NOTE: it employs AAA batteries: 2-off or 3-off depending on desired speed and configuration.
- Rides in multiple planes, tracks can be screwed into walls and ceilings.
- Average train speed is 250 mm/s. It takes only 12s to climb from floor to ceiling in a 3m high room.
- This is a PLA ONLY type of project. High material accuracy is vital and cannot be obtained with ABS
- MODULARITY: you can re-use the wires from S-LOOP and the handle of DRY3R.
HOW IT WORKS
The cart of TRAIN3D travels over tracks that are not limited to one plane only. The idea is to accelerate, steer, loop, climb and ride upside-down! This is possible due to the combination of a TRACTION and a TRANSMISSION mechanism.
Rotary motion and TORQUE are transmitted from the motor to a wheel gear which pushes the cart forward by meshing with the teeth on the track. Because the Motor spins fast and with little torque, two gears are used to reduce speed and trade it for torque (total Gear Ratio is 1:36, see project GBOX to learn more). It’s through high torque that the train can overcome its own weight and climb vertically. The motor is supplied with 3v by connecting two AAA batteries in series, or by 4.5v if friction due to the construction in the system demands more power from the motor (see Connection Diagram for the 3V configuration or for the 4.5v configuration ). The aluminium lever on the battery holder acts like a switch when connecting in series one battery on to another, thereby controlling the on/off state of the motor.
TRACTION is essential for the displacement of the cart and it’s guaranteed at all times by the separate functions of two built-in systems: i) The GRIPPING system and ii) the FOLLOWER system.
GRIPPING SYSTEM: Whether riding normally, upside-down or on a vertical track, TRAIN3D must remain attached to the track even when the pull of its own weight attempts the opposite. Trying to achieve this by locking a surface onto the track and let it slide would impose enough frictional load on the motor to keep it from spinning. Instead, spherical rollers are connected to a concave profile by which the tracks are shaped. The rollers (and anything attached to them) are locked into the profile by the action of two 3D Printed Springs ….that’s right, 3D Printed! This is how it works: two struts are arranged in scissors-like fashion and connected to a roller at each extreme. Each roller spins around its connecting screw which acts like an axis (thus minimizing friction). A spring is inserted on each side of the scissors arrangement through dovetail slots forcing the scissors closed. If the struts are attempted to be opened, the springs will compress and push back to keep them together, forming the perfect roller-to-track grip.
FOLLOWER SYSTEM: to ensure that the wheel gear remains meshed to the track sections despite dimensional variations or the action of the train’s own weight (riding upside-down), the position of the gear must self-adjust at any time to follow the track’s toothed surface. The wheel gear and transmission frame pivot about an arm which is connected to the track through the rollers. This pivoting capability allows for the Distance of the gear in relation to the track to change. If the cart slightly drops in relation to the tracks (weight pull – See picture), a gap between the gear and the track forms. The gap needs to be closed to guarantee meshing (distance from the gear to the track to be shortened from original). An O-Ring acting as a rubber band, connects one of the struts in the GRIPPING system to the transmission frame and forces the gap to remain closed. Remember, the teeth in the tracks are only 1 mm high! Any inaccuracy or change in position by this much will be enough to trigger disengagement and stop the train’s motion. The tension on the O-Ring can be finely adjusted by the screw and the hook that is dovetailed to the transmission frame (see picture).
Note that some form of a spring forcing contact is common to both systems. If contact is too strong, friction will be high anywhere in the vehicle, loading the motor and preventing or slowing down its motion. If on the other hand, contact is weak (especially in the GRIPPING system) then traction will be lost. A third spring can be added to the GRIPPING system in case the 3D Printed springs are not enough to perform this function. Both struts have holes at the front where to screw two fasteners and then connect an O-Ring to close the scissors. Because everything in the system will then be tight, friction will be high and a third AAA battery will be needed to deliver more power.
The tracks come in different types of sections: i) straight, ii) right or left bends and iii) vertical arcs. On page 4 of the Drawing you will find dimensional information for these. Straights come in lengths of 100, 150 and 200 mm. Bends come at 30, 45 and 90 degrees and vertical arcs come at 45 degrees from the horizontal. All sections are provided with a male and female linking feature at each end that helps it snap-attach to the next section. Also, every section has at least a pair of lugs to screw it fixed to any surface, wall or ceiling. Although at LAYKANICS we rarely design parts to be 3D printed with supports, vertical arcs do need them.
Print all the parts in PLA material only. NOTE: use your slicing software to orient the parts on the platform as shown by each part picture in the Downloads section.
