Robot Arm C

[chalker]

Uhh, last I checked, if you put mechanical energy into an electric motor it became a generator, not a motor. Physically the same thing, but not functionally.

But I'm not sure that's relevant to a master and slave system. The master needs to have position sensors, not motors. If you are using servos as sensor, just like a generator isn't a motor, it shouldn't matter. Of course every servo in the slave is a motor.

Course official clarification couldn't hurt.

Jeff Anderson
Livonia, MI

True, however (and to emphasize THIS IS NOT THE PLACE FOR OFFICIAL CLARIFICATIONS), the rules don't say anything about the motor being energized or being used as a motor. I suspect most event supervisors would count a device that's normal function is as a motor, yet is being used as a generator or position sensor in this specific instance, as a 'motor'. Particularly if the thing is labeled as a motor or sold as such.

[harryk]

I've been reading some things on how to do the slave and master arm set up, and in the master arm the use of servos is for the built in potentionmeters, not the motors(which are completely disconnected). Most things I've read say to leave the motors in the servo, as they provide some resistance, but if needed for the rules they could be completetly removed with no problems

[iwonder]

My experience with making an arm out of VEX hasn't been the best. First off, using the metal parts is not a good idea as it's just too heavy. Even when I didn't use that, I didn't get very good results. With the way you attach shafts to the servos (simply inserting a square shaft into the servo), you have some wiggle before the servo actually spins. So, in an arm with a few joints, it'll be wiggling around way too much even though the shaft isn't actually turning. I haven't worked with VEX in a few years so I don't know if they've changed anything.

First, if metal isn't a good option, then what would be? Surely not wood... and I don't happen to have any facilities to do work with plastics, I've never seen anyone in SO that did. And even if the servos do have backlash, gravity is constantly pulling the arm down, and taking out any of the movement in the mechanics. That being said... the VEX motors could be to weak to lift the arm in the first place, which would make it sag and bounce around, neither of which would be good for a competition.

[sachleen]

My experience with making an arm out of VEX hasn't been the best. First off, using the metal parts is not a good idea as it's just too heavy. Even when I didn't use that, I didn't get very good results. With the way you attach shafts to the servos (simply inserting a square shaft into the servo), you have some wiggle before the servo actually spins. So, in an arm with a few joints, it'll be wiggling around way too much even though the shaft isn't actually turning. I haven't worked with VEX in a few years so I don't know if they've changed anything.

First, if metal isn't a good option, then what would be? Surely not wood... and I don't happen to have any facilities to do work with plastics, I've never seen anyone in SO that did. And even if the servos do have backlash, gravity is constantly pulling the arm down, and taking out any of the movement in the mechanics. That being said... the VEX motors could be to weak to lift the arm in the first place, which would make it sag and bounce around, neither of which would be good for a competition.

The VEX stuff I used to use was steel. Aluminum would be a much better choice.

Gravity would be pulling the arm down, but when imagine the arm turning but it's swinging back and forth before it comes to rest and you can bring it down. You want something that, when you stop moving the control, it just stops moving. If you gear it down enough, the VEX servos will be slow enough that it might not be a problem, but then you're sacrificing time. Also, I think VEX has new motors that provide more torque.

[iwonder]

I see your point, and it would be a major problem if there wasn't any bearing to hold the arm weight... but with a bearing there i would think there would be enough resistance to cancel out the backlash... it cant be to bad.

[sachleen]

I see your point, and it would be a major problem if there wasn't any bearing to hold the arm weight... but with a bearing there i would think there would be enough resistance to cancel out the backlash... it cant be to bad.

Experiment and find out. The first year I did Olympiad, my coach bought a VEX kit and I just used it. I didn't know what I was doing back then so it was a good starting point. I was just advising against it for this specific event in case any team is in that situation and looking to buy a kit... and VEX isn't cheap, anyway. I don't know what else there is out there for new teams to build from so this might be the best solution for someone who doesn't have any experience. I'm just sharing my experience. If you can make it work, awesome! I'd love to see your device in action.

[Flavorflav]

The vex motors tend to work a lot better than the Vex servos, because you do have to gear them down to avoid the jumping problem and the servos just won't give you the range of motion you need. You will sacrifice some speed, but you can make some of that up in the driving. I think Vex is a good option for teams who aren't up to scratch-building.

[sachleen]

The vex motors tend to work a lot better than the Vex servos, because you do have to gear them down to avoid the jumping problem and the servos just won't give you the range of motion you need. You will sacrifice some speed, but you can make some of that up in the driving. I think Vex is a good option for teams who aren't up to scratch-building.

The motors and servos are the same thing, only the motor is modified for continuous rotation. That's what I was referring to when I said servo. You would definitely want to use the "motor" instead of the 100deg range servos.

[sj]

I have a question...

Having finally been able to look at a rule book i was wondering if # of motors impacts score. I didn't see any thing to indicate that but maybe im missing something.... all i saw was that it would be used as a tiebreaker.

[chalker]

I have a question...

Having finally been able to look at a rule book i was wondering if # of motors impacts score. I didn't see any thing to indicate that but maybe im missing something.... all i saw was that it would be used as a tiebreaker.

Correct, it's only a tiebreaker. But people are assuming that at nationals there will be a whole bunch of teams that get a perfect score and thus have to utilize the tiebreakers.