Help with disc

I am looking into building a drill motor powered disc within the build of my next robot. (exactly the same as the last Robot from me at the FWS 2004, only fully CNCd out of 10mm ali... The CNCd chassis will be lighter, and will solve many of the problems involved with the last Steel chassis).
I would be looking into using a 1:1 off the drill motor using a VERY small (about 6.5cm dia)steel disc that would be mounted on the scoop (middle of scoop at front). Could anyone (e.g Ed, Geoff etc) help me with a way to mount the disc onto such a fine (about 4/5mm steel axled) motor... I now have a CNC sponsor who can supply me with ali & steel stock (of MANY sizes) Its just I really need a way of modding this motor or something...

Any help gladly recieved,
Cheers, Ewan

Ewan - id personaly advise you to maybe mount the disc onto a weapon axel and use some sort of belt to the disc. The drill gear boxes wont take too much of a pounding like that, you whizzing around at high speed with the disc spinning, then bash.

Mr Stu

are u just using the motor or gearbox as well? either way i suggest that you have an axle supported both sides with the disc on, and like stu says, either a belt or chain to the motor.

(I am planning to run it 1:1 directly off the motor) The problem with chains etc is that A good mount onto the motor with a pulley/sproket would be difficult... Either way, I was planning on suppostion the other end of the axle with 10mm ali anyway, no matter what set-up I conclude on...

It may work, but you wont be able to use that tiny axle thats already on the motor.

First of all, I would suggest that you took a thicker axle and supported it on both sides with some bearings. Then you can just ask your sponsor to make you some adaptors that will join the two axles together!

It will still be direct drive, but the motor axle wont take any damaged from the impacts.

Secondly, I would also suggest that you mount the disc on the back. As it will take some time for the disc to reach full speed, it will be a lot more protected if mounted on the back.

Youll also be able to use the wedge while your waiting for the the disc to actually reach full speed.

Thirdly, I would suggest that instead of overvolting a single motor, you use two motors at their rated voltage.

Stop right there Ewan!...Put down that disc and motor and step away!!
If, after all I have said to you in the past, I catch you hanging a disc on a drill motor shaft, without using any extra suport bearings and a substantialy thicker shaft, I will personaly kick your back-side around the pits...If you think Im joking ...try it!! :proud:

Seriously for a moment, Christian has it about right! I couldnt put it much better my self. Think about a shaft dia. of no less than 12mm. We use 20mm on Scorpion Jr and even that is a little thinner than I would like, but testing has proved it to be safe.

Geoff.

I believe FRA guidelins are 10% of the disc diameter but that doesnt really hold when things get too small, on any featherweight disc the smallest axle I would use is 10mm, and that would be a decent axle steel not aluminium.

Joe Townsend

ewan i wouldnt ever dream of mounting a disc directly onto an axle. You should have a seperate axle for the disc and connect the two using belts etc. If you dont have the weight allowance for this then you should ask yourself if u really can afford to put on a disc as it is better to have a really well thought out disc than one that will break as soon as it spins or is hit.

I may not know about pneumatics, hydrolics etc but if theres one thing i know about, it is discs.

as well as disks, Gary is also an expert in spinning lampshade design robots :P

Seriously though Ewan, listen to these people. Ive only built one spinner - Vortex, but it didnt seem to do too badly, so Ill assume I can speak with a little authority here.

You need to think about an axle at least 15mm in diameter. You need to support it at both ends really in bearings. Were just trying to stop you from seriously injuring yourself mate !

Ed
http://www.teamstorm.comhttp://www.teamstorm.com

I am trying to make this one safe Geoff :)
I need to look at space within the robot (thus why Im not using a bigger motor) This is why I am using a drill motor. A drill motors high RPM is am advantage when it comes to discs, but Ill have to get the spinning mass perfectly balanced. I have decided on a 14mm steel axle, mounted on 10mm aliminium blocks on both sides. 14mm bearings are to be mounted within each block. The disc is to be an 8mm thick steel disc, about 6.5cm diameter, still allowong the robot to be invertable. Im having the centre of the disc milled out to 4mm, aiding the kinetic energy within the disc. I have decided to mount the drill motor (not overvolted) in the blocks Dominic is using in his UK robotics drill mod kit.
I am using a small belt to the weapon axle (from the drill motor) that will have a total reduction of 1:1.5

This setup will all be within the 8cm height of the robot. This is going to be a disc mounted under the wedge (youll know what I mean if your saw my bot at the FWS) designed to nibble at the undersides of an opponent as he goes up the scoop...

