Ah ok, here is a link to the thread
https://www.diyaudio.com/community/threads/diy-4-point-pivoting-arm.375071/
https://www.diyaudio.com/community/threads/diy-4-point-pivoting-arm.375071/
I am about to resurrect this project. I was talking to a friend on Sunday who is a developer and he suggested using a strain gauge sensor and PID to control the carriage. I have dusted off the rail and found an error in the code that was contributing to the noise in the rail.
The unit will have 3DOF vertical and horizontal arm articulation and the carriage sideways movement. However 1DOF will be constrained by the strain gauge (horizontal articulation). The goal is to have the carriage track back and forth with ideally ZERO sidways force on the stylus. My friend has assured me if we get the PID control right then the carriage will move with micrograms force on the stylus. Next to build a rig to test proof of concept.
The unit will have 3DOF vertical and horizontal arm articulation and the carriage sideways movement. However 1DOF will be constrained by the strain gauge (horizontal articulation). The goal is to have the carriage track back and forth with ideally ZERO sidways force on the stylus. My friend has assured me if we get the PID control right then the carriage will move with micrograms force on the stylus. Next to build a rig to test proof of concept.
Martin in Perth (WA) has done (I think) summat similar tho' using a clockwork mechanism
Progress is slow ATM as I have jobs for other people in the workshop. I have ditched the strain gauge idea and will use a photo sensor to drive the carriage. I have done more work on the software which is now much smoother and should step the carriage with finer resolution.
One thing I need to get right is the rail and I'm still deciding if the rail will be overhead or under the carriage. One thing the rail needs to be rigid so the arm mount does not move microscopically. I have some engineering challenges to overcome.
One thing I need to get right is the rail and I'm still deciding if the rail will be overhead or under the carriage. One thing the rail needs to be rigid so the arm mount does not move microscopically. I have some engineering challenges to overcome.
I've finally found a rail setup that is quiet enough at low speed to kick this off again. The lead screw will not make it as it's way too noisy, drive will be via some kind of belt/thread.
I have tweaked the drive code so there is no base speed, the motor now micro steps according to the sensor position, one u step is 0.1mm of carriage movement. There is only maximum speed restriction so if the arm goes x deg off tangent the cue motor activates.
I'm currently building a new SP10 Permalli ground plane plinth that will be setup to mount 2 pivoting arms and this linear tracker.
I still haven't decided on what type of pivoting arm to use. I've decided to build the carriage so I can change arms.
I have tweaked the drive code so there is no base speed, the motor now micro steps according to the sensor position, one u step is 0.1mm of carriage movement. There is only maximum speed restriction so if the arm goes x deg off tangent the cue motor activates.
I'm currently building a new SP10 Permalli ground plane plinth that will be setup to mount 2 pivoting arms and this linear tracker.
I still haven't decided on what type of pivoting arm to use. I've decided to build the carriage so I can change arms.
Yes it will use an optical sensor like the Goldmund so the sensor will be near the headshell, this increases sensitivity.
Here's a mock up on the new SP10 plinth
Yes you can see the photo interrupter in the photo. They are not linear but I think will be good enough for this application especially if I mount it on a secondary arm close to the headshell like Pierre Lurne did.
I was plannig to use a motor like the the Rabco, but now I have the microcontroller controlling everything I might switch to a solenoid this way if power is lost the arm will raise. The cueing switch will also be a photo interrupter so it doesn't matter which way the arm goes off tangent the cue motor will activate.
I was plannig to use a motor like the the Rabco, but now I have the microcontroller controlling everything I might switch to a solenoid this way if power is lost the arm will raise. The cueing switch will also be a photo interrupter so it doesn't matter which way the arm goes off tangent the cue motor will activate.
I just completed the plinth. I'm now working on the LTA. Progress will be slow and steady. From here it's working out the mechanical design of the arm/mount/carriage mounting and how the cue will operate.
A couple of the critical design criteria are good mechanical grounding and a well behaved tonearm wand. I've been doing a lot of mocking up and thinking.
I was leaning back to a split pivot, kind of like the Dynavector TA but my Physics brain is telling me don't do it make the arm wand a standard dual gimbal like the Technics and my current DIY pivoting arm. I have also been considering lowering the vertical pivot to LP level to reduce warp wow. To do this I need to model the ellipsoid of inertia to ensure it's uniform around the stylus.
A couple of the critical design criteria are good mechanical grounding and a well behaved tonearm wand. I've been doing a lot of mocking up and thinking.
I was leaning back to a split pivot, kind of like the Dynavector TA but my Physics brain is telling me don't do it make the arm wand a standard dual gimbal like the Technics and my current DIY pivoting arm. I have also been considering lowering the vertical pivot to LP level to reduce warp wow. To do this I need to model the ellipsoid of inertia to ensure it's uniform around the stylus.