Quote:
Originally Posted by VacioArconte
I can't speak to your last two questions since I haven't personally used any (non light) switches rated for the high currents of FRC bots, but I can tell you that FRC bots do indeed run at 30-40A, and technically even higher. If you check the stall current for a CIM ( http://www.andymark.com/Motor-p/am-0255.htm), you'll see that they can draw up to 133A. Now, you might ask why we have 40A circuit breakers if CIMs are running at such a high current. The thing is that 40A circuit breakers can allow current higher than 40A, but only for a limited time ( http://www.andymark.com/product-p/am-0288.htm). A simple google search returned these switches rated for 50A ( http://www.wiringproducts.com/50amp-toggle-switches).
Hope this helped! |
Quote:
Originally Posted by Ari423
Individual robot motors definitely run much upwards of 40A, just not for very long (otherwise you have a problem). A CIM in a drivetrain can easily draw 80+ amps for a few hundred milliseconds, which is too short to trip the breakers. Remember whenever you start up a motor it is initially stalled, so it will draw stall current. As it spins up, the speed will increase which will decrease the current draw. Make sure whatever breakers you decide to use give enough lead time to not trip whenever you try to start a motor.
To respond to your overall question, I know a lot of teams will take the triggers from broken 12V drills as a basic motor controller. You have to remove the drill motor and gearbox and the battery. Then connect a breaker and then Anderson connector to the input of the drill (where the battery went) and leads with your favorite crimp connector on the output side (where the drill motor was). Now you have variable speed control (via the trigger) and reversible direction (via the CW/CCW switch). You also get a handy disable switch by moving the CW/CCW switch to the middle position. If you do this, make sure the drill you are using is rated for at least 12V and less than the max amps the breaker allows.
EDIT: Don, I think the point of this low-functionality control system was to decrease the number of wires needed to drive one or two motors for a prototype. Using an old cRIO or IFI control system will probably do the opposite of that.
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Quote:
Originally Posted by DonRotolo
12V @ 40A = yes. The main breaker, rated at 120A, can carry twice that for short time.
Yes, a plain light switch will work for several hundred contact closures before it fails.
You also do not need more than 1 switch to reverse polarity; you need a DPDT (Double-Pole Double-Throw) switch instead.
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Okay cool, thank you all for the quick responses. I understand I'd be able to use switches like these then:
http://www.wiringproducts.com/50amp-toggle-switches or possibly a light switch , but they are awfully expensive for the application, would it be possible to use something like a cherry switch:
http://cherryswitches.com/us/product/rocker-yr-series/ , they do not have a DC rating listed but the AC rating is 120 at 20A, is that good enough or no?
Also with the drill trigger, is that simply a variable resistor (potentiometer) and could I implement something like that on the board? Would I need some crazy expensive potentiometer that can handle high amperage?