pic: Iso view
 

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looks nice... and simple... drivetrains that a lot of teams would go with... i dont see any pneumatics so i am guessing that gearbox cant be shifted into another speed... how fast you are expecting the robot to move and with how much torque... if possible, i would like to see a close view of the drive train... good luck... :)

Re: pic: Iso view
 

sweet drivetrain. about the weight estimates in CAD, is 60# the estimates for just the machined components, without the manufactured parts (i.e. motors, robot controller, battery) or did you already add those in? also, it looks like you might be using the cap screws in the front and back to move the wheel mounts back and forth, adjusting chain tension. is this the case? finally, how are the motors mounted? i can't tell from looking at the drawings, and its really messing with my head.

Re: pic: Iso view
 

Single speed gearbox
Top speed is 8.1 FPS
Gear ratio chip to rear wheel= 8:1
Bosch to rear wheel=32:1
wheel Dia.= 6"
you do the math

Re: pic: Iso view
 

60# total weight
Cap screws do adj. chains
Motor mounts are slotted and bolted from underneath for a cleaner look

Re: pic: Iso view
 

I should have made another thread about the gearboxes... but okay...

I am just wondering if your motor mounts are strong enough keep the drill motor from spinning out because of torque in the gearbox... i am saying that since i have experienced it... we had something like a mexican hat which held the drill motor in place and then bolted that into the gearbox plate...

The design looks great so far... whoever drew it... put some quality time in it... good luck... :)

Re: pic: Iso view
 

Thanks,
We have used this type of mount on the chip motors in the past with no problems. The mount is slotted on one side only and the hole is bored to fit tight on the motor. We'll see if it works, if not redesign

Re: pic: Iso view
 

Looks really nice.

One comment.

It seems to me like the only thing holding the rear plate in alignment is the CIM motor on the left side. You might want to consider adding something in to link the two plates together

Re: pic: Iso view
 

It looks awesome guys...

the one thing i see is that the bosch motors are being discontinued this coming year. i dont know what we are gettting but i wouldnt start anything until we find out. just a heads up...


Please dont take this post negatively... I know you must've spent numerous hours on it...and i dont want to sound like a buzzkill

Re: pic: Iso view
 

It's just ink on paper now and will stay that way until after kickoff. If they do change the motors it will be a fairly easy edit in CAD. The gears in the gearboxes are Boston Gear change gears. Change gears can be purchased in one tooth increments from 20 to 96. The gears on the motors are Stem Pinion gears and come in 5,6,10 teeth. I chose these gears because they are all 3/8" face. They are all 5/8" bore. 1/8" key way. 20 DP 14.5 PA It makes it easy to mix and match to get the ratio you want. You can see the gears at bostongear.com. Go to Bos Spec 2 , open gearing, spur gears, change gears and stem pinion gears. You can download the CAD files, .STEP files seem to work best in AutoDesk Inventor. You will need to register to access Bos Spec 2, very easy. These gears seem to be a good option for teams like ours who do not want to try and make custom gears.
Gear List
GA20
GA40
NAR5

Re: pic: Iso view
 

those gearboxes are HUGE!!! alot more material and complexity than is needed. the batery would be best placed in the front for some balance. it is a verry light tho i warn is a very flimsy chassis using the channel. swampthing is all channel and just a fwe hits tirned it into a crushed tin can. the atonomus had to be guessed everytime because after every match the wheeles would pointed in a diffrent direction.

Re: pic: Iso view
 

Perhaps it's time for FIRST robots to start using R/C car-type suspensions. You can adjust those things all day long...toe-in, camber, shock positioning, those were the days.

I have to agree--the channel (now that I realize it's channel) would probably be a little flimsy, given the robust trend lately. Perhaps some bracing would be in order? If that channel in the front or the back takes a few too many hits, then you're looking at no support to keep the sides from just ker-flumping inward. (I experienced the same phenomenon when one of my bed's rails at home warped. Ask my brother--we spent half an hour jumping on it to make it look half-decent...and even then, we had to prop a busted computer under the bed so that it'd hold my weight.) That wouldn't be too good in the middle of a match.

As for the weight distribution...I dunno. It would depend on your appendages du jour, but I think you might do well moving the battery back (more into the screen looking at that shot), and moving your RC to the other side. Or move the battery to the other side of the CIM motors and slide your RC inward some. That might help out, especially if the channel does give way. You don't want a good whack doing something to your RC.

Just my random blathering. With a few tweaks, that design should...what's the Chappelle's Show quote...SPIT HOT FI-YAH!

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Rod,

I have done the math and something is not adding up.

CIM free speed = 5,500RPM
Gear Ratio to rear wheel = 8:1
Wheel Diameter = 6"

5500 / 8 = 687.5 RPM or 71.995 rad/sec
71.995 rad/sec * 3" (or .25 ft) = 17.99 ft/sec

Assuming some losses, you will be around 14 - 16 ft/sec, not 8!

-Paul

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I figured the the top speed at 50% of the CIM free speed

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Common mistake.
The motor will run muuuch faster than Max Power.

I usually use a "speed constant" of 85%.
Basically, gear the robot based on .85*free speed or in the Chips case: 4675RPM

Real world testing of my theoretical calculations shows this to be about right.

More accurate drive modelling can be done, but this simple method comes out pretty good. Then again, your milage may vary depending on your drivetrain.

Anyone else wanna confirm 85%?

JV

Edit:
See Andy's post below.
I guess I'm a little fast. Oops.
/Edit