Need a way to control 15 (https://wiki.keyestudio.com/KS0320_Keyestudio_Electromagnet_Module_(Black_and_Environmental-friendly)) electromagnets. have tried using relays, but they only seem to use 2 connections, whereas these magnets use 3. I can get a single one to work, but when i attempt to use a relay board it does not. Complete newbie to this, but would appreciate help/ideas. Thank you. Also, I was attempting this via a raspberry pi... if something else would be better/easier im happy to use whatever.
Those electromagnets have a built in driver so they need power and expect a digital on/off signal.
Consider looking at the connection diagram and example code on the web page.
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I can get a single one of them to work fine... but i do not see any plain board that has 15 grounds, 15 powers and 15 i/o connections. I have access to an external power source, but i cannot get the relays which supposedly only use 2 connections to work with the 3 connection magnet module
You have to make that, or use appropriate wiring connectors. You will need a separate power supply, as the Arduino cannot be used to power any electromagnets.
Be sure to connect the external power supply ground to the Arduino ground.
I am completely in the dark... I have no way of wiring up my own board 
If you want to do this yourself, you will need to learn some new skills, like soldering. Adafruit and Sparkfun have excellent soldering tutorials.
These semipermanent protoboards work very well: Adafruit Perma-Proto Half-sized Breadboard PCB - Single : ID 1609 : $4.50 : Adafruit Industries, Unique & fun DIY electronics and kits
I love the description of the device in the linked web page!
You need one ground connection - and wires from that one to each individual device. The same for the power connection. You will need an external power supply for those magnets, able to deliver at least as much current as all of them draw together. You may also use this power supply to power your Arduino (if suitable voltage), at least you will have to connect the Arduino ground to the power supply ground.
If you're looking at an Uno you will see it has more than 15 I/O available. No problem there. If not enough, there are I/O extenders and there's also the Arduino Mega with dozens of I/O pins.
I need to add in some additional info... I need to have these separated into 3 groups of 5. as this will be for an archery shoot... the magnets will hold balloons in place which will be randomly launched, one at a time from each group. So this should work if i have an I/O for each magnet, to control it with, at least in theory, correct?
Yes
Hi, @mcvic0707
Welcome to the forum.
https://forum.arduino.cc/t/how-to-get-the-best-out-of-this-forum
This link will be more informative.
Tom... 
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So, when activated the balloons are freed to float up up and away?
Yes. one balloon in each group in random order for all 3 final archers at the same time... they will be attached to a string to limit their height... if archer does not shoot it before that, that balloon is not counted.
How many hours do you think you will need to power all the magnets? Seems like a strange design, however. Could use a permanent magnet to hold the balloon and then an electromagnet to momentarily apply opposite magnetic field to make a zero magnetic field and away goes the balloons.
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Hi,
The solenoids only need to release the balloon.
You make the release mechanism so it is held closed by a spring, the solenoid then briefly pulls the release mechanism open for enough time for the restraint on the balloon to lift free.
So solenoids are only used for a short period.
Tom...
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Hmmm, not a mention of duty cycle, how long can those magnets be energized continuously without smoking? I like @TomGeorge's solenoid idea, energize for 100 milliseconds to release balloon.
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