Drive Train Gear Ratio

What We Have Now

• Our current gear reduction is 12:1 in the gearbox and 20:15 between the sprockets. This means that our overall gear ratio from the motor to the wheels is 16:1. For every 16 turns of our CIM motors, the wheels turn once. It also means that we get 16 times the motor torque at the wheels.
• From the theoretical top speed of the CIM motors and our 16:1 reduction, our current top speed should be
  5310 rpm (CIM motor top speed)
  * 1 minute/60 sec
  * 2π radians/rotation
  /(16/1) (gear ratio)
  * 6.25 inches (wheel radius)
  = 18.1 ft/s (pretty fast)
• Our theoretical maximum pushing force (limited by the 40 Amp circuit breakers) should be
  98 oz-in (CIM motor torque @ 40A current)
  * 4 CIM motors
  * 80% (approximate efficiency of power transmission by the gearbox and chain)
  * (16/1) (gear ratio)
  / 6.25 inches (wheel radius)
  =50.18 lb
• We pushed against a scale with the robot and found that our maximum pushing force was 42 lb.
• The eight lbs or so of force we "lost" is because of the flat tires, the loose chains, and because the efficiency of a system like this is hard to predict. I used 80% as a ballpark, but obviously our efficiency is lower.

What We Need

• To move a 150 lb robot (120 lb + battery and bumpers) up a 45º slope, we need 150/√2 ≈105lb.
• From the calculations above, we determined that we need about three times the current gear ratio we currently have, tripling the pushing force and cutting our top speed to 1/3 of what it is now.

What We are Going to Test

• To triple our gear ratio, we are going to replace our sprockets to change our gear ratio. If we replace our 15 tooth sprocket with a 10 tooth sprocket, and our 20 tooth sprocket with a 40 tooth sprocket, our new gear ratio is 12:1*40/10=48:1. This is 3 times our previous gear ratio!
• From the theoretical top speed of the CIM motors and our 48:1 reduction, our current top speed should be
  5310 rpm (CIM motor top speed)
  * 1 minute/60 sec
  * 2π radians/rotation
  /(48/1) (gear ratio)
  * 6.25 inches (wheel radius)
  = 6.0 ft/s (not very fast)
• Our theoretical maximum pushing force (limited by the 40 Amp circuit breakers) should be
  98 oz-in (CIM motor torque @ 40A current)
  * 4 CIM motors
  * 80% (approximate efficiency of power transmission by the gearbox and chain)
  * (48/1) (gear ratio)
  / 6.25 inches (wheel radius)
  =150.54 lb (very strong)
  

Progress: Week 2

Here's what we've done this week:
Drive Train

• The wooden prototype drivetrain is fully wired up and running under power.
• On Saturday we discovered that the drivetrain is not strong enough to drive over the hump. This was probably due in part to the flat tires.
  
• We decided to replace the sprockets to get a more forceful gear ratio. The parts should be in ~Tuesday. Information about this decision is in this blog post.

Kicker

• Using a high speed camera, Caitlin, Lizzy, and assorted minions determined which of the pistons would be the best for the kicker
• Once they had selected the piston, they began experimenting with different lever configurations and the high speed camera to determine how long the lever should be.

Hanging Device

• On Friday, Arkady, Kiju, and a group of girls discussed how best to hang from the tower. They concluded that a double-hook design would be best and identified two lifting options:

1. A telescoping arm, based on an antenna design
2. An articulating arm

• Sham, Ketki, and Emma helped build a 1/2 scale prototype of the first section of an articulating arm.
• Dr. Newman has been playing with assorted winch ideas and gear ratios, and has thus far avoided killing himself.
  

Electrical

• The prototype drivetrain is running using the electronics board from the monster, stripped of unecessary components.

Programming

• Caroline and Emma have the drivetrain prototype running under default code modified for 2-joystick, 4 motor tank drive.
• Caroline has been familiarizing herself with the Driver Station dashboard and with this year's LabView code.
• Despite valiant efforts by Caroline, Emily, and myself, we can't seem to get wireless communication working between the robot's wireless adapter and the wireless router. As far as I can tell, the wireless router is not broadcasting an SSID, despite being set to do so. James has made this work in the past, so hopefully he can sort it out.

Progress: Week 1

Drive train:

• We have decided on a four-wheel drive train with 12.5" pneumatic (inflatable) tires
• James, Matt, and Arkady have led a team building a prototype chassis and drivetrain out of wood
• On Monday, James made some mounting blocks out of wood to attach the electronics from the Monster

End Effector (the device that interacts with the game piece) (Kicker)

• We have decided on some kind of kicker
• Caitlin and Dr. Newman headed up a group to test out several pneumatic cylinders, and found that none released the ball with enough speed
• Attaching the cylinder to a lever gave much better results
• A selection of cylinders are on their way from Bimba for further testing

Electrical

• Emily and I removed unnecessary components from the electronics board on the Monster
• The Monster is now ready for programmers to begin working with encoders, and can be swapped over the the prototype drivetrain

Programming

• Software is installed on Terrence (our Classmate PC) and the FIRST desktop

Field Construction

• James and I have completed a ~4ft wide section of ramp
• The goal is currently a work in progress
• All of the parts for the tower and goal should have arrived from McMaster-Carr
• Arkady may be able to get us some free carpet for the ramp. It's not quite FIRST spec, but it's free
• Any mentors who can come in this week to work on field components are encouraged to
  

New Design Idea

Everyone should check out today's XKCD - I think Randall has the perfect robot design!

xkcd 689

For the Programmers

I don't know if this will be of any use to you guys, but there are a whole bunch of video tutorials on Labview, the FRC framework, and other FIRST programming topics here: http://frcmastery.com/help/tip-jar-video-archives/

Game Hint #1

FIRST has posted the first game hint here. As usual, it's cryptic and I have no idea what it is.

Finances!

We made $1103 at the HB FLL District. More than anticipated. GO TEAM!