Robotics - Servo controlled Arm design

Aaqil Khan

Hi,

I am designing a robot arm and wanted some expert opinion on mechanical design considerations. Here is what I am looking for:
I am enclosing one of the servos in an aluminum casing as shown in the attached autocad photo. The moving part is a U shape aluminum part - one arm of which is connected to the servo horn. The servo drives this U part. However, since I cannot leave the other arm of the U shape hanging - it has to be riveted to the back of the servo, such that the rivet is along the axis of the servo shaft.
The entire U shape swivels around with respect to the servo.

What is the best method of riveting this part to the servo? I have also attached a simple drawing to simplify the question. Its a badly made paint brush job [noparse]:([/noparse]

Anyways, there is the stationary aluminum plate (part of the U shape aluminum frame) shown in BLUE. And the moving aluminum plate which is rotating around the servo is RED. The axis of rotation is shown in BLACK.

Whats the best design for this mechanical part? I am using ALUMINUM PARTS only.

I appreciate all the help. Thanks folks.

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E=mc^2

Zoot

Could you just use self-tapping screws through the aluminum bracket into the servo horn? You could check out this page for ideas on servo brackets and mounts: www.lynxmotion.com/ViewPage.aspx?ContentCode=ServoBracketBuild

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When the going gets weird, the weird turn pro. -- HST

kelvin james

I see what you are asking, too bad they don't make dual shaft servos. The structural element depends on what type of weight it has to support. If it is a fair amount, you will have to support the angular stress on the servo shaft by your original design. If not, you could probably just go with a " L " shape with a rigid connection to the horn, and some reasonable heavier gauge aluminum. If you have to go the other route, you will have to add a support shaft to the back of the servo. Since i don't recommend drilling / fastening by mechanical means into the plastic of the servo body, possibly a small plate with a shaft could be epoxied to it to support the other side of the arm. There may be some premade solutions out there, i haven't looked at that stuff for a while.

kelvin

Aaqil Khan

Thanks for your suggestions guys. KELVIN, you seemed to hit the nail right on the spot. Thats exactly wat i was looking for. After staring at my design for a few minutes and keeping your suggestion in mind, I thought of drilling a 9mm hold in the rotating aluminum plate and inserting a miniature ball bearing, through which goes the stationary shaft. This will minimize friction between the moving parts and maximize the transfered torque. As for the shaft - either attach a support shaft to the servo body, like u mentioned, or maybe screw a self threading bolt into the aluminum frame supporting the servo, like ZOOT suggested.

I will post the pics of my robot arm once i build it (perhaps in a week or 2).

I would appreciate any more suggestions or comments.
Thanks all.

aaqil

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E=mc^2