Four motors at the same speed?
 

Posted by Mark Garver at 1/13/2001 3:18 PM EST


Student on team #68, Truck Town Terror, from Waterford Kettering/OSMTech Academy and General Motors Truck Group.



Can you design a drivetrain that allows you to use four motors? The motors I am think of are the drill and Fisher Price motors. I would put the drills in back and the Fisher Price in front. In a no load simulation you could get all four motors to run at the same speed, but what about under load? Would only two motors drive and the other two act as generators? If that was the case could you write a long equation into the program to make it work? Thanks you for any help you can give me.

Disengaging two of the motor
 

Posted by Ken Leung at 1/13/2001 4:11 PM EST


Student on team #192, Gunn Robotics Team, from Henry M. Gunn Senior High School.


In Reply to: Four motors at the same speed?
Posted by Mark Garver on 1/13/2001 3:18 PM EST:



It is not hard to get all four motor to run at the same speed. However, as you said, under stress two of them will act as generators. One of the way to prevent that is to somehow disengage those two motor. I am not sure you can do it in the program, but mechanically it is possible.

One option is to make your own gear box, and disengage gears in that to disconnect the motors from the wheel. Second option is do what Team Choas did last year, which is instead of 2 wheels with the Fisher Price motors, you have those two wheels on one side of a lever and two free spinning ones on another side of the lever. Using a window lift motor to spin the motorized wheels on the ground when you want more force, or spin the free wheels on the ground when you want to move easily.

Re: Disengaging two of the motor
 

Posted by Justin Stiltner at 1/14/2001 12:22 AM EST


Student on team #388, Epsilon, from Grundy High School and NASA, American Electric Power, Town of Grundy.


In Reply to: Disengaging two of the motor
Posted by Ken Leung on 1/13/2001 4:11 PM EST:



: It is not hard to get all four motor to run at the same speed. However, as you said, under stress two of them will act as generators. One of the way to prevent that is to somehow disengage those two motor. I am not sure you can do it in the program, but mechanically it is possible.

: One option is to make your own gear box, and disengage gears in that to disconnect the motors from the wheel. Second option is do what Team Choas did last year, which is instead of 2 wheels with the Fisher Price motors, you have those two wheels on one side of a lever and two free spinning ones on another side of the lever. Using a window lift motor to spin the motorized wheels on the ground when you want more force, or spin the free wheels on the ground when you want to move easily.

I thought of the same thing for last year but we dident use it
It was the drill motors at one end provideing speed and the VANDOOR motors at the other provideing the bulldozeing ability.

Justin Stiltner
Team #388
Epsilon
Grundy Va,

Re: Four motors at the same speed?
 

Posted by Dodd Stacy at 1/13/2001 4:16 PM EST


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


In Reply to: Four motors at the same speed?
Posted by Mark Garver on 1/13/2001 3:18 PM EST:



: Can you design a drivetrain that allows you to use four motors?

Simple response: yes.

:The motors I am think of are the drill and Fisher Price motors. I would put the drills in back and the Fisher Price in front. In a no load simulation you could get all four motors to run at the same speed, but what about under load?

Gearing the motors so that all wheels had similar no-load surface speed (they don't even need to be the same diameter wheels) is the main requirement.

:Would only two motors drive and the other two act as generators?

No. This would only happen with induction type (non-synchronous) motors, like the ones in the kit, if one pair of motors was geared so "tall" that they (while under significant load) drove the bot at such a high speed that the other pair was being rotated by the moving bot (overdriven or overrun) at a speed faster than their no-load speed. Sorry for the long sentence.

Go for it, Mark. Good luck.

Dodd

More things to think about...
 

Posted by Joe Johnson at 1/13/2001 10:01 PM EST


Engineer on team #47, Chief Delphi, from Pontiac Central High School and Delphi Automotive Systems.


In Reply to: Re: Four motors at the same speed?
Posted by Dodd Stacy on 1/13/2001 4:16 PM EST:



As usual, Dodd hits the target dead on.

I have one or two things to add though.

There are other options besides gearing the motors so
that they match free speeds.

You can gear them to match stall torque for example.

Your could gear them somewhere in between these two
extremes -- for example, you could choose to gear them
to match speeds when they are loaded at the level
required to break the tires free.

In every case though, you are only matching the
performance at one torque - speed point. At every
other point there will be a mismatch of some level.

Is this mismatch a disaster? I don't think so. Our
machine in Double Trouble used matching free speeds an
our robot worked just fine.

Joe J.

Good Luck ?
 

Posted by Ed Sparks at 1/13/2001 8:13 PM EST


Coach on team #34, The Rockets, from Bob Jones High / New Century High and DaimlerChrysler.


In Reply to: Four motors at the same speed?
Posted by Mark Garver on 1/13/2001 3:18 PM EST:



I wish you the best of luck. He haven't gotten over the forward vs reverse speed difference in the drill motors (I suspect all motors) yet let alone try to sync 4 motors. This was/is a problem I was determined to design my way out of given those "unlimited gears" I was counting on this year. My "What I did this summer" paper was about my study of gears (I'm an EE but I must be a want-a-be ME). Ah well maybe next year ...............

I think I'm going the way of K.I.S.S. this year.

Re: Good Luck ?
 

Posted by Justin Stiltner at 1/14/2001 12:15 AM EST


Student on team #388, Epsilon, from Grundy High School and NASA, American Electric Power, Town of Grundy.


In Reply to: Good Luck ?
Posted by Ed Sparks on 1/13/2001 8:13 PM EST:



: I wish you the best of luck. He haven't gotten over the forward vs reverse speed difference in the drill motors (I suspect all motors) yet let alone try to sync 4 motors. This was/is a problem I was determined to design my way out of given those "unlimited gears" I was counting on this year. My "What I did this summer" paper was about my study of gears (I'm an EE but I must be a want-a-be ME). Ah well maybe next year ...............

: I think I'm going the way of K.I.S.S. this year.

I am the same way. I spent about a week designing and cading a design for a self recovery system using penumatics for this years game so that if we fell over in the heat of the battel we could stand right back up....... and then we find out that we are all on the same team and that idea basically goes out the window

oh well i got some good experance with cad that way.

Justin Stiltner
Team #388
Epsilon
Grundy Va,

Re: Four motors at the same speed?
 

Posted by Matt Berube at 1/13/2001 9:43 PM EST


Engineer on team #49, Delphi Knights, from Buena Vista High School and Delphi Automotive.


In Reply to: Four motors at the same speed?
Posted by Mark Garver on 1/13/2001 3:18 PM EST:



We have done exactly what you are talking about and I have seen many other highly succesfull teams do the same. It works just fine. Just gear them so that their no-load speed it matched. This should also match the max power speed since it equals half of the no-load speed.

Matt B.
T49

had the same idea... i know who to ask....
 

Posted by Anton Abaya at 1/14/2001 12:39 AM EST


Coach on team #419, Rambots, from UMass Boston / BC High and NASA, Mathsoft, Solidworks.


In Reply to: Four motors at the same speed?
Posted by Mark Garver on 1/13/2001 3:18 PM EST:



from what i was told, team 42 last year, PARTS they were called, made tank driven robots with treads and used a drive train that had the same principle of using DRILL and FISHER PRICE motors at the same time.

i was told that it worked great and had no problems. might i suggest getting help from them.

good luck. i was thinking of doing this too, but i was not sure exactly what difference it makes exactly and the tradeoffs by doing so.... anyone?

-anton