Gear ratios for launcher

[DampRobot]

Originally Posted by pfreivald

We're making very consistent shots from key range with AM motors and planetary gearboxes, though the spin-up time between shots is too long. We're working on that problem now!

My team is using a similar set up. Were getting about 16ft using belts driven by 1:1 sprockets off a AndyMark gearbox (the one for the Fisher Price). Accuracy is OK, but we've really been underwhelmed by its performance.

[Ether]

Originally Posted by pfreivald

the spin-up time between shots is too long.

What voltage are you running the motor(s) at? i.e. what is the motor voltage when the wheel has come up to speed and no balls are being fed to it?

[artdutra04]

Originally Posted by swwrobotics

Our mentor said the we should have as little amount of contact with the ball as possible to pervent too much deformation and loss of accuracy. So you're right, that definitely could be the problem. But just out of curiosity, would it be worth more to have a high gear ratio or a larger wheel diameter?

From what it sounds like, your shooter barely compresses the ball. If so, the best thing to try out first would be to increase the compression between the shooter wheel and the ball; otherwise every motor and wheel combination you can try will likely have the same disappointing results.

The trick is to find a balance between not enough compression (not enough energy from the wheel gets transferred to the ball, leading to wimpy shooting range) and too much compression (too much energy is taken from the shooter wheel without any shooter range improvements). If you do some experimenting, you'll find an a good balance between the two.

Once you find the ideal level of compression, then you can look into substituting other motors, gear ratios, and wheel sizes.

[Ether]

Originally Posted by swwrobotics

Has anyone found that magic gear ratio that works best for the launcher?

It depends on the motor(s) you are using, the diameter of the wheel(s), whether you are using only one wheel or top&bottom, the moment of inertia of the wheel(s), and other factors.

This post may be of interest:

http://www.chiefdelphi.com/forums/sh...5&postcount=20

[mdiradoorian]

Originally Posted by Ether

It depends on the motor(s) you are using, the diameter of the wheel(s), whether you are using only one wheel or top&bottom, the moment of inertia of the wheel(s), and other factors.

That is very true because the bigger the wheel the faster the surface speed is. Our previous shooter prototype had 10" wheels and after using a cim motor we were using a 2 to 1 gear ratio, and the surface speed was abot a 130 miles per hour.

[RRLedford]

Team 3135 has a prototype shooter with two 8" AM-FIrst (AM-0420) wheels from 2010 mounted side-by-side on a 5/8" shaft. and temporarily driven by a single CIM with 1:1 ratio using dual 30 slot pulleys and the KOP timing belt.
Opposite the wheel pair is a 1/4" plywood sheet that the balls squeeze against it with ~2" peak compression. The plywood is covered with high friction shelf liner mesh. So, we are near near 5000 rpm on the 8" wheel pair.
We had to sand a radius on the outer corners of the wheels, since they were too sharp and were making lines on the balls. The wheels are somewhat lightweight, and it seems that the RPM drops a lot during the brief interval of ball compression while in contact with the wheel, so we are considering adding a large 60-tooth aluminum sprocket that has an outer hole circle where we can add several screws with steel washers for a better flywheel effect. This should reduce wheel slowdown and raise the exit velocity of the balls.

This initial CIM driven setup has us making baskets on a real basketball court from half court into the 10" high basket.

We are replacing the CIM motor with either a pair of the Banebot CIM-U-Lator 775 (1-motor) gearboxes, each gearbox powering one end of the wheel shaft, or with a single Banebot CIM-U-lator 550-2 (dual-motor) gearbox. These gearboxes give a 2.7:1 reduction of these high RPM motors.

AN initial pair of CIM-U-lator=>775 gearboxes were ordered with a total of four 775 motors, because of the internal shorting problem. Expecting maybe one in four to test bad, our order arrived today with THREE SHORTED MOTORS out of four. We are bailing out on using the 775 motors for ANYTHING EVER AGAIN. I hope we can get a replacement pair of DUAL 550 CIM-U-lator gearboxes shipped ASAP.

-Dick Ledford

[iambujo]

As a data point, we are using a 2011 FP motor on an AM planetary gearbox (3.67:1). The shaft is then connected to a 1:1 chain drive setup. We calibrated tonight and this setup at max speed through a Jaguar gives about 2200 to 2300 RPMs. Less than we expected, I guess there is more drag than we had figured.

[Ether]

Originally Posted by iambujo

As a data point, we are using a 2011 FP motor

When you say "2011 FP motor", what does that mean?

