More in my attempt to fully utilize the differentials…
This is my EVT (Electronically Variable Transmission) based drivetrain.
I started with an attempt to build a working CVT using two differentials based on a LEGO design, but found that it relied on a friction peg to hold a 1:1 ration and then ‘slip’ to 1:5 under load, and when I did all of the math it wasn’t actually changing torque ratio but just diverting power to slipping the friction peg.
My second design was technically an EVT, but I called it an IVT (infinitely variable transmission). This design used 4 motors input to 2 nodes of a differential to drive the wheels, with the entire setup duplicated on each side. The first 2 images in the album are of this design, and the Modkit code ‘IVT-0.mk4v.txt’ is for this design. I math’d the gear ratio for this, it’s in the PDF.
My third design is also an EVT, but with only 3 motors. One motor is dedicated to each side, and the third is used to change the ratio of the other two. Because of the torque ratios between motors, and because torque is split left/right with this design, I need the same motor torque into the center shaft as I do on each side (since I only need 1/2 as much as the primary motor), so all are geared 1:1 into the differential. The output speed will be a 2:1 (faster) ratio from the side motor to the wheels when the center shaft is locked, and a 3:1 (faster) ratio from the side motor to the wheels with the center shaft is driven backwards. In software, the center shaft is the average of the two sides, so this is entirely automatic. The Modkit code ‘EVT-0.mk4v.txt’ is for this design. It is also included in the PDF.
Link to the album:
Also, a PDF going through how to calculate gear ratios with differentials, using the ‘lever method’. It also works for planetary and other multi-node gearsets, but I only explain it in the case with 3 nodes equally spaced.
IVT-0.mk4v.txt (12.9 KB)
EVT-0.mk4v.txt (12.6 KB)
BasicDifferentials.pdf (5.25 MB)