With the new beater design, I would be a bit worried about the screw heads getting hit; they would be OK when the beater is going at full speed but if it is slowed down, you might get enough bite depth to have the screw heads hit something and shear off. There are also all those tapped holes and you saw what happened to the beater on Mr Mangle - it sheared right thru the middle of a threaded hole.

If the body of the eggbeater is a softer steel then the stresses from the tapped holes may not matter so much. Here is an out-there suggestion: how about not tapping the body of the beater at all and adding a recessed nut on the trailing face of the beater? That greatly reduces the stress by removing the threads and if a screw head does get sheared off, you don't have to drill out the screw.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

The material we are using is H13, hardened to 40-45 Rockwell C.

http://www.matweb.com/search/datasheet_print.aspx?matguid=e30d1d1038164808a85cf7ba6aa87ef7

I do like your idea of adding a bolt on the other side, that would solve a lot of problems and potential problems. I don't think I would recess it though, just use a Nyloc on the back.

However the whole point of using H13 is that we shouldn't need teeth or replaceable tips... I am just worried it won't work how I want and I will be wasting money.

I'd be worried as you are using that bolt dowel of glens in a weird way, any forces acting on it will be potentially opening up the bolt hole, separating it. I'd be worried about the bolt just falling out.
In glens original one the bolt only saw sheer loads, there was no tension on the joint.
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Mechanical engineers build weapons, civil engineers build targets

That would be a problem in out-of-plane impacts. I am assuming this is for a vertical spinner of some sort, so an impact with a horizontal spinner like NST will exert a huge amount of sideways force on the dovetail section, opening it up on the side of the impact.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Things were very slow at work today, so the chance was taken to give decimator a more thorough post mortem.

Aside from the very busted blade itself the rest of the hub assembly is fine. The bearings, shaft, hub itself and pulley still fit together great. The axle even fits in the frame perfectly. Very happy with that as i was worried the holes for the axle might get mashed out into an oval.

The weapon motor is a very sick puppy though. seems that they don't like being torn from their mountings That stator tube is completely warped in every direction. Ouch!





The bearings, shaft and rotor itself are all fine though. So that's pleasing. Was very much expecting the threads to rip out but didn't have the time to sort it out pre event in the big rush. Would be a tricky job anyway because the mounting holes bisect the tube the stator sits on. It's a very odd design..

Also pulled the drives apart. Both gearboxes are fine (woohoo) but as i posted about before one motor dropped a magnet.

Not sure what to do next. The power and speed was great and the motors are cheap. But glueing them might be very tricky considering they aren't easy to pull apart.

Brushless is a definite option, but even using the slowest hobbyking sensored motors it will be too fast on the current 16:1 gearboxes. Lots of sensorless options about however. Could be worth making my own Hall effect board to sit inside a suitable outrunner... Otherwise will have to buy the higher ratio gearboxes and put the high kv sensored inrunners on those.

And for the weapon, the motor is an easy fix. Re-machining a much more substantial stator tube. Machining a single piece mount that just bolts direct to the robots chassis would be awesome, but don't think i could be buggered going to that much effort lol!

Still doing some FEA of my own on a new blade. But it's looking like a single tooth style bar waterjetted out of a prehardened block of 1 inch S7 tool steel will be cheap and tough. I'll get one cut out of mild steel for some testing. Sure it may have less energy, but given the rpm and weight its swinging, trading a bit of inertia for durability is a good deal imho.

Whether i fix the motor existing and belt drive is another thing to consider. REALLY keen to build a motor into the blade hub and dispense with the belt drive all together, but the stator is going to have to be a perfect size to make it all work. If anyone finds an old photocopier or something that has a stator with a bore larger than 20mm, hook me up!

Overall the damage total is -

- one busted drive motor (magnet fell out then blew up)
- bent blade
- the threaded brace in the middle ripped its threads out on both sides oddly enough.
- weapon motors stator tube is trashed in every way possible
- two busted fusion welds along the top from where the blades smacked into the front two panels.

Not too bad overall. Excited to get it improved for next time anyway.
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

Re. hubmotor in the weapon, in one of many Hobbyking binges I recently spotted this:

http://www.hobbyking.com/hobbyking/store/__56935__Turnigy_9014_105kv_Brushless_Multi_Rotor_Motor_BLDC_.html

and this:

http://www.hobbyking.com/hobbyking/store/__54888__9235_100KV_Turnigy_Multistar_Brushless_Multi_Rotor_Motor.html

Both of which scream "put me in a weapon". So much potential that I nearly didn't want to say . If I had the cash I would buy and take apart (for the good of science) but alas I don't. Might be worth a look?

Was looking at those earlier, they do look particularly useful for hubmotor work, but probably have too many poles to get the rpm i need for a weapon. Gotta sit down and work out if they could be rewound for 4x the kv

Harvesting stators off something else is probably cheaper anyways. Eyeing off motorbike stators at the moment. They look just about perfect.


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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

How about a 300W scooter motor? They have a small bore and then four small arms bridging what looks like a 40mm gap. The windings look easy to remove and then you could probably cut out the centre of the bore with a hole saw and bore it smooth in the lathe. The rotor is much thicker than that that one from your bike so you can make a higher powered motor from it.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

Are your drive motors 775's ? If so Jaycar has a few varieties.
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-Pickasso- Vivid Sportsman champion 2015

Yeah they are, i have a few now but need to work out how to stop them falling apart

Had a quick look at the 300w scooter and a gsxr400 stator this morn - the bike stator has really thick laminations, so probably not so great as a motor. The 300w waists down to 8mm in the center too so that would probably be a big pain in the butt to core out. Otherwise the size is right.

I'll see what can be dug up, looks like there's a few copiers sitting on the kerb down the street
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz

Here is the rotor from a scooter motor:



80mm OD, 40mm ID, 30mm thick, 16 poles. The inner part of the core would be easy to cut out with a hole saw.

Edit: DOH! Just saw your post, If you don't find a better donor motor, I think I could core the scooter motor without too much trouble.
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Australian 2015 Featherweight champion
UK 2016 Gladiator champion

can you lazor steel of any thickness?
you can make your own laminations if so
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Mechanical engineers build weapons, civil engineers build targets

Hey Glen, you're signing up. I've made your decision for you. Thank me later. Due date is the 15th!

http://robochallenge.co.uk/wc15.html

Yep, you are coming I Look forward to meeting you.

Hngg! Considering it Need to look into some logistics as I'd loooove to go to the Isle of man TT as well, but its a bit over a month later. Gah!
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www.demon50s.com - Minimoto parts
http://www.youtube.com/user/HyzerGlen - Videoooozzz