resetting window motor driven arm after each round
 

I have used cd search and looked other places but i can't seem to find a thread on this. since a window motor can't be backdriven we need a way to reset it after each round. we currently have this set-up for our arm.
A window motor is chained to the shaft with our arm on it. the arm is attached by having a metal tube slightly bigger than the shaft slipped over it with the arm welded to this tube. two bolts on each side of the arm go through the tube and the shaft to bind them together. The bolts will eventually be replaced with quick disconnect clips. these clips can be a quick fix for directly after each round by simply removing them but the shaft itself will still need to be reset before our next match. i know we can tether it in our pit and reset it that way but i'd prefer a mechanical fix since we might not have time to tether. i remember a time last year where we got done with a match, walked out of the arena, right past our pit, and we were immediately back in line for our next match. I read somewhere about a mechanical clutch but i don't know how that would be made or implemented
unfortunately our robot is bagged up right now but any help would be appreciated.

Re: resetting window motor driven arm after each round
 

You can tether in the queing line. We did this before every match, along with many other teams, to precharge our pneumatics.

Re: resetting window motor driven arm after each round
 

that's one big reason why we went with a V belt drive. It slips when it needs to. The problem is after the match, how do you get the robot out the door if the arm is extended straight up?

Re: resetting window motor driven arm after each round
 

We made a custom dog for our window motor sprocket in order to disengage the arm between matches. I'll see if I can get a picture.

Re: resetting window motor driven arm after each round
 

Remove the master-link in your chain, move the chain and drop the arm, re-apply the link in your pit or in que. Takes 20 - 25 seconds to do with 1 helper.

Re: resetting window motor driven arm after each round
 

Kid,
We wire our motors with Power lock connectors and we have modified a 12 volt drill so that the output of the trigger comes out on Power Locks. When we need to drive a motor, we simply disconnect it from the robot, attach to the drill and press the trigger. We use this method throughout the season to test motors and drive components for which software has not caught up.

Re: resetting window motor driven arm after each round
 

Consider this idea well-stolen for next year!

Re: resetting window motor driven arm after each round
 

this is a great idea! I'll see if i can find any old 12 volt drills since most people use 18 volts now.

Re: resetting window motor driven arm after each round
 

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.

Re: resetting window motor driven arm after each round
 

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.

Re: resetting window motor driven arm after each round
 

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.

Re: resetting window motor driven arm after each round
 

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.

Re: resetting window motor driven arm after each round
 

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.

Re: resetting window motor driven arm after each round
 

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?

Re: resetting window motor driven arm after each round
 

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!

Re: resetting window motor driven arm after each round
 

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.

Re: resetting window motor driven arm after each round
 

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.

Re: resetting window motor driven arm after each round
 

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

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

Re: resetting window motor driven arm after each round
 

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

Re: resetting window motor driven arm after each round
 

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.

Re: resetting window motor driven arm after each round
 

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

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.

Re: resetting window motor driven arm after each round
 

Timing is everything....:rolleyes:

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