Gravitrax Marble Run Lifter Elevator with Rope, height adjustable

Complicated (but awesome) Gravitrax Rope Elevator! Released as complete freeCad model and 3mf-files.

Pros:

• Looks cool!

• Lifts to a height between below two and above three 70mm blocks

• Minimum pickup height: 2.5cm

• Fits completely on a single hex-tile

• Runs on a single AAA-Battery

• Very quiet: No fast moving parts, and first part of the transmission is a rubber band

• Uses only 3D-Prints and a bunch of screws and other common parts

• Height adjustable because the middle of the tower is just plastic drinking straws

• Uses a common toy motor that is used in every second electric kid's toy

• Top-pulley is tensioned with a rubber band and adjusts itself

Cons:

• Fiddly for a beginner to put together.

3D-Printing:

All parts are printed with no support, no brim and 0.2mm layer height. Especially the gears require a fair amount of precision, so make sure your printer is set up well. These hints help making sure everything works fine:

• Print at a rather slow speed, don't push your printer's speed this time :)

• Disable the common "print first layer at 0.3mm layer height" setting in the slicer.

• When your gears bind up, try setting the slicer to underextruding by a small amount (e.g. 3%). Many filaments are a tiny bit too thick, so that hint is a general one.

• Use the two test prints added to the model

• Small 3D-printed holes are always tricky and vary from printer to printer, especially where 0.1mm actually matter. There are two print tests added to the model: One is a hole print test that prints the four hole sizes used in this project, see below. The other one prints the four gear axle holes on a small wall piece, to check whether your gears run freely before printing the whole frame.

All bolts are M3-Screws ( 1/8'' is the closes imperial size). There are four hole sizes used in the project, sorted by size here:

• M3 screw thread fit: for cutting a M3 thread using a tap

• M3 light push fit: Holes where bolts are pushed in

• M3 slide fit: All holes where parts (such as gears) need to move easily

• M3 screw fit: Used where a screw clamps two parts together. The part without thread has a quite forgiving hole size.

The hole print test piece has the holes in the same order. The rounded part of the print test base is where the largest hole is.

Non-3D-printed parts

• Countersunk bolts:

  • 4 × M3 25mm ( #4 × 1") :

  • 3 × head cut off to get 20mm rod for gears 1,2,3

  • 1 × head cut off to get 22mm rod for top rope pulley

  • 1x M3 30mm: for drive belt pulley gear (gear 4)

  • 5x M3 10mm:

  • 4 x for attaching bottomplate to gear frame

  • 1 x for closing the frame

• Non-Countersunk bolts:

  • 2 x for attaching battery holder to bottomplate

  • 4 x for attaching lower middle plate to frame

  • 4 x for attaching upper middle plate to top assembly

  • 2 x for attaching upper rope pulley-arm

• Reusable plastic drinking-straws (6.5mm, 1/4"),depending on height of marble lifter:

  • 4 x 40mm for a two-block lifter (lifts to 2*70+10 mm)

  • 4 x 110mm for a three-block lifter (lifts to 3*70+10 mm)

• Thin sheet metal (e.g. from steel coke can) for the two contacts of the battery holder

• small switch (1cm base width)

• Toy DC motor 1.5V, 3000rpm (about 100wdg on the rotor)

• cables, soldering tools

• zip tie for attaching motor

• kite string

• small rubber band / loom band: motor drive belt

• small rubber band / loom band: for the string tensioner

Assembly:

1. The gear axle holes in the left frame part must be threaded M3. The corresponding holes in the right frame part are a light push fit. Also thread the two holes in the bottom and in the top of each of the two frame parts. The long stud on the right frame part that reaches all the way to the left (for the closing screw) must be threaded as well.

2. Create gear axles by cutting off the head of M3-Screws, see parts list below. Screw in the gear axles and make sure they are in far enough so that they don't bottom out on the right frame piece.

3. Place the three lower gears (the lowest one has the lower rope pulley) on the axles as shown in the pictures. They should mesh and spin freely together, but not skip teeth. Push the two frame pieces together carefully, until the long standoff in the upper part of the frame touches the other side. Use a small M3 countersunk screw to close the frame.

4. Use a 30mm screw to attach the fourth gear (the one with the driving belt pulley). It goes right through the hole in the frame and meets gear 3 inside. Make sure the gear does not move sideways by too much but spins freely.

5. Battery contacts: Cut a narrow piece of tin (e.g. from a steel coke can) and scratch off the paint on both sides. There is a gap in the battery-holding-circle in the bottomplate where you can push in the tin piece so that it shows up in the circle. Make a battery contact and solder a wire to the piece. Cut a second tin piece and push it through the gap in the battery holder bracket. Fold it under the "bridge" to make the battery contact. Solder wires to the contact.

6. Solder wires to the switch.

7. Screw the batteryholder onto the bottomplate. Drill some tiny holes in the little standoffs to attach the switch with tiny screws.

8. Push the frame into the indentations in the bottomplate. The batteryholder goes left and the switch right. On the frame, the motor pulley is right. Use four screws to attach the frame to the bottomplate and baseplate. The baseplate goes flat side up against the bottomplate, and both plates are held together against the frame.

9. Place the toy motor in the frame so that the axle pokes out on the right side. Zip-Tie the motor in place and attach the wires.

10. Place a small rubber band (a loom band works great) over the motor axle and the drive pulley.

11. Use four screws to attach the middleplate1 to the frame.

12. Cut four drinking straws to size, see list above for lenghts.

13. Thread the four screw holes in the bottom of the top plate. Also thread the two holes where the pulley attaches.

14. Attach the middleplate2 to the topplate with four screws. Make sure to use only 8mm screws here, the 10mm ones are too long.

15. The top plate has two notches on the back side that are closed by a thin one-layer plastic piece. The strip was there merely for printing, so that the middle piece does not get loose on the print bed. Cut open the notches, they are for a rubber band later.

16. Thread both sides of the pulley-arm. Cut the head of a 25mm M3 screw to get the top rope pulley axle. The pulley-arm has a longer and a shorter side, and the top rope pulley has a small boss on one side. Place the pulley so that the boss is on the shorter side (so that the pulley is in the middle). Screw the axle into the pulley-arm with the pulley in place and make sure it spins freely.

17. Use two 8mm M3-screws to attach the upper pulley-arm.

18. Cut off a 30-50cm piece of thin, strong string, depending on the height of your lifter. Kite string is a good choice.

19. Thread the string from the back through the upper hole of the closer and heat-melt a blob on the end so that it cannot slip out again. (see picture)

20. Place 2-3 ball lifters on the string.

21. Thread the string around the lower pulley. Make sure the scoops of the lifter all face the right way. Thread the string through the two openings in the top plate and around the pulley. Use the two lower holes in the closer to close the string loop.

22. Now place a small rubber band through the notches you cut open earlier and around the pin in the pulley-arm. If needed, put it around twice. The rubber band pushes up the pulley and keeps the string under tension, while allowing some movement while one of the ball scoops moves over the pulley.

23. Both the ball scoops and the rope closers have little wings left and right that keep them parallel to the mechanism. Make sure they are not turned sidways or wedged behind something where they get blocked.

24. With all in place, the whole mechanism should run freely and the ball scoops should make their path around the whole system.

You made it!!

Hang a ball rail into the top-piece. Make sure it is not pushed too far into the top-piece, otherwise the ball scoops will get caught on the edge.

On the lower side, place another hex-tile directly next to the lifter, in a height of 2.5cm (on two full-height and a half-height spacer). A ball will fall right into the lower resting place and be picked up by the next scoop coming along.