Help me with my 8868 b-model please !!

[Roc_Xel]

Hey, 

So I love 8868 so much that I got me another one to build the B-model and have them both. 

Build is pretty straightforward, but once done when I activate the motor it works well but nothing happens. 

Clearly the fist grey cable connected to the tiny pump connected to the motor seems to be given air but then somehow it does stop somewhere. 

Dismantled the whole thing, found out that one tube had broken on one of the valves, and rebuilt it entirely changing the damaged tube with a new one, have tons in stock. 

Yet, exact same. I made a 20 sec video for you to see the problem, clearly first cable coming from the tiny pump seems activated but then nothing. All cables are connected where they should be, all "holes" are filled as it should, so there's not a cable not installed properly. 

A mistake is not impossible but I'm on my 50th set and built it twice now so not sure it's that. 

Was thinking more like faulty pieces but all cables really seem fine from what I see (and I checked them when rebuilding). Is it possible the tiny pump does not give enough air ? Also, put a bit of water on the valves when cleaning the bricks before building but there's no electronic involved and they seem to work absolutely fine. All 3 bigger pumps can be easily extended as well when the motor is off.

Please help before I dismantle a 3rd time, I'm sur one you pneumatics experts will have an idea. Thanks guys. 

[Milan]

Have you checked whether the small pump (driven by the motor) is able to pump air at all?
It does sound like the motor is driving the pump way too easily, which may suggest a broken pump, or a leak in the system.
I remember that the 9V motor on my 8868 sounded like it was working harder to drive the pump once the circuit was filled with air and the big pneumatic cylinders started pushing.

[Roc_Xel]

Thanks Milan, was wondering the same but the air these tiny pumps send is so light that it's tough to really say if they work when dismantled. Just grabbed my a model and will switch them to see if they work. If the one on my b model makes the A model work then i guess this was not it. Will keep you posted. 

 

Edit : So started putting the A model tiny pump into the B-model, and indeed it seems to be making the motor work a bit more, rest is now disconnected obviously so can't saay it works for sure but looks like it's better already. Will rebuild with this one and see then. 

Edited March 9 by Roc_Xel

[Milan]

21 minutes ago, Roc_Xel said:

Will rebuild with this one and see then. 

If you have another pump at hand, you can connect it, but pump it manually, to see if the system will start up. You can use the big pump, too.
That should also show if there is a leak somewhere (hoses, T piece, switch...).

[Roc_Xel]

So rebuilt with the other tiny pump from A model (the one connected directly to the motor in B - model) and it seems to be triggering better, i see more movement so this pump is probably better, but it still does not work. 

Connected to a regular manual big size pump, and same, it does not do so there's a hole somewhere. Can these T shape connectors be faulty ? 

Damn I'm so annoyed, first time in my life I don't have a working Technic set, and I can't leave it like that, all functions have to work this is basic rule of thumb. Any advice on how to determine which piece is faulty ? Will have to dismantle a 4th time in any case, this is so damn annoying. 

[Milan]

30 minutes ago, Roc_Xel said:

Connected to a regular manual big size pump, and same, it does not do so there's a hole somewhere.

If you tried the pumps by manually pumping, and they provide air, then the leak is in the system.
Make sure the pump is working properly. Close the outlet (where you attach a hose) with a finger and push the pump with sense. It should be hard to press it, and it should go up right away.
If the pumps are okay, you can check the hoses by attaching them to a pump and close the other side of the hose while pumping.
T shape connectors would have to have a visible crack, but check them, too.
Switches might also be the issue.

[Roc_Xel]

44 minutes ago, Milan said:

If you tried the pumps by manually pumping, and they provide air, then the leak is in the system.
Make sure the pump is working properly. Close the outlet (where you attach a hose) with a finger and push the pump with sense. It should be hard to press it, and it should go up right away.
If the pumps are okay, you can check the hoses by attaching them to a pump and close the other side of the hose while pumping.
T shape connectors would have to have a visible crack, but check them, too.
Switches might also be the issue.

Thanks mate for your help.

Yeah the "test" pump is working perfectly, gives lots of air to any connected tube. Clearly will have to dismantle and test every part with this big manual pump to see where the fault lies.

When I saw that the second tiny pump connected to the motor seemed much better with the one taken from A model I thought that was it while rebuilding but clearly its not.

Shame coz I looked carefuly at each cable when rebuilding the 2nd time and cant find one faulty (my kitten loves biting those when I build, I had to replace two of them that were broken due to bites, hence checked even more carefully ^^).

Will check the valves (but got 4 overall with 8868 and using only two for B model, and the other two I have available and unused work perfectly, still a possibility though) and those t shape connectors. 

Will let you know, thanks again

[Stereo]

There's an earlier version of the switch that isn't glued, it's just clipped shut, you can see the clips at the top & bottom of it plus the two parts are relatively loose.  I've had a couple of those that only hold about 7 psi unless you press the back cover into place, and even then it's less than the glued ones.  Maybe 15 psi, vs. the glued ones holding up to about 20-25 before they leak.

You might want to lever switches back and forth 10-20 times to make sure the internal rubber/lubricant is softened up and able to seal.  

[Andman]

Did you try to run the motor in the opposite direction? That fixed the problem for me.

[Roc_Xel]

Thanks guys for the answers. Switches are glued indeed and working well and as for the motor both directions gave nothing. 

Dismantled again and one of the 8cm hose had a small hole into it, and that was it. 

It now works but honestly I really dont like how the arm works and is positioned (just the grabbing part, not the black part lifting the arm). The cylinder moves freely and sometimes parts disassemble. You also have to lock it in a very specific position to make sure it closes enough and does not open too wide. Everything works perfectly but I feel like the arm part is really fragile in how it works. 

Anyway, lovely set but comes really short compared to a-model. Then again, a-model is imo in the top 5 Technic sets ever released, if not top 3. 

Thanks again for helping me fixing it and all the suggestions. 

Edited March 10 by Roc_Xel

[gyenesvi]

This is one of my favorite B models ever. I remember I was fascinated by the whole mechanism when I first built it at the age of about 14 :) Maybe fragile and weak by today's standards, but still a great one! Great that you managed to fix it!