Robot Arm C

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Re: Robot Arm C

Postby jander14indoor » October 2nd, 2011, 6:09 am

Again, NOT the place for clarifications.

But in the spirit of reasoned discussion.

I think you've got most of the items understood ichaelm. I don't think a permanent magnet would meet the definition of a motor in this case because it isn't changing any input to a mechanical output, unless you consider the mechanical act of putting the magnet near an object, but that's mechanical to mechanical.

But on your electro magnet, I think the devil is in the details. For a straight electromagnet there isn't necessarily a mechanical energy output.
- One case. The arm locates the electromagnet next to a nail. Actuate the magnet locking the nail onto it, but nothing moves. Then the arm moves the whole thing to a goal box. No transformation of electrical to mechanical motion by the electromagnet in that case. The motors on the arm did that!
- Second case. This time the electromagnet is located at a distance from the nail by the arm. Electromagnet turns on and the nail is pulled to the magnet over a distance. Mechanical motion, you have a 'motor' again.

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Re: Robot Arm C

Postby chalker7 » October 2nd, 2011, 6:52 am

jander14indoor wrote:Again, NOT the place for clarifications.

But in the spirit of reasoned discussion.

I think you've got most of the items understood ichaelm. I don't think a permanent magnet would meet the definition of a motor in this case because it isn't changing any input to a mechanical output, unless you consider the mechanical act of putting the magnet near an object, but that's mechanical to mechanical.

But on your electro magnet, I think the devil is in the details. For a straight electromagnet there isn't necessarily a mechanical energy output.
- One case. The arm locates the electromagnet next to a nail. Actuate the magnet locking the nail onto it, but nothing moves. Then the arm moves the whole thing to a goal box. No transformation of electrical to mechanical motion by the electromagnet in that case. The motors on the arm did that!
- Second case. This time the electromagnet is located at a distance from the nail by the arm. Electromagnet turns on and the nail is pulled to the magnet over a distance. Mechanical motion, you have a 'motor' again.

One view.

Jeff Anderson
Livonia, MI


I would agree with Jeff in an completely unofficial context.
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Re: Robot Arm C

Postby chalker » October 2nd, 2011, 8:31 am

chalker7 wrote:I would agree with Jeff in an completely unofficial context.


And I would officially agree with my brother's unofficial agreement;)

Just want to make sure everyone is keeping this in perspective. Motor count ONLY comes into play as a tiebreaker. Obviously our intention when writing the rules was to 'reward' teams that are able to 'do more with less'. The thought being it's much harder to engineer and efficiently operate a device that has less 'ways to move'. Thus for all you trying to figure some way around the specific wording, please keep in mind the spirit of our intent.

Of course this is all unofficial, however we've already started to have some internal committee conversations about this. I strongly encourage someone to submit a question at soinc.org so that we can formally respond there.

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Re: Robot Arm C

Postby Primate » October 2nd, 2011, 11:38 am

chalker wrote:
chalker7 wrote:I would agree with Jeff in an completely unofficial context.


And I would officially agree with my brother's unofficial agreement;)

Just want to make sure everyone is keeping this in perspective. Motor count ONLY comes into play as a tiebreaker. Obviously our intention when writing the rules was to 'reward' teams that are able to 'do more with less'. The thought being it's much harder to engineer and efficiently operate a device that has less 'ways to move'. Thus for all you trying to figure some way around the specific wording, please keep in mind the spirit of our intent.

Of course this is all unofficial, however we've already started to have some internal committee conversations about this. I strongly encourage someone to submit a question at soinc.org so that we can formally respond there.

Done. Let us know what you decide!
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Re: Robot Arm C

Postby illusionist » October 3rd, 2011, 1:42 pm

A cheap and plausible solution for most teams:
Using two Lego NXT Mindstorms sets, it's possible to create a master-slave system. Although there might be some lag between input and output (I don't think it'll be significant at lower levels). You might end up using 6 motors, but I think it offers a pretty decent solution.

Does anyone have experience with a robot arm that is of similar dimensions to this year's created from Legos? I'm thinking that it might be a little heavy and clumsy though.
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Re: Robot Arm C

Postby Balsa Man » October 3rd, 2011, 3:42 pm

chalker wrote:Of course this is all unofficial, however we've already started to have some internal committee conversations about this. I strongly encourage someone to submit a question at soinc.org so that we can formally respond there.


So, unofficially, of course, that would mean a solenoid, regardless of what the motion of the plunger was used to do, like to....flip a lever that would say, block, or allow a range of motion of an arm component, would be classified as a motor. Is that what you're thinking here?
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Re: Robot Arm C

Postby harryk » October 3rd, 2011, 5:09 pm

illusionist wrote:A cheap and plausible solution for most teams:
Using two Lego NXT Mindstorms sets, it's possible to create a master-slave system. Although there might be some lag between input and output (I don't think it'll be significant at lower levels). You might end up using 6 motors, but I think it offers a pretty decent solution.

