thirdwigg's 3-Speed Transmission with Changeover

[DLuders]

On his Brickshelf gallery, thirdwigg says that he loves "building truck trials. My MAN LE 4x4, with three speed linear transmission by two PF M, drives with PF XL, and [has] four wheel steering with PF M, pendular suspension, four PF channels for control; gears shift well."

His

shows the "Lego 3 Speed Linear Transmission with Power Functions changeover":

On Flickr, thirdwigg wrote,

"I started with my 3 speed transmission ( ) and created a way to have two power functions motors work to change the gears from one to the next. I wanted to use PF motors so I could control the system with a PF remote, and because I did not want to purchase an NXT system.

Two problems were discovered when I created the transmission: first, I would need a system that would move the drive axle one stud at a time since the transmission required three gear placements at three stud intervals. Secondly, the changeover would have to be fast, so the gears would not grind. Making this changeover fast, and to stop precisely at one stud intervals was the challenge.

The solution was to have two PF M motors powering a single axle that would rotate and translate that rotation into one stud movements. Each motor on either side is limited to one half rotation which will move the Pulley wheel ( http://www.bricklink.com/catalogItem.asp?P=4185 ) one half rotation. This moves the liftarm a total of two studs. By placing the differential in the center of the two motors, I can limit the movement of the pulley wheel to one quarter of a rotation. This in turn limits the liftarm movement to precisely one stud of movement.

By implementing this design into a truck trial, I will be able to shift between three gears with a PF remote and one channel, shift both while the drive motor is running or not running, and without having a neutral gear. In addition, this system is stronger than changeover gears, and uses fewer gears reducing total system friction."

[Alasdair Ryan]

interesting

[nielsvdv]

yes, but pretty big, i am building as we speak on my new 4x4 trucktrial for the belgium competition. it has al wheel steering and a 2 speed gearbox, it gives me a 1/5 and a 1/12.5, but it is a lot smaller than this

but i will keep the idea in mind :)