this gearbox runs purely using magnetic forces
you might be wondering where the gearbox is right now in fact if you look a little bit
closer you can see the screw heads in the middle as if they are being pushed by invisible arms
anyway here it is
super quiet there's no wear and tear and so no lubrication seriously impressive but here's
the thing I honestly don't know how efficient they are I believe they are inefficient and mechanical
gears but I have nothing to prove it yet because trust me it's not easy to find efficiency
for this we gotta figure out the mechanical Power which means measuring the shaft speed
and Torque simultaneously which is the tricky part because let's say
you want to find that mechanical Power on the output I can measure the speed
using a magnetic sensor inside the bearing block but when I try to measure the torque
as you can see this time the motor starts I can't measure the speed
it's kinda ironic but we can actually use these magnetic gear works as a solution
even though the torque arm tries to stop the output shaft the magnetic connection between the modulator and the sun
gear allows the rotors to slip over each other just as the output shaft is about to stop so
the shaft can keep moving and that way we can measure the torque without stopping the system
it's a decent solution but the issue here is since these are permanent magnets the
slipping point of the rotors is always the same so no matter how much load I applied
on the shaft the applied load stays the same I can't change the load on the shaft
so how about using tiny electromagnets instead of every single permanent magnet here to change
the load I mean that would be nice but there are so many magnets here fortunately I have another
solution so this method relies mainly on the friction between the electromagnet and the brake
disc rather than the interaction of the magnets in the previous magnetic gear and this has two
significant advantages that solve the previous issues first of all the connection between the
magnet and the disc is magnetic so the output shaft can keep going secondly we can now change
the load on the shaft by changing the frictional force between them through the electromagnet
okay before doing a quick test this steel core was machined by PCB way I just did the design
they did the rest there is also this brake disc just perfect they were machined in PCB with CNC
Services they offer all sorts of materials from plexiglass to Titanium and these two parts are
made of 1018 Steel this will also provide sheet metal fabrication 3D printing and other services
you see here and they are really good at that they could be a great solution like this one
here so big thanks to PCV for sponsoring this video okay let's see if this works
start tomorrow
okay the sound is good
oh wait
so basically it works but there's a slight issue check this out the
reading when the magnet is off is around 60 grams I'm giving power to the magnet
as you can see almost 200 grams now I'm cutting off the current
and it's at just 115 grams so why didn't it throw back to 60 grams again and even though I cut
current the brake disc is still not separated from the magnet yet the reason for this is the residual
magnetization remaining in the core and the reason for the residual magnetization in the core is
actually similar to the situation in this green film so this green film is a magnetic field viewer
and basically there are a bunch of tiny nickel particles in it that can freely rotate and when
we turn on the magnet these nickel particles try to align themselves with the magnetic field lines
in the area that currently appears bright the field lines are kind of straight and the
nickel particles also become straight which reflects the light and makes it look shiny
but once one sides don't reflect the light and so they stay dark
so we can literally see what's going on here it's really great now back to the problem
similarly this metal core also contains very small magnetic domains and when we give current to the
coil and create an external magnetic field in a certain direction these domains align
themselves like the external magnetic field and that's how this metal core becomes magnetized
the thing is when I remove the magnet from the film The nickel particles can't fully return to
their initial form the center is still a bit dark just like that the Aligned domains within
this steel color when the current is cut off cannot follow this magnetization curve exactly
and return to their initial form drops to such a retentivity value and as a result that remains
a residual magnetization within this material and this as you can see keeps the disk from separating
to give an idea of this residual magnetization I first gave power to the magnet then cut the
power off and tried to pull to this straight and repeated this for different current values
and yes I use the pulley system here because the residual magnetization is not a little
thing at all and at the maximum current we can apply to this coil wire There is
almost 40 kilo of residual Force left in the magnet I want to point out again that this is
the force required to pull the disc after the magnet is turned off and this is quite High
so how do we pull this back the main reason for this is the resistance of the domain walls which we
initially forced to move by applying current to the coil to move again after the current is removed
which it is quite normal for them not to move on their own when the current is removed because the
force acting on them is removed so in this case if we apply current in the opposite
direction domain walls will start to move in the opposite direction and demagnetizing the core
and the only thing to do for this just reversing the polarity
as you can see it really is that simple I can separate the disk from the magnet
in this way but I can only pull the disk run residual magnetization drops to zero
and to get it to zero I have to apply exactly this much opposite field
How to know that precisely mind slider for this was to make a few custom springs on the
lathe I was going to put them on a fixed Hub so that without the need to know the
exact opposite field required when the residual magnetization drops zero the Springs would sense
it and directly pull the disc back but you hear that sound coming from the late right
I think I pushed this mini too much and burned out something in the control board I gave some
3D printed flat Springs a try though it didn't work too well either then I thought why not use
