Design help to control electromagnetic

[Panovak]

Hi.
I'm in the process of designing something that requires me to pull a "raft" into water. The requirements are there can be no penetrations in the vessel.
I've decided I want to use an electromagnet to pull the raft into the water.
The raft needs to be made of some type of buyant plastic and I'll likely add either a magnet or "capable of being magnetized" object in the center of the raft.
Underneath on the outside of the vessel I'll have an electromagnet.

The raft only momentarily needs to be submerged.
I want to have the raft just barely boyant enough to keep the platform dry. This will reduce the size of the magnetic required.

Ideally this raft would be about 10"x20".

How can I have an affordable and relatively weak magnetic have longer range of force in one direction?

My concern with using a magnet on the raft is this force won't be fully turned "off" when the electromagnetic is off as it will be attracted a bit still to the electromagnetic.

That being said a "capable of being magnetized" metal mat not have force/ distance to pull the raft down.

I realize I could also just reverse polarity to "push" the raft back up but this adds more complexity when I belive good design could avoid this.

Any help/ suggestions or advice would be greatly appreciated .

I've made a sketch and will try and get that posted.

 

[Alec_t]

Could you mount something above the raft to push it down?
Welcome to maker.pro!

 

[Harald Kapp]

I've decided I want to use an electromagnet to pull the raft into the water.

Basically a sound idea. What frictional force does the raft experience when dragged into the water? The higher the friction the stronger the magnetic field you require which in turn increases friction due to the additional downward force.

My concern with using a magnet on the raft is this force won't be fully turned "off" when the electromagnetic is off as it will be attracted a bit still to the electromagnetic.

Definitely an issue with a DC operated electromagnet, although probably exaggerated. The residual magnetic field of the electromagnet is qay smaller than the field with power on. It very much depends on the material used for the electromagnet's core. With enough power available, you could even construct the electromagnet without a magnetic core to reduce the off-state magnetic field to zero. You'll nee a higher electric power in this scenario as the lack of a magnetic core means the magnetic field is less concentrated.
You coul further reduce this issue by powering the electromagnet from an AC source

Have you considered alterantives to the magnet? For example a hook that pushed the raft into the water (without penetrating the vessel, of course)? Or putting the raft onto a submersible platform which is draged into the water, taking the raft with it and releasing it "automatically" once the raft starts to become buoyant?

Is it a requirement to also drag the raft out of the water?

 

[Panovak]

Pushing the magnet from above would be more difficult because that distance will be around 4" versus about 2" from the bottom.

When I say "raft" I mean a small floating platform. The water is a medium growing liquid.

The max size of the whole vessel is 10"x20". The "raft" is always floating in the liquid so there is no frictional force to pull it down other than the buyancy force.

I'll post a picture of my prototype. This is an enclosed bioreactor to grow tissues so it'd be impossible to introduce a hook without a penetration.

 

[Delta Prime]

Are you a research scientist?
Are you building a (TIB) Temporary Immersion Bioreactor? For plant tissue cultures? A floating raft support system inside a culture vessel to support the explants?
I made one in high school for my science project.