I am happy to report the prototype is working VERY well and has filled a 68/4500 in about 20 hours. This is with a 16 RPM motor! (am I good or what?)
This was using an 85 psi shop compressor feed which is really what makes the difference. The shop compressor hardly runs at all. For the people that didn't catch this in the other thread, a 68/4500 holds about 11 cubic feet of air when full. Your typical shop compressor puts out 90 psi at 5-10 cubic feet PER MINUTE. This means it should only have to kick on 2-3 times during the entire fill.
The motor takes about 1 amp so the cost to fill a tank will be about 25 cents in electricity plus a few minutes on the shop compressor.
The pump generates ZERO heat at this rpm. This is contrary to predictions made by "knowledgeable" people on the pellet gun forums. This also means what the gauge says is in your tank is actually IN YOUR TANK. No pressure loss from cooling after the fact.
I am not getting any water in the system but I live in a dry climate. I am going to suggest that you put a water trap on your shop compressor. Adding a water trap will add expense to the product (I might offer it as an option).
Everyone was speculating on filling a scuba tank. Typical scuba's are 80 cubic feet at 3000 psi. Given you can fill 11 cubic feet in a day, you should be able to fill a scuba tank in a week or maybe a bit less. This is an ESTIMATE so don't hold me to it.
The fill rate is linear. Leaving something in your tank will help proportionately cut down on the fill time. Likewise topping off a scuba that's gotten half way down is a real possibility.
Maintenance, yep your going to need to rebuild the thing once and a while. The o-rings are under a lot of stress but the good news is that you only need to replace 6 that take the most abuse. I have not had to replace any of the urethane o-rings yet and its been running for weeks. I have been lubricating it regularly, something I know a lot of you don't do until it breaks. I am not going to the expense of putting gauges on every stage. You will need to monitor your fill rate and if it takes too long you should just replace the 6 o-rings.
I am making decisions on things like the quality of the pump shafts. As an example, you can get plain steel, chrome plated steel and hardened - chrome plated steel. The choice of shaft determines the robustness and time between rebuilds. If you tell me your going to use it once a month when you tinker with your marker, then you will be out of paintball before you have to mess with the compressor. If the majority of people tell me they are planning on filling their scuba tanks every week, the price is going to go up.
I am trying very hard to make this affordable for all players. Now I need your feedback on how often you expect to use it so I can design it properly.
Thanks!
AGD
Answers to additional questions in this thread:
Its currently running at 16 rpm because I did all the testing and baselines at that speed. I have 96 rpm motors to try next but have not gotten to it yet. The design is NOT finalized and its unlikely that the 16 rpm motor is going to be in the production model.
Without the shop compressor feed it would take several days to fill the tank (but would do it eventually).
Will higher input pressures from the shop compressor make it fill faster? In theory yes but in reality no. The motor is sized to the pressures in the first stage particularly. If you overpressure the input it will likely freeze up the motor and burn it out if your not there to catch it. I am going with 85 psi because almost every shop compressor puts that out.
This compressor will not cost less than 300 dollars and I am trying hard to keep it under 500. The motor is a huge expense and unless I can get them in China cheaper, its MORE than 200 bucks just for that. The motor is a big factor in the noise and reliability.
The chassis everything mounts too has to be heavy steel so it doesn't move. The prototype is mounted on 1/2" thick aluminum plate 2 feet long by 1 foot wide and the motor FLEXES the plate every go around.
The price difference between a best-of design and a minimum design is hundreds of dollars not 10's of dollars. A best-of design would have ball bearings not bushings, quiet, high quality, last forever motor made in America, brass instead of aluminum piston housings, hardened and plated shafts etc. Having just said all that, I don't think THAT design would be less than 500. There is a reason no one has done this before.
From what I am seeing here it looks like the compressor will run one week a month for the average customer. You have to realize how many hours this is. 7 days X 24hrs X 12 months = 2,016 hours of run time per year. To put it in perspective, a full time job = 2,000 hours a year. Imagine hooking your marker up to a machine and have it shoot paintballs all day every weekday for a year. How long would you expect it to last?? This is why there is such a quality consideration here. If it wore out in 250 hours you would be complaining because that was only a couple dozen fills.
I am listening to you and working hard on it.
UPDATE 12-10-09
I am now working with the 95 RPM motor and its filling a LOT faster. Estimates at this point are 6-8 hours for the standard 68/4500. It may be possible to downsize the motor to one less costly and go back to the 24 hour fill. I also have to try boosting the input pressure to 100+ psi. Don't give up hope on the $300 price tag!
. I really can't wait until this becomes available, go Tom 
