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Author Topic: School Bus Stop Arm system (Servo or Stepper)  (Read 1491 times)
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engr.humair
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« on: March 14, 2010, 12:59:07 12:59 »

Dear all:

I am working on Project to drive School Bus Stop Arm On & Off (Picture attached for reference).

Can anyone guide me about which motor to use (Servo or Stepper) n what should be specification of the motor?

Thanks in advance.
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pickit2
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« Reply #1 on: March 14, 2010, 01:18:44 13:18 »

if arms fold flat to side of bus then I would choose a rotary solenoid. steppers may lock in open position, and select one with very low power torque, for safety.
link just for starters http://www.takano-sanki21.com/english/product/bistable.html
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engr.humair
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« Reply #2 on: March 14, 2010, 01:31:02 13:31 »

if arms fold flat to side of bus then I would choose a rotary solenoid. steppers may lock in open position, and select one with very low power torque, for safety.
link just for starters http://www.takano-sanki21.com/english/product/bistable.html

Thanks, Any other technical specification consideration that i should take care of?
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« Reply #3 on: March 14, 2010, 01:57:22 13:57 »

Windshield whipers on some busses use vacuum to move them.  I'm not sure this would offer any advantage to your project, as it likely adds complexity.  May add reliability?
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king
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« Reply #4 on: March 14, 2010, 06:22:30 18:22 »

This can be done simply by using Dc motor and limit switch. Dc motor is used to drive the Arm and Limit switches are used to define the Arm maximum and minimum turning position so there is no need to use Encoder or in short you don't need Feedback of the motor position, Just 'ON' the motor and stop it only when it hit the any of the limit switch.

Regards

King
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engr.humair
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« Reply #5 on: March 14, 2010, 07:49:51 19:49 »

Dear all:

The weight of Stop Arm moving part is 1.5kg approx.

Can anyone guide me abt specification of DC, solenoid or any other motor type? What should be the selection parameters of motor?

Waiting for response.

Thanks

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solutions
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« Reply #6 on: March 14, 2010, 09:38:55 21:38 »

You can buy air, electric and vacuum school bus stop arms here:  http://www.schoolbuspartsco.com/WebPages/crosswalkpages/stoparms.html

Do what they do, or buy one and reverse engineer it, if you still want to homebrew one.  If you're a cheapskate, cruise the salvage yards or even a bus company parking lot to see what's being done if you think you can improve it.  Remember that it has to work as well in Phoenix as it does in Anchorage and ice is no excuse for it not to deploy.

Also, if you decide to sell them, I'd make sure I had LOTS of liability insurance, in case it fails to go out that one time it's needed.....

Sorry for being a wet blanket - just trying to help.
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engr.humair
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« Reply #7 on: March 15, 2010, 07:26:52 07:26 »

if arms fold flat to side of bus then I would choose a rotary solenoid. steppers may lock in open position, and select one with very low power torque, for safety.
link just for starters http://www.takano-sanki21.com/english/product/bistable.html

Thanks for response. Can i use stepper motor? Will it be feasible??
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sphinx
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« Reply #8 on: March 15, 2010, 07:36:16 07:36 »

why try to use electrics when on a bus u got both pressured air and vacuum that would be simplest to make, then u can use switches to detect both positions u can make a piston and u can also use a home made air-motor, why make it more difficult than u need to, simplest is most like cheapest as well. i would use air/vacuum even if i could make a stepper or motor solution.

/regards
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« Reply #9 on: March 15, 2010, 09:18:39 21:18 »

Hi,
my litle idea..
linear motor (ie actuator for dish aerial)
simply mechanics, simple electonic
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« Reply #10 on: March 15, 2010, 11:47:17 23:47 »

Thanks for response. Can i use stepper motor? Will it be feasible??

Yep, you definitely can use a stepper motor for this application.

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« Reply #11 on: March 15, 2010, 11:53:38 23:53 »

one problem with steppers they can lock if control crashers and power is still on coils, it would be hard to move arm back to closed position.
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engr.humair
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« Reply #12 on: March 16, 2010, 04:46:28 04:46 »

one problem with steppers they can lock if control crashers and power is still on coils, it would be hard to move arm back to closed position.

Dear:

Which bistable rotatory solenoid motor should i prefer from ya link:
http://www.takano-sanki21.com/english/product/bistable.html

Large, Standard, Micro, Flat or Return spring type?
« Last Edit: March 16, 2010, 04:52:11 04:52 by engr.humair » Logged
solutions
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« Reply #13 on: March 16, 2010, 05:48:09 05:48 »

Dear:

Which bistable rotatory solenoid motor should i prefer from ya link:
http://www.takano-sanki21.com/english/product/bistable.html

Large, Standard, Micro, Flat or Return spring type?

Cuuuuuuuuuuuuute!  I never knew these existed.

However, the biggest dog in the pack only puts out 0.9 ft-lb of torque.  A kid sneezes out the window at the stop sign, or the bus stops on a very slight incline, and it won't move....
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oldvan
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« Reply #14 on: March 16, 2010, 05:53:19 05:53 »

Linear actuators like used for a satellite dish are usually quite forceful but slow moving.  One I have here takes 24 seconds to move 5 inches at full voltage of 12V, but will gladly supply 150 pounds of thrust.

Perhaps you can tell us how many (mili)seconds are allowable for the sign to fully extend and fully retract, what voltage you plan to supply to the actuator, etc.  Selecting the correct actuator will be easier with an understanding of what will be demanded of it.

Stepper motors are usually preferred because they offer the ability to precsely control position or speed.  This application benefits from neither, so may as well use less expensive means.







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« Last Edit: March 16, 2010, 05:58:47 05:58 by oldvan » Logged

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