This is the second of two attempts at motorising MishaT's Nautilus gear set. In the past, I have used a rather expensive although very solid, geared DC motor for projects like this but have never had a go at 'hacking' a servo motor to achieve the same thing - low RPM, low voltage and a decent amount of torque.
The main difference between this motorised gear set and the first one which I made, http://www.thingiverse.com/thing:176570 is that here, only one gear moves around - it rotates along with its curved connecting bar around a fixed gear.
The problem with using a servo motor of course, as well as doing the hacking, is that there is no immediately obvious way of hooking up the drive shaft to turn an axle. This requires some creative thinking which is why this project is still "work in progress" - there will be better ways of coupling the motor to the M3 axle bolt which I have used no doubt so the challenge is on!
The motor is run from a standard 1.5V battery as shown in the video. http://youtu.be/qZQpdfoXxdA It is not quiet so maybe enclosing this thing in a box would be a good idea. (Please excuse the quality of the video - I will turn the radio off next time).
The choice of servo by the way was quite arbitrary - it was one of two spares I had in my work box, having used one of a packet of three for an Eggbot derivative over the summer.
As I did in the instructions for my first design, rather than go through a set of instructions, I will provide details of what each of the STL files are for and let you, the creative maker go and get on with it. Saying that, if you have any questions, please leave a comment and I will respond as soon as I can.
This is a 3mm panel onto which the gears are mounted. It is a triangle shape with a shape cut into the centre to accommodate one of MishaT's Nautilus gears as decoration. The other hole is used for the "working" gears. The fixed gear is held in place by the hexagonal hole - it is up to you how the fixed gear is orientated.
Print two of these and slot them onto the display panel above. These are feet to keep the panel upright - or should I say, tilted as the panel sits at an angle of 15 degrees. They extend backwards to prevent the display panel from falling over - it is top heavy with the servo in place.
This is similar to that used in my rework of MishaT's gear set here: http://www.thingiverse.com/thing:172034 The bar accommodates two hex headed M3 bolts. Take note that once printed, you will need a 3mm drill bit to remove the support material in place in the STL.
This piece (green in the photographs) takes a standard M3 nut and screws onto the back of the moving gear. Once in place - don't make it too tight - it is locked in place by screwing a second M3 nut above it. I used an M3 'half nut' as the lock nut as I had one to hand, a full M3 nut should work but clearance may be tight.
This comes in two parts, both in the STL and need to be glued together once the servo horn has been trapped between them. (It is the horn which pushes onto the servo motor). I am not a great fan of trapping components and holding them in place with glue and I guess that this is the weakest part of this design but it works. I tried holding the pieces together with a piece of heat shrink tubing as you can see in the photographs - it helped keep things together while the superglue did its job but does not provide enough grip on its own. When the two halves are secure, the part of the servo horn which is sticking out needs to be cut off using a craft knife otherwise it will catch on the display panel posts which are used to support the servo motor.
This slots into the display panel as described above - no glue needed, it is a tight fit and should not fall out. The M3 bolt which is fixed to the connector bar then passes through this gear and after enough M3 washers to pack the gap, into a nylon M3 nut which is fixed into servo connector.
This is MishaT's original file. You will need two of these - one to rotate (mine is Faberdashery Mercurial Red) and one for decoration (Bling Bling gold in my case).
The Servo and its Hack
The servo motor - once 'hacked' is screwed onto the two pillars on the reverse of the display panel. I found a couple of smaller screws than those provided with the servo motor itself although I guess you could drill holes to accommodate those provided if you wish.
The principle behind the 'hack' is to disconnect the electronics inside the servo motor from its DC motor, remove what is used to limit the movement of the DC motor shaft and then connect wires to the DC motor to power it from a 1.5V battery. Specifics will vary from motor to motor so I suggest and internet search using terms such as "servo motor hack".