Need to increase efficiency during flywheel ramp-up

[RichLeimbach]

I'm currently using a small (35mm can) motor to ramp a 2" dia x .5" wide flywheel from 0 to 15K RPM in ~ .5s. Because of the inefficiency of the motor at the low-end range, I am exploring both mechanical and electrical improvements to the current design. I belive that you can link to the motor discussion here:

http://www.eng-tips.com/gviewthread.cfm/lev2/11/lev3/47/pid/237/qid/35300

I'm making this thread to see if anyone out there has a mechanical solution to the problem. What I'd like is a compact continuously varibale transmission design or a auto-shifting gear set-up. The main point is to increase efficiency in the low-end range of the ramp-up. I'm open to anything.
Any ideas?

 

[nbucska]

Before you try to increase the efficiency perhaps it is
worth to check, why you are worried about it ? Energy
cost, overheating ( and MTBF ), etc.? Perhaps there is an
easier or cheaper solution ! <nbucska@pcperipherals.com>

 

[dvd]

The magnetic coupling will also generate heat when there is a relative slip between the coupling halves. Think about induction heating.

 

[RichLeimbach]

dvd ... good point, I didn't think it all the way through. forgot about the induced current and the resistance heating. Thanks for the reminder.

nbucska ... I need efficiency for 2 reasons. One is heat related (durability, cooling, etc.), but the other is cycles per charge. I can add cooling fans, fins, etc. to get the some of the heating down (although battery heating would be extremely difficult to dissipate effectively), but the cycles per charge cannot be impacted positively by anything other than an efficiency improvement.

 

[ve7brz]

Rich, a comment on this one. Although energy loss due to heating was the first thing that crossed my mind, if this coupling allows the motor to operate at a more optimal current flow then you'll still have a net gain in efficiency.

If we go back to basics, for maximum efficiency we need the motor to operate under (variable) load conditions which will keep the motor within its optimum current range.

 

[sancat]

Hi Rich,

I do not know how important is your search for efficiency in the cost-result curve involved, but here are my two cents
Why not turn the flywheel into a motor itself?
You can build a synchronous type motor; by drilling your flywheel six holes 60 degrees apart, ¾ inch diameter each (and if you need to avoid air friction, you can fill them with nylon plugs or polyurethane). You should place 2 U shaped coils, whose magnetic circuit are 30 degrees phased of each other, then, you can close alternatively each coil’s circuit, at an increased frequency, making your motor gain speed very fast, and not loosing power. This should be the most efficient way to do it, since mathematically you could know how fast it will accelerate, and therefore increase the frequency as needed
Sancat

 

[RichLeimbach]

sancat... Wouldn't this design require the use of electrical energy to generate both the rotor and stator fields? Then wouldn't it be difficult to get to the higher efficiency ranges seen with PMDC motors running at high speeds? I understand how I could get more low-end efficiency, but I do not yet see how I could increase total efficiency with this type of system. Do you have any links to synchronus motor curves that are close to what you are suggesting or any idea on the highest efficiency I could see with this type of motor? Thanks for the post.

 

[sancat]

Rich,
Well, I do not have curves at all for this <<device>>, but you could be right that a Perm magnet motor could do better. I thought you just wanted to accelerate the thing and not have it running steady.
So why dont combine both ideas; you could use a magnet and some carbon steel to build a magnetized flywheel with the desired dimension, and provide a rotating magnetic field that increases its frequency, perhaps using a variable frequency drive. Some can provide frequencies as high as a 1000 hz, and they are off the shelf. With 500 hz, and a 4 pole configuration, you could achieve 15000 rpm
sancat

 

[automatic2]

The best way to gain your effiency is to keep the motor running at rated speed. The rotating mass of the flywheel offers energy to the task being performed. If the task robs all of the flywheel energy, your starting from zero on each cycle. Very inefficient by design. Retain energy in your flywheel after each cycle to keep your motor speed within an acceptable range. This of course can be achieved by reducing the task load, or increasing the flywheel energy. Adding gadgets inbetween will increase your inefficiencies.

 

[RichLeimbach]

automatic2...
Unfortunately, I can't do that, for 2 reasons: The first is this is in an application where the mechanism will be moved between cycles and the gyroscopic effect of moving a flywheel of 3x the necessary inertia will definitely be unacceptable. Also, since the cycles are very sporadically placed, the energy necessary to maintain the flywheel at the high speed becomes a big source of loss (it is a battery operated mechanism).

The short answer is... If I could I would, but I can't, so I need to add gadgets in between to make the efficiency the best I can get it under the circumstances.

 

[automatic2]

Sounds then that the flywheel does not serve your purpose. You may well need a wind up, release style device where the motor builds tension between sporadic cycles. Regardless, similar to the flywheel concept, you'll need to provide enough energy storage to maintain anticipated duty cycles. One would need to know the power required per cycle and the consumption rates to make usefull suggestions. Maybe you could list your criterim.