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cost efficient robot actuator

creating a root actuator based for high cost efficient components for high torque applications

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One of the core components of your robot is its actuator. To ensure a safe, reliable and efficient movement I was looking for a solution which is cost efficient and has a high performance.

In the following you will find all steps I am working on. Feel free to discuss!

Follow this project to see how a robot actuator is developed with the target to be compact, cost efficient and high performance. I started with a raw scheme on existing designs and realized there is more room to play.... 

overview of costs:

- Motor 8308 - 50$

- Gearkit - 25$

- sliding gears for planets - 5$ (the more you buy the cheaper they get)

- one ball bearing for the main output - 5$ 

- cooler (not defined) 5$

- housing and cage will be printed (not defined) maybe 10$

- Mjbot Controler - 85$

Mechanical components are around 100$.

With the Controler/Encoder 185$.

Feel free to discuss 

  • First production prototypes

    Y.club4 days ago 0 comments

    a lot of detail work was done over the last few weeks. Experimenting with several print parameters. Reducing the support materials to a minimum. Following images show the latest version in real:

  • So cool...

    Y.club05/30/2021 at 21:31 0 comments

    With further surface action and detailed investigation on whats available on the market the next steps in the fine tuning of the duct collector could be done:

    With the connection to the main housing on the outsides. The controller will be positioned only by pins inside the backside of the main housing, where the its fixed by the cooler duct in axial direction. First blower is ordered and waiting for more detailed measures of the blower case.

  • Detailed work of the cooling

    Y.club05/26/2021 at 19:25 0 comments

    Following steps describes the new details of the cooling design:

    In this step we are cooling now the motor and the controller. The integration of both elements to cool is done via a collector chamber. 

    Following image displays the collection of the ducts. Several challenges were between the the connection between the parts and the sealings.

    The thickness is quite a lot. There needs to be done some tests. Duct design is based on input output area equations.

  • Cooling!

    Y.club05/22/2021 at 17:11 0 comments

    The core problem we want to solve is following:

    The Red marked area will get hot over time and we need to cool it active. Active means we will use a blower/fan or any device to force air to move around. 

    In best case scenario it would be useful to only have tunnel where to flow goes from one side to the other. To be as close to the ideal case the cold air will join the red hot area in an angle. Inside the case of the engine a low pressure area will be created with the active cooler/blower/fan. The hot air will be guided to the inlet of the cooler via ducts in green.

    Why not the way round? - It might be practical not to blow polluted air in to the gears....

    From different angle with a radial blower: 

    Radial blower is used as its very compact and the space behind the complete actuator is not free.

    The challenge is now to integrate it into the complete system....

  • Further Details....

    Y.club05/21/2021 at 23:06 0 comments

    When you look after some time again on your design you realize there is room to improve?


    So I redesigned the back of the housing with new Y-shaped ribs:

    Like this the Mjbot controller will fit better into. 8x M3 Screws are used. 2x 3mm pins will be used to locate both housing parts.

    Additional Cover is added to ensure a save position of the gear system. Thanks to a dashcord friend!

    Finally a vane added. Primary for safety.

    All in all above a section through the current state. 

    Yeah now the cooler needs to be added....

  • Cooling?

    Y.club05/19/2021 at 21:44 0 comments

    To get the max out of the motor it will create enough heat which needs to be active cooled. The gearbox is external and in a smaller diameter. This gives us room to open up some space to cool the actuator.

    Furthermore the housing will be printed out of 2 parts. They are screwed around the housing. The position is defined by 3 pins.

    The cutouts are in a conic shape. Ideally the flow will be directed straight through the magnet/copper wires. A negative pressure is created with a radial fan. This fan will suck the air from the back.

    Yeah. the Mjbot controller is also embedded now into the design. The radial cooler will be added at the back. Later more....

  • A bit of static stress analysis

    Y.club05/19/2021 at 21:29 0 comments

    As we are using 3D printing to produce the housing for the actuator its worth a look into simulating the forces acting on the housing. We make following assumption: 

    - Housing is out of ABS plastic (as this was in the library available)

    - 10 kg of load outside the output of the engine "hanging"

    - one housing part

    - contant force

    This is just to estimate the deformation of the complete body. Have in mind that the ball bearing is not installed, which will provide additional stiffness. With 100N (10kg) we have a deflection which is ok. It's not great but a starting point. 

    I also tried a topology optimization loop. The results were not really promising.

  • Compare the stage...

    Y.club05/18/2021 at 21:08 0 comments

    After switching the gears from a 3D printed option to a metal one which already exists on the market. We could slim the actuator without adding any major cost (25$). Thats the step from black (OpenTorque) to the yellow one. 

    The yellow and the black one have the same 8318 motor. For the next step I decided to reduce the motor as the weight is significantly reduced, so the energy consumption for the complete robot goes down etc. 

    Switching then to the next step the blue/green one...

  • the gear in detail....

    Y.club05/18/2021 at 18:11 0 comments

    So how do we actually combine the gear with the motor?

    Following flange should to the job....

    On the 8308 looks like this.... same connection as to 8318 ... I will explain later why i switched for a smaller motor....

    If we now combine this with the gear kit from @Josh Pieper we get following:

  • I found a planetary gearset!

    Y.club05/18/2021 at 18:00 0 comments

    After realizing there must be a more compact way to create an great actuator... I needed to check whats on the market....

    I found a gearset in the shop of @Josh Pieper. Its very compact, cheap and easy to use.

    Integrating this now in a new design it looks like this:

    We have the 8318 motor with its stator connect to the case. Where its rotor is connected to the sun gear of the planetary gearkit as above mentioned. 

    I am not using ball bearings for the planets of the gear. We are not facing high rpm rates. These sliding bearings are cheaper, lighter more easy to install than conventional ball bearings.  

    I only use one ball bearing at the output. 

    Target is to print the cage of the planets out of filament with carbon fiber.

    A bit more soon....

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Y.club wrote 06/01/2021 at 18:33 point

You are absolutely right! 

This will create the base for the future legged robot. I had the central cooling unit idea with water cooling for the complete bot. As for now I cannot estimate how the energy consumption /real efficiency for one leg will be. Therefore any assumption at this stage is too much.... 

Do you already have a concept in your mind? 

  Are you sure? yes | no

rraetz wrote 06/01/2021 at 15:01 point

This is a very cool project, thanks a lot for sharing! I see that the intended application is a quadruped robot with 12 actuators. Did you ever consider to have one central cooling unit? I don't know if it makes sense, but I was thinking if you could replace the fan on each motor with one larger fan/blower and distribute the cold air to each motor with some flexible tubing. Keep up to great work, I am looking forward to more updates!

  Are you sure? yes | no

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