"Compressed Air" vs. "High Pressure Blower"

We are investigating the feasibility of a ball launcher using a cannon design. I want to avoid the complexity of compressed air and use a high pressure blower. Approximate blower specs:

  • 2.9 psig “dead head” pressure
  • 1.5 psig working pressure
  • 750 CFM (200 CFM if accumulator)
  • Velocity 35 ft/sec

I’d like to use an accumulator (reservoir) but if this will be considered compressed air, this will nix the design (Cv issues).

Any thoughts on this subject?

Thanks in advance!

I’m on my DROID so I can’t give you exact text but r73 I think is the number that states the only source of compressed air is the KOP compressor or its equivalent.

Compressed air on the Robot must be provided by one and only one compressor. Compressor specifications may not exceed nominal 12V, 1.05 cfm flow rate, 120 psi maximum working pressure. Off-board compressors must be controlled and powered by the Robot.

Blue Box

If an alternative compressor is used, the team may be required to provide documentation to show compliance with the performance specifications.

The only difference between an on- and off-board compressor is that the off-board compressor is physically removed from the Robot. The intent of this rule is to permit teams to take advantage of the weight savings associated with keeping the compressor off-board. However, using the compressor off-board of the Robot does NOT permit non-compliance with any other applicable rules.

The compressor may be mounted on the Robot, or it may be left off the Robot and used to pre-charge compressed air in the storage tanks prior to bringing the Robot onto the Court.

Standard “This is not an official reply” disclaimer applies here:

If I was being asked to inspect such a system, my first question would be “Does the pressure of the air in question at any time exceed atmospheric pressure?” If so, then it is considered “compressed” and all pneumatics / compressor rules apply.

Technically when a robot drives forward it compresses the air in front of it, thus (according to your definition) all drivetrains are illegal.

Fans and blowers, in the past, have been deemed legal and not part of the ‘pneumatics system’ as long as they were powered by a legal motor.

I would Q&A this question, and I would expect a blower system to be legal. Whether it’s effective or not is another question :wink:

During Lunacy, we explored the idea of using blowers to add down force and/or thrust vectoring. We abandoned the idea for feasibility issues.

Sure enough, someone at GSR added some big fans, and didn’t seem to have any problems with inspection. Can’t remember their number (Peterborough, I think), but it seemed to add to their maneuverability.

Compressed air has a far, far higher energy density than the blast of air from a blower, which is why FIRST hasn’t seemed to come out against it, so long as the motors are legal (as stated before) and the blades are properly guarded.

The difference is the accumulation of air. If you are constraining air in a high pressure environment, it’s a pneumatic system. The concern here is mostly one of safety - any constrained high-pressure (in this case, greater than normal air pressure) system carries with it the risk of sudden rupture… aka something similar to an explosion. Fans and blowers, on the other hand, simply push air from one point to another - they can create a current of air that might be higher pressure than the surrounding air in the venue, but it’s not constrained. The dissipation of that higher pressure stream can occur naturally, and there’s no worry of rupture or danger to others since its not constrained. Of course, the design of such a fan or blower would be scrutinized for safety in and of itself, the same as any moving mechanism on a robot.

That was us. 1729 :smiley:

I agree. Which is why I said I expect the Q&A to call blowers and such as non-pneumatic (With respect to the pneumatic rules) as long as it’s not ‘contained’.

Al Skierkiewicz (Lead Robot Inspector) answered the question of what qualifies for the compressed air rules in another thread:

This makes sense as any stored energy from CA is a potential danger and following a standard CA safety standard is needed.

DAN! Yes it was…sorry I forgot your number.

Saw your bot zip around with those blowers, seemed to work pretty well.

I inspected a large number of fan/blower robots during Lunacy, and I agree that the use of a fan or blower in those applications was not “pneumatics”. The air was free flowing in those applications.

The deciding point for me is when the air becomes contained somewhere in the system at an increased pressure, be it in an accumulator, shooter barrel, etc. Does the ball just fall into a free-flowing air stream, or is it constrained in a barrel with the blower building pressure behind it? There’s a difference between the two. Just too many questions at this point.

I love the idea, and would be very impressed to see it well implemented on a robot. I don’t think I could make a call on “legality” without actually seeing a specific implementation…

As long as FIRST doesn’t pretend that a ducted fan is a traction device,1 I’m happy. (In all seriousness, the distinction between accumulating pressure and blowing air seems to be a good, practical one.)

