Topics created by EdChamberlain

@dc42 said in Is it possible to put 3 motors on one driver?:

@Phaedrux said in Is it possible to put 3 motors on one driver?:

With independent motors you've got to get them in sync constantly after the fact and with only a single drive that's not exactly trivial either.

Not trivial, but here is how you could do it. Use the mechanism here
https://duet3d.dozuki.com/Wiki/Using_the_manual_bed_levelling_assistant but set the screw pitch parameter to be the amount of Z movement per 4 full steps. Run it, then reduce the Z motor current, round the suggested corrections to the nearest integer and turn the leadscrews by hand that number of motor clicks.

RRF 3.01 may keep the motors better in sync through power cycles than older firmware.

Of course! That's clever.

It's already supported in RRF3. You need to use M308 to configure a sensor that uses the thermistor, then specify that sensor to provide the temperature compensation in G31.

There is also this that may be usefull https://duet3d.dozuki.com/Wiki/Gcode#Section_M675_Find_center_of_cavity

To add some maths to what @T3P3Tony said above.

Assuming 1.8 degree motors and 20 tooth pulleys we have:

120,000 steps per second limit.

Full steps per rev @1.8 deg per step =200.
So using 16X micro-stepping we have (200x16) = 3200 micro steps per rev.
So dividing the pulse limit by the steps per rev we get (120,000/3200) = 37.5 revs/second
A 20 tooth pulley using 2mm pitch belts gives us (20x2) = 40mm of belt movement.
So maximum belt speed becomes (40 x 37.5) = 1500 mm/second.
But belt travel does not correspond to axis travel on a coreXY - I'm a little rusty here but I believe it's a factor of 1.4(ish) so max axis speed would be (1500/1,4) = 1,071 mm/sec.

So somewhere around 1,000 mm/sec axis speed but anything which increases the steps per mm will reduce this. e.g. 0.9 degree motors will halve it and 16 tooth pulleys instead of 20 will reduce it by about 20%. Worse case 0.9 degree motors and 16 tooth pulleys comes out at about 600/1.4 = 428mm/sec axis speed at 16x micro-stepping.

Edit. Going back to the OP and the question of gearing:
If it helps I'm throwing around about 1.5Kgs on each of my XY gantries without any gearing. I use 1,000mm/s^2 accelerations but can go higher and my default non-print move speed is 350mm/sec. So unless the motors are very small and/or the moving mass is more than 1.5Kgs, it is unlikely that gearing would be necessary or advantageous.

@edchamberlain said in Duet wifi 24 V short - Ethernet Module VERY hot.:

@voodoobane Youre Right! I forgot to flash the firmware to the wifi board (Doh!). Have done that now and can confirm after forgetting my wifi password a few times it is now working! I can accsess the DWC and will now assume it is fully working.

Your welcome! I didn't think it was be that easy you know? hahaha I am really you glad you got it working!

@EdChamberlain and @dc42 - I've been back at researching this variable arm-length delta format and have found that it's called a tripod or hexapod-tripod. LinuxCNC and MachineKit (a variant of LinuxCNC) call the kinematics for it "tripodkins".

See: https://github.com/LinuxCNC/linuxcnc/blob/master/src/emc/kinematics/tripodkins.c

I've also located a video of a proof-of-concept model on YouTube
https://www.youtube.com/watch?v=LJYhz5aTMnA

I'm still very-much interested in building this one.

Any thoughts?
Thanks,
Todd.