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Firestorm65
04-06-2009, 09:03 PM
This is a CAD glimpse of what we are putting together. It is still unclear if we will be able to attend, but we plan on building it anyway. This is not a completed picture and is missing some important things like the scoring plates, sensors, and camera.

Features:
6 DoF Legs
Unlimited Pan Rotation
Metal Mechbox Cannon

Well, I guess I just feel like sharing. Feel free to comment.

lnxfergy
04-06-2009, 09:24 PM
You're gonna build that for $30? Cool, where did you get the servos that cheap?

-Fergs

Azinman
04-06-2009, 09:26 PM
Nice design! It looks like it uses around 12 servos with the servo erector set peices from lynxmotion if I'm correct. :D

Firestorm65
04-06-2009, 09:44 PM
You're gonna build that for $30? Cool, where did you get the servos that cheap?

-Fergs

Two different projects. This involves a considerably larger budget.

The entire skeleton is standard lynxmotion pieces. Plans call for 13 5990TG's and 1 1425CR, although we are looking for a more powerful CR standard size servo. The pan/tilt is hidden inside the shell.

DresnerRobotics
04-08-2009, 04:01 PM
How do you plan on aiming using a continuous rotation servo on the pan?

lnxfergy
04-08-2009, 04:05 PM
How do you plan on aiming using a continuous rotation servo on the pan?

Aim? nah, you just spin around real fast and shoot everything...

-Fergs

DresnerRobotics
04-08-2009, 04:11 PM
Aim? nah, you just spin around real fast and shoot everything...

-Fergs

If you had a fast enough gun and turret... that could work! :D

Firestorm65
04-09-2009, 12:41 AM
Why would continous rotation be any different to aim? The design simply removes limits in that axis.

Adrenalynn
04-09-2009, 01:38 AM
Because there is no repeatability there can never be any precision?

lnxfergy
04-09-2009, 09:16 AM
Why would continous rotation be any different to aim? The design simply removes limits in that axis.

To make a servo continuous, you snip the endpoints, and disconnect the potentiometer (the feedback). Thus, you go from a closed-loop positional feedback system to a completely open-loop system.

-Fergs

darkback2
04-09-2009, 09:53 AM
In defence of a CR pan servo for the gun...If, the camera and gun are mounted on top of the CR pan, and perhaps you use a laser or cross hairs...or something, then having CR pan could be to your advantage. How many of us have a mech that can shoot behind itself. As for an open system, the closure comes from you. You are looking through the camera, and you can figure out when the gun is pointed towards what you want to shoot.

I can also see the advantage of using a standard servo for the pan tilt for your gun. If you have the servo well calibrated, then you can tell it to aim at a given point and fire.

To be honest, I don't know which of these ideas will work better...only time will tell.

lnxfergy
04-09-2009, 09:57 AM
In defence of a CR pan servo for the gun...If, the camera and gun are mounted on top of the CR pan, and perhaps you use a laser or cross hairs...or something, then having CR pan could be to your advantage. How many of us have a mech that can shoot behind itself. As for an open system, the closure comes from you. You are looking through the camera, and you can figure out when the gun is pointed towards what you want to shoot.

I can also see the advantage of using a standard servo for the pan tilt for your gun. If you have the servo well calibrated, then you can tell it to aim at a given point and fire.

To be honest, I don't know which of these ideas will work better...only time will tell.

You know DB, right after I posted I realized that the human might be able to do the feedback. That said, I have a feeling that you'd want to add a few indicators (such as when you are pointing straight forward) otherwise its gonna be tough to remember which way your legs are facing when you start moving your head around...

-Fergs

darkback2
04-09-2009, 10:05 AM
Ok...this isn't my thread, so I'm not sure I should post this...

What if, you use software so that the robot responds as if the position your head is facing is forward at all times. So if your head is facing at some angle, and you tell the robot to walk foward, it would interpolate the command and walk in the direction you are facing...

Easier idea would be to have two cameras...one for the gun/aiming, and the other for walking...and if your running multiple cameras...then maybe 5 would be the way to go one for each direction and one for the gun...

Ok...that was obserd.

lnxfergy
04-09-2009, 10:07 AM
Ok...that was obserd.

I concur... 5 cameras... on a scout... whoa....

-Fergs

Firestorm65
04-10-2009, 01:02 AM
The way we are aiming is just move left or right to the target, with a few software based adjustment or manual control. It is never fire at 10 degrees. As far as orienting with the legs, we were looking at optical shaft encoders or switches at certaiin positions. Does anyone know of a standard size continous rotation servo with a buit in shaft encoder?

