Using Air Motors

First off, Im new to pneumatics and I have found loads of information on rams but nothing on air motors. So anyone who knows a thing or two about them please help.

Ok, I want to build a vertical spinner using an air powered Cut Off Tool I found in the screwfix mag (vol 65 P247). The air motor spins at 20,000rpm at 90psi and has an average consumption of 4cfm.

How do you work out how bigger bottle of co2 I need for the length of a match, bearing in mind its continuous consumption? Would powering it off a bottle of compressed air work while its being topped up with an electric car tyre pump?

And lastly, How do you connect one up to a robot for a low pressure system, is it similar to how a ram would be connected?

Thanks
Martin

P.S. Anyone know where to get better air motors?

Hmmm, 90 psi = 6 bar. 4Cfm=36L/min
A carcompressor gives us at best 42L/m at 1.1 bar, and dropping fast if any power is aquired.
Let us say 7L min when providing 6 bar, and it will get hot fast, unless you replace the cheap motor with a way better one(and then you will ruin the compressorpart itself-I know this from experience, the bearings on the crankshaft die in 30 seconds)

For example, a small commercial hobby compressor can give 6 bar 30 l/min and thats with mains.

So, Youll need a better DC powered compressor.

Now the volume of air needed-or CO2- to power this motor during a 5 minute fight is , when everything goes well, 36L*5=180L on 6 bar
Giving us 1080 L gas atmosheric. Thats a 2 kg bottle of CO2.-1 kg of liquid CO2 gives us 512L of gas, on room temperature- and the bottle will chill-so you need more CO2 to compensate.

I believe the top up with 1 car compressor wont do you any good, except draining batterypower you desperate need for drive.Even running on max flow it will provide only 42*5= 210L, when more than a 1000 is needed.

Also, if I calculate it correctly, this airmotor has the power of 36*6/500=432 watts. And thats peak rpm.

Now, can you spare the weight of a 2 kg CO2 bottle in a feather? Average weight of those is 3 kg.The lightest available,and approved 2kg CO2 bottle Ive seen is 2.7 kg.The regulator you need will set yau back for 1 kg. For 4 Kg I can build a way more nasty spinner, with more power.


There is a reason airmotors are used in the industry, and that a lot less than electrical motors.They dont compare in power or ease to use.
Why do you think there are cordless drills, and no cordless airmotors?

And to answer your last question. It would be connected like a single acting cylinder.Or even simpler with a 2/2 valve.

Ok, thanks for that, you have some very good points there. I was planning to make a walker so I could use the extra weight for the weapon, but I see now that may not even work. Maybe for a middle weight though.

Short of using a gas turbine, air motors are the fastest motors I could find (unless anyone else has found anything faster). What motors are other people are using to power their discs and whats the rpms if you know it?

Disk motors in use on Feathers.

Drillmotors, giving up to 20K rpm unloaded

Astroflight-in Scorpion Jr RPM trough the roof

Mag S28 150 - in Vortex approx 6000 rpm

EV warriors rpm?

EV Warriors are 2200rpm on 12v and 4400rpm on 24v.

Mini EVs are around 12500rpm on 12v and if your pushing your luck, they will peak 25000rpm on 24v, with a bit of heat generation. Now for those who are indeed crazy, such as myself, bumping the voltage up to 36v, will result in the epoxy on the resin flying out of the motor smacking you in the face after leaving the armature at 37500rpm.

I could rattle on more information about motors and past experinces, but I could be here all night...

The problem with drill motors is that they produce almost no torque at their top speed, and they arent the most efficent of motors.

But what about a methanol RC motor? Some do about 40000RPM and peak at almost 2000W yet only weighs about 300 grams each.

Youd normally need some monster gearing to bring that down to a sensible speed, but for a spinning disc?

http://www.osengines.com/engines/osmg2071.htmlhttp://www.osengines.com/engines/osmg2071.html

Hwy not look at Burshless motors. Yes i will agree there expensive but where else can you get a motor on 9.6v that does 34560rpm no load? They also have very good torque. In the states the use these on 3:1 in drum bots and they easily flip the opposition.

Regards
Ian

VDD 3.3 uses a 24v EV Warrior with a vert flywheel and it launched Sunflower about 3m into the air and threw it clean out the arena from the centre!

I kid you not! Email me and Ill gladly send you the 900kb video of it! ice_demon000@hotmail.com

Im sure it was a 14.4v ThinGap weapon motor in VD3.3HF when it launched Sunflower.

Edit: Sorry thats there 12lb bot VD2.0 that has the ThingGap powered disk sorry.

