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-   -   Globe motor backdrive!! (http://www.chiefdelphi.com/forums/showthread.php?t=25940)

Srkasner 24-02-2004 08:55

Globe motor backdrive!!
 
Our team is using a globe motor to use the mast system on our robot to pull the robot off the ground after attaching to the bar. It has enough torque to pull up but it back drives awfully! Has anyone come up with a way to stop the globe motors from back driving? Thanx!

~Steve
Team 1124

Joel Glidden 24-02-2004 09:24

Re: Globe motor backdrive!!
 
Have you tried simply putting that globe motor on a speed controler in brake mode? If that doesn't work, you'll have to design some form of locking mechanism. You could use a servo to insert a locking pin, or you could design a ratchet similar to this one.

Joe Johnson 24-02-2004 09:29

Re: Globe motor backdrive!!
 
Quote:

Originally Posted by Joel Glidden
Have you tried simply putting that globe motor on a speed controler in brake mode? If that doesn't work, you'll have to design some form of locking mechanism. You could use a servo to insert a locking pin, or you could design a ratchet similar to this one.

Good advice. It is pretty easy to make a catch that only locks in when your robot is fully lifted. One down side is that once you are up, you are up. This is probably not a huge issue but your drivers will have to make sure they are not going to have to get down again.

Joe J.

Justin Stiltner 28-02-2004 20:34

Re: Globe motor backdrive!!
 
Take a look at the gate latches at any hardware store, one of those was the cause of us nearly winning the vcu regional and getting into the finals at nationals our rookie year. Sometimes the simpleest solution is one of the best.

Rich Kressly 28-02-2004 20:52

Re: Globe motor backdrive!!
 
We're using another motor to lift but have a brake that is applied to our tower at any elevation with a small pneumatic cylinder so we hang steady after the power is cut.

sanddrag 28-02-2004 21:00

Re: Globe motor backdrive!!
 
You can use a standard ratchet (like what you tighten bolts with) driven by your motor.

russell 28-02-2004 21:11

Re: Globe motor backdrive!!
 
Another way I think you could do it would be to put a latching relay between the two leads on the motor, and have it off until you want the motor to lock then switch it to the on position. That will at least slow it down.

Greg Needel 28-02-2004 21:32

Re: Globe motor backdrive!!
 
Quote:

Originally Posted by russell
Another way I think you could do it would be to put a latching relay between the two leads on the motor, and have it off until you want the motor to lock then switch it to the on position. That will at least slow it down.



true but you have to beable to stop back drive after the power is shut off....i really think some of the mechanical soultions mentioned in this thread will help you out. i also was thinking of a wrap spring ( like inside your tape measure) around the shaft of your motor...since you know the total distance you will traven you can have it set to put pressure on in the forward direction of motor travel that way when if starts to backdrive the spring would be working in your favor.....

also if you use another mechanciacl method why don;t you activate it by a limit switch on your grabber that way when you are at the height you want it will automaticly trigger eliminating the back drive which would take place untill the trigger is activated

Justin Stiltner 28-02-2004 22:30

Re: Globe motor backdrive!!
 
While the relay thing might work for a hobbie robot their are a few issuses with using that system in FIRST.
The speed controllers can already be set to do this automatically see the section about the coast/brake jumper on IFI's site
Only speed controllers my be attached to the globe motor
and the relay wouldent stay latched after power was removed, all of our compeition legal relays arnt latching and cant legely be made so.
this isnt ment to down the idea, like I said its a good idea, and has uses however its illegeal for us.

jacob_dilles 28-02-2004 22:56

Re: Globe motor backdrive!!
 
we have a simple sensor on our lift that once the "on bar" switch is fliped, if the button is not moved and the sensor sais that the lift is moving, to aply current in the opisot direction. this works at least till the bot is disabled. it is just a quick programing fix, but it works... im sure its tearable for the motors tho

KevinB 29-02-2004 02:24

Re: Globe motor backdrive!!
 
Yea we have problems with Globe motor backdrive ... Setting the speed controller to break mode doesn't help.

What we did was use a pneumatic cylinder to engage a "lock" mechanism.

FadyS. 03-03-2004 07:38

Re: Globe motor backdrive!!
 
Hi, we're a rookie team and we're also experiencing backdrive on our Globes, since the robot has already been submitted we need to find a solution for this and fix it at the competition. Can anyone please provide me with a picture of this solution. Any help would be greatly appreciated because the Globes play a vital role in our bot because they operate the drum that raises and lowers the arms of our bot. Thanks in advance.

KevinB 03-03-2004 17:05

Re: Globe motor backdrive!!
 
Is this arm used to hang the bot?

Or is this just an arm used for manipulation during the match itself?

FadyS. 03-03-2004 18:13

Re: Globe motor backdrive!!
 
Quote:

Originally Posted by KevinB
Is this arm used to hang the bot?

Or is this just an arm used for manipulation during the match itself?

The arm is used to hang the bot and to pick up the 2X ball.


EDIT: Hanging isn't the problem because we set stops at that point when the arms are pointing all the way up. It's picking up the 2X ball that we're having trouble with.

Greg McCoy 04-03-2004 09:39

Re: Globe motor backdrive!!
 
Quote:

Originally Posted by KevinB
Yea we have problems with Globe motor backdrive ... Setting the speed controller to break mode doesn't help.

I think that setting our Globe motor Victors to brake did help keep our arm's wrist from "drooping" back down when the control was at neutral. There might not be enough "brake" for a robot-lifting application though...


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