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Unread 24-06-2002, 01:04
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Backdrive disable for the van door motors?

Posted by Brandon Heller at 2/18/2001 7:46 PM EST


Student on team #449, Blair Blazers, from Montgomery Blair High School and NASA Goddard, Sigma Space.



My team is trying to use two van door motors to lift a ball-grabbing arm. The problem is that when we cut the power to the motors, the arms come back down. Does anyone know how to disable backdriving? We think it may have to do with the torx screw on the top of the motor, but we're not sure.

Can anyone help us out?

Thanks!

-Brandon
-Lead Mechanical Engineer, team 449


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Re: Backdrive disable for the van door motors?

Posted by Rimple Bhakta at 2/18/2001 8:49 PM EST


Other on team #438, Gladiators, from Jack Yates High School and Mrs. Reagan Flowers.


In Reply to: Backdrive disable for the van door motors?
Posted by Brandon Heller on 2/18/2001 7:46 PM EST:



you need a counter balance
in otherwords u need spring action to keep the tenion on lifting to arm ...the weight of the arm is bringn it back thas what we had a problem with and we fixed with springtype action counterbalance






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Re: Backdrive disable for the van door motors?

Posted by Lloyd Burns at 2/18/2001 8:52 PM EST


Engineer on team #188, Woburn Robotics, from Woburn Collegiate and TorDistSchoolBrd, ScotiaBank. OntPwrGen, Enbridge.


In Reply to: Backdrive disable for the van door motors?
Posted by Brandon Heller on 2/18/2001 7:46 PM EST:



: My team is trying to use two van door motors to lift a ball-grabbing arm. The problem is that when we cut the power to the motors, the arms come back down. Does anyone know how to disable backdriving? We think it may have to do with the torx screw on the top of the motor, but we're not sure.

: Can anyone help us out?

: Thanks!

That's a Crispy Creme : Absolutely doughnut do it !!!
It tightens the end bearing on the worm, eventually causing failure as the worm loosens (Isn't that a soap ? No, ... that's "As the Worm Turns&quot.

If you need to _slow_down_ the back drive, you can use the brake setting on the Victor. This puts a short across the terminals of the motor, which is acting as a generator in backdrive. The short makes it hard to backdrive, but hanging (last year's sport) a robot with a van door motor with the Victor on brake is not guaranteed, because at slow speed, the generator isn't generating enough voltage to stop itself, just remain slow.




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Re: Backdrive disable for the van door motors?

Posted by Nate Smith at 2/19/2001 1:53 AM EST


Other on team #66, Frostbite, from Willow Run High School and GM Powertrain.


In Reply to: Re: Backdrive disable for the van door motors?
Posted by Lloyd Burns on 2/18/2001 8:52 PM EST:



: If you need to _slow_down_ the back drive, you can use the brake setting on the Victor. This puts a short across the terminals of the motor, which is acting as a generator in backdrive. The short makes it hard to backdrive, but hanging (last year's sport) a robot with a van door motor with the Victor on brake is not guaranteed, because at slow speed, the generator isn't generating enough voltage to stop itself, just remain slow.

We used a winch with the two van door motors in last year's competition to hang, and with the brake mode on for the speed controllers, it was enough to keep our robot in the air...

Nate
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Re: Backdrive disable for the van door motors?

Posted by Janna at 2/20/2001 8:37 AM EST


Student on team #349, The RoBahamas, from International Academy and Ford Motor Company and Robert Bosch GmbH.


In Reply to: Backdrive disable for the van door motors?
Posted by Brandon Heller on 2/18/2001 7:46 PM EST:



Last year our team had this problem when we were hanging from the bar. We took an extra gear that fitted to the ones on the arm, sliced most of it off, and mounted it with a spring on one end and a pivot point on the other so it acted like a ratchet. It was extremely reliable when the ratchet was engaged.


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Tighten the brake, but be careful

Posted by Adam Krajewski at 2/20/2001 2:00 PM EST


Engineer on team #221, MI Roboworks, from CCISD and Michigan Tech..


In Reply to: Backdrive disable for the van door motors?
Posted by Brandon Heller on 2/18/2001 7:46 PM EST:



I have not taken apart one of the van door motors identical to the ones used this year, but the ones used in previous years (allen head screw instead of torx screw on the top of the motor if looking directly down the shaft) a mechanical brake is present. The brake can be used effectively to decrease backdrive. The brake works well when a small amount of force is needed to stop backdriving (using it to stop the cable spool on the lift of the '99 T3 robot), but not so well when a large amount of force is needed to stop backdriving (using it to hold the arm in position on the '00 T3 robot). The brake consists of a setscrew and a spring mounted "plunger" that makes contact with the large plastic gear inside of the van door motor. Overtightening the screw causes the "plunger" to wear until you reach the setscrew. The shape edge of the setscrew then tends to bind on the gear. I do not believe this has caused any of our motors to fail, but it does change the motion of the arm and may cause failure down the road. In short, don't try to use the van door brake to hold a heavy arm for long periods of time.
Your best option would be to try to incorporate some type of closed-loop proportional control system. For more info on that type of control, check out the "Industrial Control" book at www.parallaxinc.com

Adam
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Re: Tighten the brake, but be careful

Posted by Mark Garver at 2/21/2001 2:59 PM EST


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


In Reply to: Tighten the brake, but be careful
Posted by Adam Krajewski on 2/20/2001 2:00 PM EST:



Very true Adam, you must be careful when tightening the brake. As you know we did take one apart over the summer and took all of those pictures! Anyways I believe this year you have to tighten the brake with a torgue wrench instead of an allen wrench. Other than that they are the same. The interal works are identical. Later Adam



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Re: Tighten the brake, but be careful

Posted by Adam Krajewski at 02/22/2001 1:42 AM EST


Engineer on team #221, MI Roboworks, from CCISD and Michigan Tech..


In Reply to: Re: Tighten the brake, but be careful
Posted by Mark Garver on 2/21/2001 2:59 PM EST:



Ha. I wouldn't find it too hard to believe that at T3 a torque wrench was required to tighten down the brake... But I think you mean it contains a torx screw...

Adam


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your right

Posted by Mark Garver at 02/24/2001 10:08 AM EST


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


In Reply to: Re: Tighten the brake, but be careful
Posted by Adam Krajewski on 02/22/2001 1:42 AM EST:



Your right we do have Denny!!!
: Ha. I wouldn't find it too hard to believe that at T3 a torque wrench was required to tighten down the brake... But I think you mean it contains a torx screw...

: Adam


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Re: Backdrive disable for the van door motors?

Posted by Stephen at 2/21/2001 4:01 PM EST


Other on team #122, NASA Knights, from Grafton High School (Robotics team is at NHGS) and NASA.


In Reply to: Backdrive disable for the van door motors?
Posted by Brandon Heller on 2/18/2001 7:46 PM EST:



Sorry I'm too late to be of any help, but sense no one else gave a programming solution (my specialty), I thought I would.
Depending on how much rotation you need, you could use a potentiometer, we actually have 4 on our robot, 3 10 turn pots and 1 one turn. If you want background information on how it works, how to program it, etc. just e-mail me at Steven3554@yahoo.com

: My team is trying to use two van door motors to lift a ball-grabbing arm. The problem is that when we cut the power to the motors, the arms come back down. Does anyone know how to disable backdriving? We think it may have to do with the torx screw on the top of the motor, but we're not sure.

: Can anyone help us out?

: Thanks!

: -Brandon
: -Lead Mechanical Engineer, team 449


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