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[DPRG] RE: [SeattleRobotics] I bought the wrong gearmotors

Subject: [DPRG] RE: [SeattleRobotics] I bought the wrong gearmotors
From: Kevin Ross kevinro at kevinro.com
Date: Sat Feb 26 07:48:50 CST 2005


You can also use slightly larger wheels. A 5" wheel on a 128rpm base will do
5*128*3.1415 =2010 inchs/minute. 

A 75rpm motor needs a 2010 / (75*.31415) = 8.3" wheel. 


>-----Original Message-----
>From: Rick Mann [mailto:rmann at latencyzero.com] 
>Sent: Friday, February 25, 2005 11:18 PM
>To: dprglist at dprg.org; SeattleRobotics at yahoogroups.com
>Subject: [SeattleRobotics] I bought the wrong gearmotors
>I have two shiny new Pittman GM8724S021-R1 60.5:1 12V gearmotors with 
>500 CPR encoders. I bought them for a project similar to DPA's 
>nBot. On 
>his website, he mentioned how he used similar 19.1 V motors. 
>For a long 
>time I put off buying motors because of the price ($195 each), but I 
>finally decided to go for it.
>Unfortunately, I didn't check the specs carefully enough, and 
>my output 
>shaft no-load speed is about 75 RPM, whereas nBot has more like 128.
>The worst part is that the distributor wants a 50% restocking fee.
>So, what are my options? A) I can sell them at a small discount to 
>someone on the list, and buy new ones. B) I was going to drive 
>my 'bots 
>wheels with a timing belt & pulleys, so I can put a larger pulley on 
>the shaft and recover some of the speed (not sure what this 
>does to the 
>efficiency). C) I can drive the motors at a higher voltage, 
>but part of 
>the reason I wanted 12 V motors was to not have to have a 
>higher source 
>of voltage, and I don't know what overdriving these will do.
>Any ideas? Anyone want a beautiful pair of motors (they're 
>really quite 
>Visit the SRS Website at http://www.seattlerobotics.org 
>Yahoo! Groups Links
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