1 I’m not making that up. In 2009, a fan thrusting the robot downward was allegedly a traction device. That was ridiculous.

The concept is simple (implementation not). I can’t imagine that this would be considered constrained compressed air. The only constraint is the inertia of the ball when fan creates pressure to move air and ball.

  1. The ball is loaded into the barrel and rolls to stops
  2. Fan motor is energized to a variable voltage (volts determine exit velocity)
  3. After ball leaves cannon, fan motor is de-energized

My opinion is that such a system would not be Pneumatic. I base this opinion on the lack of separation between the “pressure area” and atmosphere. That is, if no ball was there, you;d just get some wind with a barely measurable pressure difference above ambient.

Of course, my opinion doesn’t count at competition.

I would strongly recommend you submit this, carefully worded please, to the official FIRST Q&A system for a ruling. That, you can take to competition.

I looked at power requirements for a blower @ 750 CFM and 40 inWC (~1.5 PSI) --> 20 HP ballpark. Yikes!

That would require something like sketch below. I think this is getting too complicated and error prone. I’m abandoning this idea…

That sounds prudent. The use of compressed air, blowers, or even vacuum often sounds like a good way to move game pieces around. The problem is that compressed air is expensive to make. And I mean expensive in time, energy, space, and weight. This problem is even more apparent if all your power comes from a modest 12 volt battery. Take a look at the compressors used to power pneumatic tools in even a small industrial shop sometimes. They need to be quite large and powerful to keep up with even a few small tools. Pneumatics (or blowers in this case) can be a good choice to do some things on a battery powered robot. Just be very aware of the limitations and only apply them when the “expense” works out.

Your approach of applying some simple estimation techniques to see if your concept is practical is a common and valuable technique in any engineering discipline. Too often people want to cling to an initial concept that does not hold up to this type of analysis and insist on wasting time with prototypes to prove to themselves it won’t work. The short build season in FIRST emulates the real world pressures engineering teams often face. The ability to brain storm and quickly come up with a bunch of good ideas for a robot seems like an important skill to succeed here. But equally if not more important is the ability to quickly sort through those ideas to find the few that are actually practical given all the other constraints of the competition.

I’m guilty… :slight_smile:

I couldn’t let go of the idea. I had to know how the leakage around the ball would affect the performance.

I rigged up an Extrol tank (hydronic expansion tank) to a short length of Sonotube (big toilet paper tube). The ball is fairly tight with less than 1/16 gap = (tube ID - ball OD)/2. I had my son hold down the rig and I jammed a baseball bat in from the back to get a good force on the diaphragm. The ball went about 10’; OK but not great. A SWAG of the leakage is about 1/2 the volume pushed by the diaphragm leaks by the ball.

There is also an affect I’ve observed from testing with a reversed shop vac:

  • I had the hose stuck into a bucket that fit on the OD of the Sonotube
  • Before I put stops at the bottom of the Sonotube, I tried the rig letting the ball fall into the bucket where gap was large
  • When I turned on the vac, the ball was held in the bucket = the rig sucked the ball back

Maybe there is some back pressure from the leaking air creating high pressure in front of ball (drag).

Extrol sketch --> http://www.arttec.net/Solar/12-24-10/Amtrol-Extrol_diaphragm_diagram.jpg

By using a rubber diaphram, you are basically creating your own compressor (without the bellows valve, and using the ball as a poppit valve).

As such you may run into issues with <R69> and proving <R73>

[R69] All pneumatic components must be COTS pneumatic devices rated by their manufacturers for working pressure of at least 125psi (with the exception of [R71]-D).

[R73] Compressed air on the Robot must be provided by one and only one compressor. Compressor specifications may not exceed nominal 12V, 1.05 cfm flow rate, 120 psi maximum working pressure. Off-board compressors must be controlled and powered by the Robot.

I’d suggest you Q&A this before you bring it to competition.

Tristan this is an interesting comment… why did you use the fan?

My guess is that it was used to increase the “apparent weight” of the robot which would increase the normal force on the wheels which would increase the friction of the wheels with the surface. Therefore this would increase traction…
hence a traction device.

That being said… .the battery and every other part on the robot are also traction devices by this definition …


Increasing the nominal downward force was, indeed, the reasoning of the rule. Fans / props were allowed that year as long as they did not increase the nominal downward force of the robot (I know, we used propellers horizontally for additional thrust).

As far as ‘every other part’ on the robot … all those needed to be within the 120LB max weight (plus battery and bumpers) and thus were already accounted for in the maximum traction attainable.