Begin by making the battery box and switch.
1. Cut the lever from one of the holed-corners of K1-AS. Print handle: 12-TRAIN3D and insert through the free end of the aluminium. Fold the aluminium onto the handle The aluminium lever attaches to the battery box through a screw K1-F8 which also makes contact with one of the batteries negative pole. Once the battery is in, make sure to screw in K1-F8 until contact is guaranteed.
2. Insert all contacts into their corresponding cavities as shown on page 1 of the Drawing. Then clamp the tab of the positive contact C2 by using a screw (K1-F8), two washers (K1-WSR) and a Nut (K1-NT). The Head of the screw is used as the contact to the lever switch .
3. Cut and assemble the wires to the right lengths using spade terminals K1-TS.
4. NOTE: for a 4.5v configuration, you will need to insert the tab of a negative contact (K3-NCON) on to the position of the positive contact as shown in the picture
5. Insert the batteries only after the complete cart has been made and it is ready to use.
1. Insert gears K1-G60 and K1-G10 to their respective shafts at respective lengths (page 2 of Drawing). Do the same for gear K1-G30 and motor K1-M2.
2. Using a metal file, Post-process frames 1 and 2 (01-TRAIN3D & 02-TRAIN3D respectively) by slightly opening the holes at the bearing locations. Holes must be opened enough to make the shafts spin freely but not much as to make them loose inside. NOTE: differently to the geared-shafts, the pivoting axis (Shaft3 ) DOES NOT rotate and its assembly to the frames must be as tight as possible. If too loose, the frame will sway too much with respect to the track. Also, file as needed to make sure torsion bar 05-TRAIN3D fits into its respective slot on both frames.
3. Insert Shafts 1&2 on to 01-TRAIN3D and lock Shaft 1 by flushing the second K1-G60 gear to the opposing extreme. Insert the motor into its housing and manoeuvre through the flexible, un-screwed clamp to make it mesh with gear K1-G60 of Shaft1. Tighten the clamp using K1-F12 and a nut K1-NT.
4. Insert the torsion bar into position and Shaft3 through both arm (06-TRAIN 3D) and battery box (11-TRAIN3D)
5. Close with frame2 (02-TRAIN3D) and before screwing both frames to the torsion bar, spin by hand any of the shafts to make sure all gears mesh properly. A “teeth grinding” sound must not be present or be minimal and resistance to shaft rotation should be small (shaft1). Correct if otherwise by repeating step 2 and opening clearance on the shaft bearings a little more. Screw both frames to the torsion bar.
6. Lock the battery box to the arm by running a K1-F12 screw. Angle the battery box at its lowest level possible, as it usually helps with the weight distribution when riding upside-down.
7. Snap fit the tail bar (08-TRAIN3D) on the rear of the frames. Then insert the hook on the Dovetail slot of frame2 and screw through the frame lug.
8. Form the scissors by locking strut 03-TRAIN3D to the arm 06-TRAIN3D and then screwing in strut 04-TRAIN3D to the arm. NOTE: the screw will find a natural stop that will be just enough to make the scissors open and close with minimum resistance. DO NOT overtighten this screw as it will prevent the springs from performing their functions.
9. Attach the rollers to the frame by screwing K1-F12. NOTE that the screws go in at a slight angle . Screw until you find a stop and then back-off by 1 /4 of a turn to get the rollers to spin freely with a minimum gap between them and the struts.
1. Plan your track first. It is suggested to start with a planar track and once familiar with the system to expand onto vertical walls. Use page 4 of the drawing as a reference to determine the overall size and needed sections if space is a constraint.
2. Make note of the assembly convention: the MALE joint on a section always points in the direction of motion of the cart (Drawing – page 5). This gives definition to what “right” and “left” means in the bends.
3. Print the tester “13-TRAIN3D”. This section helps to test the joint features of every newly printed track. If distortion has occurred or the print is not clean, the tester will allow you to realize the type of post-processing needed on the section before you try to assemble it to a track on progress, where most sections have been fixed. The sections attach to each other by inserting them at 90 degrees and giving them a snap-twist). If the joint is not correct, the track surfaces will not flush ( See picture). Post-process accordingly.
4. To assemble to a track in building progress, loosen the fixing screws on the lugs of at least two previous sections and bend gently to perform the twist. ( See picture )
5. Because of the difficulty of printing vertical arcs, these DO NOT have a MALE connecting feature. Instead, adaptor (23-TRAIN3D or 24-TRAIN 3D) must be used and inserted on the corresponding end before mating to another section on the track. The adaptor can be printed to have a right or a left lug.
