bearings - I'd say they're good for the job.

[teamshock]

Here's a pic of the bar setup I'll be using for next years champs. Yep it's the one from Buzzbar

[Mouldy]

Yes car turbos have bushes.... And you can buy upgraded ones with bearings in... I work with bearings and bushes every day at work and my personal preference is bearings in this application. I've built quite a few spinners with bearings now and been happy with the results.

[Liftoff]

Yes car turbos have bushes.... And you can buy upgraded ones with bearings in...

...you can if you wanted to...ceramic ones, less drag more speed...but what I'd be worried about is the impact loading on those bearings, every time you hit something with that spinner you transmit the impact to the bearings, and I have my doubts as to how long those type of bearings will last.

But then I dont have a spinner like you do, so if it worked fine for you it should be fine for the rest...all I wanted to say, having as well worked "with bearings and bushes every day at work" is that plain bushes should work just as fine without fear of breaking anything

[Mouldy]

As I said... Personal preference. Although for people that don't have access to a mill etc it's probably going to be easier to mount a flange mount type bearing to a robot built in a shed then it would be to bore a hole accurately enough to take a bush without it falling out/being to tight.

[Mouldy]

Irony.... After that conversation the bush has worn out in the turbo in my car

[typhoon_driver]

That's why I'm not a fan of em in robots. Lose your lubrication system and it's. Bearings will take a hell of a beating and be near falling to bits and still work