Suomeksi Image Map



FINALLY - NON-SLIDING DRIVE WHEEL

The sliding drive wheel really pissed me off! I tried all kinds of solutions.



By this trick I tried to get the drive wheel grab the long paddles - Waste of time!


This pair of small wheels was meant to push the track better to the drive wheel.
It helped a little, but not enough.

Finally I needed to do some radical surgery and reform the drive wheel to a "through-the-track" -kind. I reformed the original drive wheel as an eight stud drive wheel and I made studholes to the track - and it worked like a toilet in a train! My joy was infinite - for at least a moment.



Reformed drive wheel and the holed track.





THE TRACK OF THE FOURTH GENERATION

In the fall 2008 a new motor appeared. I was bored to play with old engines, so I bought a new brushless engine. Now when there were the new engine and a working drive wheel, the riot begin! Sled were rushing like a real racer all over the yard, snow was flying and the drive wheel grabbed like glued.

At the end of the first test run I suddenly noticed that the sled started to run wounded. When I inspected it closely, the slide tracks appeared to be bent because of the torque power of the track. My first aid given was to bend the sliders in the U-shape. This allowed me to continue driving.


Bended slider



Brushless engine and Team Losi kevlar spur.

Overall everything was ok, but there was still a couple of problems:

- The track tension was too loose - I made the conclusion that it stretched a bit.
- Continuous tightening of the track by making the sliders longer caused something what is difficult to explain in English. But I'll try: The rotating track had an torque effect which turned the end of the slider up. This happened because there were too much of the slider behind a the attachment point of the rear suspension arm and too much friction in the trackwheels. This turned the slider so efficient that the front suspension couldn't resist the torque and barely didn't move. If you drove slowly the track front suspension worked.
- The front of the track suspension should have sunk even more inside the track tunnel.
- The "spikes" in the front of the slider went to the studholes every now and then and stopped the running like a wall.
- It was possible to turn the sled only in slow speed.

It was time to go back to the workshop and build the fourth generation track suspension. There were some significant improvements:



I moved both upper and lower attachments of the rear suspension arms backward - as also the rear bumpers.
I also lowered the upper attachment downward and shortened the arm. These things allowed the front wheels
to sink even more into the tunnel and the rotating track didn't turn the slider up anymore.
I made the new front arm one cm longer.



The attachment of rear arm moved out from the tunnel.


Old attachment spot.


The old spot is marked by red arrow. The new one was moved three centimetres farther.


I made the rear arm wider from the top and moved the bumpers to the side.
This gave more space to the front arm and front wheels inside the tunnel.


I also made the front arm top wider. This gave more space to the front end of slider to sink.
Front flexibility was now 3,0 cm.


I put bearings to the rear end turning wheels. There are holes
for moving the turning wheels backwards 1,5 cm by 3 mm steps.


I removed small wheels from the middle and replaced them with narrow wheels from the front.
I put two small wheels to the front end spikes to prevent them from penetrating the track.


The rear suspension in the lowest position. The rear suspension travel measured
from turning wheel is 5,9 cm. (It's 47 cm in 1:1 sled - In a real Crossfire the rear
travel is 43 cm, so it's quite realistic.) The rear suspension is adjustable 4,8 - 6,6 cm.


Mostly because I'm lazy, I made the structure simpler - I didn't feel like making so many parts and putting them together in a complicated way, anymore. I also gave up polishing and detailed finishing. I was only interested in getting the sled to the snow. Anyway, the structure was now much steadier. Video below gives an idea how the suspension is workin in practice. Another video in the end of the page.






TUNING

I made a firmer aluminium rack for the steering servo. I also replaced the old servo with a 6,5 kg semi-high torque servo.


By mounting wear bars to the skis, turning improved a lot.



To improve sliding, I melted paraffine to the skis.


The wear bar is made of 2 mm metal bar which has M2 thread in the other end.
Thread end is mounted to the ski with M2 nylock nut.


The other end of the wear bar is mounted by penetrating the ski with the bar and bending the end of the bar in to the "furrow".



The engine and the ESC had a tendency to heat too much inside the hood. I had to do something about it.


I cut holes to arrowed spots.


I mounted a fan inside the hood.


For the air the fan blows away I drilled a bunch of holes behind the windshield.

This system worked surprisingly well.

Now when the sled was finally tuned, it was fun to drive and it goes well in the snow.



DRIVER

The Dimensions of legs and torso of the old driver weren't so good. Upper body was too short and this made whole sled looking too big. I decided to make the new driver also to turn the handlebar.


Upper body and the arms are made of polyurethane sprayed foam. Elbows and shoulders are made by wire.


Making the helmet made me swet, but then the Ebay came to rescue: I found 1/6 scale motocrosshelmet. The helmet was almost like made to this Action-figure head I found also from Ebay.


Helmet and goggles.


Helmet is almost like made for the action man, althought it's not.


And the goggles!


Th new driver in the new clothes. I have to confess I didn't make the sewing.
Notice the nice zipper-pocket.


Turning handlebar was easy to make. The driveshaft was made of thin threadbar. I set this inside brasstube. I drilled a hole to mountingspot and glued the tube there. The pictures tells more than thousand words:


Small servo was easy to mount under the hood.









The new driver and handlebar in the short movie:




Here you can find a few videos after the tuning.
Speed sample (2,9 Mt)
Track assembly working (1,5 Mt)






And now? I'd like to modify the driver to turn the handlebar. Or then I'd like to make a whole sled from a to z by myself. You never know.