Cable reel with automated layering
This cable reel design evenly spools up a 500m length of a 5mm diameter cable. This automated system ensures the cables wraps up evenly and neatly around the entire width of the cable drum. This allows for a compact system and prevents the cable from becoming bunched up and messy.
CAD Model
Manufactured
System components
The major aspects of this cable reel are:
A motor, drive train and cable drum
Timing pulleys & a self reversing screw to guide the cable wrapping
An encoder wheel to measure how much cable is spooled out
Electronics
These points are discussed further below
Motor drive and drum sizing
A motor mounted on the outer side of the reel links to a pair of spur gears. In this design a gear ratio of 1:2 was chose to give an increase in torque. The force applied on the cable as well as the speed it can be pulled back at should be considered for the specific application. Note that the force on the cable as well as its speed will depend on how much of the cable is spooled up. If most of the cable is spooled up and the effective diameter of the drum is large then the cable will be pulled back faster but with less force and vice versa. The force and speed of the cable are proportional to the effective diameter of the cable drum - force is torque divided by perpendicular distance.
The gear pair also allow for a slip ring to be mounted concentric to (inside of) the driven gear. This allows electrical signals and/or power to pass from the electronics on the outside through to the cable. In this design a series of rods form the inner diameter of the drum, it is important to note the inner diameter should conform to the minimum bend radius of the cable being used (generally 6-8 x cable diameter).
In order to calculate the required size/dimensions of the cable drum the below formula can be used. In this design, the length of cable was already determined and the width between flanges, ‘C’, was chosen to match the working length of the self reversing screw. The winding depth, ‘A’, was found using the formula below with help from an online quadratic solver.
Self reversing lead screw
Also known as a level wind screw or diamond screw, this component is crucial to this design:
Two sets of spiral cuts which link into to each other allow the nut to reverse directions once it reaches the end of the screw. This facilitates back and forth motion without the need to change the rotational direction of the screw
The nut on the screw should move over one width of the cable per revolution of the cable drum. This guides the cable in such a way that it wraps up in a tight layered manner around the drum. The working length of the screw should match the width between the drum flanges such that the nuts direction reverses once the cable reaches the edges of the drum
The cable drum and the screw can be linked together with pulleys and a timing belt, however we must alter the effective pitch of the screw to match the thickness of the cable. In this design the pitch of the screw was 25mm so a pulley ratio of 1:5 was used. This meant that one rotation of the cable drum would cause the screw to rotate 1/5th of a rotation and the nut would move 5mm.
Encoder wheel & cable guide
A rotary encoder measures angular position
In this design this is an effective way to measure how much cable has been spooled out. A knurled wheel of a known diameter was mounted to the encoder. Keeping track of the number of rotations can be converted to a distance measurement of how much cable has been spooled out. Distance = wheel circumference multiplied by number of revolutions
In the case of a land or pipe crawling robot this is a useful way to know how far the robot has travelled
A cable guide ensures the cable comes out at some controlled angle. In this design Teflon guider blocks minimise friction, alternatively rollers/bearings could also be used
A cable was sourced which was rated for the required pulling force and a wire mesh grip was used for the cable strain relief (not shown in CAD but visible in photo of manufactured unit)
Manufacturing
This system was a one off prototype not optimised for manufacturing
In this design off the shelf components where possible
Several custom parts where made mostly using CNC machining - STEP files and detailed drawings where sent to a supplier
Some 3D printed parts where used for basic electronics covers
