How to disassemble the propulsion wheels of the LEGO/DUPLO train engine base part# 28743 drivetrain?

Question

I have a push and go motor, also known as Hub No5 model also known as engine base part #28743

The issue I have is that the train can not climb the bridge anymore, unless using the locomotive alone and also stops in curves. After looking carefully I noticed that one of the wheels was slipping.

When I take it in my hand upside down, make the front wheels rotate (the one with the sensors), the propulsion wheels starts rotating. At that moment, if I try to slow down one of them with my finger, I feel it generate torque. For the other one, it just stops easily and I feel the wheel axis continuing to rotate. And I feel some steps.

With the help of the thread How to disassemble LEGO train engine base part #28743 I managed to disassemble nearly everything.

Now, I would like to remove the wheel from it's axis to see what is "broken" inside, and hopefully with the help of a 3D printer, rebuild the broken part.

Any idea how to unmount that ? Is it simple "press fit" (I don't know the exact english name for that).

EDIT

I have to precise two things.

1. The batteries are fully charged so it's not an issue
2. I have two locomotive #28743 and one of them has an issue. I really feel something broken in the "wheel", the wheel is loose from the gear and can rotate nearly freely. So it's not some kind of a kid protection you really feel something is broken inside and that's why I wanted to know how to disassemble the wheel.

Answer 1

My back wheels do the same thing. There is no metal axle that connects both back wheels like the axle design does for the front wheels, but I'm sure LEGO designed it that way.

So, imagine the train's motor being in an "ON" state just a rolling. Now enters a kid, just being a kid. Grabs the thing, and starts a rolling in whichever direction kiddie wants to roll. Not a caring that the motor is doing it's own thing too. How does LEGO protect the device from the free rolling madness of a child?

So, I think this slippage is a built in feature to kid proof protect the motor from being over torqued. Some type of reverse rocket booster dampening system. Analogous maybe to a circuit breaker which, is an automatic device for stopping the flow of current in an electric circuit as a safety measure.

Possible solutions:

(01) Battery check. You said it no longer can pull extra weight, and that it stalls even on flat normal gravity leveled curves? Huh? So, before we go too deep, I would recommend first replacing the batteries with new ones. Then, retest it.

(02) Balancing our time vs. the money justification check. Tearing down the housing to get inner access to remove excess hair and debris from this unit is fairly easy, and just requires buying a T9 Star Torque from the local hardware store and maybe 15 mins of our time.

Even though this thing is LEGO engineered like a tank, we can still imagining extensive damage, let's say a smoosh over by car, where we'd need to replace the circuit board, motor, or destroyed plastic gears.

Then, maybe it might be time to do a price check and consider purchasing a new/used unit versus the time to invest and produce a 3D printed replacement.

(03) Axle wheel hub tear down (setup only). I'm not taking mine apart, becasue I haven't justified a reason that works out for me, but this is my observational approach if anyone else wants to venture further into the unknown.

So, let's look at the wheel design and note the similarities/differences between both wheel hubs.

Break down wheel hub anatomy consists of at least three pieces.

1. Inside hub piece.
2. In between trans-clear rubber tire tread.
3. Outside hub piece.
4. Unknown non-visible pieces. Possible notched out axle bar.

The inside hub pieces and in between trans-clear tire tread all look to be the same molds, where the outside hub pieces differ in aesthetic design, but function in the same way when interlocking with the inside hub piece.

Here's where things get dicey. There seems to be six interlocking tabs that need to be simultaneously unhitched to separate the pieces without permanent damage. Unless you happen to be a six clawed mutant named Wolverine, this will be a challenge.

Six interlocking tabs release damage free setup and approach:

1. Hot glue one end to work desk for stability.
2. Insert six flat head precision screwdrivers.
3. Wiggle until it's free.

Six interlocking tabs release egg breaking, omelette making approach: Goal: 3D print a replacement, so permanent damage doesn't matter.

1. Using a Dremel rotary tool, carefully drill out 4 of the 6 interlocking tabs ONLY. Don't go deep. We can 3D print plastic, but not the clear-trans rubber treading.
2. Insert two flat head precision screwdrivers to disengage the locking function of the 2 remaining tabs.
3. Using a digital caliper measure out the dimensions of the working 2 remaining tabs.
4. 3D print replacement piece.
5. Consider using some Loc-Tite glue adhesive when reassembling the wheel hubs.

Answer 2

Regarding to wheel split and interlocking tabs:

There is simpier way to do it, hopefully without permanent damage to the wheel.

Requires: 2+ flat precision screwdrivers.

Howto:

1. Push screwdriver in between the rubber part and top (side) part of the wheel
2. Push another screwdriver to the closest hole with tab - push from the centre to the edge
3. Optionally - repeat 2 with another screwdriver in a hole close by
4. Repeat 1 to 3 in another segment of the weel.

Part 5135cx1 specific: Rember the center is sitting tight on axle. You need to leverage opposite sides equaly.

Answer 3

FOLLOW UP POSTED AS AN ANSWER

So, I managed to disassemble the wheel axle from the gear axle, which show what I was expecting, a broken piece in the freewheel.

As my question is on how to disassemble the wheel itself @Rin Rio-Oki answer is the correct one.

A picture is worth a thousand words so put picture ...

The wheel axle is simply force in the gear axle, so simply by pulling firmly but carefully disassemble both.

The small teeth in the wheel axle interact with the 4 white teeth of the gear axle to create a freewheel, and that's one of those that is broken in my case and that explain the slipping.

Note that I don't know what could have caused that teeth to get broken.

COMMENT

I solved the problem by drilling a small hole and putting a piece of copper from an electric wire (without the insulation, only the copper) and twisting it at both ends. However the solution of @Greg Dubicki is cleaner. It would be interesting to see if we can redo the part on a 3D printer.

Also note that there was a discount price on Duplo Locomotive a few weeks after the issue, so I also bought a new one ....

Answer 4

This is more of a follow up to the HpTerm's "FOLLOW UP POSTED AS AN ANSWER":

Firstly I did manage to disassemble the wheels pretty easily. Similarly to Murder.exe's answer I did push the screwdriver in between the rubber part and top (side) part of the wheel. However I did not use a 2nd screwdriver - I just slowly pushed the external part of the wheel away from the internal with the 1st screwdriver. I didn't make any photos as I had to quickly put my kid to sleep though. :P I will add them here on another day.

Secondly in one of the wheels an EXACTLY the same breakage happened as for HpTerm. What I did to fix it is the following:

1. I glued the broken part back into its original place with an instant glue.

2. I used a small rubber band to protect the part from breaking again (I hope) by putting it around broken part like this:

I had this rubber band from a new set of tools that I just opened - the tweezers there were blocked from opening with such a thing.

My original plan was to put this band AROUND the whole light plastic part but it wasn't big enough.. However when I put the axle through the band it did spread and looked pretty solid.

So far we have just made a 3-minute test but for now the results are great - the train is not slipping at all anymore. \O/

I will keep you posted how it hold up after A LOT of playing that will happen soon over Christmas. :)

Answer 5

Fixed sliding wheels by add rubber on and tie it few times. I hope engine will not burn too fast.

Answer 6

The issue is indeed with insufficient friction. I have managed to fix it. I used the same rubber band idea. As I did not have a rubber band at hand I used a random piece of thin-ish rubber like material and glued it around cogwheel. Works like a charm - no more slipping (for now).

Disassembling rear wheel is very simple. I just pried open one side with a knife (not cutting, just getting a thin thing in to pry it open). Then I put a small screwdriver there to hold it open and worked the other side of wheel the same way until it popped open.