Thread: Blowing drill motors
View Single Post
  #7   Spotlight this post!  
Unread 23-06-2002, 21:58
archiver archiver is offline
Forum Archival System
#0047 (ChiefDelphi)
  
Join Date: May 2001
Location: Pontiac, MI
Posts: 21,214
archiver has a reputation beyond reputearchiver has a reputation beyond reputearchiver has a reputation beyond reputearchiver has a reputation beyond reputearchiver has a reputation beyond reputearchiver has a reputation beyond reputearchiver has a reputation beyond reputearchiver has a reputation beyond reputearchiver has a reputation beyond reputearchiver has a reputation beyond reputearchiver has a reputation beyond repute
Re: How is our gear ratio?
Posted by Dodd Stacy.

Engineer on team #95, Lebanon Robotics Team, from Lebanon High School and CRREL/CREARE.

Posted on 2/24/2000 8:56 AM MST


In Reply to: How is our gear ratio? posted by nuts4first on 2/23/2000 1:27 PM MST:



: Is a 15 (on the drill axle) to 18 (on the wheel) gear ratio bad? We are locked in low gear and driving 2-6' wheels with each motor. Our robot weights 130 lbs. I've tried to use some of the speadsheets, but I'm not sure now to read them.

: What does everyone think?

: -Team 340

Nuts,

This is gentle gearing in terms of loading the drill motors and heating them up. Your top speed is probably about 6.3 ft/sec. We have in the past run direct drive (1:1) in LO range to the 6' wheels, 7.6 ft/sec top speed, with no problems.

A suggestion to consider, tho, is to run the drill gearbox in HI range and take a larger, compensating, ratio reduction in the final chain and sprocket stage, netting (nearly) the same overall gearing. This reduces the maximum torque transmitted by the gearbox and any joints in or to the output shaft (like your 15 tooth sprocket), reduces the reaction torque that the drill housing and its mounts need to absorb, and reduces the tension in the chain. And I mean reduces by a factor of 3+.

With all the front/back maneuvering these bots do at max acceleration, it really works the whole system thru a lot of stress reversal cycles. I'll take a factor of 3 load reduction any time, but that's just my opinion. Some folks love tearing down gearboxes, drifting out snapped pins, and fussing with master links in the calm, well-lighted pits. I would also wager that the chain/sprocket reduction stage has a better mechanical efficiency than the plastic planetary stage in the gearbox that is eliminated in this approach.

A 40 T (3/8' pitch) sprocket can fit your 6' wheel (4.78' pitch dia.), and paired with a 10 T drive sprocket and the drill gearbox run in HI, would give you a 6.0 ft/sec top speed vs your present 6.3 ft/sec. A 12 T drive sprocket nets about 7.2 ft/sec. This is working with sprocket availability from SPI - you can probably find a finer mesh of ratios available thru other suppliers, but this is a pretty minor speed range as is. Good luck.

Dodd



__________________
This message was archived from an earlier forum system. Some information may have been left out. Start new discussion in the current forums, and refer back to these threads when necessary.