Any more suggestions gladly recieved :)

Youll have trouble mounting the motor in Doms mod kit without the gearbox attached - after all thats what stops the motor rotating with the torque.

-- Kev

Im going to fit a small polycarb flange to the front mount, thus stopping the motor from moving... (anyone know when the new technobots store is coming?)

In terms of disc mountings, that dosnt sound too bad. the only thing that comes to mind is disc 65mm dia. by 8mm thick in steel weighs only 208g and has a moment of inertia of 0.003876 ft/lb/s^2 before machining. So even if you are going to spin that at 10,000 RPM you are only going to deliver a little over 89j of kinetic energy into your opponent..I seems a hell of a lot of work for very little energy!
Something to think about!

Geoff

Maybe 20mm steel sounds better...

What, you mean a 20mm thick disc? or a 20mm dia. shaft?

Disc (do you have MSN?)

Im not sure if Dominics drill mounts are suitable if youre only going to attach a single motor.

If Im not mistaken, there should be three small screws in the front of the drill motor.

My suggestion is that you use those screws to attach the motor to the 10 mm aluminum blocks (picture in my profile).

As the pully will be very small, the belt will probably slip every time you activate the disc. A chain would work much better!

In order to get a little more energy out of the disc, I would suggest that you actually exchange the disc for a drum. As you will then be able to increase the weight of the whole thing, and still keep the robot invertable/invertible.

If youre only going to use a single motor, then Id suggest that you overvolt it.

Or Ewan why not just use a gold motor or silver motor.

I think A Sliver motor would be almost perfect. Give a bit more power than just a drill motor

Regards
Ian

Im using a timing belt so slippage shouldnt be a problem. And Ill look into the aluminium mounts as being part of the motor mount also (thanks for the pic)... Im overvolting a 9.6v motor on 14.4v...

Ive been now thinking of using two 14mm steel discs bolted together, this would be an effective 28mm spinning steel mass. again 65mm diameter... And also milled out in the centre...

Ill release pics of the build soon... (on http://www.micro-maul.co.ukwww.micro-maul.co.uk) Oh and Geoff, When will your website be up?...

A silvers RPM is not anything close to a drill motors. A drill WILL gat a small disc, like the one I plan, Up to speed farely quickly...

Ewan,
Even if you make the disc 20mm wide then you only increse the KE to 180j (still not a lot!!)
If you have access to cnc facilities why not have them cut you, as Christian sugested, a rim biased drum
if you could get say 70 - 80% of the mass at the rim and a width of say 75mm your KE rises to around 0.61Kj @10000 RPM BUT you are looking at around 1.9Kg in weight!! The fundermental problem here is that your dia. of 65mm is too small to allow a reasonable rim speed and therefore an acceptable KE, unless you are going to run it at silly RPM!! +/- 17500!!
If you want my advice, I think you need to have a serious think if this really how you want to go on this bot.

Sorry I dont have an MSN id. I use Yahoo IM

This is just an add-on weapon, just something active to keep the robot exciting as it will be mounted up the wedge, the disc will have very mini teeth, just the nibble the opponents underbelly. I am not looking at anything OTT, and the weight I have remaining in the bot after the fully CNCd chassis is quite small...

Fair enough Ewan, just keep it SAFE!!

Actually, most drill motors does something about 20000 RPM at their rated voltage. So with a bit of overvolting, that speed is reachable!

Has anyone thought off using friction drive for disc weapons? I have used friction drive in 2 feather weight disc weapons. The first was in Hellbringers saw using a RS-540 (next size smaller then a drill motor) with a foam wheel giving a 2:1 ratio. It was only good at hitting coke bottles (6m up in the air) but the friction drive did make a good clutch.
My next robot, The Aggressor, used a RS-775 (next size up from a drill) with a 6:1 ratio onto a 12 inch bicycle wheel. The bike wheel made an awsome fly wheel and at the last event I bent the 5mm steel teeth 30 degrees back rather then the wheel deforming. It also hit our opponent 15cm into the air in the process too.
Anyway the motors are of the high speed kind and even with the light weight saw fixed between bearings and 2:1 ratio it wouldnt have hit 4000 rpm. Thats all I wanted to say.

