pic: Shooter damaged a Boulder

[bobl]

We put a small tear in the skin not by the spinning wheels but by hitting a corner inside the tower. We have since put a stop (piece of lexan) in the tower to stop the boulder and roll it back.

We are using 4" plaction wheels spinning at 2950RPM and have only minor scuffing on the skin. We are compressing the boulder 2" and are able to hit the high goal consistently (19 for 20) sitting on the outer works.

[Ether]

Originally Posted by bobl

We are using 4" plaction wheels spinning at 2950RPM

How are you controlling the 2950RPM?

[bobl]

We aren't really controlling it. Using a Banebot RS775 with a 3:1 transmission. Running at full power our tach shows a constant 2950 +- 15RPM. No encoders installed. The shooter is a prototype but it shows a lot of promise.

[Ether]

Originally Posted by bobl

We aren't really controlling it. Using a Banebot RS775 with a 3:1 transmission. Running at full power our tach shows a constant 2950 +- 15RPM.

The Banebots M7-RS775-18 motor has a 12v spec free speed of 13,000 rpm.

But you say the motor is spinning at only 2950*3 = 8850 rpm with a fully charged battery.

8850 rpm is only 68% of free speed. Of course the motor speed will be less than its free speed, but 68% is quite a bit less. Some rough calculations indicate the motor would be drawing in the neighborhood of 30 amps. Can you measure the amps the motor is drawing to confirm this?

Originally Posted by bobl

We are using 4" plaction wheels spinning at 2950RPM and have only minor scuffing on the skin. We are compressing the boulder 2" and are able to hit the high goal consistently (19 for 20) sitting on the outer works.

Try reducing the motor voltage by half a volt and see what happens to your RPM and whether you still hit the goal.

[Type]

We are running 4" stealth wheels that are connected 1:1 onto mini cims. The only time we damaged the ball was when we were testing, and somebody forgot to reverse the left motor. This made both motors spin the same direction. It made two small gashes in the ball but it's still usable. We have another ball we bought, but we don't want to use it until we get the final version of our shooter made. Has anybody noticed a difference in performance in a wheeled shooter from a new ball compared to an old vall? And does anybody know how often they will switch balls out in the game?

[Ether]

Originally Posted by Type

We are running 4" stealth wheels that are connected 1:1 onto mini cims

What speed are you running it at?

[Type]

Originally Posted by Ether

What speed are you running it at?

To be honest, I don't really know. We have all of our electrical on a practice robot so we just plugged the motors into an old power distributor, with no motor controllers. It shoots more than far enough, just need the correct angle.

[Ether]

Originally Posted by Type

To be honest, I don't really know. We have all of our electrical on a practice robot so we just plugged the motors into an old power distributor, with no motor controllers. It shoots more than far enough, just need the correct angle.

The correct angle when you are running it straight off a fully-charged battery may not be the correct angle toward the end of an actual match when your battery is getting tired.

That's why it's important to test your prototype to see how much the correct angle is affected by voltage. If the effect is enough to be a concern, you will want to design your shooter to operate at a lower voltage (say 9 volts) and then used a closed-loop controller (PID, bang-bang, Take-Back-Half, etc) to hold the wheel speed constant as the battery gets weaker.

[Type]

Originally Posted by Ether

The correct angle when you are running it straight off a fully-charged battery may not be the correct angle toward the end of an actual match when your battery is getting tired.

That's why it's important to test your prototype to see how much the correct angle is affected by voltage. If the effect is enough to be a concern, you will want to design your shooter to operate at a lower voltage (say 9 volts) and then used a closed-loop controller (PID, bang-bang, Take-Back-Half, etc) to hold the wheel speed constant as the battery gets weaker.

We were planning on getting a gear box to run at 2:1 so we could decrease the speed of the motor but still shoot the same. The mini cims have no issues with shooting the ball through a 7" opening, the motors don't really even make a noise as the ball goes through. We just need to figure if we can afford to run all the motors we want on our robot (11 total).

[Ether]

Originally Posted by Type

We were planning on getting a gear box to run at 2:1 so we could decrease the speed of the motor but still shoot the same.

2:1 would reduce your wheel speed, not your motor speed.

Did you mean to say 1:2 ?

If so, you might want to instead consider increasing your wheel diameter by 50% and reducing your motor speed appropriately.

[Type]

Originally Posted by Ether

2:1 would reduce your wheel speed, not your motor speed.

Did you mean to say 1:2 ?

If so, you might want to instead consider increasing your wheel diameter by 50% and reducing your motor speed appropriately.

Yes, that is what I meant. So every 1 rotation of the motor, the wheel rotates twice. But it appears you understood what I was trying to say atleast. Thank you for correcting me.

[Ether]

Originally Posted by Type

Yes, that is what I meant.

You might want to ask around for opinions from other teams who have tried that, before investing too much time in it. Just a thought.

[Chak]

Originally Posted by Type

Has anybody noticed a difference in performance in a wheeled shooter from a new ball compared to an old ball?

We made a second iteration of our shooter that uses 4'' colsons and no longer rips up boulders. We're running that shooter off 2 775pros. We've noticed a significant and problematic difference between a fairly new boulder and the boulder pictured here, which is now even more torn up than before. I think that this is caused by the torn up boulder losing air faster and not "pushing back" as much on the shooter wheels. I guess catapults have the edge on this problem, although they might have their own problems.