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Found 10 results

  1. This video presents a revised version of an earlier Lego Technic Powered Up 3 speed automatic gearbox that I created. The previous gearbox used a differential for torque measurement and used a powered up large motor to convert the differential rotation into a torque measurement. However as many viewers have pointed out, it is possible to simply use the main motor speed measurement to infer the torque on that motor simply through the inverse linear relationship between the motor speed and it's load or torque. This saves the entire torque measurement portion of the gearbox resulting in a more compact and robust design. I also discuss the optimal gear switching points based on the gearing ratio R between the higher and lower gear. Thanks to philo (https://www.philohome.com/) for the torque vs speed graphs for the powered up motors.
  2. The lego Powered Up motors and functions have been used to create a 3 speed automatic gearbox. With the Powered Up functions you can accurately control motor speed and motor position, as well as being able to measure the angular position of a motor. These new possibilities have been used to create a three speed automatic gearbox. One motor is used to measure the torque at the output of the gearbox by detecting the rotation of an output differential; another motor is used to accurately set the position of an orange rotary catch controlling the switching between three forward gears, and finally one large powered up motor is used to drive the gearbox. The gearbox implements 3 forward speeds at gearing ratios of 1 to 1, 1 to 0.6 and 1 to 0.2 as well as one manual reverse gear. The Powered Up app has been used to program the gearbox controller on an iphone. Thanks to (racingbrick.com) for providing a great guide to all of the available programming blocks. Hope you enjoy this video. https://youtu.be/CRkvFffDef8
  3. Hi all, This 2 speed automatic gearbox implements it's second gear by using a two degrees of freedom configuration and blocking and unblocking the lower gearing ratio path by using a switch and rotary catch. The rotary catch is driven by a torque detector and once enough load is detected at the output it is rotated 90 degrees to unblock the low gearing ratio path. Upon the path being unblocked it becomes the path of least resistance and the output gearing ratio is reduced to give a higher output torque. Alternative lower gearing ratios can be implemented in this by changing out the lower gearing path gears. This gearbox operates in a bi-directional manner - meaning the input motor can rotate either way and the automatic gearbox still functions.
  4. Here's my 3 speed automatic gearbox using a servo motor to drive the gear change mechanism. The servo motor is activated by an electric switch which in turn is driven by a torque detector using a differential at the output. The automatic gearbox will switch to a lower gears automatically as load is detected on the output of the gearbox allowing it to generate more torque to overcome the load.
  5. My 2 speed automatic gearbox is put to the test by incorporating it into a 2 speed automatic car. This gearbox implements a number of design principles aimed at improving the gearbox performance - namely of placing the torque detector on a separate path to the main gearing power path to reduce torque and power losses in the gearbox, and using gear disengagement to switch gears instead of gear engagement. A simple derivation is presented of the physics involved in driving up a ramp in order to determine the amount of additional torque required at the motor output to be able to overcome the gravity and the corresponding potential energy. The torque of a large power function motor is measured by measuring the output axle speed using a laser tachometer and relating that to the linear torque/speed relationship of the motor. These measurements are demonstrated for the car without any loading and with simple horizontal motion. Finally the car is put to the test by attempting to drive up a 40 degree ramp.
  6. This 2 speed automatic gearbox design uses a worm gear for torque detection and gear switching combined. Some of my previous 2 speed automatic gearboxes have used a differential for torque detection to drive an orange rotary catch to switch gears using a switch component. The worm gear switches gears by disengaging one path to the input differential, thereby reducing the overall gearing ratio. In this 2 speed gearbox design the output gearing ratio is halved when switching from gear 1 to gear 2. By disengaging the 2nd path, the efficiency of the lower gear is improved due to the simplification of the gear train reducing the friction and power losses in that path. The overall power of the Lego technic automatic gearbox is demonstrated by testing it against a ten level torque generation device, as well as using a rubber band pulling instrument to measure the output pulling force for both gears. Hope you like it.
  7. Hi All, Here's a video I did on optimal gear switching ratios for PF motors. A formula presented relating the power operating point as a percentage of peak power. From this an operational power range band is defined based on maintaining a power efficiency of at least E percent. From this, optimal switching points relative to the motor torque are derived and the correct gear switching ratio determined. These are presented as formulas and graphs. The peak torque and power points are shown for Lego technic PF medium motors, Lego Techinc PF Large Motors and Lego Technic PF XL Motors.
  8. This video is about putting a 2 speed automatic gearbox in a test car and seeing if it will go up a steep ramp. I am not a car designer so very minimal detailing.
  9. Hi all, the instructions for an MOC automatic gearbox that I made a while ago are now available on Rebrickable. https://rebrickable.com/mocs/MOC-48521/TechnicBrickPower/3-speed-automatic-gearbox youtube video on how it works: :
  10. Here's my 3 speed automatic gearbox MOC. The gearbox automatically switches between one of 3 gear ratios, namely a ratio of 1, 1/3rd and 1/9th depending on the load on the output. It uses two 2 speed automatic transmissions in series to create the three speed automatic gearbox. It works on the principle of 2 degrees of freedom within a pair of differentials. This creates two gear paths for the transmission of force and the path of least resistance is taken. The loading points at which this lego gearbox switches gears is adjustable via two linear actuators at the bottom of the gearbox, which adjust the amount of artificially introduced friction to control the switch over points. Hope you like it.