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View Full Version : BACKDRIVE PLEASE HELP!!!!!


archiver
06-23-2002, 09:58 PM
Posted by Patrick.

Coach on team #409, Flaming Eagles, from Oak Grove High School and NASA Ames Research Center.

Posted on 2/22/2000 12:12 PM MST



DOES ANYBODY KNOW HOW YOU PROGRAM THE ROBOT CONTROLLER TO SEND A SIGNAL
TO NOT LET THE MOTORS BACKDRIVE? PLEASE EMAIL THE CODE TO ME IF YOU HAVE IT,
OR EMAIL IT TO ME AT SLIKKRIKK6@AOL.COM.

THANX

-PATRICK WESONGA

archiver
06-23-2002, 09:58 PM
Posted by Nate Smith.

Other on team #66, GM Powertrain/Willow Run HS, from Eastern Michigan University and GM Powertrain.

Posted on 2/22/2000 12:24 PM MST


In Reply to: BACKDRIVE PLEASE HELP!!!!! posted by Patrick on 2/22/2000 12:12 PM MST:



It actually can be done without code if you are using the speed controllers to control the motors you want to keep from backdriving. Just set the jumper on the speed controller(right under where the PWM cable plugs in) so that it is on the left two pins. This will put the speed controllers into dynamic braking mode, which will keep the motors from backdriving under weights equal to that of a robot. We almost thought our winch lift was in trouble last night, until I remembered that you could do this...

Nate

archiver
06-23-2002, 09:58 PM
Posted by Patrick.

Coach on team #409, Flaming Eagles, from Oak Grove High School and NASA Ames Research Center.

Posted on 2/22/2000 1:22 PM MST


In Reply to: Re: BACKDRIVE PLEASE HELP!!!!! posted by Nate Smith on 2/22/2000 12:24 PM MST:



: It actually can be done without code if you are using the speed controllers to control the motors you want to keep from backdriving. Just set the jumper on the speed controller(right under where the PWM cable plugs in) so that it is on the left two pins. This will put the speed controllers into dynamic braking mode, which will keep the motors from backdriving under weights equal to that of a robot. We almost thought our winch lift was in trouble last night, until I remembered that you could do this...

: Nate

Nate, it turns out that our speed controllers had already been put into that mode and it sill backdrives. We have a 93 pound robot. CAN ANYONE PLEEEEASE HELP?

archiver
06-23-2002, 09:58 PM
Posted by Nate Smith.

Other on team #66, GM Powertrain/Willow Run HS, from Eastern Michigan University and GM Powertrain.

Posted on 2/22/2000 2:59 PM MST


In Reply to: Re: BACKDRIVE PLEASE HELP!!!!! posted by Patrick on 2/22/2000 1:22 PM MST:



: : It actually can be done without code if you are using the speed controllers to control the motors you want to keep from backdriving. Just set the jumper on the speed controller(right under where the PWM cable plugs in) so that it is on the left two pins. This will put the speed controllers into dynamic braking mode, which will keep the motors from backdriving under weights equal to that of a robot. We almost thought our winch lift was in trouble last night, until I remembered that you could do this...

: : Nate

: Nate, it turns out that our speed controllers had already been put into that mode and it sill backdrives. We have a 93 pound robot. CAN ANYONE PLEEEEASE HELP?

If it's the drill motors, it might be caused by the clutches in the gearboxes, and there's not much you can do about that...otherwise, put a routine in your control program similar to this(simulating the dynamic breaking, but at a slower cycle(roughly 40Hz v 60Hz on the speed controllers):
PS - I know my formatting isn't the best, and there's probably a better way to do this in PBASIC, but this should work...

if p1_x .gt..lt. 127 then skipbraking
if pwmout = 126 then go_high
pwmout=126
goto skipbraking
go_high:
pwmout=128

skipbraking:

--------
Notes:
.gt. = Greater Than Symbol
.lt. = Less than Symbol
pwmout = VAR byte output to the desired speed
controller
p1_x = Desired joystick axis to be monitored

archiver
06-23-2002, 09:58 PM
Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


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

Posted on 2/22/2000 3:50 PM MST


In Reply to: Re: BACKDRIVE PLEASE HELP!!!!! posted by Nate Smith on 2/22/2000 2:59 PM MST:



Dynamic Braking has it limits.

