Tuesday, January 24, 2006

Tuesday Build (the diagram on the floor)

If you've read Chrissy's post, you'll know what I'm talking about. Just in case you don't want to get your butt over to the science project room.

[Click on the image to the left to enlarge it. After that, you might have to hover your cursor over the image for another 'enlarge' button to show up.]

A few things that we've been thinking about and stuff to do:

1. Wednesday (that's tomorrow), January 25, with 27 days left. IDEO shop 5:00 pm sharp. Bring skyway wheels and the 3/8" bore bearings that need to be press-fit into the wheels with the arbor press. Once you have the wheels with the bearings pressed in, you can start assembling the chassis. Leave out the middle wheels until Thursday - I have two more wheel sprockets coming in for you from IFI robotics. You can definitely start laying out the approximate amount of chain needed.

2. Thinking turret, yes! So Chris made a good suggestion that we could probably mount the motor to drive the turret directly. I think this is a good idea, but see my qualms below (mostly about gearing things down and being able to sense the angular change with our GTS). Less parts and thus less things to break. We'll need to plan accordingly i.e. probably build an adapter plate to mount the shaft to the turret. For now, I suggest we procure the following:

* 2'X2' 1/8" thick steel plate for the base (nice and heavy, and a hard surface). We'll bolt the motor to the plate from the underside.

* 5 ball casters (get one extra) from Mcmaster to support the turret and take the weight of the turret off the shaft off the motor (the motor should only be driving axial loads). The part number is 5674K51. Thanks to everyone who helped to figure what this widget was called!

* 2'X2' of some material for the turret. I say we can do 1/4" thick aluminum sheet or perhaps even easier, 1/2" MDF (particle board material, like the stuff that Bud used for his coolio prototype).

We might want to get some FLAT steel sprockets from Mcmaster, just in case we don't want to drive the turret directly. We can drill out holes to make them even lighter. I think mounting flat sprockets is much easier. Steel because Sophia reminded me that we need a ferromagnetic material if we're going to try to implement gear tooth sensors. As well, we might need to gear down the van door motor to run it slower!! Type in 'Steel hubless plain bore flat sprocket' at mcmaster to see what I mean.

3. Finally, blah blah. Actually, more important than that. Chris asked for some specs on the van door motor and it is biased. From last year's 'FIRST Guidelines' booklet, I find the following on the Van Door motor:

CLOCKWISE: Stall torque 34 Nm @ 44 Amps; No Load Speed 75 RPM
COUNTER CLOCKWISE: Stall torque 30 Nm @ 44 Amps; No Load Speed 75 RPM

Not a big deal, but what I read is that right now, you get a little more than 1 full rotation PER SECOND! That's 360 degrees in less than a second. We want to scan a field of view of 45 degrees for a total of 90 degrees - that would happen in 1/4 s! Eeek! Okay, that's at no load, but still!

Chris or Doug, I suspect if we gear down the Van Door motor 2:1, we'll hit the middle of the speed-torque curve, get max power, while slowing down the panning of the turret to something reasonable?

Okay, see you tomorrow at 5 pm at the IDEO shop!

- Emily

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