force required to spin vaccuum fan

[Daniel_LaFleur]

Originally Posted by Bruceb

Anybody know a way to figure out the force needed to spin a vaccuum fan at a given speed?
Bruce

That depends on a LOT of things, such as prop angle, prop size, RPM needed, Drag coeffecient, Amount of airflow wanted/needed, etc, etc ...

How much vacuum are you looking to pull? and how much volume are you looking to evacuate?

[Bruceb]

I have a 120 volt 5.7 amp shop vac that seems to handle the soccer balls well. I want to use the JVN design calculator to figure gear ratios to drive it at the same speed using 1 CIM and 2 FP motors so I need to have some number to plug in the formula for force required to spin it.
Does that help?
Bruce

[skimoose]

Also, remember that the load on the motor will be greatest when moving air before your block air flow. As the vacuum is developed, the air resistance decreases and the lowest loads will be when the impeller system is rotating in a near complete vacuum.

[Greg Needel]

Originally Posted by skimoose

Also, remember that the load on the motor will be greatest when moving air before your block air flow. As the vacuum is developed, the air resistance decreases and the lowest loads will be when the impeller system is rotating in a near complete vacuum.

Also I would like to point out there are 2 underlying concepts that define each vacuum's performance. Flow (CFM) and Static Pressure ( in-H20). Each one of these things brings something different to the table to create a concept known as Air-Watts. A vacuum impeller/motor combo can be configured for many different applications and the cost of the vacuum is directly dependent on this factor. Most Sub $100 vacs are designed with Flow in mind, as the average consumer interprets high velocity of air as power. The real thing is the static pressure, which determines the "mussel" of the vac.

If you are planning on stripping the blower out of a Vac try to get one with a higher static pressure and lower CFM, That combination will allow you to hold on to the ball better with a lower power consumption than one that has both a high CFM and static pressure.

If teams are interested in just getting the impeller/motor instead of the entire vac, check out AMETEK http://www.ametekfsm.com/ as they are the industry leader and you will probably save money then getting a vac a home depot and tearing it down.

[martin417]

in 2008 we used 2 FP motors to drive a shop vac blower to good success.

Here is another picture.

We were driving it at 1:1 and had to vary the speed of the motors because we were generating too much suck. I mean we couldn't get the ball off the manipulator at full speed.

[Bruceb]

Martin, how did you adapt that belt sprocket to the FP motor shaft?
Bruce

[martin417]

Originally Posted by Bruceb

Martin, how did you adapt that belt sprocket to the FP motor shaft?
Bruce

It's just a timing sprocket from Stock Drive Products. It has a setscrew to hold it on the shaft. If I remember correctly, we may have had to enlarge the bore slightly due to the knurling on the FP shaft.

[martin417]

Another though on vacuums: some are single stage, and some have two or more. A single stage will have one rotating disk, while a two stage (like the one we used) will have two rotating disks separated by a stationary flow straightener. A single stage will flow more air at a given size and power, while a two stage will create a higher static pressure differential.

If you can get a two stage, you will probably be better off in this game because the ball area is relatively small.

[Bruceb]

What kind of devices have a 2 stage vac?
Bruce

[martin417]

Originally Posted by Bruceb

What kind of devices have a 2 stage vac?
Bruce

Ours came from a shop vac, but my old Rainbow at home has a 2 stage impeller also.

[Bruceb]

Martin, what belts did you use. Is the cheapest o.k.?
Bruce

[DonRotolo]

Originally Posted by Bruceb

Is the cheapest o.k.?

Cheapest is always just that: Cheapest. Over the years we have found that Best tends to work better and last longer. Build using the highest quality components you can afford.

Of course, for prototypes, cheap is usually fine.

[martin417]

Originally Posted by Bruceb

Martin, what belts did you use. Is the cheapest o.k.?
Bruce

Avoid "shade tree engineering"! Don't just guess and try it, the build season is too short!

Belt manufacturers publish data on capacity of belts, advantages of construction and materials, etc. The data is often in the form of a graph, plotting belt capacity (in horsepower) against the speed (in RPM) of the fastest pulley. do not exceed the spec.

You should also look at the max torque. You will probably have to ramp up up the speed of the motor to avoid slipping the belt or the pulley.