resetting window motor driven arm after each round

[Gary Dillard]

Originally Posted by Joe Ross

It looks like someone asked if it was legal on Q/A, and the answer was no. See http://forums.usfirst.org/showthread.php?t=17253. However, I'm not sure the GDC read the question correctly, so some followup may be necessary.

I would also consider that "special equipment" which can't be brought into the arena per T25, since the GDC has ruled pretty narrowly on what's allowed.

We don't plan to have any game pieces in our posession at the end, but if we do (and since the inspection template says we need to demonstrate how we would do it) we will remove the belt from one of the gripper sprockets and rotate it down.

[Al Skierkiewicz]

We design the robot so that game pieces do not need power to remove them. The question was how to return an arm to rest position, I assumed off the field.

[DarrinMunter]

Originally Posted by Al Skierkiewicz

The question was how to return an arm to rest position, I assumed off the field.

The rules only stated that you can't bring the items on to the field....Nothing about once you get your robot off to the side and onto the its cart.
They do this to keep the matches going on time.

[Nuttyman54]

Team 190 is using a mechanical solution (see attached pictures), similar to what Chris mentioned. We have the motor on a spring-loaded mount, which allows it to be pulled back out of the coupler, and the system rotated out of the way. We still have to power it up in the pits to drive it back to the correct position, but this lets us fold up our systems quickly on the field so they don't get damaged in transit to the cart and back to the pits.

It's fairly easy to do, we used 3" long #10 bolts and lock nuts, some standard SAE washers and springs we had lying around (you can find springs like these anywhere, Home Depot, McMaster, etc.). The plate was made with a band saw, drill press and a hole saw to allow the coupler to fit through. We did cut off the disk on the coupler, but there are ways to make this mechanism that doesn't require that.

The springs don't need to be super strong, since the spline on the coupler does a pretty good job of staying in there. We have about 0.5" inches of engagement on the coupler and it works great.

[Da Kid]

does anyone know about a gear box with a wormdrive in it that uses a cim motor? our mentor was thinking about doing this because of the cim motors' strength.
in a related matter, what would the gear ratio need to be for a denso window motor to rotate a 10 lbs, 50 in. arm that extends to 62 in? we want it to not put too much strain so that the thermal breaker doesn't get tripped. we do have a spring on the arm so that makes it a little easier, but what would the gear ratio be without the spring, just to be safe?

[pfreivald]

Originally Posted by Da Kid

in a related matter, what would the gear ratio need to be for a denso window motor to rotate a 10 lbs, 50 in. arm that extends to 62 in? we want it to not put too much strain so that the thermal breaker doesn't get tripped. we do have a spring on the arm so that makes it a little easier, but what would the gear ratio be without the spring, just to be safe?

That should depend largely on how quickly you intend the arm to rotate.

There is a relationship between torque and power that isn't more than algebra to compute... Do the math -- an engineering mentor or physics teacher can help!

[LLogan]

Originally Posted by Da Kid

does anyone know about a gear box with a wormdrive in it that uses a cim motor? our mentor was thinking about doing this because of the cim motors' strength.
in a related matter, what would the gear ratio need to be for a denso window motor to rotate a 10 lbs, 50 in. arm that extends to 62 in? we want it to not put too much strain so that the thermal breaker doesn't get tripped. we do have a spring on the arm so that makes it a little easier, but what would the gear ratio be without the spring, just to be safe?

Just do the math. 10lb *16oz/1lb * 62in = 9920 oz*in. A window motor's stall torque is 1501 oz*in.

That means you need about a 7:1 reduction with a single window motor. That'll give you an angular velocity of about 12 rpm. You also should design it so that the window motors don't operate at their max stall torque, so you may actually need to increase the reduction some more or add another motor.

[Torbots 1197]

Originally Posted by Da Kid

does anyone know about a gear box with a wormdrive in it that uses a cim motor? our mentor was thinking about doing this because of the cim motors' strength.
in a related matter, what would the gear ratio need to be for a denso window motor to rotate a 10 lbs, 50 in. arm that extends to 62 in? we want it to not put too much strain so that the thermal breaker doesn't get tripped. we do have a spring on the arm so that makes it a little easier, but what would the gear ratio be without the spring, just to be safe?

We're powering our arm through a combo of a fisher-price and RS-775 motors. The F-P is fed into a banebots P60 gearbox with a 20:1 reduction and the 775 through a P60 with a 16:1 reduction. The output of both motors are then fed into a torque summing gear that is also tied to a custom 30:1 worm gear setup. For us, this results in around 20 RPM at the output of the worm gear under a load.

If you're to just use one CIM motor to drive this setup, I'd expect a noticeable reduction in speed as you'll probably be driving the motor somewhat close to it's stall condition. Our arm is designed to still limp along even if one motor happens to die during a match. Don't be fooled by the size of the motor; the F-P motors have the highest power ratings of all the motors available to us.

[Mike Betts]

Originally Posted by Torbots 1197

...Don't be fooled by the size of the motor; the F-P motors have the highest power ratings of all the motors available to us.

Brrraaappp! That's one down, Kitty Carlisle...

Are you saying that the posted motor specifications are incorrect?

The CIM has a peak mechanical power of 340W versus the FP at 292W. Add to this the additional gear reduction required to gear down an FP, and the CIM wins every time.

Now, if your intention is to build a smoke generator, the FP is a natural choice...

JMHO,

Mike

[Al Skierkiewicz]

I am guessing that the phrase "for it's size" was left out.

[Pjohn1959]

Originally Posted by Nuttyman54

Team 190 is using a mechanical solution (see attached pictures)

Evan,

That has to be one of the coolest things I have seen. Great idea!

btw, I absolutely love your robot this year! Good luck at WPI this weekend.

[Chris is me]

Okay, I'm not going to let 190 get all the "cool credit" anymore

Here's some pictures of our spring loaded window motor disengager. We use it to lower our arm after a match. We still have to power the robot arm to get it in exactly the place we need but we use it to save on time a little bit as well as making it easier to carry to the pits.

http://i.imgur.com/O1NR1.jpg

We have the window motor coupled to a 3/8 hex shaft, which drives everything. The "seam" in the sprocket is where our makeshift dog connects to the sprocket in order to drive it.

http://i.imgur.com/2NsiC.jpg

Here clearly shows how the dog and sprocket connect, transferring power to the shaft. There's a hex pattern in the sprocket, but it rides on a round portion of shaft so the arm can free spin when disengaged.

[Pjohn1959]

Originally Posted by Chris is me

Okay, I'm not going to let 190 get all the "cool credit" anymore

Timing is everything....

My school is blocking the pictures, do you have any other way to display them?