Help needed with my 8043

[calypso]

Just finished the build and I am now doing a bit of tweaking and applying some lube (Super Lube)

I must say I did enjoy building this model. I have been involved with Techic since the '80s, but I still found it quite challenging for my old hands.

Everything seems to be working well except for the tracks. I find that the movement over the tracks is lumpy and even on a smooth non-slip surface, the model does not travel smoothly but jerks along.

I checked the chassis build twice and all seems to be as per the instructions.

Could it be the track is too tight?

Thanks for any suggestions.

[Rodeown]

Hi there, I just got two of these yesterday and finished the first one earlier today, it seems to be that they do rattle and jerk a little on the tracks, I made sure everything was running smooth and there was no gripping gears etc but mine does the same as you describe, all I can think is that we are working with plastic gears and shafts and they have some longitudal flex in them, when put under load ie: moving forward on the tracks they flex then once moving the flex is released then applied again etc etc, probably very little we can do with this, just search on you tube for 8043 videos and you will see they are all the same. :-)

[Kronos]

I agree with Rodeown. Mine was the same. Was, it's now been sacrificed for parts. Great build and a fun set though.

-Mike

[Rikus]

Unfortunately, I confirm...

The model is really wonderful, but it has a problem with jerking tracks; the reason is the very long drivetrain from the motors (on the upper body) to the tracks.

Especially, the jerking is produced by the elasticity of the long axles that go through the Turntable and by the many gears used in the motion transfer...

Even Jurgen, in his Ultimate 8043 MOC, speaks about this problem, but even his revision of the model (that I already built) shows the same problem.

[calypso]

Thank you both. I can certainly live with it.

I just wanted to know if I had screwed up somewhere.

I'm working on a fix. I'll let you know how I get on.

[DLuders]

@ calypso: Welcome to Eurobricks! It's good to see someone older than me that's interested in Lego Technic too!

[rener]

What seemed to work for me (haven't tried it recently...) is inverting the 20t and 12t double bevel gears of the drive shafts. The 20t gears were added on step 39 (book 1, p47), the 12t on step 44 (book 2, p12). As I remember the model moves not jerky anymore, and of course also a bit faster.

[Rodeown]

What seemed to work for me (haven't tried it recently...) is inverting the 20t and 12t double bevel gears of the drive shafts. The 20t gears were added on step 39 (book 1, p47), the 12t on step 44 (book 2, p12). As I remember the model moves not jerky anymore, and of course also a bit faster.

I looked at this and thoght at first it was not possible but now i think it may be.

Also if anyone else can confirm that a problem i am having is similar to what they experienced, when the batteries are running low does the selector switch stop working first?

Edited April 15, 2012 by Rodeown

[rener]

I looked at this and thoght at first it was not possible but now i think it may be.

I saw your edit. Of course I meant the 20t double bevel gears as wel as the 12t ones. I just rechecked my own model and it works very fine!

[Rodeown]

I saw your edit. Of course I meant the 20t double bevel gears as wel as the 12t ones. I just rechecked my own model and it works very fine!

Yes i misread your first post and thought you meant just to swap the thin bevel gears on page 47 book 1 but as soon as i reread i realised my mistake, you did state double bevel

and also the other page with the 12t gears on, i will give it a test and see how it operates

I just quickly, (inspired by your post) changed the 20t single bevel gears (page25 book 1) for a couple of the 12t black double bevel gears i had spare moving the 12t single bevel to the 20t single bevel spot and substituting the 12t double black for trhe 20t singles. (if that makes sense lol) it has speeded the tracks up and as a result has also reduced the jerkiness slightly, but i may be wrong.

i will do as per your suggestion and see how things go, doing both my gear it up too much and reduce the power too much so will perhaps just do yours.

The more i fiddle the more i am thinking the jerkiness is related to the tracks running on the 6 plastic rollers underneath them, if you put light pressure on the tracks and roll them by hand they jerk as they pass over the plastic rollers, maybe it is just bad desgn of the track system?

Another update: just removed all of the idler wheels and brackets that hold them in place and ran the excavator on its tracks with just the large track wheels, no little wheels or frames touching the tracks...... this makes the jerking of the model 5 x worse ! not what i expected at all, so it must not be related to the tracks. must be the drive system. Hope all this helps.

Edited April 15, 2012 by Rodeown

[calypso]

I agree. I think I can confirm that the problem lies in the track/wheels design.

I removed the tracks and fitted four wheels with rubber tyres. The model runs smooth as silk. Absolutely no jerkiness from the drive train.

I believe that the cogs on the large track wheels are too rounded and too short, so that there is no continuous take up of the track by the drive wheels.

It is a take up, slip, take up, slip action.

The small track wheels are also badly designed in that they sink into each track link and have to climb over each link to then sink into the next one.

Strange how something so obvious got past Lego's designers.