Basic Walker


Basic WalkerThe basic walker is a walking mechanism to which skins may be added to create a range of walking toys.

Print in place bearings and gear trains have a relatively large amount of backlash. In the ordinary way this would be a hindrance but here we take advantage of the backlash to create a stomping gait.

Requirements.

In addition to the printed parts you will require:

Print and check the parts.

All prototypes illustrated were printed on a Prusa Mk3 with a 0.4mm nozzle.

Print everything at 0.2mm layer height. No supports are required. You will need some elephants foot compensation, 0.2mm should be enough, higher values may cause small print-in-place parts to lose adhesion. I use 3 perimeters with 10% fill, this is not critical but more perimeters strengthens the screws.

If your build plate is big enough, you are confident that your printer is in peak condition and if you are happy to run 23 hour prints then print:

BWplate1 BWplate2 BWplate3 is just the battery box and cover

Otherwise print the individual part files.

Post Print Part Preparation:

If your extrusion is correct there may be a few tiny, almost invisible tags of filament on the upper surface of some of the prints where the nozzle finally lifted away, you will feel them as slight prickles; a few seconds with some fine sandpaper will remove them.

Screws:

This project includes 3D printed screws. DO NOT FORCE THEM. They are strong enough for this project but not as strong as metal screws. If one is reluctant to turn coax it, turn it backwards and forwards, going a little further each time ... there is probably a small blob or string in the thread which will quickly wear away.

Bearings:

All the roller bearings will have printed seized, DO NOT FORCE THEM to turn, they are designed to be freed one roller at a time.

Take either a stout needle, a fine screwdriver or an allen key and push it all the way through the hole in each roller in turn, wiggle it gently to and fro to break the seizure and then move it sideways by a few millimetres. It may be necessary to go round twice. Once this is done the bearing should turn but it will be rough. Exercise it for a few minutes until is spins freely. You have eleven bearings to free, each with eight rollers.



There are eight simple bearings in the legs. They will probably print free but if they are seized move them up and down in place to break out of the seizure.

Running In:

Body FramesAt various stages during the assembly you are asked to run the partially completed walker mechanism until it is smooth: This is very important. The 3D printing process sometimes leaves whiskers or small blobs of plastic which might jam the fully assembled power train unless each stage is run-in until all parts are worn smooth when the whole will operate as designed.

Assembly:

First assemble the battery box according to the instruction on [Page ref. to be inserted. All test assemblers have a ready-made battery box included].

Take the two largest parts, the body frames and offer them up, the writing on both parts is at the bottom of the walker, use the four short frame-screws to join the parts.

Bearer BarSlide the bearer bar inside the frame and fix it with the six long frame-screws.

Drive and distributor cogsTake one of the small cogs, they are identical, whichever you choose becomes the motor drive cog, fit it on the post in the centre of the bearer bar, the one in the centre of the roller bearing.

Fit the two distributor cogs either side of the drive cog on the stationary posts. Lock the distributor cogs in place with two of the seven sided, short, mounting screws.Secure Cogs

Spin this section of the gear train by hand until it runs smoothly either way.

Shaft assemblyTake a six sided shaft and attach a crank to it with one of the single-slot leg-screws.
Shaft insertionHold one of the small cogs against a distributor cog, slide the shaft through a leg bearing, the small cog and the leg bearing on the opposite side. Attach a crank to the other end at 180 degrees from the first crank, if one is facing up the other must face down. Fix it with another single-slot leg-screw.

Repeat the process with the second crank assembly at the same end. The cranks on each side must be aligned so that both cranks on each leg are at the same angle, if they do not line up remove the small cog, rotate it by one or two teeth, and try again.

Then continue with the other end. The crank positions must match diagonally so that if both cranks at front left are up, those at front right are down, those at rear left are down and the ones at rear right are up.

Motor case partsTemporarily fit the EMPTY motor case, line up the two halves and push them through the rectangular slot and hold them in place with the motor locking screw, this will keep the motor drive cog in place while you:
Motor case temporarily inserted

Spin the gear train by hand until it runs smoothly both ways.

LubricationNow it's time to lubricate the roller bearings.
Bear in mind you are lubricating the walker as a toy, not as an industrial mechanism. Any general purpose light oil will do; I use one with PTFE included. You need very little oil. Share about two drops between all of the roller bearings, just touch the inside of each bearing with an oily tip and add another drop to the gear teeth; that one drop will quickly spread around the entire gear train.

Spin the gear train by hand until it runs very smoothly both ways.

Motor and casingUndo and remove the motor locking screw, remove the motor case.

Fit the motor into the closed side of the case with the wires leading upwards, Close the case leading the wires through the slot and slide the assembly into the rectangular slot. At this point the 'D' shaped shaft will press against the similar shaped hole, rotate the gears until you can slide it home. Secure it in place with the motor locking screw.
Fit the motor Close the case Secure in place

Temporarily fit the batteries and plug the motor into the battery box to ensure the gear train runs smoothly under power. If the motor stalls remove power immediately then remove the motor and work the gear train by hand for a little longer. The specified motor is small and is easily damaged if stalled for more than a few seconds.

Reverse the motor connection and ensure the gear train runs freely in the opposite direction.

Add legsDisconnect the battery and remove the motor.
Use the cross headed leg screws to attach the legs, the feet point inwards. If the cranks are fitted correctly the legs will slot in place easily.

Work the mechanism by hand until it runs smoothly. Now lubricate the simple leg bearings by inserting a fine pointer that has been dipped in oil, again a very little oil is enough. Work the mechanism by hand again for a while.

Run upside downRefit the motor. Stand the walker, upside down, on a block so that the legs are free to move without bearing weight and attach the battery. Allow the walker to run on the spot for a few minutes. If the motor stalls remove power immediately then remove the motor and work the gear train by hand for a little longer.

Reverse the motor connection and ensure the gear train runs freely in the opposite direction.

Fit battery boxDisconnect the battery, turn the walker right side up and attach the battery box with the short, seven-sided mounting screws. If you are planning to fit a 'skin', a structure above the battery box, you might exchange the mounting screws for longer ones later; use the short screws for now.

Insert some batteries. Fit the battery cover.

Power circuit.Complete the assemblyComplete the electrical circuit according to the diagram. You may make the connections by whatever method suits you; point to point wiring is perfectly acceptable but here I have used a short piece of stripboard to mount some plugs and a switch. The switch is on a flying lead as I intend this walker to be part of a larger toy and the switch will be mounted elsewhere on the body.

In this case I have mounted the circuit board on top of the battery cover with some double-sided tape, this is so I can take a clear picture; often this will be inconvenient and it will be better to make the connections somewhere out of the way.

Do not allow this to happen.However you arrange your wiring make certain the wires cannot stray into the gearing or the whole mechanism will jam. Tape, cable ties and glue are all suitable for fixing wires in place.

Next?

Use the Basic Walker as a mechanical toy as it is, or create a 'skin', a body structure to turn it into something exciting: A robot unicorn, an Atat, a mechanical tortoise, the only limit is your imagination and the difficulty the Basic Walker has in balancing heavy weights.

So: break out the papier mâché and string, or Lego and tape, or even start 3D printing something wonderful...

Such as: The Roboboxasaurus.