Robot Arm C

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Re: Robot Arm C

Post by illusionist » March 2nd, 2012, 2:34 pm

I have to agree that there is no need for expensive equipment, such as those 300 dollar kits. I'm just saying that more teams prefer to use kits. It's not that people think it's too expensive. Personally, I would love to learn the electronics for the arm, but I'd rather spend time working on the current arm than learning/researching and then implementing. I usually save the learning stuff like this for the summer. Just my two cents.

As for revisions, the D battery is something that will definitely be a little difficult. Perhaps something like a pea instead. I remember in Robo Cross, there were coins we had to pick up. They didn't require any special equipment, just a couple pieces of cardboard taped to the end of the gripper that allowed it to slide under the coin.
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Re: Robot Arm C

Post by GoldenKnight1 » March 2nd, 2012, 5:33 pm

chalker wrote:
wlsguy wrote: All schools should be able to compete at a similar level with a reasonable amount of money.
Science Olympaid should be more about effort and less about $$$$.
As the comments have shown, for some reason teams aren't wanting to put in a ton of effort on the design. It amazes me that certain people will become essentially materials sciences experts for events like helicopters, but don't want to do rather basic electronics stuff for robot arm.
illusionist wrote:Just my personal experience-

... Also, I have very little experience with the electronic (control) aspect of robotics, and so trying to build a system from scratch using some transmitter I found online with motors, which I don't know if they'll even work with my transmitter, was somewhat of a daunting task. So chalker(7), the issue isn't (in my eyes) that teams want something that they can snap together using someone else's engineering or designs, but rather that we don't know how to work with the electronics. Thus, our team ended up using Vex electronics with our own hardware.
I agree with Chalker here. Yes, my kids and I did not come into this event with a degree in circuits or engineering but because of this event we have all learned a lot, but we did start in October. They took the time to do research, look at what others had built from scratch, looked and equipment specs and reviews, and have come out of it with a rather competitive robot. Our lack of knowledge, while making this challenging, I think is part of the point. We want to expose these students to science and engineering. I doubt most of the students that start studying Disease Detectives are already knowledgeable about what the CDC does, but they learn it. I think every coach has experienced the kind of feelings towards certain events like Illusionist is stating. We all have our field of expertise and when we need to help students in event that we are less comfortable it can be a challenge for us to. So I don't think that "they don't know electronics" is any more valid of an argument than me saying "I don't know enough about Biology so can we please get rid of Microbe Mission."

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Re: Robot Arm C

Post by mrsteven » March 2nd, 2012, 5:50 pm

Ill throw a different view point here:
I actually do know alot about circuits, engineering, programming and this type of deal.
I'm having issues with costs. Our school has no vex kits (Im not sure how anyone is getting them for "free") or anything equivalent regardless if I could use them. We have speed controllers, receivers and such for a larger system than the arm allows. I find that LARGER items like the sumobots and other things make it EASIER because more schools have set ups for larger type things.
I more or less deterred from making one myself after seeing the costs involved with motors and sensors, so I was forced into a kit (cheap cheap kit) by our SO budget. I was going to steal the motors from the kit and use them in my own design but more or less the cheap cheap kit (surprise surprise) were cheap motors and fashioned to be used solely for the purpose they came for (or simpler process) which is unhelpful for how it is intuitive to use them.

Honestly, cost is the huge issue for me and because of it I won't be able to make a truly competitive bot.

If, however, we were talking about a larger system (like sumo bots or something larger) we totally have the tools have equipment set ups for that and really would only need to buy minimal material.

My thoughts.
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Re: Robot Arm C

Post by illusionist » March 2nd, 2012, 6:18 pm

Just to make sure we're clear, I'm not advocating for removing Robot Arm by any means. I was just trying to show what some teams might feel (mainly those that don't compete). I would love to see the return of this event next year.
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Re: Robot Arm C

Post by mrsteven » March 2nd, 2012, 6:28 pm

illusionist wrote:Just to make sure we're clear, I'm not advocating for removing Robot Arm by any means. I was just trying to show what some teams might feel (mainly those that don't compete). I would love to see the return of this event next year.
I'd like to see sumobots for illinois. We never actually had it, ISO outruled it.
Some sort of robotics event that is larger based for larger components and bots.
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Re: Robot Arm C

