Turbiter

Turbiter is an add-on solution for cooling the Orbiter stepper motor. With this the Orbiter can be used with max extrusion force in heated chamber of 60°C +.

Weight is about 16grams not including the two standoff and M3 fixing screws.

For the casing design I was inspired by the motor cover designed by Ben Levi for his NF sunrise setup. You can find that here.

Introduction

The Orbiter stepper motor is rated to 180°C, but the main limit is given by planetary gears material which has a temperature deflection rating of about 120°C. To have a safe margin it is not advised to run the stepper over 100°C.

With this add-on the Orbiter can be used with max force even in enclosed chamber.

Weight is about 16g not including the two standoff and M3 fixing screws.

Having the orbiter stepper running @ 0.85A RMS (Root Main Square) will reach about 65-70°C at room ambient temperature (~25°C). Approximate stepper to air thermal resistance is ~11K/W. Of course, this is too hot to touch, however for the Orbiter is well within its safe operating area.

Active cooling will reduce the temperature of the stepper, in this condition to about ~40°C (see picture). Approximate stepper to air thermal resistance is ~5K/W.

Using the Orbiter in enclosed chamber with higher environment temperature will increase the stepper temperature by the same amount. In the next picture you can see the stepper temperature reached about ~90°C, having chamber temperature of about 45°C (20°C more temperature increases the stepper temperature by the same amount 70+20 = 90°C, see picture). This is still in the safe operating area of the stepper, I have well over one hundred of print hours in this condition and everything works just perfectly fine. However it is very close to the maximum temperature limit.

A safe approach when using the Orbiter in a chamber with over 45°C requires lowering the motor current which will reduce the extrusion force and acceleration performance.

Another interesting use case is extending the Orbiter performance by increasing the motor current.

With active cooling, the motor current can be increased even above its maximum current limit defined in the datasheet of 1A RMS. Can be set safely up to 1.2A RMS. This increases the extrusion force by ~46% with motor temperature ~60°C.

Some might wonder why we would need more extrusion force.

In most cases the Orbiter extruder has plenty of extrusion force which is enough for most of the hotends. Increasing extrusion force will not extend too much the volumetric flow since there is a limit to how much plastic it can melt, after this the hotend pressure increases exponentially and the stepper will start skipping or the filament is grinded.

However, we have seen now some new high performance hotends and nozzles on the horizon like the Phaetus Rapido UHF, or Bondtech CHT nozzles which makes a considerable difference in volumetric flow for those willing to push their printers to the maximum.

Having more melting capacity meaning higher flow also means more material to be squeezed through the nozzle. If your nozzle is 0.4mm and having twice as much melted plastic available higher extrusion force is required to reach these new ultra-high flow hotends maximum potential.

Next chart shows the extrusion performance test results using Dragon HF + Bondtech 0.4mm CHT nozzle. Performance was evaluated for PLA+ tested @210°C, PETG, ASA and ABS tested @250°C.

One disadvantage of the Turbiter is the additional noise of the blower fan. Even if you use the Orbiter at its nominal current of 0.85A RMS you still need to have the blower active. You may reduce its speed to limit noise but it cannot be turned completely off. This is because now the Turbiter housing acts as a heat insulator, with the blower turned off and the stepper temperature will increase above 70°C.

Warning! If you use his add on for boosting the Orbiter extrusion performance by increased current you have to make sure the blower always works! If it stops by accident or some defect, the stepper temperature can increase over the maximum limits allowable by the planetary gears and permanently damage them. Use it at your own risk!

A protective measure would be to attach a temperature sensor to the stepper motor and if the measured temperature exceeds 90°C the printer shall be stopped and extruder driver disabled.

Build and BOM

During the design I focused to use commonly available parts, no special custom designed part is required beside the printed housing.

Bill of material:

· 1x 3010 blower (good quality blower with double bearing)

· 2x M3 L8mm screw

· 2x M3 L20mm screw (replace the two screws of the orbiter for longer ones)

· 2x M3 washers

· 2x M3 hex female/female standoffs, L20mm (L15mm is you use sensor add on, Orbiter v2.0 only), you may use plastic standoffs to reduce weight

Housing shall be printed out of ABS or ASA (PETG - possible but not preferred), with supports, and oriented as shown in the next picture.

Download design and printable files here.

Explorable 3D design file.

I’m aware that this solution cannot be adapted for all printers with space limitation on the back side of the Orbiter. In the near future I will design another variant having the blower mounted over the top of the Orbiter, but for mow I want to concentrate to finish some ongoing awesome projects I’ll show later.

Design history

As usual most designs are a result of a design iteration. The Turbiter is no exception of this and for those curios how different ideas worked out here I summarized my investigations results.

Passive cooling

Fist I tried to add a passive cooling solution. There are plenty of 36mm heatsinks available. They are mainly designed for DC motors used in RC applications.

I bought one of these 36mm heatsink, cut in half and attached it to the Orbiter stepper.

One issue is that the Orbiter stepper motor diameter is not constant. The back plate diameter is ~36.5mm but the magnetic core diameter is just 35mm. This creates a gap between the magnetic core and the heatsink which needs to be filled with a thermal conducting gap filler. I used 1mm thick soft silicone based thermal sheets for this purpose.

A passive cooling solution do not make any noise and ads negligible weight (~9g) but its cooling performance is limited. It reduced the motor temperature by ~4-5°C, reaching about 65°C in normal conditions @0.85A RMS current.

Active cooling

Since pure passive cooling has limited performance for the given size, I focused on active cooling ideas.

First, I have designed a cooling solution using 25mm fan. Even if in theory it has enough airflow, in this application it does not provide enough air pressure to squeeze air through the ventilation channels.

I tried orienting the fan in both directions.

When airflow is directed towards the stepper back side, the generated turbulences and air reflected back reduces the airflow drastically, it even reduced the fan RPM by more than 50% due to lack of power.

Directing airflow towards the outside, means the airflow has a free path, and the air needs to be sucked through the ventilation channels, cooling the stepper. I found that distance between the stepper and the fan plays a crucial role having it too close the fan is not able to keep airflow. It needs some buffer space where the lower pressure to be built up creating the suction.

Based on some test I reached a conclusion that about 5mm gap between the stepper and the fan is a good compromise between cooling effectiveness and overall length of the Turbiter.

The cooling performance is limited due to low power of the 25mm fan, I reached about 10°C temperature reduction (~60°C stepper temperature @0.85A RMS). Which is far below my expectation.

Next, I tried a 30mm axial fan. Fitting this was a bigger challenge since its diameter is bigger than 36mm (40mm). However, cutting down the fixing hole “ears” I managed to squeeze it inside.

The performance was improved, ~15°C temperature reduction (~55°C stepper temperature @0.85A RMS). Not bad but I had the impression that the main limitation is due to the fan pressure not airflow.

This led to me think of using radial fan (blower), it does have lower airflow but higher pressure, so maybe the overall cooling airflow will be increased.

Indeed, my assumption was correct, the temperature is reduced by ~28°C to ~40-42°C stepper temperature @0.85A RMS room temperature of about 24°C.