Electromagnet design (newbie) 2

[tallyjay]

I'm a hobbyist designing a walking robot for competition in the RFL (

http://www.botleague.com).

The floor of our arenas is 1/4" steel, so I am wanting to build electromagnets into the robot's feet that I can turn on when I need traction and off when I need to move a specific leg. I need to design and build several electromagnets of approximately 1 pound each that would have a holding strength of around 150 pounds. I'm thinking that a bi-polar magnet would be best, since it appears to be more effective in dealing with air gap (the only air gap I anticipate is from swarf on the floor - in general there should be good contact between the feet and the floor). Based on info from this site:

http://www.magnetechcorp.com/Bi-polar.htm

it looks like what I want to build is feasible, but I need some help locating design guides to determine wire gauge, number of turns and overall physical dimensions. Voltage in the rest of the robot's systems is 24v DC. Any pointers would be appreciated.
Thanks!
tallyjay

 

[MagMike]

Hello tallyjay,

A bipolar electromagnet seems like a good choice.

The key thing to electromagnets is to get as many turns that'll physically fit, but not so many that the voltage from your power supply can't push many amps through.

The 24VDC power you mentioned, would that be available for each electromagnet or is shared? Would it power two electromagnets simultaneously?

I would guesstimate you'll need an electromagnet with 3 to 4 square inches of contact surface area to generate 150 lbs. pull. I fear that might put you over your weight limit.

 

[MJR2]

You should realize that 150 pounds of force is a straight up or away from the floor force not sliding. It appears that you want a sliding force and it will be much less. And the example is on 1/2 plate. You will be on 1/4 so it will be less.

However try 30 AWG copper wire. Figure the volume you can fit in the space available. Allow for less than a perfect fill. Assume some core dimensions. Volume of wire gives you weight and from that length of wire and resistance. Remember your formulas

V=I*R and W=V*I

Or save youself some grief and buy them from your reference. Round electromagnets will be somewhat more efficient for the same power. Do some more searching.

 

[tallyjay]

I have 24 volts on board for the other systems and can easily spare 10 amps for the electromagnet system. The 24 volts could be wired so that either each magnet sees 24v or I could split it between electromagnets. I bought an assortment of magnet wire in various gauges and will try out some test windings next.

 

[MJR2]

Keep in mind all of the energy in a DC electromagnet goes to heat. I suppose in your robot competition the event is short enough that you can run higher power than if you needed continuous duty. However if you must return to the ring quickly you will find your magnets losing power and getting really hot. If you should short due to an insulation failure you'll quickly drain your batteries and be out of competition.