Mag Thruster Drawing - RC Groups
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May 27, 2012, 04:12 PM
R.O.V. Man
hargard's Avatar

Mag Thruster Drawing

This is the drawing of the Magnetic Thrusters I am using ATM.
Have used this design now for 2 years with not even opening up to service.
Not possible to leak and very little power loss though magnetic coupling.
I use Brushless motors as they deliver more "umph" per amp.
Machining can be to a novice level as tolerances are almost non existent with this design.
The stainless steel disk's are from Ebay Very high quality laser cut at a very low cost. Delrin Also from Ebay..
I am open to any questions.

Regards Antony.
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Jun 11, 2012, 12:48 AM
After doing a lot of experimenting and working with people who have a long history in ROV development, I think you are much better off designing the proper shaft seal instead of using a magnetic coupler. The loss is too much, but more importantly just about anything that gets in the prop/impeller will stop it and then your are stuck. Probably not a big deal when your playing in the pool, but when your running around at the bottom of the Mariana Trench you can not afford a thruster failure.
Jun 13, 2012, 10:44 PM
Registered User
Hi Anthony,

Just starting to research building a ROV, so early days and lots to learn.

A few questions:
- I spotted your earlier Thrusters types thread and noticed that you have moved the o-ring in this design so it's no longer in contact with the stainless steel plate between the two discs. I would have thought that this could be a problem point. All other accesses points to the internal (dry) areas seem to be well covered with o-rings except the stainless steel plate. I'm assuming you haven't noticed a problem, but was wondering the reason for the change from the previous design?

- I assume the only reason for the two internal(dry) chambers is to give you a place to mount you motor.

- How are you attaching the magnets. Are they just press fitted in or are you gluing?

- Do you have any pictures of the finished thruster? Together and in parts?

Jun 14, 2012, 11:13 AM
R.O.V. Man
hargard's Avatar
Hi Nic
You are correct. The seal in now on the plate face.
As for power loss. This method is a lot less than a mechanical seal.
Also machining is much less tolerance and makes it more able to be done by a hobbyist.
Yea the extra bulkhead is motor mounting only reason.
The magnets are a press fit with loctite glue.
I will put the updated drawing on tonight. Oops to me putting a old drawing on.
And yes I will dig them out and post them.
Starting this week to make new set of thrusters so will photo every stage and pressure testing down to 500 metres...Yes 500 metres. Have friend that is able to do this for me locally.

Regards Antony
Last edited by hargard; Jun 14, 2012 at 11:21 AM.
Jun 14, 2012, 01:39 PM
R.O.V. Man
hargard's Avatar
The Right drawing this time.
Sorry to misslead u
I will messure the toqure required to break the magnetic link.
I will do this with weights on a 12 inch bar just to have some type of messurement.
I first used 6mm dia magnets but found that I had room for 8mm dia.
Ebay is a good resource atm
Item number: 320912055830 Stainless Steel Diameter Discs Will do any size.
Forward Metals Ltd for large size tube again on Ebay

Regards Antony
Last edited by hargard; Jun 14, 2012 at 02:01 PM.
Jun 14, 2012, 10:55 PM
Registered User
Thanks Anthony,

Diagram makes more sense to me now with the extra o-ring.

Look forward to the build pictures.

500 meters sounds impressive. Hope it holds up well.

Jun 15, 2012, 02:31 PM
R.O.V. Man
hargard's Avatar
A bit of info on the Torque that the coupling holds.
The Gap between is 3mm see photo.
One part was held in a lathe chuck. the other was free to rotate on a shaft.
The chuck was rotated to get a measurment. You can see by the photos..
The arm distance to the measuring point was dead on 10Cm (100mm)
The pressure exerted on the scales was 0.424Kg.
If you do your math’s that a lot of torque and more than enough for hobby RoV transmission.
But in saying that too much torque is a bad thing as if you get seaweed in the propeller its better to disengage the magnetic coupling rather than stall the motor.

While in the setup I wanted to measure the friction of the magnetic coupling. It was imposable to measure with the scales. the free end would spin quite freely if spun with the fingers.

That about it.
Regards Antony
Jun 18, 2012, 07:18 PM
Registered User
Nice test setup.

Seems that there is a bit of debate about how stalled motors/ESC will respond.

But it would seem best to try and reduce the torque to try and prevent stalls. I assume that the easiest way would be to increase the separation of the magnets, either by increasing the size of the disc separating the two sections or larger ball bearings?

Jun 20, 2012, 07:48 AM
R.O.V. Man
hargard's Avatar
Made a complete thruster in 4.5 hours. Have taken loads of pics on the machining and finished parts.
Just the finished are here atm.
Testing will be in late July as busy atm.
Any questions ...ASK

Regards Antony
Jun 21, 2012, 06:45 PM
Registered User
Looks good.

Any problems with the machining? I'm going to have to do some more looking into tools for this, I'm not at all equipped yet. Although there are a couple of guys from the local RC flying club who I expect would be keen to help out.

Are you planning to put ESC (assuming it's brushless) in the forward dry section? Space looks fairly tight.

Just to confirm your cable exit point is from the front center?

It looks pretty solid, will keep an eye out for your testing results with interest.

Last edited by which.wabbit; Jun 21, 2012 at 06:47 PM. Reason: Clarify if using ESC
Jun 21, 2012, 10:35 PM
SlowStick Test Pilot
patrickegan's Avatar
Nice work... I dig the mag work.
Jun 22, 2012, 03:16 AM
R.O.V. Man
hargard's Avatar
The machining is easy BUT you need to get tooled up for the O ring slots.
The ESC'S fits into the front void and the cable runs out through a gland or a alloy tube welded onto the side of the spacer tubes. You can make the tubes any length you want.
Or you can not have the ESC'S in the thruster. It's your choice.
Some brushless motors have the three connections at the shaft end. If so you can weld the support tube onto the rear spacer tube and have the ESC'S in the sub.
I can give you a sequence on the machining if wanted.
Regards Antony?
Jun 22, 2012, 10:01 AM
R.O.V. Man
hargard's Avatar
Was thinking about making it simple as possable.
Still need a small lathe but this Drawing is as simple as I can get it.
The only area that needs even close tollerances are the O rings.
The whole lot can be made from Acetel or Delrin.

Regards Antony
Jun 22, 2012, 10:50 AM
SlowStick Test Pilot
patrickegan's Avatar
I'm mentoring a group of high school students. We did the Sea Perch last year and the kids are ready to move on to a more capable ROV. So during the next school year I may ask for assistance.
Jun 22, 2012, 12:56 PM
Registered User


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