Newsgroups: comp.robotics
Path: brunix!sgiblab!swrinde!ihnp4.ucsd.edu!usc!howland.reston.ans.net!torn!nott!cunews!ccs1.carleton.ca!Brian_Sullivan
From: Brian_Sullivan@Carleton.CA (Brian Sullivan)
Subject: Re: tennis robot
Message-ID: <Brian_Sullivan.28.2DB6C0A9@Carleton.CA>
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References: <1994Apr19.182413.10317@lds.loral.com> <ZDT4kc1w165w@sfrsa.com>
Date: Thu, 21 Apr 1994 18:06:33 GMT
Lines: 36

>> Tennis Ball Server:
>> 
>> Two electric motors each drive a 5" diameter wheel in opposite directions
>> ( the left one clockwise, the right one counter clockwise.)  The wheels
>> are placed so that the distance between them is about 1/2" less than the
>> diameter of a tennis ball.  A ball feed ramp directs a tennis ball to
>> roll between the two wheels.  The ball is pinched between the wheels
>> and is shot out the other side at 60 MPH.  ( see figure 1 below )
>> 
>> 
>> 
>> This is my problem.  Suppose I have a maximum time I want to wait
>> for the RPMs to recover to the rate needed to serve a ball at 60 MPH
>> ( Trecover ).  The wheels each have the same mass ( Mwheel ) and
>> each motor is rated to deliver torque ( TQmotor ).  I want to
>> ignore friction in my calculations.
>> 
>> Can someone with a fairly fresh memory of dynamics tell me 
>> how to figure what TQmotor needs to be based on fixed values 
>> of Trecover and Mwheel ??
> 

OK I've read a few of the replies to this post, but ....

If I recall 60 mph is ~ 88 ft/second. The 5" wheels will need to turn ~ 10-12 
cycles /sec. or 600-700 rmp. At that speed the thing is going to have a 
fair amout of rotational mass.  Just a guess but you are going to 
have trouble feeding balls (not much mass there) to it fast enough to 
have any real effect on it? 

I've seen what a radial arm saw will do to a 2x4 if you feed it to quickly. 
Shot the thing 6 feet across the room and put a nice neat hole in the 
cinder-block wall. While the saw did slow down a bit, it was back up to speed
in /12 a second.


