Air Machinegun Forum
General Air Machinegun Discussion Category => Drozd and Blackbird Discussion => Topic started by: DU-BB on November 30, 2015, 07:59:04 AM
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This will tell you how well your auger and motor assembly are working, the maximum rate of fire you can support. I think of this as the "dump test".
Get a bucket or container to catch bb's in.
Take the "Ramp" used to clear the magazine out of the bottom of it. You have to push the button on the side.
Hold your gun over your bucket, and power it on. The magazine will run for 2.5 seconds then stop, spitting out bb's.
Count the bb's in the bucket, and multiply the number by 24, to get the number per minute.
The easiest way to count bb's is to weigh them on a digital postage scale. Use the grains scale, and divide the total by 5.5, the weight of one steel bb.
If you only have a gram unit scale, divide the total by 0.356. Or 0.0126 in ounces.
This number doesn't take into account restriction imposed past the ramp in the circuit, that is, obstruction in the feed neck tube, or in the valve head/breech itself, and the weight of the bb's, those will effect the feed rate as well, this will just tell you what the practical limit of your auger drive is, that's the maximum you can possibly get out of your mag motor.
If you are getting "airshots" at high cyclic rates, because you have started to modify things, this is where to start.
Try doing the same basic test, but hold it down in full auto, and note how the bb's flow out, is it a steady stream, or in spurts?
Factors that effect the rate of flow are the motor and the voltage you give it, and the slip disc clutch. The clutch is there to keep the motor from stalling, since that is almost as bad as a direct short on the electronics, and is just as bad for the motor. If you have upgraded your magazine motor to the Nichibo, and better still if you have Sergey's board and good batteries (double the stock voltage) you can give that motor as much power as you have, and crank that slip disc as tight as you can, that motor makes more torque than the slip disc can transfer no matter how tight it is. Sergey uses transistors that can handle the Nichibo's power requirements, as long as it doesn't stall, and the slip disc can't stall the thing.
There is a jumper on Sergey's boards, that bridges any 2 of 3 pins. This is to protect the stock magazine motor if you use more than 15v power supply. His boards can take up to 24v, and the solenoid needs 14v, or so, at least, if you use HPA. It uses or alternately bypasses a 15v regulator to supply the magazine motor. The idea is that you don't need, or want to use that regulator if you supply 15v or less, only if you have more than 15v, the limit of the stock motor.
But if you have the Nichibo motor mod, those can take 30v. So in that case, set the jumper to bypass the regulator no matter what batteries you use. Herein lies the key to feeding 2000 bb's per minute.
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To add to that; if you have Sergey's circuit board installed and with the "ramp" still out of the mag, you can use the shot counter to compare to the collected bb's to see if the rate of fire matches the motor speed for the voltage you are supplying.
It is a reason I like the motor speed controller I installed in one of my Blackbirds. Easy to tune motor speed to ROF.
But still there are limitations to the mag design in the Blackbirds.
---Cam