Shawn I'm building this instrument, thought I'd let you know :) I'll keep you posted on my progress. One question I have involves dampening rotation. The q-tip you use dampens vibration, but doesn't much dampen rotational oscillation, which I'm finding can persist for quite some time, and is easily induced. I wonder if filling the cavity with some liquid would act to dampen rotational oscillation, but not to hamper the magnetic torque being measured. Essentially, it would be a low-pass filter. Thoughts?
Wonderful news! I thought about enclosing the sensor in a liquid to damp the rotational motion, but I didn’t try it. (I was concerned about biofouling over the long term, but I think this is a perfectly viable option.) Another way to do it is to use eddy currents to damp the rotation. Suppose you cut a channel in copper plate that was just wide enough to allow the magnets on the sensor to swing through. Mount the channel just behind the sensor with the magnets penetrating the channel. Then as the magnets rotate they create eddy currents in the copper which, by Lens’s law, creates their own magnetic fields which act to oppose the motion of the sensor magnets. I’ve used this method in other magnetometers, but I didn’t have the tooling required to machine the part. I think either approach should work. Another way to kill the motion is to bring a magnet 🧲 in on the zero line so that the sensor aligns to it, then withdraw the magnet exactly along the zero line so that it’s influence gets weaker and weaker. When it’s removed completely the sensor magnet will be it it’s zero position.
Let me know what you think about these these options. I encourage you to experiment with low viscosity fluids. I suspect that they would prove quite suitable for this application as it should be easy, with the relatively large sensor area to achieve critical damping.
@@citizenscientistsworkshop1948 I think I'll give the fluid a try to start with. I'm 3D printing my enclosure, so it won't be much of a trick to keep it sealed. I'm thinking something like isopropyl? I don't want to weaken the nylon. Incidentally, working with single strands of nylon is incredibly challenging. I managed to get down to a few strands, but could not separate out a single one. It's just too thin. I don't think it makes much difference, though. The eddy currents idea is very attractive, though, because it would let me explore that regime. I have a friend with a CNC that can machine channels in copper-clad printed circuit board, so maybe at some point I'll give that a try too. Do you think this idea would also serve to dampen the vibrational mode you use the q-tip to dampen in your video?
@@citizenscientistsworkshop1948 I've done some research on low viscosity liquids, and am having a hard time coming up with one that's not toxic, corrosive, explosive, or some combination thereof! The eddy current dampening is sounding better to me. In fact, I just taped a prototype to the back of my prototype enclosure (maybe a half inch away from the magnets) and that improved the dampening time quite considerably. No doubt a fluid would really do better, but unless I can find one that is relatively safe to have sitting around the house, I'll probably go with copper. Thoughts?
@@tdstone4s Why not use water with a dash of dash of sodium metabisulfite, potassium metabisulfite or idorophore? The first two chemicals are used to sanitize wine making equipment, and the latter is and iodine-based compound that is used in the medical industry. I think all three are stable and that they should prevent biofouling over fairly long times. Concentrations needed to kill microbes are not dangerous to humans, which is why these chemicals are used in these industries. I’m glad to hear that eddy current damping is an option for you. Since you are printing your own housing, you can create one that has little clearance for the motion of the magnets. Then you can place the copper on the outer surface. Ideally, you’d like to have the long magnets pass through a channel that’s cut in the copper. Such a device might come close to being critically damped.
Good project with excellent instructions.
Part 2! Part 2!
Great project! I’d like to see part 2.
Shawn I'm building this instrument, thought I'd let you know :) I'll keep you posted on my progress. One question I have involves dampening rotation. The q-tip you use dampens vibration, but doesn't much dampen rotational oscillation, which I'm finding can persist for quite some time, and is easily induced. I wonder if filling the cavity with some liquid would act to dampen rotational oscillation, but not to hamper the magnetic torque being measured. Essentially, it would be a low-pass filter. Thoughts?
Wonderful news! I thought about enclosing the sensor in a liquid to damp the rotational motion, but I didn’t try it. (I was concerned about biofouling over the long term, but I think this is a perfectly viable option.) Another way to do it is to use eddy currents to damp the rotation. Suppose you cut a channel in copper plate that was just wide enough to allow the magnets on the sensor to swing through. Mount the channel just behind the sensor with the magnets penetrating the channel. Then as the magnets rotate they create eddy currents in the copper which, by Lens’s law, creates their own magnetic fields which act to oppose the motion of the sensor magnets. I’ve used this method in other magnetometers, but I didn’t have the tooling required to machine the part.
I think either approach should work.
Another way to kill the motion is to bring a magnet 🧲 in on the zero line so that the sensor aligns to it, then withdraw the magnet exactly along the zero line so that it’s influence gets weaker and weaker. When it’s removed completely the sensor magnet will be it it’s zero position.
Let me know what you think about these these options. I encourage you to experiment with low viscosity fluids. I suspect that they would prove quite suitable for this application as it should be easy, with the relatively large sensor area to achieve critical damping.
@@citizenscientistsworkshop1948 I think I'll give the fluid a try to start with. I'm 3D printing my enclosure, so it won't be much of a trick to keep it sealed. I'm thinking something like isopropyl? I don't want to weaken the nylon. Incidentally, working with single strands of nylon is incredibly challenging. I managed to get down to a few strands, but could not separate out a single one. It's just too thin. I don't think it makes much difference, though.
The eddy currents idea is very attractive, though, because it would let me explore that regime. I have a friend with a CNC that can machine channels in copper-clad printed circuit board, so maybe at some point I'll give that a try too. Do you think this idea would also serve to dampen the vibrational mode you use the q-tip to dampen in your video?
@@citizenscientistsworkshop1948 I've done some research on low viscosity liquids, and am having a hard time coming up with one that's not toxic, corrosive, explosive, or some combination thereof! The eddy current dampening is sounding better to me. In fact, I just taped a prototype to the back of my prototype enclosure (maybe a half inch away from the magnets) and that improved the dampening time quite considerably. No doubt a fluid would really do better, but unless I can find one that is relatively safe to have sitting around the house, I'll probably go with copper. Thoughts?
@@tdstone4s Why not use water with a dash of dash of sodium metabisulfite, potassium metabisulfite or idorophore? The first two chemicals are used to sanitize wine making equipment, and the latter is and iodine-based compound that is used in the medical industry. I think all three are stable and that they should prevent biofouling over fairly long times. Concentrations needed to kill microbes are not dangerous to humans, which is why these chemicals are used in these industries.
I’m glad to hear that eddy current damping is an option for you. Since you are printing your own housing, you can create one that has little clearance for the motion of the magnets. Then you can place the copper on the outer surface. Ideally, you’d like to have the long magnets pass through a channel that’s cut in the copper. Such a device might come close to being critically damped.