Daniel, a friction drive usually contains a lot of resistance. When youre dealing with drill motors, thats exactly what you dont want.

Ewan, if you want this weapon to actually do some damage, then a drum is your only option.

Just buy a 65 mm steel tube of suitable lenght and thickness, then persuade your sponsor to weld a small disc to each side. Cheap, easy and very effective!

Seeing as an output of 20,000rpm is quite possible with this type of motor (when overvolted slightly), I have recalculated, using the http://www.teamcosmos.comwww.teamcosmos.com kinetic calculator, that even a tiny disc like this has 1705j of energy stored within it (this is when you take the energy with centre milled out to a smaller thickness...

As long as most of the weight is on the outer rim, then it should work fine.

But I still think you should mount the disc on the back. As your scoop still will be your main weapon, the disc will stall then every time you push your opponent.

So it will never actually reach the kind of speed youre hoping for, unless you mount the disc on the back!

Im not complaining on your design, these are just suggestions. If you manage to get that kind of energy, then it would be sad if you didnt use it properly!

What I was trying to point out is a motor will never hit its quoted top speed once there is a load on the motor. Even with the weight of the shaft of the motor itself will put a load on it and slow it down. We had a problem in Australia (and still do) with builders quoting blades and discs spinning at 12000 - 15000 rpm and blade tips speeds over 1000 km/h from simple drill motors. Im just trying to say be reasonable with your calculations.
And the bit about the friction drive was something Ive never heard any pommys talk about. I know I dont have problems with friction because with the motor is stationary the foam rubber wheel is 1mm away from the bike wheel and with the speed of the motor itll expand to meet it.

About 63% of the qouted top speed is reasonable.

Guys,
We are starting to talk about some very silly RPM here, just be careful if you are thinking about using speeds like this, are any bearings being used going to be up to the job?
Also remember that any teeth on said disc need to be seriously well attached as at those speeds the forces trying to tear them off the rim are colossal!
I wouldnt want to be anywhere near one of these discs if it spat off a tooth, I know, I have seen a tooth part company from a disc at a mere 5000 rpm and that was quite scary enough thank you!

I am making the disc + teeth CNCd out of a solid lump of steel (therefore teeth are part of the disc)... Im going to get some CADS done of this today...

Who has been borrowing a few ideas from Vortex?

mmm... not me :) (my new CNC sponsors are called oldlandcnc) they are going to be making the complete chassis of the next robot (from team Mini-Maul, see http://www.micro-maul.co.ukwww.micro-maul.co.uk, soon to get an update) and believe me, (I just did a tour around their warehouse) they are one BIG company. They will be doing all parts CNCd (YAY Im as good as Ed now :)) out of aluminium and titanium...

Im trying to be as professional as possible with the next robot, using the best components I can get for it... It should be good :)

That brings up a question Ive been meaning to ask before. Its all very well making the teeth part of the flywheel, but arent they the most likely bit to get damaged? If so, isnt there an issue that if you lose a tooth you need a completely new wheel that way?

Also Id have thought theyd be easier to sharpen if theyre separate, and you can keep several sharp sets handy for switching between matches.

Not that I ever intend to build a spinner (Im too much of a pacifist, and scared), but Id like to know whether Im inventing issues which just arent there.

--
Fluppet

This is fantastic news ewan, but remeber theyll make a really badly designed robot to withing +/- 0.001mm if you ask them to, but it doesnt change the fact that its badly designed. What I am saying is, BE SURE you think the design is as good as its possibly going to get before one of their end mills gets within a meter of any metal. To slightly mangle an old proverb: design twice, cut once.

Be sure... Im being careful... :)

The only problem I can see with a one piece cncd job is at that sort of speed any tooth damage will cause MAJOR balance problems..you may be better with replacable teeth, but see my last post.

A little bit OT, but the friction drive on Daniel Kerrisons The Aggressor works pretty well. It spins the flywheel up fairly quick with the 300psi Compressor motor and weve seen it damage a few bots, including our own. Just resently it bent 5mm thick tangent teeth on impact with a robot, and we were surprised it was going to even get the much power. I cant wait to see it with the 24v EV Warrior

is the point not that a solid cnc one piece disc/teeth is not as likely to throw a tooth?