ScrewDriver
ScrewDriver Rapid prototype speed tests
Author/s: Saba Theodory (Electronics and Control engineer)
Table of Contents
Introduction
This post will be displaying rapid prototype and final tests including calculating the experimental values of the maximum speeds and showing the ScrewDriver’s capability to go over obstacles. The type of movements the ScrewDriver can execute are limited to movements parallel and perpendicular to the axis of rotation of the screws. Only the prototype is able to move in the parallel direction since it has more power and the belts provide more grip to the screws. A special case of movement will be discussed here as well. The parallel and perpendicular speed tests needed to be carried out differently since parallel motion can only be achieved in loose terrain that can be displaced such as sand or in our case twigs while perpendicular motion can take place on almost any surface. The expected speed calculations can be found here.
Speed Test (Perpendicular to axis of rotation)
In this test, the experimental perpendicular speed is calculated by measuring the time required for the robot to traverse a set distance. In this case our distance is 7 ft. The perpendicular motion is faster than the parallel motion since both screws rotate in the same direction meaning all the force is focused in one direction allowing the ScrewDriver to move with more ease. This video shows the test. The motors were running at maximum speed when this test was done.
Figure 1: The test is shown where the prototype is timed and the distance on the tape measure is 7 ft.
Figure 2: The same test was carried out on a rough surface but the speed was roughly the same.
The results of this tests were: The robot required 15.66 seconds to traverse a distance of 7 ft meaning that the maximum speed is 0.447 ft/s or 0.1362 m/s.
The same test is done again for the 3DoT version of the robot. This video shows this test. The results of this experiment were: The 3DoT robot required 13.38 seconds to cross a distance of 7 ft. This means that the maximum speed is 0.523 ft/s or 0.1595 m/s.
Speed Test (Parallel to axis of rotation
This test was more difficult to do since the robot cannot move parallel on smooth surfaces. The surface needs to be relatively rough and requires some sort of loose material so that the threads of the screws can push it back allowing it to propel forward. This speed is much slower than the perpendicular speed since the screws oppose each others’ rotational motion and the only thing propelling the robot forward is the shifting of the threads on the screws. The reason why this test was not shown on different surfaces is because if the surface friction is low and there is no loose material to displace, the robot will stay in place as there is no force propelling it in the parallel direction. The motors were running at maximum speed for this test. The video is shown here.
Figure 3: The test is shown here where it can be seen how the robot dug through the ground in order to propel itself.
The results of this experiment: The total time taken was 5.85 seconds and the total distance was 11 inches. The maximum forward speed is then 0.1567 ft/s or 0.0478 m/s which is about 1/3 the speed of the horizontal motion.
Obstacle Test
As described in the requirements, the prototype should be able to go over obstacles up to 0.5 inches in diameter while the final should overcome obstacles up to 0.25 inches in diameter. In this test, we show how the prototype overcomes some small branches fulfilling this requirement and the final robot overcomes cables of diameter 0.25 inches. A special case of motion that was discovered during testing and can be achieved by increasing the speed of one of the motors by about 50% while lowering the speed of the other motor by the same rate. This results in the ScrewDriver spinning in place by having one screw move faster than the other. This case will be shown in the video below as well.
Test Video
In this video, the ScrewDriver prototype goes over some branches that are 1 inch in diameter which are larger than specified in the requirement. The robot also displays its ability to turn in place by having one screw move faster than the other as discussed in the section above.
In this second video, the 3DoT final robot demonstrates its ability to overcome obstacles of diameter 0.25 inches as described in the requirements. In this case we used cables of diameter 0.25 inches.
In this final video, the 3DoT final robot displays its ability to turn in place. This process is possible when one of the motors is 50% faster while the other motor is 50% slower. This can be done by switching the steering trim on the ArxRobot application.
Conclusion
From this test we concluded that the perpendicular speed for the prototype is about 3 times as fast as the parallel speed keeping in mind both tests were carried out in ideal conditions. The 3DoT robot turned out to be faster than the prototype despite its smaller size and that is because the prototype has more torque than speed and it’s also heavy while the 3DoT robot is small and agile and has more speed than torque. The 3DoT robot was not able to go in the parallel direction because it did not have enough power and the O-rings did not have enough grip. We also learned that the prototype is able to go over branches 1 inch in diameter which fulfills the requirement while the 3DoT final can overcome obstacles of diameter 0.25 inches. When an obstacle is too large for the robot to overcome, the screws keep spinning but the robot stays in place with the screw turning against the obstacle. The best orientation for the robot to go over obstacles is when the screws’ axis of rotation is perpendicular to the direction of motion because the robot moves faster and it is easier for the screws to roll over an obstacle than try to use the threads to propel forward. In addition, if the direction of motion is parallel to the screws’ axis, it is very difficult to overcome obstacles since the obstacle might not have enough friction.