You basically have four choices:

1) more ratio

2) less efficient drive mechanism (worm drive, lead screw, etc.)

3) an 'over center' mechanism (i.e. in the 'hanging' position, the mechanism tend to rotate the motor TOWARD engagement not away -- think of it as a piston with a crank that goes 10 degrees or so beyond top dead center and hits a dead stop. No matter how hard you push on the piston, the crank is not going to backdrive).

4) a brake of some kind. This is not that hard or weighty. You can use a sevro to drive a catch into some chain links or into the cogs of the sprockets or (be careful) in the teeth of a gear.

I hope this helps.

Joe J.

P.S. I didn't get this message until after the ship time. Sorry if it is too late.

archiver
06-23-2002, 09:58 PM
Posted by Thomas A. Frank.

Engineer on team #121, The Islanders/Rhode Warrior, from Middletown (RI) High School and Naval Undersea Warfare Center.

Posted on 2/23/2000 3:02 PM MST


In Reply to: Dynamic Braking has limits... posted by Joe Johnson on 2/22/2000 3:50 PM MST:



: Dynamic Braking has it limits.

Joe then proceeds to point out several excellent approaches to avoiding backdriving.

But there is one limitation on dynamic braking that wasn't mentioned - it only works when the control system is communicating with the robot. At the end of the match, when control is turned off, there goes your dynamic braking.

I didn't see this until this morning, so it's too late for shipping. But you could design a fix and make it in the pits at the regional.

Tom Frank

archiver
06-23-2002, 09:58 PM
Posted by Nate Smith.

Other on team #66, GM Powertrain/Willow Run HS, from Eastern Michigan University and GM Powertrain.

Posted on 2/23/2000 3:25 PM MST


In Reply to: Re: Dynamic Braking has limits... posted by Thomas A. Frank on 2/23/2000 3:02 PM MST:



: But there is one limitation on dynamic braking that wasn't mentioned - it only works when the control system is communicating with the robot. At the end of the match, when control is turned off, there goes your dynamic braking.

With our winch system, which uses the dynamic braking to keep the machine from sinking to the ground, we unplugged the OI to simulate an end-of-round cutoff, with no real problems(only an inch or two of height loss, as compared to a slow, steady slide down before the braking was turned on.) Since the dynamic braking is based entirely at the speed controller, which is powered from a source other than the signal from the RC, I am assuming that the braking circuit is still active when the control system is not transmitting. As for when the system is officially disabled, i don't know, because I do not have a 'competition adaptor' to test it with. Will have to find out at Great Lakes...

Nate

archiver
06-23-2002, 09:58 PM
Posted by Daniel.

Coach on team #483, BORG, from Berkeley High School and NASA Ames & UC Berkeley.

Posted on 2/23/2000 3:32 PM MST


In Reply to: Re: Dynamic Braking has limits... posted by Nate Smith on 2/23/2000 3:25 PM MST:



The speed controller will go into dynamic breaking while it is sent either no signal, or a neutral signal. You know how the lights are all on and blinking while the robot is not being given a signal? That means the speed controllers are alive and saying 'must. keep. robot. in. position.'

Dynamic breaking is very useful. I myself preferred not worrying about that and using the window motors for my team's bar-lift system. However, this makes our arm considerably more volatile. It's a tradeoff either way.

-DL

archiver
06-23-2002, 09:58 PM
Posted by Thomas A. Frank.

Engineer on team #121, The Islanders/Rhode Warrior, from Middletown (RI) High School and Naval Undersea Warfare Center.

Posted on 2/24/2000 9:51 AM MST


In Reply to: nate is correct. posted by Daniel on 2/23/2000 3:32 PM MST:



: The speed controller will go into dynamic breaking while it is sent either no signal, or a neutral signal.

I stand corrected. Very interesting.

Tom Frank

archiver
06-23-2002, 09:58 PM
Posted by Nate Smith.

Other on team #66, GM Powertrain/Willow Run HS, from Eastern Michigan University and GM Powertrain.