Adrenalynn
04-10-2009, 01:03 AM
Left - whiiiir wait, stop, right! whiiiir, no now a little left whiiiir - darn. I'm dead. :)

Firestorm65
04-10-2009, 01:07 AM
As opposed to 89, no 91, no 90 - darn I'm dead? We are not slamming the gas in every direction, we will slow down as we get close...

Adrenalynn
04-10-2009, 01:14 AM
Ahh. I guess you could do it that way. A couple people here, their gun points wherever they point their mouse [I helped with a little linear algebra for one of 'em]. I've got a pan-tilt working that points where ever I look on the screen (eyeball following). I was just naturally assuming people would be focusing on a more "fly-by-wire" approach.

Firestorm65
04-10-2009, 01:20 AM
Do you know of a standard-size continuous servo with a shaft encoder build in? It would be much easier than converting it ourselves.


Pretty cool that you just have to look at a target. The camera and gun move together, so we are always pointed where we are looking. Two approaches to the same solution.

robologist
04-10-2009, 01:26 AM
Check the Wheelwatcher (http://www.nubotics.com/products/ww01/index.html).

Firestorm65
04-10-2009, 01:28 AM
Can you put a servo horn on with that kit? If not, is there anything built-in or more reasonably sized?

Adrenalynn
04-10-2009, 01:35 AM
@ Robologist - ok - that's a pretty spiffy turnkey solution. +Rep - that belongs over in the link library (http://forums.trossenrobotics.com/links), imho [hint nudge]

@ Firestorm - your camera has more than a 3" field of view at 12ft, right? Mine has more like a 10ft FOV. So if you can see them you can hit somewhere in the vicinity of the neighborhood the other bot is in, hopefully in the same arena. The solution to that, of course, is to have crosshairs in the camera view. The down side is that we're back to "a little to the left, no right, no left". Mouse tracking, eye tracking, other forms of tracking within the FOV means that you can pinpoint the location within the FOV without having to dance around too much. Especially bonus if the other guy is doing something obnoxiously inconvenient like moving or shooting at you. :)

Adrenalynn
04-10-2009, 01:36 AM
Can you put a servo horn on with that kit? If not, is there anything built-in or more reasonably sized?

Put the printed disk on the back of a servo horn.

Firestorm65
04-10-2009, 01:38 AM
Center equals target... the camera is inline with the gun. They don't move separately so it never changes.

Adrenalynn
04-10-2009, 01:47 AM
Center equals target... the camera is inline with the gun. They don't move separately so it never changes.

Right. So instead of centering the gun, you have to center the camera.gun. Same diff, right? Pointing a camera.gun is no different than pointing a gun within a fixed camera view.

Firestorm65
04-10-2009, 03:00 AM
Exactly. I think I no longer know what, if anything, we are disagreeing about.

Adrenalynn
04-10-2009, 03:56 AM
I do. But I'm lettin' it go. "It's your funeral". :D

CogswellCogs
04-10-2009, 09:23 AM
Firestorm, are you planning to use a CR servo to make sure you have a full 360 degrees of rotation ? Or, is there some other reason ? I agree it seems that setup will be difficult to aim.

What about using a mult-turn servo like the HS-785HB ? That way, you get the ability to aim like a positional servo and you also don't have any rotational blind spots.

robologist
04-10-2009, 09:36 AM
@ Robologist - ok - that's a pretty spiffy turnkey solution. +Rep - that belongs over in the link library (http://forums.trossenrobotics.com/links), imho [hint nudge]

Duly added, that went pretty easy. Glad you liked them. I thought Pete did a good job putting those together, even though I haven't bought any from him yet.

lnxfergy
04-10-2009, 09:45 AM
The way we are aiming is just move left or right to the target, with a few software based adjustment or manual control. It is never fire at 10 degrees. As far as orienting with the legs, we were looking at optical shaft encoders or switches at certaiin positions. Does anyone know of a standard size continous rotation servo with a buit in shaft encoder?

No hobby servos are meant to be continuous rotation - they all leave the factory with some limited range (typically about 180 degrees, although a few have more or less). The singular exception to that is the Hitec CR servo, but it has NO feedback. Some retailers sell continuous rotation servos that they have modified themselves of course.

Those wheelwatchers are probably the only encoder solution made specifically for servos.