magnetic forces as a spring I'll Place permanent magnets on the disc and the Hub with opposite
poles facing each other in this way just like a mechanical spring continuesly trying to pull
the disc back here the interaction between the opposite poles will continuously try to pull
the disc back and this could definitely work so the electromagnetic brake is ready it turned out
a bit heavy though considering it's made of steel I made some changes to the gearbox the
previous one was falling apart the last move is to include it in the test rig as the output shaft
so let's see if our invisible Springs work okay the magnet has attracted the disc
I'll cut the power now it didn't come back as expected again now I will apply
opposite field and the magnets will attract the disk just as residual field drops to zero
oh okay residual magnetization dropped to Zero by reverse field that this came back
but since I didn't cut the power right at this point it attracted disk Again
by opposite magnetization I need to quickly turn off the power supply right at this point
yeah so maybe it's not exactly a mechanical
spring but there's basically an invisible spring here right now
okay let's give it a little try
all right let's slow down dude
no way seriously it was clear though
okay first of all these are not even warm consider it cold but there has definitely
been a lot of friction here the core is in better condition compared to the disc with not as much
wear however the disc will definitely thin out over time by the way I got all the data while
the system was running now getting back the main point of the video as you can see we are now able
to measure both speed and 4 simultaneously this allows us to calculate the mechanical
Power at the output shaft however when it comes to gearbox efficiency we also need to find the
mechanical Power at the input shaft and make a comparison and the good news is there is
no need one more bridge for the input power I'm sure many of you have seen this before
when the rotor starts to rotate the stator and therefore the motor body also starts
rotating the opposite direction with an equal but oppository and if the sport is
smaller freely we can measure the torque on the other I am in the torque on input
shaft using a torque arm attached to motor body okay don't mind how crowded looks I've just got
the model freely mounted and the brake is in place as before and in between we have
this herringbone gearbox whose performance I'm curious about so let's start the motor
and here comes first data so first of all I'm measuring the input and output speed throughout
the process there's a difference all about 12 times between them that matches the gear ratio
and I'm getting the forces measured from these load cells multiply them by a token
distances to calculate the breaking tokens output and the reaction talk at the input
currently the braking force and torque are zero because the brake disc is not contacted with the
magnet yet but since the motor is spinning there's a reaction force although it's not affected the
reaction talk ideally this should be zero because when calculating efficiency it's crucial to
compare the applied load with the corresponding reaction in the current script with no load
applied that should also not be any reaction force so rather than zeroing this force of about
2.5 grams I'll deduct it from the total Force for now so okay let's just give some load to the shaft
as you can understand from the sound the output shaft
is now under a certain load the braking torque is around 0.4 Newton meter and in
response to this load the model creates a reaction torque of 0.04 Newton meter
now let's move on to the mechanical Power on each shaft using this
and here are the mechanical Power ratings in Watts according to the calculation there's
a power loss of about 2 Watts between the input and output shafts as you can see around 10 watts
are entering to the gearbox but only around 8 watts are coming out this loss inevitably due
to some reasons such as tooth friction or bearing losses in this case if we compare
the input and output Powers this gearbox has an average efficiency of around 82 percent
so it's not too bad for now but the performance of these gears actually varies depending on the
speed and load as well this was the performance on robot 1800 RPM and 0.5 new to Middle load so
I tested it again by keeping the load constant and varying the model speed
and I found that the efficiency increased with the increasing speed up to a certain point and again
under a load of 0.5 Newton meter this gearbox performed the best around 4200 RPM with an
efficiency of around 84 percent so consisting of these two stage hanging one gears with
12 gear ratio notification poorly aligned and supported and most importantly the 3D printing
gearbox cause the power loss of about 15 when converting a power from any speed and torque to
another speed and torque how about magnetic gear racks okay let's put this onto the output shaft
this magnetic gearbox is a single stage design with four reduction ratio
so the electromagnet is not connected now because this magnetic gear has an
incredibly low torque capacity so even with very little touch I
can't stop the shaft and as you can see the rotors just slipping on each other
even though it's a very small I applied a load of about 0.03 Newton Middle on the output shaft
which is very close to the slipping torque of the others in response there is a reaction
torque of 0.01 Newton meter created on the input shafts and as you can see there's roughly a four
speed ratio between the input and output so in this case this magnetic gearbox has an average
efficiency of only 55 percent 30 lower than mechanical gears which is a huge loss indeed
I only get half the power I give
I went on increasing the speed as before went up to 5000 RPM
I would like to say that the efficiency increased but it
dropped to around 20 and surprisingly the magnetic connection did not break
but that tiny magnet I was using to measure the speed came of its place
and I didn't go longer because the situation is already obvious
in the end the efficiency decreased significantly as the speed increased likely due to Magnetic
losses Unfortunately they don't appear to be very efficient but since the load is very low
I cannot Place much confidence in the test results after this part but either way it's
lower than the mechanical gears the ironic part is properly aligned Metal Gears although they
have an efficiency over 95 percent so I don't know if I expect it to be 120 or something
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