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nap
Wed 30 December 2009, 11:41
Hi Guys,
I've been reading the forums for a while and I'm ready to start seriously planning a build. I want to start with the kitchen table project and work from there.

Read the selecting motors thread and I've decided on the Motionking 34HS9801 motors with the intent to add belt reduction after it's up and running (making money). Also for cost reasons I'd like to use the Gecko G540. Has anyone used this combination? Feedback would be great.

Thanks,
Neil

Kobus_Joubert
Wed 30 December 2009, 12:25
Welcome Nap. Cannot help you on the G540, but I am very happy with the performance of the Motinking steppers. For the work that I do I don't need gearboxes at the moment.

bradm
Wed 30 December 2009, 14:14
Welcome, Nap. I'm just a mile or two away in Somerville, and I'm using a G540.

The MotionKing page: http://motionking.com/Products/Hybrid_Stepper_Motors/34HS_Stepper_Motor_86mm_1.8degree.htm says that the 34HS9801 motor exceeds the specifications for the G540. Only the 34HS6803 appears to be a match, and it's very close to the specs on the OM motors (with gearboxes).

If you go with the smaller motor, you'll probably want belt reduction. So you have a cost tradeoff to calculate. You could use the larger MK motors with more expensive individual drivers (and a BOB), or you could use the smaller MK motors with belt reduction and the G540, or you could use the OM geared motors with the G540. You'll want to cost out all the parts in each case; I suspect you'll discover they're closer in overall expense that you might think, at which point you'll need to weigh the advantages or disadvantages of each solution for your intended purposes.

shaper
Wed 30 December 2009, 21:11
Welcome Nap

I'm building based on the same combination that you are considering. My intent though is to go straight to belt drives as I'm not convinced it will be up to the task as a direct drive setup, though maybe I'll try just to answer the question (I wouldn't wait for my answer though I'm a slow builder :)) As brad pointed out the 34HS9801 is not ideally suited to the G540, the reason however that i settled on it is that i plan to upgrade to a new box once I've got my head around the whole thing and have it working, in this case I'll take the current box and use it as the basis for a slightly lighter machine (smaller motors, probably the 34HS6803) which will be built just to cut foam and the upgraded box will use this (http://www.driver-motor.com/ProductContent.aspx?ID=92).

If you are looking for a cheaper option on the drivers there are others out there, at least a couple of examples complete or in the works are using leadshine drivers (either the link above or a similar product from the same manufacturer) still works out more expensive than the G540.

If memory serves there are others out there using this combination, at one stage I had a PM conversation with dragonfinder (dave) about this not sure if he ended up going this way but if they did then they have machines running but again using belt drives.

bradm
Wed 30 December 2009, 21:36
Hey, one more thought to add here. I've been trying to present an unbiased tradeoff, but I realized that I'd failed to mention that the direct drive option with the big motors has three important characteristics: It has the potential to give significantly faster moves (3-7x), although you can only actually use them for positioning (or bragging); cutting at those speeds is impractical, and some of us would consider it pointless. The second characteristic is lower precision by the same factor. This is most likely unimportant for cutting wood, as atmospheric conditions will affect the accuracy more, but it becomes a factor if you are cutting curves in harder materials like plastic or metal. The final characteristic is that you may have lower holding torque than the geared down or belt reduced options, despite the larger motor.

nap
Thu 31 December 2009, 09:18
Thanks everyone for the input so far.

Per the advice I've gone back over the motor / driver combinations and tried to put a cost to all the different scenarios. Brad as you said all the combinations are close in cost except the smaller MK motors + G540 + belt reduction this is about 2/3 the cost of the OM + G540.

So my next question is are those smaller MK motors up to cutting plywood cabinet parts all day? I've looked at the specs but I have no frame of reference as this is new to me.

bradm
Thu 31 December 2009, 13:17
Nap, if you would indulge me, where did you price the belts, pulleys, and bearings, and what was your budget estimate? And, hey, you're in Medford, even closer!

nap
Thu 31 December 2009, 14:16
No problem,

Someone the forum offered to sell me the machined aluminum plates and supplied a list of the other parts I would need... total came out to about 300 bucks for all four motors. Parts from http://www.sdp-si.com So...

G540-314 ( includes shipping )
MK 34HS6803 - 300 ( includes shipping from china )
belt reduction - 300

That's under a grand and I just need the power supply and wire/connectors.

To contrast that on the high end of what I looked at the G540 with the OM was $1400

Still more head scratching to do...

bradm
Thu 31 December 2009, 20:59
Okay, since I'm spending your money, Nap, I'll say that with that set of evidence, I think if I had a chance to do it again, I'd take a shot at that belt reduction route. Ya wanna buy my OMs for $1k?

Ooops, so much for avoiding bias :)

I'm totally happy with the performance of my OMs, and at the time I made the choice, belt drives were a lot more experimental for MMs. I took the throw money
at it and not sweat it approach to the motors.

Someday, maybe I'll talk about my experiences building my own drivers for geared BLDC motors in an earlier, failed CNC project. Hint: I'm not as good an electronic designer as Mariss is, and while they worked on the bench, they didn't like real world situations much.