Re: Gear ratios for launcher
 

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.

Re: Gear ratios for launcher
 

using RS-775s with 4:1 reduction direct driving to 8" wheels with about 3" of compression we are getting very consistently balls going well over 30 feet

Re: Gear ratios for launcher
 

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?

Re: Gear ratios for launcher
 

We took a decent amount of data with ball compression, I'll see if I can't dig that up and compile for public posting.

We're gearing for a top speed at the wheel edges of about 80 ft/s (54 mph!), since this is about double the speed of 40 ft/s that worked well for basically any shot in the near half of the field in our testing. So for a 4" wheel that's a 5:1 off of FPs (0673) and we have nearly the equivelant of 4 of them (2 FPs, 2 550s), so we're making up for lost torque (see here for more of the reasoning behind that). We're using the same 8" plaction wheels we tested with because that tread seemed to work better than others we tried briefly. I pushed for wheels smaller than the ridiculous 8 inches, but nobody ever tested anything smaller (we have screwed up ways of setting priorities, working on fixing that...) and people were worried about differences in traction with smaller wheels, we stuck with 8". The reasoning for smaller wheels was mostly weight, with a marginal benefit in how the frame could be layed out (more freedom), as well as just not having ridiculously huge wheels. But no one listens to me anyway... In any case, with our 8" wheels we have 10:1 total reduction off of 2 FPs and 2 550s in the works.

Re: Gear ratios for launcher
 

Two weeks ago I made a pitcher using two rollers made out of 2.5" PVC covered in wedge top tread. This was powered by two 775s on banebot 46-1 gearboxes with no chain reduction. The compression of the balls was about 2 inches.

I would be comfortable shooting from half court with this thing. It is also good for rapid fire, the 775s have so much torque that the rollers will spin at a steady speed no matter what.

Re: Gear ratios for launcher
 

Accuracy at key range will be more important than being able to chuck a ball 30+ feet, IMO.

They were using home-built speed controllers with a knob control -- I'm not sure what the duty cycle voltage was. (I wasn't there... had a funeral this weekend, so Saturday was the first FRC day ever without me there. Quite weird, I must admit!)

Re: Gear ratios for launcher
 

Not weird, but impressive. I hope your students recognize and appreciate your dedication!

Re: Gear ratios for launcher
 

I believe they do!

Re: Gear ratios for launcher
 

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.

Re: Gear ratios for launcher
 

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

Re: Gear ratios for launcher
 

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.

Re: Gear ratios for launcher
 

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?

Re: Gear ratios for launcher
 

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

Re: Gear ratios for launcher
 

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.

Re: Gear ratios for launcher
 

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. :)