justin_le wrote:Very interesting data coming up next!jk1 wrote:awesome thread, interesting if you could compare the data with ferro fluid as well.
Justin answered this about 10 pages back, but I wanted my own proof.icecube57 wrote: And would it to be better or faster to keep rolling at a lower speed and load or just simply stop to aid in motor cooling.
For sure, but what surprised me is that the fluid which remains in the motor is quite LOT less than required to fill the gap, and even with this fractional fill it still has the same thermal benefits as the full coverage. I wish I could quantify it easily but from peering in with a flashlight I'd estimate maybe like 20-30% of the gap is bridged by the fluid. In the case of a rotating motor I'm guessing that this gets distributed and pushed around enough to keep the thermal transfer coupling well over all areas.flathill wrote:this is pretty much the same with loudspeaker drivers. you only add enough just the fill the gap. adding more will just reduce the efficiency (more drag on voice coil) while providing almost no additional benefit thermally.
Curious, what's the presumed reason for that? Just that there wouldn't be enough to bridge the air gap and be held in place by the complete flux path?also note adding too little will make it more likely to leak
this would mean the carrier fluid would leak out the motor while the particles remain in the gap. the ferrofluid likes to travel along crevices. u may want to add grooves to make sure it cant cross the road
The latter is what I think. What we could do now is install a side cover plate with large holes around the perimeter to encourage every drop that breaks free from the air gap to get flung out, and then see what's left after spinning for a few days. My hunch is that not a whole lot more would come out than already did, but I could be wrong.icecube57 wrote:Do yo think a thick stator fluid would have less leakage and running.. assuming at the cost of added drag. Or do you think that if the remaining amount is probably the perfect amount that would remain intact by magnetic forces without it slinging it every where.
It wouldn't hurt I suppose, but the benefits to be gained are a lot less than when you are starting with a sealed unvented motor. Once you have fresh ambient air flowing directly over the stator and motor windings, there isn't much need to move the heat from the stator over to the rotor shell and then to ambient.Any benefit with a vented setup.
Yeah yeah, nobody should read the fact that oil escaped the side plates here as a downside. I deliberately didn't seal them because I was curious if the magnetic forces alone would keep it in check, but in any kind of production run they already put a sealant on the side plate covers to keep water out so this would all be par for the course.Punx0r wrote:Excellent work The options you're exploring for sealed motors are particularly interesting because open-sided motors just aren't practical for many and almost certainly unsuitable for a commercial product.
FWIW, I don't think it's at all unreasonable to install the sidecovers with a bead of sealant to prevent leaks. It's a lot to ask the ferrofluid to resist the considerable centrifugal force in a spinning motor, it'd be nice if just refrained from escaping via the bearings or phase wires
Yeah, this is what we had planned to do. The first drag test after 20cc's was added was performed with a cold motor. We were going to repeat the test when it was hot, but as you know most of the fluid escaped so it wouldn't gave been a fair comparison. And then when we repeated the drag test with the fluid that remained, it was indistinguishable from having no fluid, and so not much point in doing that again at a higher temp.flathill wrote:also note the viscosity lowers as the fluid warms up. there is another "loosening" effect that is not temp related (less particles clumping) after being "worked"
make sure to do the drag test on a "cold" motor as-found after a fresh fill and then repeat the test after the fluid has been worked/warmed
That would be one nice consequence of potting the stator too, we would present a smooth circular OD for the fluid to move around over without all the stator teeth edges and gaps and such. The magnets in this MXUS case are already butted up and make a fairly smooth ID, but in my other motor project I've got a gap between the magnets and would certainly want that filled to be smooth.Also filling the gaps between the magnet and teeth may help with long term fluid stability (less shearing)
Indeed it will a fair amount of burn in "field testing" to see if there aren't other consequences here. Are you speaking in this case from firsthand experience of having had the ferrofluids react with chemicals in this kind of environment or just precautionary? We wouldn't want it to react in any way with the magnet wire enamel or the adhesive holding magnets in place, but given how the intended application for the product is around magnets and wire I'd be surprised if they used compounds that were incompatible with coatings typically used on those.and also make sure any glue/paint/whatever is ferrofluid compatible or it can cause fluid separation long term
I can't say that I do. You're right that I was aiming for "best case" in this experiment for air flow, which means having a smaller number of large holes, but don't have any firsthand experience running a drilled hub with this little metal remaining in an offroad situation. There's no motor torque transfer along the side plates so I think (similar to a spoked wheel) that the remaining metal could be pretty thin and still strong enough.Hyena wrote: Those are some whopping big holes in the size covers! They are larger than I'd be comfortable running from a strength/reliability and foreign object entry point of view. I know this was largely to test the best case scenario for the experiment but do you have any thoughts on the biggest holes people should run ? Personally, and without any quantitative science to back it up, I think around 20mm is as large as I'd want to go.
