Dual Drive Setup (Dual Motor)

discussion of design changes / improvements / suggestions
Aaron Seltzer
Posts: 46
Joined: Tue Apr 10, 2012 4:33 am

Dual Drive Setup (Dual Motor)

Post by Aaron Seltzer » Sun Apr 15, 2012 8:34 pm

On the old Forum Edward was discussing his dual drive set up, driving two motors from the same driver.

On this forum, the drive shaft concept has survived, but not the dual motor one.

I think I am going to build mine with the dual motors, but can't seem to find a parts list for the additional parts needed.

Based on the prior discussions, there was two ways to route the belt, basically the default Shapeoko way and a new way using only one idler. I would be interested in the parts list for both, and a relative merits of each routing method.

Also wondering if Inventables was considering this as an option, and if they were considering a spare parts kit for the Shapeoko. (Who out there would be interested in that convienece?)

sea2stars
Posts: 93
Joined: Mon Apr 09, 2012 9:54 pm
Location: Cromwell, CT

Re: Dual Drive Setup (Dual Motor)

Post by sea2stars » Mon Apr 16, 2012 1:12 am

The info you're looking for was on the blog I think. You'd need 2 extra idlers, extra belting, another timing pulley, and extra belt clamps.

Now that the Makerslide offering on Inventables has gone past the 500 piece quota, they should be offering additional Makerslide components. For your needs, you'd only need to order the idlers; everything else could be sourced elsewhere.

It probably wouldn't be a bad idea to pick up some replacement components though.

Jim

JCPhlux
Posts: 124
Joined: Tue Apr 10, 2012 2:31 pm
Location: Dallas, Texas
Contact:

Re: Dual Drive Setup (Dual Motor)

Post by JCPhlux » Mon Apr 16, 2012 1:31 am

I thought there was a experimental design Edward was working with that reduces the needed Items thus giving spare parts for the other half. Edward what was the final design on the new design.
--
John R Cutburth II
Twitter @JohnCutburth

nogthree
Posts: 62
Joined: Mon Apr 09, 2012 8:48 pm
Location: Brisbane, Australia
Contact:

Re: Dual Drive Setup (Dual Motor)

Post by nogthree » Mon Apr 16, 2012 3:19 am

If you look at the driveshaft post (http://shapeoko.com/forum/viewtopic.php?f=11&t=6) there's a picture of the new idler setup. Aside from that, there's the post with his frankenoko which included this image:

Image (http://shapeoko.googlegroups.com/attach ... rt=4&hl=en)

The original post is viewable at the web copy of the email thread at http://groups.google.com/group/shapeoko ... a4ec211d0/
- Brendan Halliday.
ShapeOko Wiki Userpage

pourcirm
Posts: 44
Joined: Mon Apr 09, 2012 6:25 pm
Location: Saint Louis, MO
Contact:

Re: Dual Drive Setup (Dual Motor)

Post by pourcirm » Mon Apr 16, 2012 4:49 am

That image isn't completely right though if I remember correctly. What I mean by that is Edward mentioned that the rear section of the belting was interfering with the V-wheel. To solve this problem I'm pretty sure he said that he had to keep the rear section of the belting elevated in the original clamp position. You can see in the attached image that the belting makes more of a "Z" shape if that makes sense.
It ended up that the belt coming off the top of the pulley (heading towards the back of the machine) rubbed against the rear v-wheel. To remedy that I just used the regular belt anchor system to raise the belt up.
- Edward
edwards_test_rig.jpg
edwards_test_rig.jpg (305.63 KiB) Viewed 4110 times

Aaron Seltzer
Posts: 46
Joined: Tue Apr 10, 2012 4:33 am

Re: Dual Drive Setup (Dual Motor)

Post by Aaron Seltzer » Sat Apr 28, 2012 1:02 pm

Hmmm, I recall from the old forum that Edward wired his two motors in parallel. Each getting the same voltage, but half the current from his single driver.

Is that the correct way to share a driver (if you are going to) or would it be preferable to wire them in series, where they get the same current but at 12v instead of 24v.

I know many people are concerned about sharing a driver, and possible racking of the carriage but Edward seemed to find benefit from this setup.

calica
Posts: 107
Joined: Wed Apr 11, 2012 8:13 am

Re: Dual Drive Setup (Dual Motor)

Post by calica » Sun Apr 29, 2012 7:21 am

My understanding is as follows (easily wrong):

Wiring the motors in series keeps the current the same but halves the voltages. This keeps torque but reduces max speed. Because there are now two motors torque is effectively doubled. I don't think speed(voltage)= is linear.

Wiring the motors in parallel keeps the voltage but halves the current. This keeps speed but reduces torque. I don't think torque(current)= is linear either.

Mendel derived repraps drive two steppers for the Z axis. The current recommendation (for repraps) is series. The Z can be slow because its only used to move to the next layer.

orcinus
Posts: 21
Joined: Wed Apr 25, 2012 8:23 pm

Re: Dual Drive Setup (Dual Motor)

Post by orcinus » Sun Apr 29, 2012 1:14 pm

Voltage has nothing to do with speed in this case (at least as far as i know).
Speed of a stepper is governed by the frequency - the speed at which the phases are switched (energized in an alternating fashion).

Voltage does affect the torque, though (as does the current).
I guess it also affects the maximum speed at which torque is still acceptable (although that probably depends on current as well).

calica
Posts: 107
Joined: Wed Apr 11, 2012 8:13 am

Re: Dual Drive Setup (Dual Motor)

Post by calica » Sun Apr 29, 2012 8:46 pm

orcinus wrote:Voltage has nothing to do with speed in this case (at least as far as i know).
Speed of a stepper is governed by the frequency - the speed at which the phases are switched (energized in an alternating fashion).
You can't just increase frequency forever. Stepper motors have a mid-band instability (aka resonance) which limit speed. Increasing voltage moves torque-speed curve out allowing greater speed. Some drivers (like the geckos) can compensate for the resonance (by adjusting voltage-current phase) allow much higher speed.
Voltage does affect the torque, though (as does the current).
I guess it also affects the maximum speed at which torque is still acceptable (although that probably depends on current as well).
Stepper drivers limit current. Look at the specs for the 400 step Sparkfun NEMA17 steppers. They're only rated for 3V. That rating is for a non-limited current drive (like a simple h-bridge). For a current limited drive, motor inductance is the key stat. Vmax = 32 * L.

Gecko has a really good guide to motor theory. Gecko has an amazing reputation on cnczone. I don't have experience with them but plan on using them when I cnc a G0704.

orcinus
Posts: 21
Joined: Wed Apr 25, 2012 8:23 pm

Re: Dual Drive Setup (Dual Motor)

Post by orcinus » Sun Apr 29, 2012 10:04 pm

calica wrote: You can't just increase frequency forever. Stepper motors have a mid-band instability (aka resonance) which limit speed. Increasing voltage moves torque-speed curve out allowing greater speed.
That is what i've said, albeit not that clearly.
My point being that lowering the voltage, while keeping the current (series) won't get you same torque and lower speed. It will result in somewhat lower torque and lower *maximum* speed.

Didn't know about geckos and vector control, though. Thanks for that, nice to know they have it.

Post Reply