Go to Post If it's not a sport, and it's not an art, it might as well be criminal behavior, because that's how you're going to be treated. - jasoni [more]
Home
Go Back   Chief Delphi > Technical > Technical Discussion
CD-Media   CD-Spy  
portal register members calendar search Today's Posts Mark Forums Read FAQ rules

 
Closed Thread
 
Thread Tools Rate Thread Display Modes
  #1   Spotlight this post!  
Unread 09-12-2003, 14:39
Joe Johnson's Avatar Unsung FIRST Hero
Joe Johnson Joe Johnson is offline
Engineer at Medrobotics
AKA: Dr. Joe
FRC #0088 (TJ2)
Team Role: Engineer
 
Join Date: May 2001
Rookie Year: 1996
Location: Raynham, MA
Posts: 2,648
Joe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond repute
I need more power Cap'n!

I disagree with the statement that there is no reason to have multiple motors if you have a shifter.

They cover similar problems, but not EXACTLY the same problems.

If you need or want more power (e.g. for faster accelerations) multiple motors gives you that. Notice that I use the term "power" in the engineering sense. I do NOT mean "more low end torque" as many do when they use the term on these fori.

POWER = WORK PER SECOND <-- SPEED X TORQUE in our case.

Switching gear ratios can help you get more power up to a point by choosing to load the motor such that it is providing its peak power (i.e. at 1/2 its stall torque) but if you need or want more power than that, more motors are your only real solution.

Joe J.
  #2   Spotlight this post!  
Unread 10-12-2003, 02:05
Matt Adams's Avatar
Matt Adams Matt Adams is offline
b(o_o)d
FRC #1525 (Warbots)
Team Role: Engineer
 
Join Date: Dec 2003
Rookie Year: 2000
Location: Arlington Hts. IL
Posts: 375
Matt Adams has a reputation beyond reputeMatt Adams has a reputation beyond reputeMatt Adams has a reputation beyond reputeMatt Adams has a reputation beyond reputeMatt Adams has a reputation beyond reputeMatt Adams has a reputation beyond reputeMatt Adams has a reputation beyond reputeMatt Adams has a reputation beyond reputeMatt Adams has a reputation beyond reputeMatt Adams has a reputation beyond reputeMatt Adams has a reputation beyond repute
Send a message via AIM to Matt Adams
Re: I need more power Cap'n!

Quote:
Originally Posted by Joe Johnson
I disagree with the statement that there is no reason to have multiple motors if you have a shifter.
Quote:
Originally Posted by Joe Johnson

They cover similar problems, but not EXACTLY the same problems.

If you need or want more power (e.g. for faster accelerations) multiple motors gives you that...
<SNIP>
...if you need or want more power than that, more motors are your only real solution.

Everything you said is completely correct, as I would expect out of any Purdue alum...

I guess that my two cents come in that I think that you can have "enough acceleration" and your max speed can be "fast enough" and your max torque can certainly be calculated to be sufficient with one pair of motors and a well designed shifting gear box. And by "enough", I mean reasonably competitive.

Obviously a robot with 4 motors will be faster and accelerate more quickly than one with only a single pair. My opinion comes in saying that the estimated 10-14 feet per second you can get out of a high speed ratio gear set gives sufficiently competitive speed and acceleration for most applications.

This is only an opinion. I belive that often for many teams, the weight required and additional engineering time could be better used elsewhere. Certainly that is debatable, and your point is definitely well taken.

Matt
__________________
Matt Adams - Engineer at Danaher Motion
Team 1525 - Warbots - Deerfield High School
  #3   Spotlight this post!  
Unread 10-12-2003, 13:34
Joe Johnson's Avatar Unsung FIRST Hero
Joe Johnson Joe Johnson is offline
Engineer at Medrobotics
AKA: Dr. Joe
FRC #0088 (TJ2)
Team Role: Engineer
 
Join Date: May 2001
Rookie Year: 1996
Location: Raynham, MA
Posts: 2,648
Joe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond reputeJoe Johnson has a reputation beyond repute
"Enough" is relative...

I agree that depending on the game, your choosen strategy and the skill of the operator, it is quite possible to make competitive robots with only one motor per side and a shifter. I'll even go farther than that. It is possible to make competitive robots without a shifter and only one motor per side (again, depending on the game, your strategy and the skill of your drivers).

My point was that power is a main reason for adding motors, even with a shifter.

How much power is "enough" is up to each team to figure out.

One more comment on this more power issue. When I say "more acceleration" I do not just mean quicker changes in velocity. While it is possible that this will be an important design consideration, I think that it is quite unlikely that the time savings alone are sufficient to justify needing more power in your drive system. Think about it. Is it likely that the half second or so you saved because you got up to full speed in 1 second rather than 2 seconds is going to win you a match? I doubt it.

Having more power for acceleration is more than just having a high DV/DT. It also includes moving at a constant speed up a ramp for example.

Another reason that acceleration is important is that until your robot gets moving, your motors are effectively stalled. The breakers cannot tell the difference between stalled motor current and current from accelerating your robot. So... ...by having more acceleration your motors are operating at this "stalled" condition for a shorter time period. Translation: your breakers will not trip as often from hard accels and decels. Cooler Breakers give you more margin for operation. You will not have to shift out of high gear for a minor skirmish with an opponent because your breakers will have that reserve of current for just that much longer than they would have.

Margin of error for the operators. Now THAT wins matches!

By the way, I am not a huge fan of multiple motors per side, but I just think that the decision should be made with a fair accessment of the merits of each case rather than a hard a fast rule that shifting is the answer, or multiple motors is the answer, or that multiple motors + shifting is the answer, etc.

Just some more things to ponder as you weigh things in the balance.

Joe J.

Last edited by Joe Johnson : 10-12-2003 at 13:44.
Closed Thread


Thread Tools
Display Modes Rate This Thread
Rate This Thread:

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Regional & Division winners, did you shift gears or not? DougHogg Technical Discussion 34 02-05-2003 16:10
Helical gears that come with new drill motor Joe P Technical Discussion 4 12-01-2003 11:09
Best source for gears? Smallparts? drivetrain advice wanted! Frank(Aflak) Technical Discussion 11 10-01-2003 17:22
gears....? archiver 2000 16 23-06-2002 22:58
Need help! What kind of gears are we allowed to use?? Randy_Ai Technical Discussion 3 23-01-2002 22:56


All times are GMT -5. The time now is 23:02.

The Chief Delphi Forums are sponsored by Innovation First International, Inc.


Powered by vBulletin® Version 3.6.4
Copyright ©2000 - 2017, Jelsoft Enterprises Ltd.
Copyright © Chief Delphi