Please can someone size us a couple of actuators??

[daveimi]

Hi. We're looking to start designing a featherweight robot based on the below shonky drawing. The main information I'm interested in is the power needed for the electric actuator (coloured blue). If we manage to build a featherweight version of this without killing ourselves, we have plans to go on and build a heavyweight. Therefore could those folks in the know provide a rough estimation as to the kg rating that would be needed for an actuator for both a featherweight and heavyweight. Or 2 x smaller actuators for each design etc. We are completing the Roasting Dish of Doom this Spring to take to some events this year, and hopefully beginning work on these pair of robots in the Autumn. Any thoughts / opinions more than welcome.

Dangerous Dave

[plargen]

for actuators you best bet is the gimson range http://www.gimsonrobotics.co.uk/

but i used a car seat actuator in scruffy and it can lift about 24kg but there not the fastest actuators
if you know the actuator lifting capacity then and where the actuator connects to the lifter , on your drawing it looked about half way between hinge and wedge then you would divide the actuators lifting capacity by 2, and if it were 1/3 away from the hinge you would divide by 3......

as far as im aware its im correct but someone please correct me if im wrong

[daveimi]

Yeah I understand. So if an actuator with 20kg of push bolts up half way along the arm it will have 10kg of push at the tip or the arm. So if the actuator bolts up roughly half way along a heavyweight arm and I'm trying to lift a heavyweight opponent I need 200kg of shove from the actuator to get 100kg at the tip.

[typhoon_driver]

You always want a safety factor in there as well. So I would aim for around 200kg lift at least for a heavy

[daliad100]

Required force depends on arm geometry. Assuming worst case scenario where you're lifting the entire other robot on the end of your arm the force required to start things moving is:

Actuator force = Weight * Lifter ratio / Sin(Theta)

Where:
Weight is how heavy the object to be lifted is
Lifter ratio is (hinge to tip distance)/(hinge to actuator pivot distance)
Theta is the angle between the actuator and lifter arm when closed

That scenario is unlikely to happen but extra force is better.

[Max]

You'll probably want more power than 200kg or it will be slow and draw a lot of current and you will only get doubel the speed of the actuator. To get some reasonable speed you probably want double that if not more- that way it will be under less stress and you could bolt it closer for the pivot to get more speed.

[daveimi]

I understand so if the actuator has to push from a relatively flat angle it'll be an awful lot harder to shove up than if it were stood straight up below the lifting arm. So realistically then with this basic shape and angles we want around 40kg of push for a feather and 300 - 400kg of push for a heavy...if not more.

[daliad100]

Assuming ~35 degrees between the actuator and lifter arm when it's closed then that sounds right

You can also look at mechanisms like a bell crank to reduce the torque requirement by making the angle more perpendicular.

[daveimi]

Yeah the old man mentioned a bell crank, from memory that was Biohazards trick.