Using Air Motors

[mpinner]

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...

[knightrous]

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

[robotic_ants]

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

[glen]

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.