Post by ichaelm » March 2nd, 2012, 7:13 pm

Sounds like an interesting discussion, and it reminded me of something. When I was in 6th grade and Borders was still around, I bought a book called "Junkbots, Bugbots, and Bots on Wheels." I still recommend that book to anyone who wants to learn about building robots as a hobby. One of the extremely important things it taught me was how to scavenge. You can go to your local junkyard, ask your friends from broken stuff, or ask an electronics store for the broken stuff they can't resell. For this event, printers are a goldmine! You'll get these great stepper motors, which can do a whole lot for you if you combine them with the right gearing. Gears can be trouble, but you can usually get them out of the same printer, or maybe an old cassette player. (This may be a little dated!) Printers also have timing belts, perfect for relocating your elbow motor and gears to a more weight-conscious position, and long plastic or steel poles for construction. As for electronics, if you're using DC motors, you'll probably want to spend some cash on a real ESC - you can't really scavenge those unless you have really awesome friends. And the radios are cheap anyway, or you could go with a custom wired control system with a few of those cheap potentiometers from Radio Shack, or an old stereo set, or a gamecube controller! Stepper motors are conceptually harder to control, but in terms of electronics, it's a lot easier to jury-rig a stepper controller than an ESC, assuming you have some brains in the form of an Arduino, or if you want to be cheap about it, a FREE sample PIC microcontroller from Microchip! Almost anything you scavenge will have some BJTs you can use to drive a stepper, or you can spend $10 or so on some relatively high-power MOSFETs. For me, the most expensive part of my bot was the gears - I've just had too much experience with cheap plastic gears stripping at some critical moment, so I went with a legit steel planetary gearbox from the internet. I also used a relatively expensive ESC, since I already had it from the sumobot. Personally, I didn't go the stepper route, instead I made my own servos from some $5 scooter motors, radio shack potentiometers, and those gears I talked about. The way I see it, it would be great to make a whole robot arm out of scratch like this, and theoretically it could be as good as an expensive one. But besides experience, there's one major constraint that the money really helps you out with: time. You can't spend 5 months crafting your bot from the junkyard, and then have only a weekend to practice, or maybe even not finish it in time. Teams with the resources will buy big expensive servos, electronics, and kits because they just don't have the man-hours to do it from scratch. That is where money helps you, and that is why we're not bringing my bot to regionals. Mine isn't finished. Luckily, my friend went through a more traditional process (plus he's a genius) and ended up finishing in time for regionals. Also, mine is kinda aimed at breaking the tiebreaker, but that's beside the point. I encourage anyone to try to build the El Cheapo robot arm, since it's a great experience, but I'm warning you, expect to have a much bumpier ride than the team who decides to spend $300 off the bat. Like, sure, it's probably possible to see Europe for $25 a day, but it won't be comfy!

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Re: Robot Arm C

Post by ODoyleRules » March 2nd, 2012, 7:20 pm

In terms of the current rules, I think you have three issues Chalker that are really driving up the cost. One is the time issue. As someone pointed out earlier, you have roughly 6 sec per object. That means speed, and that can cost money, especially since you are dealing with kids who in general are having their first real experiences with building a robot. This can be fixed in future rules by either slightly reducing the number of objects, or a slight increase in time, like say 30 sec or so.

Your second issue is weight, which I pointed out earlier. Kids tend to over build things. You should see some of the arms I have seen this year. They could be used as baseball bats, their that solid. But my point is that since you know the arms are already going to be heavy, the objects need to be light.

Lastly is your motor tiebreaker. I get what you folks were trying to do, but for many teams decreasing motors means increasing electronic controls, which increases cost. To me, time is always the best tiebreaker for robotics events in S.O. as they reward practice, and getting your robot done in time to practice.

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Re: Robot Arm C

Post by chalker » March 2nd, 2012, 7:33 pm

mrsteven wrote: If, however, we were talking about a larger system (like sumo bots or something larger) we totally have the tools have equipment set ups for that and really would only need to buy minimal material.
The sumobots size limit last year was 40 cm x 40 cm x 40 cm. The robot arm size limit is 30 cm x 30 cm x unlimited height. Is there really that big of a difference that it's noticable? I don't understand how a the 'tool and equipment' you have couldn't work in a space slightly smaller.

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Re: Robot Arm C

Post by chalker » March 2nd, 2012, 7:35 pm

ODoyleRules wrote: Lastly is your motor tiebreaker. I get what you folks were trying to do, but for many teams decreasing motors means increasing electronic controls, which increases cost. To me, time is always the best tiebreaker for robotics events in S.O. as they reward practice, and getting your robot done in time to practice.
We had time as a tiebreaker last year in the trial event rules, but deliberately removed it. Anytime you require timing for an event it puts a burden on the event supervisors in terms of manpower needed, and we had feedback that there was already too many things the supervisors were having to watch out for during the competition. We can reconsider it for next year, but personally I'd rather find something else that rewards practice but doesn't burden the judges.

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Re: Robot Arm C

Post by chalker » March 2nd, 2012, 8:44 pm

ODoyleRules wrote: First of all a servo with only 2.5 kg of torque will not have enough torque at the base to put a battery in the north goal. Especially if it is built by your average student.
I disagree with this, and it appears that there is a misconception amongst a lot of people regarding the 'strength' needed by the servos or motors. A lot of this comes down to making the servos work 'smarter' instead of 'harder';)

First some basic calculations:
Average weight of a D battery: 170 g (yes I know it varies a bit by type / manufacturer)
Approximate distance from center of robot square to center of north jug = 50 cm
(assuming worst case scenario in that you have a servo mounted at the center of the robot square with a long rod holding the D battery at the end)
Torque on servo = 50 cm * 170 g = 8500 g cm = 8.5 kg cm

Now the servo I quoted isn't even close to this strength (it's only 2.5 kg cm), and I haven't taken into account the weight of the arm or gripper / servos mounted on the arm. If you really want to brute force this estimate a doubling of the torque needed to compensate for all that extra weight and buy yourself a 15 kg cm servo for $10-$15 instead of the $2.60 I quoted (still nowhere near the hundreds of dollars cost I've heard people are spending).

But the key is you DON'T need to brute force it. Don't use the servos as the actual joints for your arm. Use some simple hinges or axles and offset the servos with control rods or small gears. Here's a good example diagram that shows that concept: http://www.tu-ilmenau.de/fakmb/typo3tem ... 6d1de5.jpg This is very common the RC airplane world, where you never mount a servo directly inline with the pivot point of a control surface, rather you always offset them and use small control arms to gain additional leverage.

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