Direct drive: the extruder right on the print head

How direct drive works

In an ordinary direct drive a motor is connected straight to the driven part, with no gears or long linkages. In 3D printing this means that the extruder and the hotend are in one head, and the filament has only a few centimetres to travel from the gear to the nozzle.

The motor moves together with the head, so it has to be small and light. A gearbox is often used (gearbox) to make the motor smaller while keeping its force.

Advantages over Bowden

• Short path. During retraction the plastic is pulled back immediately, so there is less stringing (stringing).
• Flexible materials. Soft filament tends to buckle and jam in a long tube, and with direct feeding the path is shorter.

The drawback is the greater weight of the head. Quick changes of direction then cause more vibration, which is dealt with by tuning, for example with input shaping.

What this means for your order

You do not have to deal with this on your order. A short filament path generally helps give a clean surface without strings, especially with PETG, which tends to string. We only print PLA and PETG, and we do not print soft materials such as TPU.

If you need a flexible part, write to jakub.novak@boostello.com, but we do not promise to print it.

Retraction and surface quality

While the head moves from one spot to another, you want to stop plastic from leaking out of the nozzle. That is why the filament is briefly pulled back (retraction). With direct drive a pull-back of around 0.5 to 1 mm is enough, while with Bowden it is usually 4 to 6 mm. A shorter movement is quicker and more precise, so fewer strings and drops are left on the surface (blobs).

Another benefit comes at a colour change: the filament is pulled out and pushed in over a shorter path, so less plastic is wasted. In multicolour printing that means a smaller wipe tower, and so lower costs.