Chris - http://www.featherweights.org/forum

vd3 uses two makita drill motors in its spinning weapon. pestering the rfl chat gave me an estimate of 7000rpm and 4kg on the disc..

vd2 (the 12lber one) uses a thingap.

I stand corrected then.

Do any of you know any suppliers in the UK for mini EVs or makita drill motors?

Just remember, speed isnt everything.

There are no UK supplier for either of them. You have to order from the states.

i have some motors out of a bunch of makita drills. the 9.6 v version uses 42(!?)mm dia motors.Although, the ones i have are older stuff, with the gears supported in the plastic outer shell.

Best spinner motors i reckon would have to be a Stihl 46.6cc chainsaw. Ive got one here but conning the ole man into giving it to me is like trying to run an Etek on a AAA battery.

But what about a methanol RC motor? The better ones might be a bit expensive nearing £200 or so, but there are motors for about £50 that weigh peak at about 400W or so.

Even the slowest of those motors are capable of reaching around 20000 RPM or so.

But the main advantage is that you dont need any battery for it, so a motor and fuel tank will weight about 300 gram (leaving more weight for the disc).

Ask your local hobby shop, see what they can dig out for you.

The only thing about using a two stroke RC motor is that they have a habit of stalling, at least in my RC car anyway. What sometimes happens is air gets in to the fuel pipe (as the fuel sloshes around in the tank) and the engine stops.

Unless an electric starter, glow starter and maybe a slip clutch is used the engine could stall on the disc€™s first hit and then your out of the comp because your weapon in immobilised.

But I do like the initial idea though, just need to iron out those bugs.

The main saftey issue with running methonal R/C engines is that methanol burns clear. This means to safely run you need to put dye in the fuel so itll burn with a colour that could be seen. I know from building model planes theres nothing worse then starting a plane which then catches fire, because you dont know if the flames are over the carberator port for fuels lines. The only problem with dyes is they eventually degrade the engine, but I think life expectancy is a little consideration is this hobby.

What kind of fuel tank do you use in your car? I dont know about cars, but fuel tanks in planes have a small length of pipe with a wieght at the end so they can run even when upside down.

You may already have one of these, but I thought Ill mention it anyway.

I also know that Kyosho and some other brands sell complete sets with an engine, starter motor and glow starter. Just plug in a battery pack and the engine starts itself.

Of course youd need an extra channel to be able to this be remote control.

The fuel tank in my car has baffles which are supposed to stop or limit the movement of the fuel in the tank; the small length of pipe in my fuel tank does not move even though it has a rather large metal filter at the end, there€™s just not enough room. I guess that it doesnt have to move as the car spends most of its time in the up right position and there is no need for it to operate upside down.

In fact when the car lands upside down (doing the mad jumps I do in it) the fuel leaks out the carburettor filter.

The fuel I use in my car has coloured dyes as standard, I use the illuminous yellow coloured fuel but for all you flamboyant ones out there a pink coloured fuel is out there too. The colours in the fuel also tell you the quantities of the oil to fuel ratio mixture you are using.

Depending on your application you can choose to use a throatier mixture (like yellow) or a more oiled cooler running mixture (like pink) as the engine gets its oil from the fuel.

I€™m sure you already knew all this but my point is RC car engines are designed to run on dyed fuels and shouldn€™t harm them if the correct fuel is used when the engine is run in on it.

The electric starter kits you saw; are they the nose prop starter kind or are they built in with the engine? I have not seen those, my engine is a pull starter.

Its basically a RS540 motor and gearbox built into the back of the motor, and a small glow starter on the top. Its designed for cars, so they should work fine.

Is there really any point in the highspeed motors and engines everybody is talking about?
They just need gearing down alot anyway, meaning loosing weight for gear systems. Why not just buy a hefty low speed motor such as the EV warrior, or car fan motors. They can be placed directly onto discs, with all the grunt to get them upto speed in no time(Tantrum was run off a car fan motor and pimp2 off an EV warrior)
Much more simple and realiable than engines!!!

Grant-PloughBot-Team Rc Wars

You dont have to gear them. Faster motor equals a smaller disc, meaning less weight.

it also means its one hell of a lot harder to get the disk to bite in, look at the trouble pimp 2 had at newark, the disk was moving so fast the big blunt teeth kept skimming off the opponents. fast disks are also harder to balance.

No, he kept skimming off the opponents, because they were armoured with 10mm Hardox :)

That thickness in a featherweight?

Jep :)

What grade then?

500 :)