Scioly.org

chalker wrote:

twototwenty wrote: It would be quite possible to build a sucessful arm with only three motors, as can be seen with this example:
http://www.youtube.com/watch?v=62HaAmbV ... afe=active

Nice robot arm. Is that your team? If so, any rough idea of the cost of all the parts? We've been having a bit of a debate at the national level of how much it would cost to make a competitive arm (which that design seems to be).

That design appears to cost around 65 dollats max.

I just finished my arm before a competition last week, it is a master-slave system and still has A LOT of calibration to do, it works but it needs to be a little more precise and I need to get more practice with it, and then I should be set to go for a perfect score

harryk wrote:I just finished my arm before a competition last week, it is a master-slave system and still has A LOT of calibration to do, it works but it needs to be a little more precise and I need to get more practice with it, and then I should be set to go for a perfect score

Sorry, a few questions

Where could I go to learn how to build one?
How much would it cost?
What kind of knowledge would someone need to build it?
How much knowledge did you have before building it?

What kind of servos are you all using for your arms. How much torque do you need. I'm making an assumption that servos are the way to go for a master slave system but if someone could provide some model numbers or links it would be much appreciated.What i'm seeing are "high torque servos" which are rated at about 240 inch ounces of torque... is this sufficient? Also is it possible to gang two servos on opposite sides of a joint so as to double the available torque?

To chalker:
That was not my arm; I had found that on youtube, and liked the way it managed well with only three motors. However, i have built a quite vallid arm with a budget of roughly 50 ollars

sj wrote:What kind of servos are you all using for your arms. How much torque do you need. I'm making an assumption that servos are the way to go for a master slave system but if someone could provide some model numbers or links it would be much appreciated.What i'm seeing are "high torque servos" which are rated at about 240 inch ounces of torque... is this sufficient? Also is it possible to gang two servos on opposite sides of a joint so as to double the available torque?

More torque than you'd think. The Olympians I've been coaching have been experimenting with so-called High-torque servos rated to as much as 17N-cm at 6VDC and they've found that by the time you factor in the weight of the end-effector mechanism and a battery (the heaviest item, by far), even 17N-cm isn't quite enough. Every servo I've seen that has more torque than that is no longer "standard" size, but 1/4-scale or larger. I'm coaching three teams but only one is doing a master-slave system and they've had to "create" servos for a couple of joints using largish DC motors, add their own feedback pot, and use an outboard servo amp.

OK thanks for the feedback. That is what i had figured and i was debating wether we wanted to go through the trouble rather than making a well built and polished vex arm.... We are a rather uncompetitive state in robot events typically so we may not bother unless we make nats again.

NinjaChicken wrote:

harryk wrote:I just finished my arm before a competition last week, it is a master-slave system and still has A LOT of calibration to do, it works but it needs to be a little more precise and I need to get more practice with it, and then I should be set to go for a perfect score

Sorry, a few questions

Where could I go to learn how to build one?
How much would it cost?
What kind of knowledge would someone need to build it?
How much knowledge did you have before building it?

1. I learned a lot from the lynxmotion forums
2. Now I definetly went overboard on this(because I love robotics ) and paid for the fancy bits, where I could have otherwise improvised, but I'd say on a tight budget I could have built a very similar one for under $200
3. Well, a fair amount of both technical and engineering expirience, and basic coding knowledge
4. The only thing I really lack knowledge wise is coding, but I was able to get some good help from online

sj wrote:What kind of servos are you all using for your arms. How much torque do you need. I'm making an assumption that servos are the way to go for a master slave system but if someone could provide some model numbers or links it would be much appreciated.What i'm seeing are "high torque servos" which are rated at about 240 inch ounces of torque... is this sufficient? Also is it possible to gang two servos on opposite sides of a joint so as to double the available torque?

For instance my shoulder and elbow servos are 1/4 scale and output 343 ozin which is still not enough to lift a battery, though I can accomplish that through the use of some load balancing springs
You could certainly use two servos, though you would have to make sure the programming turns them in opposite directions

Here is a handy torque calculator: http://www.robotshop.com/robot-arm.html

illusionist wrote:

chalker wrote:

twototwenty wrote: It would be quite possible to build a sucessful arm with only three motors, as can be seen with this example:
http://www.youtube.com/watch?v=62HaAmbV ... afe=active

Nice robot arm. Is that your team? If so, any rough idea of the cost of all the parts? We've been having a bit of a debate at the national level of how much it would cost to make a competitive arm (which that design seems to be).

That design appears to cost around 65 dollats max.

The transmitter & receiver alone is $40, plus the claw is another $20 if you buy the parts from VEX. I would estimate it to be around $100.

sachleen wrote:

illusionist wrote:

chalker wrote: Nice robot arm. Is that your team? If so, any rough idea of the cost of all the parts? We've been having a bit of a debate at the national level of how much it would cost to make a competitive arm (which that design seems to be).

That design appears to cost around 65 dollats max.

The transmitter & receiver alone is $40, plus the claw is another $20 if you buy the parts from VEX. I would estimate it to be around $100.

That arm in the video didn't use VEX. They appeared to be using just plain old hobby servos and possibly a homemade controller. The controller is obviously wired which eliminates the need for a transmitter and receiver.
3 hobby servos are probably around 20 to 40 dollars depending on which type you get and the controller was probably around 20 bucks. I'd say Illusionist was probably right in assuming it was around 65 bucks.