Posted on 2/23/2000 4:40 PM MST


In Reply to: Re: Dynamic Braking has limits... posted by Nate Smith on 2/23/2000 3:25 PM MST:



Here's what I just got back from Innovation First when I e-mailed them about this...

With no signal, brake is always on if the controller is powered up, and the
jumper is set. Brake can also be turned on and off by means of a limit
switch across the 'B' and 'C' jumper pins dynamically.

Nate

archiver
06-23-2002, 09:58 PM
Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


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

Posted on 2/23/2000 3:30 PM MST


In Reply to: Re: Dynamic Braking has limits... posted by Thomas A. Frank on 2/23/2000 3:02 PM MST:



Tom,

I could be mistaken, but I think you are not wholly correct regarding when the Victors dynamically brake their outputs.

If you UNPLUG the robot from power, then there is no dynamic breaking, but if the Victor looses signal and it has the jumper in the dynamic braking mode (pins C & B shorted), then the internal CPU on the Victor continues to short the motor leads to each other (a.k.a. dynamically brake the motor). When power is lost to the Victor, then the CPU can no longer do the job of turning on the correct FET's which short the leads, so dynamic braking is not possible.

I have not actually read the manual on this one, but I know from much experience that the battery must be unplugged to turn off the dynamic braking. It is not enough to just disable the Basic Stamp 2 CPU, or even to unplug the PWM signal wire.

Can anyone dramatically break the tie on this dynamic braking issue?

If so, please do.

Joe J.

archiver
06-23-2002, 09:58 PM
Posted by Daniel.

Coach on team #483, BORG, from Berkeley High School and NASA Ames & UC Berkeley.

Posted on 2/23/2000 3:35 PM MST


In Reply to: One man's experience posted by Joe Johnson on 2/23/2000 3:30 PM MST:



Try completely unplugging your onboard control system sometime. You'll see those lights flashing. That's all you need to know to tell you they're still doing their job. All that matters is that they're still connected to power. Look at your wireing. There's nothing you can do to that control system that will cut off power to those speed controllers. All power lines are direct.

Your controllers WILL function while the control system is shut off by FIRST.

-DL

archiver
06-23-2002, 09:58 PM
Posted by Nate Smith.

Other on team #66, GM Powertrain/Willow Run HS, from Eastern Michigan University and GM Powertrain.

Posted on 2/23/2000 5:03 PM MST


In Reply to: One man's experience posted by Joe Johnson on 2/23/2000 3:30 PM MST:




: If you UNPLUG the robot from power, then there is no dynamic breaking, but if the Victor looses signal and it has the jumper in the dynamic braking mode (pins C & B shorted), then the internal CPU on the Victor continues to short the motor leads to each other (a.k.a. dynamically brake the motor).

I don't have a Victor right here to look at, but I believe it's the left two pins that turn breaking on, pins A and B.

archiver
06-23-2002, 09:58 PM
Posted by Joe Johnson.   [PICTURE: SAME | NEW | HELP]


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

Posted on 2/23/2000 8:40 PM MST


In Reply to: Re: One man's experience posted by Nate Smith on 2/23/2000 5:03 PM MST:



I think Nate is right. My brain just skipped. The way I remember it (if I do remember it correctly) is that C is for COAST (i.e. not braking).

Look it up or try it both ways to be sure.

Joe J.

archiver
06-23-2002, 09:58 PM
Posted by Nate Smith.

Other on team #66, GM Powertrain/Willow Run HS, from Eastern Michigan University and GM Powertrain.

Posted on 2/23/2000 9:00 PM MST


In Reply to: Re: One man's experience posted by Nate Smith on 2/23/2000 5:03 PM MST:



now THERE'S a mistake i'm glad doesn't actually happen...

archiver
06-23-2002, 09:58 PM
Posted by Tony K.

Student on team #292, PantherTech, from Western High School and DaimlerChrysler.

Posted on 2/23/2000 5:54 PM MST


In Reply to: One man's experience posted by Joe Johnson on 2/23/2000 3:30 PM MST:



Yep, you're right. The output will be shorted even when transmission is stopped, as long as the Victor 883 has power. Also, if you lose the jumper, don't panic: The default position for the Victor is to dynamically brake, not to leave the output open. So, no jumper will brake it also....... as long as there is power on the input side.

Tony