Ha, that's a bit of a stretch, but if you're needing to use a cromotor as a mid-drive then you certainly have some serious hill issues! One of the things that I'll detail later and which will come up for sure with anyone playing with the updated trip-simulator is that the heat capacity of the motor still plays a huge role in short term hill climbs. If you run a really steep ascent of realistic length and compare the unmodified motor to one that is vented or with ferrofluid, you'll often see that the peak temperatures don't differ all that much. Often it's only like 5-10oC, even though the modded motors have less than half the thermal resistance. But those that are modded for better cooling will cool down much faster on the downhill or flat section following the hill, and will be better prepared for the next climb.spinningmagnets wrote: Dave Kaufmann has a Yuba that needs to tackle extra-steep hills, and he kept moving up in "mid mount" motor size to keep from overheating until he got to a de-spoked Cromotor. If we add ventilation holes and a 20-inch rear wheel, I'm sure a 406 would have been more than adequate.
Moreover I should thank all our loyal customers who support us and the Grin shop which is really what makes this whole shared R&D thing possible. Without them there wouldn't be any funds for any of this.Hats off to Justin and the team for not only doing this, but for publishing it.
Done! All the 4 and 6 turn MXUS variants are updated now too. Refresh your browser:icecube57 wrote:Will the 4T Mxus be updated in the simulator?
It's shown right there in the subtitle of the graph data which summarizes the numerical results. 6.67 rpm/v without the ferrofluid, and 6.62 rpm/v with it. I suppose technically that's a decrease in Kv of 0.8%, but I can't really say if it's within the margin of measurement error or not. Pretty insignificant in any case. That said this particular fluid has very low magnetic attraction, the jar of fluid itself can just barely pick up and support a rare earth magnet. It's like its overall magnetic interaction is pretty low, just enough to keep it in the air gap, and I doubt the relative permeability is far from 1. I mentioned to the supplier that it would be in an environment with strong ~1T magnetic fields and wanted the least amount of drag friction in those fields so they produced or spec'd the compound we got accordingly.John in CR wrote:Great work Justin!
Regarding the ferrofluid, you mention the drag, but did you see any decrease in Kv?
I think to see this effect we'd need to spec a ferrofluid that has a high relative permeability and isn't saturated at the already quite strong air-gap fields in the hub motor, and I'm not sure if there is such a product that would help out much when the air gap field is already as strong as it is. IIRC in the research paper talking about the use of ferrofluids to decrease motor Kv's, they mentioned fields in the 50-100mT range with large air gaps.That's what sparked my interest in ferrofluid added to a hubbie, to increase Kt without increasing copper resistance. If there's that benefit too with the very slight amount that you showed has little effect on drag torque it gets even more attractive.
Oh we've talked in the shop about machining an all clear plastic side cover for a while now, or easier installing some relatively large clear windows on a stock metal side cover. It would be hard to see much of anything going on when the motor is spinning without a high speed camera though, and for getting the thermal analysis the plastic side plates would skew the data. So until we have a suitable ~>1000 fps video recorder to see the fluid motion there isn't too much point in making the clear side plate. Another option is to use a stroboscope with a more conventional camera, but it's not an endeavor I could justify the time/money input yet.Cowardlyduck wrote:Not sure if you missed it, but what did you think about my idea for a clear side cover and UV additive above Justin?
1+speedmd wrote:Great work Justin. Now we know the stuff is worth looking at more deeply for certain.
With several different blends/ different volumes of liquid and long test times make this a perfect candidate for a design of experiment (DOE) to get to the pay dirt in much shorter order and have better feel for what is driving the results. You could also add in several cooling fin and venting options into the experiment at the same time. It will blow your mind!