kkeerroo
Experienced Roboteer
Joined: 17 Jun 2004
Posts: 1459
Location: Brisbane
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Here's a good post from the RFL forum.
quote:
Ok, first I gotta back up a bit.
Motors turn current into torque (force). Force times time = energy.
Spinners get like 5 seconds worth of 'burn time'. Over that 5 seconds, the spinner builds up a lot of energy, which is imparted to the opponent in a short time. A directly driven hammer only gets to turn the motor on for like 0.1 seconds - that's just not enough time to build up as much energy (assuming similar motors/batteries)
If you change it so that the motor drives hard for 5 seconds to compress a spring, you get to build up a similar level of energy, again released in in a (hopefully) quick big hit.
Now pneumatics are a bit different... on one hand, an air cylinder at pressure is like a compressed spring - a lot of energy ready to be released quickly. On the other, you don't get to go from zero to full pressure instantly - it's all about the flow.
Like a spring, you could envision a pneumatic hammer where the cylinder is pressurized, but the hammer held by a catch (like the spring hammer). Then when you fire (release the catch), the full force is instantaneously available, without flow limitations. This would allow pretty simple pneumatics (small valves)... but to my knowledge, nobody's tried this - again, maybe the problem is the structure to hold the forces, and the tricky release mechanism.
And another:
quote:
There's an interesting discussion to be had here with respect to energy, I think. Hammering is arguably a more effective method of energy delivery, because the floor naturally forces the opponent to absorb the bulk of the blow.
The disadvantage spinners have is that they're forced to go through the entire power curve of the PMDC motor. This means that at the onset of spinup, they draw disastrously inefficient and huge levels of amps, and past 50% rpms, they are making progressively less power.
With a nautilus style gear, not unlike what BETA employs, You could maintain the output torque of the the motor-gear system so that it is matched with a certain ratio to the spring constant, in an attempt to hold the motor around full power IIRC, with 50% efficiency. The nice thing about springs is that they can be tremendously energy dense, in the same way that a spinning flywheel is, but without the spinning. Perhaps if the design was worked on, and taken to the next level with I-L style pneumatics, or spring-hammer systems coupled to infrared switches to avoid missing the opponent and losing alot of time.
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