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Lab1Question5AmberAmber Stangroom Lab 1 A Drive command can easily be converted to be a Drive Direct command using simple circle formulas and concepts of beginner physics. I will demonstrate this through an example. Let’s say we have a Drive command that looks like this: 0x89 0x00 0x64 0x00 0xC8 The speed would be 100 mm/s and the radius would be 200mm. Now we have to think about how the robot drives. From Question 4 on the lab, we found out that the Create measures radius and velocity from the center of the robot. Also, to make the robot accurate, each wheel and the center would have to finish a specific rotation at exactly the same time. If that is so, then the wheel on the outside of the turn would have a higher velocity than the command gave, and the wheel on the inside would have a lower velocity than the command. The two wheels’ velocities averaged should result in the speed given by the command. The left wheel, right wheel, and center all form concentric circles as they turn, depicted below.  First we need to calculate the time it takes for the center of the circle to travel 360 degrees. We already know the radius and the velocity. Ccenter = 2(pi)(rcenter) = 2(pi)(200mm) = 1256.6 mm = circumference of center circle 1256.6 mm x (1s/100mm) = 12.566s = time to complete center circle Now we have to find the velocity of the outside wheel. The outside wheel must go 360 degrees in the same amount of time. This time we must add in our knowledge of the radius of the Create’s wheel base, which is 129 mm, to do our calculations. Coutside = 2(pi)(routside) = 2(pi)(200mm + 129mm) = 2067.2 mm = circumference of outer circle 2067.2 mm / 12.566s = 164.5 mm/s = velocity of outside wheel The velocity of the outside wheel must be rounded since we don’t know how to input decimals, so the velocity of the outside wheel would be put into the Drive Direct command as 165 mm/s. We could repeat the same calculation to find the velocity of the inner wheel by changing +129mm to -129mm, but there is a better way. Since we know the velocity of the center must be the average of the velocity of the wheels, we can calculate the velocity of the inner wheel. (164.5 mm/s + z )/2 = 100mm/s z = 35.5 mm/s where z is the velocity of the inner wheel Once again, you would have to round this number to 36 mm/s. In this case, the outer wheel is the right wheel and the inner wheel is the left wheel. Your input for the Drive Direct command would look like this: 0x91 0x00 0xA5 0x00 0x24 From this example you can derive equations for converting a Drive command to a Drive Direct command. The velocity of the outside wheel can be found by using this equation: (v (r + 129)) /r where r is the commanded radius and v is the commanded velocity. The velocity of the inside wheel can be found using this equation: (v (r - 129)) /r where r is the commanded radius and v is the commanded velocity. |