Duplo hitches

[Peter Blomberg]

Now that more duplo trains and cars are modeled, we should think about the primitives for the hitches aka tow pins, tow loops, and tow clips. Duplo hitches come in many types and variants. However, when minor differences are ignored, it boils down to a handful tow pins and tow hooks.

Long unreinforced tow pin
Suggested archetype: 4883a in LDraw
The classical tow pin has a long neck and no topside reinforcement.
4559, 4580 (Corrected), 4883a, 4883b, 53053, 31300 (Corrected), 59273a (Rebrickable)

Long fully-reinforced tow pin
Suggested archetype: 22307 in Rebrickable
The classical tow pin with long neck and full topside vertical reinforcement.
31507 (Corrected), 22307 (Rebrickable), 59273b (https://www.ebay.com/itm/365018516343)

Short unreinforced tow pin
Suggested archetype: 2312 in LDraw
This tow pin has short neck, no topside reinforcement.
2312, 31300a, 4580b, 6505

Clasped tow pin
Suggested archetype: 52071 in Rebrickable
This tow pin has short neck and horizontal triangle covering the topside
1326, 2034, 18520, 52071, 54007

Short fully-reinforced tow pin
Suggested archetype: 11248 in LDraw
This tow pin has short neck and full topside vertical reinforcement.
11248, 31300b, 15313, 15314, 31174, 95462, 98214, 58234, 53899, 4354

Short half-reinforced tow pin
Suggested archetype: 28759
This tow pin features a curved topside reinforcement.
28759, 28743, 2092

Tow loop
Suggested archetype: 4883a in LDraw
Features a closed tow loop/hook
4883a

Rectangular tow clip
Suggested archetype: 53053
Features an open tow clip/hook on a triangular rectangular support.
2320, 6505, 53053

Rounded tow clip
Suggested archetype: 2312&11248 in LDraw
Features an open conically-tapered tow clip/hook on a rounded support.
2312, 11248, 31174, 52071

Untapered tow clip
47450

Trailer tow clip with wheel, horizontal
18520, (87657), (87658), (89198)

Trailer tow clip with wheel, angled
14923

This list is not exhaustive. Some additional cases were omitted.
4883b reinforced clip/hook (https://www.ebay.com/itm/186383419871)
4820 reinforced trailer clip/hook
All movable clips/hooks

[Gerald Lasser]

Thanks for this compilation!

I think we should also consider where the centre of the hook and the clip/hitch is located. And we need kind of a family tree to see what we can reuse.

I am currently working on 4580, 4559 and the 31300 Train Bases, which have a movable clip. Interestinglz the 4580 comes with two variants, the earlier with a "Returnto zero/neutral" function and a loose one. Unfortunately these assemblies are glued, but I got some below one EUR each, so I could take them apart.

4580cxx is nearly done, I need to do the bottom lid and fiish the rod. 

Here's the overview of the clips, I am waiting for the 4580 to finish in order to adjust the centre of the clip.
   

[Peter Blomberg]

Movable tow clips come in two main categories; the former of which has multiple variants.

Category 1:
4559 likely has one version pre2000 and another 2005-2012 including the red color in the latter.
22307 has only one variant.
2092 has probably only one variant.
31300a and 31300b may have two different variants, totaling 4 different combinations when tow pin variants are included.
31507 has probably only one variant.
4580a and 4580b are likely to have one version pre2000 and another 2005-2012 including the red color in the latter.

Category 2:
28759 Yellow rounded movable clip/hook

[Gerald Lasser]

Movable tow clips come in two main categories; the former of which has multiple variants.

Category 1:
4559 likely has one version pre2000 and another 2005-2012 including the red color in the latter.
22307 has only one variant.
2092 has probably only one variant.
31300a and 31300b may have two different variants, totaling 4 different combinations when tow pin variants are included.
31507 has probably only one variant.
4580a and 4580b are likely to have one version pre2000 and another 2005-2012 including the red color in the latter.

