Will torque be a factor to consider?

Hi,
I have slight problem. I am building an excavator using linear actuators as the hydraulic cylinders. I can’t afford the ones from (budget 30-50 dollars) http://www.firgelli.com/Uploads/L12_datasheet.pdf so i decided to make my own linear actuator from http://www.instructables.com/id/Quick-and-easy-electric-cylinder-prototype-.../ however I am also considering http://makezine.com/projects/make-34/the-mighty-lip-balm-linear-actuator/ as another way to make the linear actuato, the latter using a servo motor with continuous rotation as oppose to the dc motor used in the first one.

One of the requirements of the project is that I show positional control with feedback at differing load conditions. Meaning that if i put want the bucket to move to a specific position it must hold for that position under both no load and heavy loads. Also I have to show that when a heavy load is placed, in the event that it(bucket) moves out of place due to the high load that the it automatically moves back to that position. So with that said, i was thinking that when it moves out of position. Also the only way i see this moving out of position is if the DC motor is physically moved backwards because the actuator’s arms are firmly intact on the bucket joints ( atleast thats what i think it should move out of position to compensate for the movement of the bucket)
Will increasing the torque of the DC motors serve as a solution to keep the bucket in place for the heavier load?

I am accepting any thoughts or ideas. If anyone needs me to clear up my problem I will gladly try to clarify any problems in understanding my situation.

feedback.

if you expect the arms to be a 30° under and load, then you need to measure the angle.

if you can measure distance, that could work as well.

in reality, the screw will probably be 10 times stronger than the weight, so machine flexing will probably the the problem if the machine does not flex, then the weight should not have too much impact on position.

they make both rotary devices to measure angles, may be able to use a rotary pot ? and they make linear ones, linear pots are also common.

degree of precision was not mentioned.

for CNC, you do not control the motor, you move the motor and watch the encoder (feedback) and see where you are. PID comes in to play so you do not overshoot or hunt around set-point.

since you have to show positional feed-back, that is all you need measure.

Thanks going with an angle sounds like a good idea.
To measure the angle with the pot, for me I don’t see how that pot could be aesthetically be placed on the excavator (a picture of it is a attached).

I was thinking along the line of a gyroscope. Maybe i’m not sure. :expressionless:

What do you mean by CNC?

degree of precision was not mentioned

I am going with 1 degree.

Regards
Isaiah

exca.jpg

CNC: seriously! search engines are available!

Another way to get positional feedback is use a gear motor with an encoder to drive the lead-screw. That gives you a measure of the linear displacement of the actuator, not the angle directly, but will be more precise.

That instructable, like many instructables is pretty shoddy - you cannot get away with superglue in a high stress metal component like that, some sort of proper metal coupler between motor shaft and lead-screw is needed. These are available in many sizes for CNC machines and robotics on eBay and so forth.

The friction in the screwthread itself will hold the load if you use normal threaded studding. Stainless steel is worth finding if you can for studding and nut for corrosion resistance. Failing that galvanized/passivated.