Drive Sizing 101

[AdamHeard]

I agree with Tom's guess...

When do we hear the answer?

[Tom Line]

We looked at doing that exact thing, but the torsional force on the tower scared us away - over half a ton that your end effector would have to hold. I'm sure it's doable, but we didn't want to deal with the high forces.

[Paul Copioli]

O.K. here are some of the answers:

1. We are NOT going in the tunnel. 1/2" of clearance on either side is just not enough for us and making our robot skinnier is just not something we are willing to do.

2. We are using a single rotational joint to do our lift.

3. We are inverting ourselves

Calculations:
We make sure our design point is at Max Power. As the torque goes down the speed picks up and we have plenty of torque at start-up.

F-P speed at max power = 7800 RPM
F-P torque at max power = .1648 ft-lb
CG location from pivot = 18"
Robot Weight = 150 lbs
Required Torque = 225 ft-lbs (150 lbs * 1.5 ft)

F-P Torque at 1500:1 at max power = 223.45 ft-lbs
F-P Speed at 1500:1 at max power = 31 deg / sec

Rotation angle = 90 degrees so total time is ~3 seconds.

Now at various points along the rotation the speed will change based on the CG moving closer to the pivot. We can also always add Latex tubing if our CG is further out than we think.

[IKE]

For those looking for the extra credit, what Efficiency did 217 use in their calculations?

[Tom Line]

Nice. I would challenge someone to now tell us how much torque will be on the vertical tower post in worst case, and how thick the end effector will need to be to handle that torque....

[Chuck Glick]

Originally Posted by IKE

For those looking for the extra credit, what Efficiency did 217 use in their calculations?

I am going to say somewhere in the 60%-70% range, but it could also be as low as 50%. The reason I would guess 50% is it is half of the full power, so if it could do it in the set constraints at 50%, then at 100% or anything greater than 50%, it would be guaranteed every time.

[Paul Copioli]

Tom,

The force on the latch is much lower than you think. The design we are using is made such that the contact forces on the vertical pole are greatly reduced.

Paul

[Tom Line]

I'm very anxious to see your comp bot then. With our initial design, when the bot was out at the end of the 36 inch arm plus the 18 inch riser, we had 54 inches (call it 4.5 feet). With the 150 pound robot at the end, that's 675 foot-lbs. However, our initial end effector was only 6 inches tall, so the torsion on the top point was 675 ft-lbs / .5 ft = 1350 lbs. Of course, we were trying to package within a 16 inch tall robot, which is why we limited it to 6 inches tall.

Since you're not worried about the tunnel, I suspect you didn't have that constraint regarding packaging.