Do you really need fully continuous? Won't your cabling get snagged up at some point... 300 degrees (ala bioloid/dynamixel AX-12) wouldn't suffice?

-Fergs

lnxfergy
04-10-2009, 09:46 AM
Duly added, that went pretty easy. Glad you liked them. I thought Pete did a good job putting those together, even though I haven't bought any from him yet.

I have a pair of the ones for solarbotics motors.. fit and finish is superb.

-Fergs

Firestorm65
04-10-2009, 11:38 PM
We want continous rotation so we can aim entirely independant of motion. That way we can run and gun. No blind spots to be shot at either, particuarly important with only one gun. The turret and legs will be connected, but not with wires that could become twisted or wireless that would require extra ciruit boards.

MSpurk
04-12-2009, 06:41 PM
The turret and legs will be connected, but not with wires that could become twisted or wireless that would require extra ciruit boards.

It's so obvious. He'll use magic. J/K.

It sounds like you don't need a servo, but a gearhead motor with an encoder or perhaps a stepper motor.

-Matt-

Firestorm65
04-13-2009, 12:07 AM
Not majic, just contact strips on a disk...

The reason for a CR servo was ease of assembly. Also, it wouldn't require a separate motor controller, we want everything to go to one board (minus scoring, obviously).

CogswellCogs
04-13-2009, 10:44 AM
Not majic, just contact strips on a disk...


Aka a 'slip ring'. Commercially, these are pretty bulky and expensive components. Some of my tank building buddies have investigated them. How many circuits do you need ? If you're really committed to 360 degree rotation and just need four circuits, a small and cheap solution is a phone cord de-tangler. Like one if these
Amazon.com: TwisStops Telephone Cord Untangler, Black SOF1501: Office Products

MSpurk
04-13-2009, 10:05 PM
"The reason for a CR servo was ease of assembly. Also, it wouldn't require a separate motor controller, we want everything to go to one board (minus scoring, obviously). "

There are a couple options to this problem. If you don't need true continuous rotation, but 360 degrees or greater would do, you can break-out the pot and use gearing or cog belts. It gives you the advantage that you can always get back to your center, plus or minus.
Edit: you also need to remove the physical stops in the geartrain.

You could go with a gearhead motor with an encoder. Small brushed esc's are pretty reasonable. The encoder can be done with one chip and a PIC. Sorry I don't have my notebook with me that has the encoder chip from digikey. Very limited extra work.

Simplest, Cheapest Solution yet. Just use a standard servo and live with not being able to rotate all the way around, or stack them one on top of the other if you want more rotation. For CR with feedback and no encoder simply stack an infinite number of servos on top of each other. :D

-Matt-

Zacattack
04-14-2009, 08:59 AM
on mine, im just using a kindof cheap 180 degrees servo for the waist rotation, to keep the wire out of the way i was going to use a bent paperclip sticking off the back and a coiled wire, since my funding is kindof depleated.

Azinman
04-14-2009, 10:06 AM
"Simplest, Cheapest Solution yet. Just use a standard servo and live with not being able to rotate all the way around, or stack them one on top of the other if you want more rotation."

On a rover with a sensor on a "head" that I was designing I put 2 servos stacked and that gives a nice 360 degrees. You get a nice controllled 180+180 from each servo. Like MSpurk said, a simple and cheap solution.

Grand Robot Master
04-16-2009, 11:20 AM
couldn't you just file off the servo stop?

jes1510
04-16-2009, 11:37 AM
couldn't you just file off the servo stop?

Nope. A servo has a stop on the gear train that keeps is from rotating all the way around. There is also a pot that provides feedback on the position of the horn. The pot won't allow complete rotation either.

Grand Robot Master
04-16-2009, 11:45 AM
I take it that to hack the pot would be more trouble than it's worth.
i'm new to this whole servo thing.

DresnerRobotics
04-16-2009, 01:39 PM
I take it that to hack the pot would be more trouble than it's worth.
i'm new to this whole servo thing.


But a Grand Robot Master shouldn't be new to anything! :p

Adrenalynn
04-17-2009, 02:10 AM
You don't "hack pots"

The physical construction of the potentiometer dictates its rotation and its resistance. "hacking" it means designing your own or replacing it with some other. And since the pots in servos are generally custom built by the manufacturer to the servo - that's a big "good luck"

4mem8
04-17-2009, 07:59 AM
Agreed I would never hack a pot on a servo. good call Adrenalynn.