Intro: How to Make a Robot Pull Weights!
Brief Description of Project
The goal of this project is to push as many weights as possible.
The first thing you need in order to push weights is a fully assembled VEX robot. It looks like this...
Step 1: Prerequisites
1. Materials needed
a. Parts: two big gears (25 tooth), two small gears(12 tooth), chain for gears, the materials listed above, 4 large rubber wheels, 8 flat bearings, 25 short screws, and the materials listed above for the sled.
b. Tools: one skinny hex wrench, one wider hex wrench, and one wrench for the keps nut.
Its always good to have plenty of fasteners, shafts, and other extra materials.
Step 2: Building Directions
1.) First take apart the robot and screw the control unit on the two bottom bars
2.) take off the current gears and wheel and replace them the the 12t in the front and the 24t in the back (since chain sizes vary, be sure to make sure that your gears are far enough apart to make the chain tight)
Step 3: Building Directions Cont.
3.) connect the 127mm wheels to the bars with the 24t gear
4.) place a 6t gear on the outside of the robot but on the driven gear bar
5.) attach another set of 6t gears to the bar with the front wheels
Step 4: Building Cont.
6.) connect the two 6t gears and the 12t and 24t gears with the chain
7.) put extra 127mm wheels on the back axles and put two more 65mm wheels on the front axle 7.) repeat steps 3-6 on the other side of the robot
Step 5: Gear Ratio
a. Our gear ratio is 12:24 so 1:2
b. We chose this ratio because it has a lot of torque but is not too slow.
c. The input rpm is 127 and output rpm is 63.5.
d. Our input torque 1.67 newton meters is and our output torque is 3.34 newton meters.
Step 6: Wheel Size
Our wheel has a 127mm diameter.
a. Our theoretical speed 46.40 cm/s
b. Our actual speed is 42.9 cm/s
Step 7: Initial Proposal
At first we used normal gears.
Our gear ratio was 1:7. we had 3 gears from an 84 tooth to a 12 tooth to a 60 tooth.
Step 8: Changes Made With Reasoning
The gears did not work because there was a lot of teeth grinding and gritting.
If this happens then make adjustments to tighten the gears.
We changed our gear ratio to 1:2 and used a chain to connect the gears.
Step 9: Final Design
Our final design had a 1:2 gear ratio on the back wheels.
We connected the front wheels to the motor as well to make a 1:1 gear ratio.
We had two 127mm wheels per axle in the back and three mm wheels connected to the front axle.
Step 10: Results
Trial 1: 5lbs, 2.81s, 1.78 Power Rating
Trail 2: 7.5 lbs, 2.81s, 2.37 Power Rating
Trail 3: 10lbs, 4.42s, Power Rating