|
|
|
![]() |
|
|||||||
|
||||||||
![]() |
| Thread Tools |
Rating:
|
Display Modes |
|
#16
|
|||
|
|||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
This might help you,
This is our team's robot from 2005. On the first stage of the arm we used two of the 6v FP motors (they messed up that year and gave a bunch of teams the wrong motor). On the second stage we used a single van door motor. We used cable and bicycle wheels to gear down the main arm about 18 to 1* and we geared the small arm down to about 9 to 1*. It had no problem holding a single 9 lb tetra 13' out. Here is a link to a picture of the robot. http://www.chiefdelphi.com/media/photos/21524 As for programming we used a potentiometer on each arm and compared the value they gave us to a target position for the arm. Based on that information we passed a value to the motor to move. If you have any questions please feel free to ask. -Dan Karol *numbers are a guess and may not be what we actually used. Last edited by Dan_Karol : 23-01-2007 at 17:33. Reason: I didn’t answer all questions |
|
#17
|
||||
|
||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
While some of the motors may "take the heat", its a good design practice to attempt to minimise the load on the motor when the assembly is static. Counterweights help greatly with this. Another option is gas shocks like the ones used to hold up car trunks and hatchbacks. They not only put out alot of force but provide some dampening. Worm gears are definately a good idea as well. I would highly recomend them. I should note that the gearset in the van door motor is NOT a worm gear set. It is a healical gearset which can be backdriven.
Also, if you plan on using PID, you must make every effort to minimize the amount of backlash in your system or else put the sensor directly on the motor. Chains are especially bad about backlash unless active tensioners are used. |
|
#18
|
||||
|
||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
Keep in mind that when you need high-torque motors (like in a programmed non-back drive mode), it helps to use two of them, if possible. If you wire the two motors together (+ to + - to -, then the combined + and - to the victor controlling them), now you are taking two circuits and combining them into one, distributing the power evenly. Not only will the two motors operate in perfect harmony, it will also multiply your torque and stall rating by two.
|
|
#19
|
|||||
|
|||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
Quote:
|
|
#20
|
||||
|
||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
Hmm...I had no clue this way illegal. Looks like we'll have to do it in programming then.
|
|
#21
|
|||||
|
|||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
I thought so too, and was about to respond saying so, but I couldn't locate the relevant rule to quote. Can you help me find what I'm certain I'm overlooking? So far, I haven't seen anything in the manual that says each Victor can connect to only one motor. The closest is <R98> which limits Spike relay modules to a single motor. <R91> restricts things in the other direction: "Each motor, actuator, and compressor must be connected to one, and only one, speed controller or relay module." But it doesn't say you can't connect multiple motors to the same speed controller.
|
|
#22
|
|||||
|
|||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
You should have received two Y-connector pwm cables in the Kit of Parts. You can use them to control two Victor speed controllers from the same pwm output on the Robot Controller.
|
|
#23
|
||||
|
||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
That will work as well...but I'm starting to think that two motors on one victor is legal. We did this last year with two CIMs in the '06 gearbox...or at least I did - somebody could of changed it.
|
|
#24
|
|||
|
|||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
Quote:
(Also BTW each motor had it's own victor, although one victor is plenty to drive this setup if this years rules allow it, Also triple check wiring so the motors work together, I tended to label with arrow which way things turned with a marker on the part of the motor showing so I knew if red went to pos or it it was the other way) Biff Last edited by Biff : 24-01-2007 at 01:27. |
|
#25
|
|||
|
|||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
Quote:
The control software then uses a small dead band window. Once the motor gets the arm into the window the power can be completely shut off in order to prevent overheating. The FP and the motors on the small bane bots gear boxes will overheat quickly if run at stall. Have fun, Eugene |
|
#26
|
|||||
|
|||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
This is looking like a good solution....thanks! McMaster Carr offers a nice selection of "gas springs".
|
|
#27
|
|||||
|
|||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
Quote:
Quote:
Quote:
Quote:
Quote:
|
|
#28
|
|||
|
|||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
In the past it has been a rule that only one motor may be attached to a Victor 884, however the rules seem to leave that open to interpretation this year. All I can say is that it's a very bad idea, as at stall torque the current draw of two CIMs well exceeds the rating of the Victor 884 and you'd be likely to see magic smoke at least once before the end of a regional...
Ask yourself this: Would you rather buy one extra victor and plan in the few ounces extra, or continually replace burned out victors because they overload and release magic smoke every few matches? //Dillon Compton |
|
#29
|
|||
|
|||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
In the Good Practices manual, section G.6.3.1 V884 Speed Controllers it states "Only one large motor (CIM, Fisher-Price, Globe or similar motor should be controlled per speed controller". Didn't look, but there is probably a similar statement for the Spikes as well.
In any circumstance, the motors should be individually fused. |
|
#30
|
|||||
|
|||||
|
Re: PID How to hold an arm in a fixed position without a locking gear box
With the motors we have used, we have never done special programming. Usually, they won't back drive with power applied (IE the robot is on). If, however, you turn off the motor, they will backdrive...such as our arm did in 2005. This year however, we made specific checks to make sure our arm will not come crashing down on a robot on our ramp at the end of the match. We also build a custom gearbox to use two motors.
|
![]() |
| Thread Tools | |
| Display Modes | Rate This Thread |
|
|
Similar Threads
|
||||
| Thread | Thread Starter | Forum | Replies | Last Post |
| PID without a Ph.D. | Joe Johnson | Programming | 3 | 07-02-2006 17:37 |
| Drive Straight C Code using Encoders without PID? | Chris_Elston | Programming | 17 | 15-02-2005 23:41 |
| White Paper Discuss: Locking the Bosch 3360 Drill in low gear | CD47-Bot | Extra Discussion | 4 | 05-08-2003 02:10 |
| how do you hold pins in? | archiver | 2001 | 4 | 23-06-2002 23:45 |
| How do teams hold their brainstorming meetings? | Anton Abaya | General Forum | 10 | 03-01-2002 18:02 |