Making the seat height adjuster

When I received the Russell seat which was made in the frame of and earlier model LT I found the seat height adjustment rod being different and if I remember correct it did not quite fit in the new bikes frame. Unfortunately this was already back in the winter of 2006 so I cannot remember exactly...

In any case, I started playing with the thought of having the seat height adjusted with motor. Quite soon I started looking at the windshield adjuster motor of the LT which I found to be quite powerful. And the electrical connection was not so complicated.
I brought up this plan on the BMWLT.com forum and right away I got support form the forum members. One member (sorry cannot remember his name anymore) even went all the way and donated his old windshield adjuster to me! (I had his name mentioned on the Picasa photo album texts but we all know what happened to those...)

In the photos above I had received the windshield adjuster motor and I was playing/planning how the heck I could fit it under the seat. The rear spring preload adjuster was the first one to be taken out of the way. Luckily that was the only item that had to be removed.

I made my first prototype that looked like this. This worked fine raising the empty seat. But if I was sitting on it...no way!

OK enough of playing around! I realized that a crucial demand was that the mechanism must be self braking or self locking which means that if the seat is any position above the base position and when I hit a bump on the road, the mechanism must hold and not break up. I figured the lifting mechanism has to be able to raise my weight (85 kilos) without breaking down right away. In order to produce the power the speed of the lifting cannot be very fast, so I would have to discard the WOW -effect on the traffic lights to the next door car driver...

So I started over my designwork and looked at the car jacks or other lifting devices with scissor mechanism. I realized that this was the way to go and made a 3D sketch of the mechanism in which I studied the various positions and lifting heights:

I needed two of these sets, one for each side of the seat. And the trapezoidal screws must be one right- and one lefthanded.

Here is the lifting mechanism in "low" position,

And here it is in "high" position. The difference is about 72 mm. The system has also two limit switches that stop the mechanism at low and at high position and I have indicator lights in the dash for them too. The good feature of this mechanism is that regardless of the weight or even impact that is applied to the mechanism it does not give any stress to the gear motor. It has actually a plastic sprocket so it would not tolerate any extra stress anyway. And the system still works, since 2006 and about 200.000 km ago...

The mechanism rests on the bike frame. Here I was preparing the piece that bolts through the existing holes of the frame

bracket.

Here the second and final version is in place and in low position. This picture also shows my two rear fuse blocks which have nothing to do with the seat height adjuster. The Baehr box is the bike-to-bike radio. 

The next task was to make the base of the seat in such way that the lifting mechanism has a proper place to meet the seat.

I prepared a steel structure that is mounted on the bottom of the seat base.

And because there are two roller bearings on each side touching the seat base counter pieces, I had to make them in such way that the counter pieces can pivot. It is important as the angle of the seat changes during the lifting because I'm only lifting the tail of the seat. The pivot point is in the original place.

This is how the seat looks from underneath now.

Here the seat is in low position.

And here it is in high position.

Making the seat adjustable that much resulted of course to other changes as well. The seat locking mechanism had to be altered.

I had to raise the seat lock mechanism to allow the seat to travel up and down the distance of 72 mm.

The next headache was the BakUp backrest which is normally fixed on the bike frame but now my seat was going to travel up and down...

Here is the original BakUp backrest. I cut off both ends of the curved bracket so that I could fasten it directly on the rider's seat. I drilled some five or six holes through the bracket and applied some epoxy glue and pop riveted the bracket right on the plastic base of the rider's seat. 

Unfortunately I did not document this phase of work properly but here you can see the back side of the rider's seat. I had to open the upholstery in order to fasten the bakup steel support right on the rear part of the rider's seat. The plastic piece is for protecting the leather from getting damaged by the seat lock mechanism.

Anyway, here is the backrest in place and it is fixed of the seat and thus moves up and down with the seat. The backrest has also a motor for adjusting it back and forth but that is again another story... 

I don't go into the electricals of the seat adjuster at this stage but if you are interested in how it was done give me a comment and I will shed some light on that subject, too.