Quote:
Originally Posted by Mike Betts
Dick,
This "specification" has been floating around these boards for a while now.
I'd love to find out the exact source of the 20"/sec specification. I downloaded the Bimba manual and can find it nowhere.
I calculate a 1" bore cylinder will move at about 70" per second (unloaded, 45 PSI delta with about a 2 CFPM airflow).
This was brought up in another thread. Upon reflection, my thoughts are:
1. If the cylinder is rated at 125 PSI, I would think it should be built to survive a 110 PSI delta actuation over tears of use.
2. The rules state no more than 60 PSI as a working pressure.
3. Assuming that the piston is used to deflect the spring assist at a 45 PSI delta, then the effective contribution of the spring is that of a 45 PSI delta.
4. Added to the 45 PSI delta of the pneumatic system, you have an effective force of 90 PSI delta acting on the piston.
Even with pre-charged cylinders at some percentage extension to maximize speed and direct exhaust at .3 cv, I'm having a difficult time getting a dangerous material fatigue scenario for an expected lifetime of a couple of hundred two minute matches.
Like I said, I'd love to get to the source...
Regards,
Mike
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Mike,
I'm not sure that that 'spec' is actually a spec, but instead is a 'recommendation' from Bimba.
Additionally, the speed of the cylinder is not an issue. What is an issue is the impact on the endcap of the cylinder. Consider that some teams are using upwards of a 2 pound mass on the end of a 8-10" lever and accellerating that to 50 ips and you have some serious forces trying to unseat the endcap of the cylinder.
My suggestion to all teams that are using this type of system (including elastomer assist) is to have a hard stop on your robot so that the cylinder does not 'bottom out' against the endcap.