Category 2:
28759 Yellow rounded movable clip/hook

Do you have a reference for the variants?
4580a/b
-> I can find only "4580", but the two I took apart are differrent (only on the inside)

31300a/b 
-> I can only find 31300c, I wonder where this number comes from, the one I took apart (ordered as 31300c) has 91973 for the top, and 6444 for the bottom

[Peter Blomberg]

4580 a and b
I was under the impression that the yellow base with red movable clip/hook may have had a short tow pin.
Looking more closely at real pictures instead of only computer-generated images, I see that all 4580 are indeed long, unreinforced tow pins.
https://www.ebay.com/itm/314972993887
https://www.leboncoin.fr/ad/jeux_jouets/2974892858

31300 a and b
First of all, I had erroneously marked down an "S" for short instead of "L" for long. Both are long-necked tow pins.
It's relatively easy to find real pictures of sets having both the long, unreinforced tow pin and the long, fully-reinforced tow pin.

31300 with long, unreinforced tow pin:
http://www.peeron.com/inv/parts/31300cx3
https://www.ebay.co.uk/p/7053432934
https://www.ebay.ca/itm/176166169336
https://cdn.myonlinestore.eu/94f6360e-6b...1002134303
https://aukro.cz/lego-duplo-set-5607-opr...6960480777
https://bebefreear.click/product_details/2334662.html
https://bebefreear.click/product_details/2334682.html
https://www.worthpoint.com/worthopedia/l...1877794355
https://www.ebay.com/itm/275871019394
https://www.duplarna.cz/lego-duplo-2937-...csVwhVbV2u
https://www.mimibazar.cz/inzerat/8006579...-auto-2937

31300 with long, fully-reinforced tow pin
https://www.youtube.com/watch?v=KTa8eiXqAU0
https://www.ricardo.ch/de/a/lego-duplo-5...275364244/
https://www.ebay.de/itm/353245796876

However, I discovered e.g. that black had replaced yellow in some sets. I also found that Rebrickable lists 31300 as an alternate for 31507 and 31507 as an alternate for 31300. I also found sets having 31507 of both types. This suggests that BrickLink, Rebrickable, Peeron, Brickset, etc have it wrong. Perhaps one of the two was first with a long, unreinforced tow pin and this was later replaced with the other, perhaps differing schedules for different colors/geografic markets, etc.

The only difference between 31300 and 31507 seems to be the tow pin reinforcement. To conclude;
All 31300 with reinforced tow pins were actually 31507.
All 31507 with unreinforced tow pins were actually 31300.
If reality follows these assumptions, then the variant space became a lot smaller.

[Gerald Lasser]

I ordered quite a number of Duplo Train Parts, luckily I found some broken engines, so they are quite ok from a price perspective:

I have in order:
22307, Gordon/Spencer Base
2961 plus top (6408) (Electric)
2961b plus top (31298) (Electric)

I have an auction till tomorrow, hope it stay ok as well for:
6172 plus canopy.

[Gerald Lasser]

I finished the 4580cxx parts to such an extent that I can upload them and you can have a first look at them.

The basic version, blue body, red wheels, yellow rods and black hitch  is available in three different versions, ONLY distinguished by the different design of the push rod.

The "middle" one is the one with the most designs as they coloured the wheels for the Thomas series.

There is also a fourth version for Percy, who misses one axle.

[Peter Blomberg]

There are currently two subparts/primitives for a common geometry of the tow pins:
4883s01.dat https://library.ldraw.org/parts/44458
and duplo_hook.dat https://library.ldraw.org/parts/47864

They differ only in the sharpness of the top lip overshoot.

The angle of the lip overshoot was larger (rounded to 1/16th above), but has now become smaller (very close to 0, i.e. half of the circumference of the pin, see e.g. fourth pic https://www.ebay.com/itm/125708641270). Some vehicles have an additional dent at the base of the pin (see e.g. sixth pic https://www.ebay.com/itm/364292486127). We should also keep in mind that one of the variants have a triangular plate instead of the top lip (perhaps plain cylinder would do). On the side, the attachment of the triangular "arm" occur at different angles, tending to be narrower for vehicles lacking the underside centre reinforcement. The pin top also has a few different shapes, ranging from fully flat to elevated centreline to circular dent.

I propose the following simplifications:

• Tops are modeled flat.
  
• The lip is reduced to half the circumference.
  
• Dent at base is ignored.
  
• Differing angles of "arm" attachment are ignored.
  

That would leave underside centre reinforcement and topside reinforcements as optional additions for the reusable subparts and allow a single primitive to be used with both older and newer tow pins.

[Gerald Lasser]

some heads up on the trains, the first engine is nearly done...