You're not the only one!
I finished rewinding the motor the day before yesterday, so here it is ready to varnish:
Checked the back-emf constant was correct by spinning it in the lathe and measuring the peak voltage with oscilloscope. Then powered a small light bulb with it for general amusement...
I tested the motor with my driver last night, just open loop control - will post a video if anyone's interested.
I started a job at university yesterday, so progress will be slower for now. I'll instead concentrate on finishing off the motor driver design and making them.
A setscrew works by applying a force which results in a contact force between the opposite side of the shaft and bore. Based on the tightening torque of the setscrew, we can calculate this force and if the co-efficient of friction between the shaft and bore is known, the holding torque can be determined - approximately of course.
For one screw it's very simple - the axial force on the screw is equal to the contact force (C) between the shaft and bore, so:
The motor shaft diameter is 12mm, we can fit M5 grubscrews, they're black and according to this list the tightening torque is about 4.7Nm, so substitute that lot in:
With multiple screws, we have to resolve the forces to find the effective contact force. Define the angle as the angle between the two screws, then resolve the force on one screw in the radial direction and double it to get the radial force for both screws:
I put the screws spaced at 90° because it makes milling the flats on the shaft easier, but this formula shows that the smaller the angle between the screws, the greater the holding torque, so 60° would have been better. For 90° that reduces to , so now we have . That torque is a little greater than the motor rating, but shock loads could impose much higher torques so I added another two screws further along the shaft to double the load capacity.
Some pictures I forgot to post of testing the motor:
Last edited by Jonathan; 14-07-2014 at 07:38 PM. Reason: Missing attachments
A week ago I made some progress with the power drawbar in preparation for the ATC system, here's a quick video to demonstrate:
More to follow in a couple of weeks, other projects getting in the way...
The Following User Says Thank You to Jonathan For This Useful Post:
I got the ATC working this weekend - at least in principle:
I've made quite a few parts for the carousel etc, but they're all quite simple so it didn't take long. There's a few issues I've mentioned in the video - the main things are to add sensors, change the coupling between the carousel and gearbox for something stiffer and check the clamping torque upon the toolholder. It's currently just controlled using a few lines of gcode - the air solenoids are currently controlled from LinuxCNC via relays just using the M64/M65 commands and delays. When I've got time I'll do it properly, so sensors are checked at each stage (using M66) to avoid mishaps.
Looking good, it will be interesting to see it working under real load conditions but it looks like a first on this forum.
Well done. ..Clive
Now that's porn,16 tools..it looks smart..i vaguely remember you mentioning mesa/pico hardware for this mill,did you bother.
will the turret be bidirectional and take the shortest route to the next tool or..not that it matters it seems quick enough.
Originally Posted by diesel
Originally Posted by diesel
Yes - that shouldn't be a problem. I've currently tuned the carousel motor to run with quite low top speed and very low acceleration as the low stiffness of the coupling means it oscillates too much if I run it faster, so it will certainly be quick enough when that's fixed.
Believe it or not, I found some time to work on this project again!
Decided I should do some sort of drawings for the X & Y axes, so here's the rough idea. I say rough as most of these parts are just blocks to show the general arrangement of things - I've not added detail:
The X axis uses a bed from a different machine. I'm adding HSR35-1100mm rails to this and SHS25 rails to Y. These rails sizes are based on what I've got good deals on. For the ballscrews I'll be buying TBI DFU ballscrews, similar to Z, sized to get a reasonable stiffness for each axis.
As a 'first pass' look at it, I've tabulated the stiffnesses of each component, then combined these (as springs in series) to get a value for the stiffness of each axis:
This implies that the stiffness is dominated by that of the ballscrews, as these are by far the smallest numbers in the table, so it is worthwhile to invest more in 'large' ballscrews as improving these should have the biggest effect on the overall stiffness of the axis. For the table above I've calculated the stiffness's based on DFU2005 on X and Y, with angular contact bearings on both ends of the X-ballscrew, to compensate for the lower stiffness of such a long ballscrew.
This analysis is still too basic though, as it assumes the forces are all applied at the respective axis center of stiffness, since moments aren't considered, so I need to re-calculate including the 'pitch' and 'roll' stiffness of each axis. If this shows that the ballscrew stiffness is still significantly lower than the linear bearing stiffness, then I'll consider using even bigger ballscrews.
So far I've started machining the bed and steel spacer strips to mount the rails, that's about it...
So today, I got from this:
Via lots of this:
To this (cute little HGH15 bearing is for scale):
Next job is to drill and tap more holes than I care to count in the bed, which I can barely lift as it weighs more than me, so that's going to be fun... then I'll make the aluminium plates which fix on the steel strips that poke out of either end. Finally, I plan to get both sides of the bed surface ground so that the rails have a nice accurate surface to mount upon.
I also started drawing how I plan to mount the X-axis ballscrew drive end:
Last edited by Jonathan; 02-01-2016 at 02:32 AM.
Fantastic build Johnathan, thanks for posting, always get very envious looking @ your projects.
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