I looked at the 2011 KoP, and there's a FP 00801-0673 listed, and a FP gearbox with a 9015 motor. These motors are very different. Which one are you using?

We calibrated tonight and this setup at max speed through a Jaguar gives about 2200 to 2300 RPMs.

How did you measure the RPMs?

Less than we expected, I guess there is more drag than we had figured.

What were you expecting?

[iambujo]

Originally Posted by Ether

When you say "2011 FP motor", what does that mean?

I looked at the 2011 KoP, and there's a FP 00801-0673 listed, and a FP gearbox with a 9015 motor. These motors are very different. Which one are you using?



How did you measure the RPMs?



What were you expecting?

Sorry, we are using the 00801-0673 on the AM 3.67:1 planetary gearbox. The motor curve data shows a free speed of over 20,000 RPMs. Starting with the 3.67:1 ratio on the motor and 1:1 final chain drive, the theoretical no load/free speed RPMs are over 5000 RPMs. Certainly there is the mass of the wheel, axle, chain, drag, etc. In the end all this loads it down by more than 50%, for a final max speed of 2200 to 2300 RPMs.

To detect wheel speed we are using a custom Hall Effect Latch encoder we built based on the US1881, and verified the data via a Logic analyzer (clean and consistent square wave), frequency counter on a multimeter, and via counters in Java on a digital input. So I am confident with the actual axle speed we are getting.

Under load with all the variables I am not complaining about the 2200 RPMs, it was just a data point for the original poster on our FP 00801-0673 plus AM 3.67:1 geared shooter.

[Ether]

Originally Posted by iambujo

we are using the 00801-0673 on the AM 3.67:1 planetary gearbox ...and 1:1 final chain drive...final max speed of 2200 to 2300 RPMs.

2250 * 3.67 = 8258 motor RPM

0673 @ 12 volts @ 8258 RPM is pulling 68.5 amps and generating 512 watts of waste heat.

This seems like it would either trip a breaker or smoke the 0673.

Are you sure of your numbers?

[iambujo]

Originally Posted by Ether

2250 * 3.67 = 8258 motor RPM

0673 @ 12 volts @ 8258 RPM is pulling 68.5 amps and generating 512 watts of waste heat.

This seems like it would either trip a breaker or smoke the 0673.

Are you sure of your numbers?

I was pretty certain until you put it that way. It doesn't appear to run very hot so far. I can certainly check the current today by measuring the voltage drop across a high wattage, low resistance power resistor in series.

I have seen plenty of shooters on CD this year with the same kind of setup - AM gearbox, FP motor, aiming for about 3 to 5,000 RPMs. If your concern is correct aren't we all in the same boat? If not, any idea where my assumptions have gone wrong?
Thanks!

[Ether]

Originally Posted by iambujo

I have seen plenty of shooters on CD this year with the same kind of setup - AM gearbox, FP motor, aiming for about 3 to 5,000 RPMs. If your concern is correct aren't we all in the same boat?

Yours is the first I've seen on these forums with an 0673 running at 39% speed at full voltage.

If not, any idea where my assumptions have gone wrong?

If you are sure of the motor part number and the gearing, then I'd suspect either the wheel speed measurement is incorrect, or else the 2250 rpm is not at full motor voltage.

[iambujo]

So we just rechecked wheel speed, and it maxes out at about 3500 RPMs, or 12,991 RPMs motor speed. We measured the voltage across a .01 ohm power resistor and it was about 210 mv. So at max speed it looks like we are drawing about 21 Amps. In-rush current when the wheel starts up peaks out at about 50 Amps for a brief moment.

Now we need to check the motor voltage, maybe that is where the flaw in the applied math is. SW is sending a "1" to the Jaguar, but I guess there is more voltage drop that I expected.

Thanks again for the insight. Everything is working ok, at this point it's just a study of the real world numbers we are collecting compared to the expected data based on the motor curves.

[Ether]

Originally Posted by RRLedford

our order arrived today with THREE SHORTED MOTORS out of four.

For the record, did you call Banebots to report this, and what was their response?

[RRLedford]

Originally Posted by Ether

For the record, did you call Banebots to report this, and what was their response?

Yes we did call. They found it hard to believe and wanted us to retest, but ZERO ohms is ZERO ohms. How many zero readings are we supposed to get?

They were very helpful though and sent us (2) gearbox face plates for converting both the 775 gearboxes over to dual 550 gearboxes via overnight ship.
So, we can finish our shooter now.