efficiency- motor vs. pnuematic

[BenB]

Hey,

I was wondering which would be more efficient, a motor or a pnuematic piston assuming each needs to do the same amount of work, say, lifting a single jointed arm. Is there more energy lost in the motor or the compressor to supply enough air to move the piston. I realize the draw backs of pnuematics, slow and limited (2) positions.

On the side, I understand we are not allowed to make "lightning holes" in the flag holder but how much are we allowed to modify it for mounting purposes. Also, does anyone have a better picture of the lap indicator? The one in the manual is only from above and Im not 100% sure about how it mounts.

Thanks

[Betty_Krocker]

Pneumatics doesnt have to be slow...
It all depends on the weight of things and how far you have to get them.
The good thing about pneumatics, is once you supply air, AN object is going to move. The reason I say AN object is going to move, is depending if it was all rigged up correctly, it should work. The downfall to pneumatics is when using cylinders to raise heavy or large objects, they require enormous amounts of air. Motors on the other hand are reliable, and you know are going to work when you supply power. Downfall to motors is that you can burn one out. As everybody knows, you dont want to release the magic smoke... (you can't burn out a cylinder!!!)

To make this short, it all depends and the wieghts and mounting places of both...
Also what system would the team use if you guys did in fact use a motor to raise the arm?

[m3ch4num470r]

In terms of efficiency for a single movement, motors are more efficient than pneumatics. This is because your compressor is driven by a motor which gives it all the inefficiencies of a motor drive. Add this to the fact that as air pressure increases, it becomes harder and harder to compress and you get a system that uses significantly more power (and weight) than a simple motor drive.

However, I am unaware of a team that has killed its battery in 2 minutes of competition. You should probably be looking at the other features of each. Motors have more than two positions, but that isn't necessarily a disadvantage. With a cylinder, you will be reliably able to hit the two posistions, while a motor may need additional controlling systems (like a potentiometer or wheel encoder). Also, pneumatics give you holding power while a motor may slide under load. After a cylinder is energized, you don't have to add any extra power to keep it in its position, while a motor may need constant pulsing to keep it even close to where you want it. Finally, you have to consider weight since adding a compressor and 4 air tanks is a lot of extra load. My team was considering not using pneumatics just because of the weight, but our designs made pneumatics a whole heck of a lot more convenient.

Bottom line is there's a lot more to consider than pure energy efficiency.

[Al Skierkiewicz]

Ben,
The lap indicator is attached to a rubber stopper that is mounted to the flag. You will be given the flag with the indicator attached and you will then insert same into your flag holder and connect to your provided PWM cable.

As for the holder see this...
<R17> ROBOTS must use one of the two FLAGS provided at the event
queuing location to display their ALLIANCE color (red or blue). The
FLAG shall be held in a flag holder mounted on the ROBOT. The
only acceptable flag holder is a 12 inch long piece of 1/2” (nominal)
Schedule 40 PVC tube. The tube must be a single, contiguous
piece, capped with a commercial PVC pipe cap cemented at the
bottom end. The tube must not have any “lightening holes” or other
modifications other than mounting holes, paint, or other decorative
surface finishes.

I read that as "mounting holes" are acceptable. R18 specifies that a 2" radius around the top of the flag holder must be maintained for the lap indicator.

As to the pneumatics vs. motor, this is a long standing debate and there is no good answer. All things being equal, if this was the only thing you needed air for, I would tend to go with a motor. If you need air for other parts of your design, then it would require some additional thought on your part as to what your actual requirements might be.

[MrForbes]

There are advantages and disadvantages to each. Motors allow precise position control. Pneumatics allow you to put the heavy motor and storage tanks down low on the robot, and use a lightweight cylinder where it is needed, which might help the weight balance. Usually it is much simpler to connect a cylinder (two bolts!) than to rig up a gear/sprocket reduction system for a motor, and you can store energy in the tanks for relatively quick release.

So, as usual, the right choice depends on way too many variables, and you need to evaluate each situation individually.

Notice that none of the considerations I mentioned have anything to do with efficiency! because that is usually not a very important factor in this type of robot design.

[GaryVoshol]

Originally Posted by Al Skierkiewicz

Ben,
The lap indicator is attached to a rubber stopper that is mounted to the flag. You will be given the flag with the indicator attached and you will then insert same into your flag holder and connect to your provided PWM cable.

As for the holder see this...
<R17> ROBOTS must use one of the two FLAGS provided at the event
queuing location to display their ALLIANCE color (red or blue). The
FLAG shall be held in a flag holder mounted on the ROBOT. The
only acceptable flag holder is a 12 inch long piece of 1/2” (nominal)
Schedule 40 PVC tube. The tube must be a single, contiguous
piece, capped with a commercial PVC pipe cap cemented at the
bottom end. The tube must not have any “lightening holes” or other
modifications other than mounting holes, paint, or other decorative
surface finishes.

I read that as "mounting holes" are acceptable. R18 specifies that a 2" radius around the top of the flag holder must be maintained for the lap indicator.

Please note that 1/2" nominal Schedule 40 PVC does not have a 1/2" dimension anywhere. http://forums.usfirst.org/showthread...hlight=nominal

Originally Posted by Q&A

Please refer Rule <R17> as amended in Team Update #4. The flag holder must be made of 1/2 inch (nominal) Schedule 40 PVC tube. This material has an outside diameter of 0.840 inches and an inside diameter of 0.622 inches