Does anyone have experience with a robot arm that is of similar dimensions to this year's created from Legos? I'm thinking that it might be a little heavy and clumsy though.

I'm not saying this is a bad idea, but unless you already have the kits, the same amount of money could go to making a decent custom arm
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Re: Robot Arm C

Postby illusionist » October 3rd, 2011, 6:37 pm

harryk wrote:
illusionist wrote:A cheap and plausible solution for most teams:
Using two Lego NXT Mindstorms sets, it's possible to create a master-slave system. Although there might be some lag between input and output (I don't think it'll be significant at lower levels). You might end up using 6 motors, but I think it offers a pretty decent solution.

Does anyone have experience with a robot arm that is of similar dimensions to this year's created from Legos? I'm thinking that it might be a little heavy and clumsy though.

I'm not saying this is a bad idea, but unless you already have the kits, the same amount of money could go to making a decent custom arm

Yeah, our team has like 4 kits combined so... =P
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Re: Robot Arm C

Postby blue cobra » October 21st, 2011, 10:35 am

Was tipping a problem at Nationals? D batteries probably weigh about 150g and the North Goal is nearly the full 70cm away.

What was successful for moving the parts of the arm? Is a servo the standard? The arm has to be able to fold up into the 30cm square, so I'd imagine that limits things that would extend beyond the arm itself.

What types of control systems are typically used? I have some, but very limited, rc experience (typically just forward/back, left/right controls), and I'd imagine that for each moving part you have you would need another control. What systems are used for these robots, and where could I learn about them?
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Re: Robot Arm C

Postby harryk » October 21st, 2011, 12:44 pm

blue cobra wrote:Was tipping a problem at Nationals? D batteries probably weigh about 150g and the North Goal is nearly the full 70cm away.

What was successful for moving the parts of the arm? Is a servo the standard? The arm has to be able to fold up into the 30cm square, so I'd imagine that limits things that would extend beyond the arm itself.

What types of control systems are typically used? I have some, but very limited, rc experience (typically just forward/back, left/right controls), and I'd imagine that for each moving part you have you would need another control. What systems are used for these robots, and where could I learn about them?

As for tipping over, I'm going with the traditional SO method of bringing a couple 10lb dumbells to weigh down the base
This is a good intro to the mechanics but not so much the electronics:http://www.societyofrobots.com/robot_arm_tutorial.shtml
And this is a torque calculator: http://www.robotshop.com/robot-arm.html(very helpful)
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Re: Robot Arm C

Postby jander14indoor » October 21st, 2011, 2:46 pm

One master slave system showed up at nationals. Worked pretty well, main deficiency was slop in the system. Slave didn't follow master real accurately. That said, it was easy to control and see what was going on. Less slop though would improve time and reduce learning curve.

PS, before counting the servos on the master as motors, see unofficial discussions above.

As to tipping, I didn't see it much, more a problem of arm strength with the batteries and the far goal. I saw more arms buckle or flex excessively than robots tip. As already said, no weight limit, easy to add mass for stability. Smart too.

Arm size vs robot box. Keep in mind its a square, there's no top to that box! The larger devices I've seen have just pointed everything up until the timer starts. I didn't see much in the way of fancy folding.

What worked? Powerful servos. Stepper motors.

Is there a 'standard' solution? Not yet, event is too new.

Jeff Anderson
Livonia, MI

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Re: Robot Arm C

Postby gh » October 22nd, 2011, 7:43 am

By the way, I should note that designing and operating a many-degree-of-freedom (DOF) robot arm is actually quite difficult, from the perspective of computerized control. The more joints you put into the arm, the harder it becomes to solve the problem, "how do I rotate the joints so that the end actuator is at <x, y, z>?"
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Re: Robot Arm C

Postby ichaelm » October 24th, 2011, 8:50 am

Speaking of computer control, has anyone here done any work on actually using computer programming to control the arm, such as with VEX, Legos, or some other custom system? I would think it could be a big advantage over traditional servo systems, not just because of easier control but also because of the 5-6V limit on traditional hobby servos.

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Re: Robot Arm C

Postby sj » October 24th, 2011, 12:19 pm

Personally i'm against straight computer control of the arm due to the possibility that one slightly not up-to spec piece on the competition board could lead to major disasters. Of course the rules are very explicit about how the board should be set up but even the slightest variation could throw off the whole system. However i believe programing and partial automation is very important. Personally i'm looking into a master slave system once i finish tweaking the actual arm.
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Re: Robot Arm C

Postby Saturiea » October 26th, 2011, 6:59 pm

In theory the best programmed arm would also have some sort of visual sensor to check the board before starting. However this would be a bit unfeasible for most things. Back to reality. I think that a well practiced team can do just as well as a programmed robot in terms of getting the most/all of the points.


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