PLACING THE CART ONTO THE TRACKS.
If a closed circuit has been built, the train can be placed on the tracks by:
1) Opening the scissors, placing the cart on the track top surface and manually closing the scissors. Then inserting springs (08-TRAIN3D) into the dovetail slots on each side of the scissors. Alternatively, you can force open the scissors with the springs already assembled and mount on to the track (less recommended)
2) Hook O-Ring K1-OR16 to both strut 04-TRAIN3D and tensioner (10-TRAIN3D) and tension slightly the O-Ring. Note that for climbing and upside-down riding, best results are achieved if O-RING is not too tight. You will know if it is too tight as the aft rollers will get out their position in the tracks.
THE PROBLEM OF ANY DESIGN ENGINEER: MANUFACTURING TOLERANCES AND CLEARANCES.
The manufacturing of any mechanical component is never exact and this must be factored in during the design process. Although the degree of accuracy in metal parts is nowadays extremely high, for Desktop 3D Printers there is still a long way to go. To add complexity, 3D Printed parts have limited shapes, as printing cannot be done over air without the use of supports. This represents problems at many different levels for a mechanism like TRAIN3D. Below we share some of the design work-arounds of these problems.
For a vehicle to ride upside-down, the tracks must be able to lock the vehicle and prevent it from detaching under the action of gravity. It is natural to think of a channel with a C-shaped profile, but this is difficult to print without angled surfaces. Also, any cart or wheels moving inside would face a problem of dragging friction against the channel walls which would either slow down the motor (prevent it from climbing vertical sections) or require more power. More power means more batteries and hence more weight to overcome when climbing and the solution begins to depend on many factors to work. Friction is minimized, if instead of dragging, there is rolling and spheres are par excellence the best rolling elements (no surfaces to drag). Then a concave section can also help them to lock against gravity and its completely 3D Printable. A concave profile would solve the first two questions but at the expense of developing something to keep the rollers contacting the profile: A SPRING!
Attaching different track sections together brings a new problem: What if a track is slightly higher than the other? How about slightly wider? Do rollers seize at an edge sticking out at the junction of one section on to the other? Also, if a gap forms between one section and the other the teeth on the gear wheel would go out of sync and fail to mesh. To solve this, the first thing to do is to add a chamfer to the edges at the end of the section. With these, even if the next section is wider than the previous, the rollers will not find full-stop edges standing out but slant surfaces that will aid transition onto the next section of the track.
The second action is to develop a locking mechanism that will close the tracks together with no gaps in between. What kind of locking feature can solve this and be 3D Printable, bearing in mind the variations in dimensions from 3D Printing? The answer is found in concentric cones. The beauty of cones is that they naturally mate regardless of whether there is a variation in diameter or not. This is a cross section of the male and female connecting features at the end of the tracks. To keep the conical surfaces forced into contact, the sphere above has been slightly oversized to interfere and exert pressure into the opposite track, keeping the conical surfaces mated.
THE NEED FOR SPRINGS
Regardless of the actions taken above, there will always be a slight dimensional variation somewhere in the system. Flexibility is then required and thus the use of springs. Springs are extremely important mechanical components. They allow for changes in positions with the possibility to restitute to the original once external forces are removed. There are many forms of springs but the basic principle lies in the elasticity of the materials. A rubber band may equally work as a spring as well as an actual coil, although deformation characteristics will be different.
For TRAIN3D, the spring in the FOLLOWING mechanism has been designed to be adjustable. It is very important to have this capability as different tracks will need different types of restoring forces.
Having learned that contacting of elements is forced in different places on TRAIN3D, it is important to realise that some of the parts must be structurally integral so as not to deform out of their contacting positions. 3D Printing materials are extremely flexible and chances are that any part with a big enough span will deform. This is prevented with the addition of ribs. For this project, it became important to reinforce 3 different locations:
STRUTS: due to the action of the O-Ring tension and their relative long span with thin cross section, the struts were deforming at early testing of TRAIN3D. To keep this from happening, ribs were added in the shown location.
FRAMES: these parts are very thin and with long spans. To reinforce them, ribs where added across the main body and around the external contour.
TORSION BAR: The shaft bearing holes in frame 1 must be concentric with those on frame 2. Otherwise, the shafts will not run parallel and seizing can occur. If frames1 is at an angle from frame2 concentricity is lost. Therefore, we need a bar that can withstand torsion but space is limited for the addition of material. In order to make the frame as robust as possible, a rib runs along torsion bar (05-TRAIN3D) as shown to minimize the possibility of any torsion occurring.
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