We are going to build a tractor out of the VEX robot so that it will be able to pull the most weight in the least amount of time.
Step 1: Materials for the Tractor
The materials needed to modify the VEX robot to make the tractor are:
- (4) 60 Tooth Gears
- (2) 36 Tooth Gears
- (2) Motors
- (4) 100 mm Wheels
- (4) Angle Bars
- (6) Square Bars
- (1) Battery
- (4) Threaded Beams
- (6) Plastic Spacers
- (12) Collars
- (1) Plate
- (1) Controller
- (4) 6-32
- (38) 8-32
- (12) Flat Bearings
- (1) Hex wrench
Remove the current wheels connected to the robot. Detach the 2 motors from the robot and move them to the back of the robot.
Move the motors, using the middle spots from the angle bars, place them two spaces before the backside of the robot.
Next, add a medium sized square bar to each motor. Add spacer, gear, and a collar in between the angle bars and the square bars as well as a flat bearing.
Move three more spaces forward and place another square bar along with a flat bearing.
Add a 60 tooth gears, a spacer, and a collar. Move three more spaces down and repeat steps 6 and 7.
Take one 100mm wheel and add on to the first and last square bar, leave the middle alone. Use a collar to tighten and keep the wheel in place.
Repeat steps 4 to 10 on the other side of the robot to even it out.
Take out (8) 8-32 screws and 4 threaded beams. Attach two threaded beams two spaces from the back part of the motor.
Once that is done, move two spaces and add on two more threaded beams with 8-32 screws. Once the beams are attached and secure, add a plate on top center. Secure the plate down by using 8-32 screws (2 of them) where the threaded beams and the plate meet.
Before attaching the plate, put the controller on top of it. You will screw the controller down with the plate by using 4 8-32 screws
Make sure it goes inside the holes in the controller before you start screwing it in the threaded beams because it will be difficult if you don't.
Step 12: Materials for the Sled
Materials and tools needed to constructed the sled of the Tractor:
- (1) Plate
- (5) Bearing Blocks
- (10) 0.318'' Plastic Spacers
- (10) 8-32 BHCS x 3/4''
- (13) Keps Nuts
- (1) 9 Hole Long Bar
- (1) 5 Hole Angle Bar
- (2) 0.182 Plastic Spacers
- (2) 8-32 BHCS x 1/2''
- (3) 8-32 BHCS x 1/4''
- (2) 2'' Threaded Beams
- (1) Hex Wrench
Step 13: The Sled
Here are two videos showing how to construct the sled that goes on the back of the tractor. The sled will be the object pulling the weights the tractor is trying to pull across 100m. Though in the video I tighten the keps nuts with my hand, I advise that you back and use a hex wrench to tighten the screws once you are done as a precaution. You don't want your sled falling apart on you!
Step 14: Final Design
This is what the tractor looks likes once its build along with the sled.
Step 15: Gear Ratio
- The gear ratio of our tractor robot is 1:1.67
- We chose this gear ratio because we believed that it would help the robot pull the most amount of weight it could. It can pull more weight because the torque will increase.
- The input RPM for this robot is 118 RPM while the output RPM is 70.66 RPM
- The input Torque 1.67 N*m and the output torque is 2.7889 N*m
Step 16: Wheel Size
The theoretical speed of our robot is 36.997 cm/s.
The actual speed of our robot is.....
Step 17: Design Iterations
We made several changes to our original VEX robot.
- We decided to take 2 out of the 4 36 tooth gears the robot had and replace them with 2 60 tooth gears (2 on both sides). We made the change because we believed that bigger gears would help the robot pull the most weight even though it would decrease the speed.
- We decided to add bigger wheels since we were going to use 60 tooth gears because we thought that if we used bigger gears, then bigger wheels were going to be needed to accommodate the change to the robot.
- We moved the motors to the back of the robot from their original position in the middle because we wanted to make the robot smaller and look less crowded.
- We made the rack of the robot lower and put the controller on top of it so the robot would look spacious and it would allow a place for the battery as well.