Has anyone used G Penny Nema 34s?


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Thread: Has anyone used G Penny Nema 34s?

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    Default Has anyone used G Penny Nema 34s?

    I've bought a G Penny spindle and am stoked with it. Super good for price.

    I see they are selling a Nema 34 closed loop 8.5nm steppers for cheap ie approx US$110.

    Has anyone used a G Penny stepper before?

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    Default Re: Has anyone used G Penny Nema 34s?

    It sounds like we have a similar shopping list. It was recommended to me to get 3-phase stepper motors / drive as they are significantly smoother and have a wider torque curve.

    I am considering either Jichuan or JMC. JMC is less expensive.



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    Default Re: Has anyone used G Penny Nema 34s?

    I was wondering if this is the time to switch over to servos. I'm not looking for the cheapest Nema 34s but more the best option for money. The ones I am looking at are some closed loop 6A with the standard stepper torque curve.

    I am in a slight problem as I have spent quite a bit of money on this machine the last 12 months. These Nema 34s are only US$375 for 3 delivered.

    I am also not sure if upgrading to Servos is going to be needed? Like I would never run my screws at a high rpm. Tbh I should research them I actually know very little.

    Which models exactly are you looking at?

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    Default Re: Has anyone used G Penny Nema 34s?

    I'll repeat what I was told recently. This made me decide to go for the 3-phase steppers (plus more cash for spending on an ATC setup) it's a bit long but worth reading. Thanks to Dean / JazzCNC on the mycnc.com forum.

    Quote Originally Posted by JazzCNC
    Servo's are lovely things when they are set up correctly, they are super smooth, powerful, and fast. But they are a bit like high-performance engines, where they need careful tuning and the slightest changes can cause them to drop in performance.

    Like resonance.? They are actually more affected by resonance than steppers but in different ways, well it's more vibrations/backlash than resonance.
    For instance, rack n pinion drives and belt drive systems can make setting up a servo a nightmare. The tuning software works great on a direct drive system where the motors are nicely coupled with stiff very ridged couplings which have good dampening but when it as to deal with systems that have a little more flex in them they get confused very easily.

    This is because the encoders are so accurate they detect even the slightest amount of movement/backlash so the software tries and often fails to tune it out, so you need to do it manually and this again can be a nightmare as it overshoots or undershoots position. This gets compounded even more on a machine like your wanting to build that will have long ball-screws which by their very length and nature cause vibrations by the whip effect at higher feeds and are heavy with high inertia which the servo as to deal with.

    Servo's are not like steppers where they move a certain number of steps instantly settle, A Servo is never settled at a position, it's constantly moving back n forth trying to find the commanded position. It's tuning this settling time along with a few other settings which make it hard and even the tiniest of slop in the system affects the tuning and performance difficulty.

    So because of all these different things which can and DO affect tuning servos then I would only fit GOOD QUALITY servos like Yaskawa, Mitsubishi, Panasonic, etc which have very good tuning software and features built into the drives to help deal with all the factors which affect tuning.

    Oh, then you have electrical noise to deal with.? Servo's are very unforgiving of poor wiring practices or low-quality cables, etc, the effects of noise on a servo can range from just twitching the motor a little to it completely ****ing off at full RPM if it hits the encoders hard. Scary **** when it happens.!!
    So Again on a big machine with long cable runs, this becomes a factor you have to be aware of and quality shielded cables don't come cheap.

    This is why I said at the start "What you want from the machine" because if you want a High-performance sports car and are prepared to pay the price and keep up with the tuning then go for it because servos are awsome things when done right.

    But if you want something that just gets the job done and works tirelessly with minimal fuss then Closed-loop steppers do the job perfectly fine.

    One other thing to bear in mind as well before going taking the servos route.? If you are chasing speed/power they offer for cutting purposes other than smoothness then a Sub £2K spindle might not do the job.




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    Default Re: Has anyone used G Penny Nema 34s?

    Ok interesting read. Personally my experience has been steppers, followed by closed loop steppers. Currently using Nema 24s, of "P" grade (apparently the best.... ha). Anyway. These 24s are pushing a couple of 2510 screws at about 2300mm long. And everything is about 95%. I can easily get quite a quick gantry on positioning moves and have been trying some higher speed cutting at 2000mm min without any issues at all. I do occasionally have one stall on the very first start - kind of they don't like being cold which is weird.

    So as for speed and accuracy, this machine is great. Cutting alloy the parts are of a good finish for a large bed router. Good work holding is key for this I have found along with a really rigid machine.

    Back to my reason though, is the mass of the 25mm screws is causing just a tiny bit too much inertia for the 24s. They at the end of each direction have begun bumping a few steps after a stop. And they have only just started doing it immediately after installing the larger ballscrews. These were originally 1605. Well this is my guess.

    I think I am going to stay with steppers. I feel to get the same or better performance I would need to spend a lot more? And I don't really need anything better. But I do also keep myself open to other ideas?

    Oh. I wouldn't mind cleaning up my radius cuts a bit but think it's not hardware.

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    Default Re: Has anyone used G Penny Nema 34s?

    Hi,
    my experience is largely with 5 phase Vexta steppers with a low lash 10:1 planetary gearbox driven by Vexta direct off-line drivers. They have been great.
    They spin at 2400 rpm no trouble courtesy of the 150VDC drive. Through the reduction gearbox the output shaft is only 240 rpm though. None the less I have been
    using them on my mini-mill direct coupled to 20mm ballscrews for six years.

    I'm building a new mill, much bigger, more rigid, faster and way more powerful. For this purpose I have bought three 750W B2 series (160,000 cpr encoder, 34 size) Delta servos/drives/cables.
    They eat ANY stepper ever made. I have the servos direct coupled to 32mm diameter ballscrews and they can accelerate the screw and 100 kg plus axis to 25m/min in
    under 20ms....without using overload, that is to say using rated torque only. The performance gain over steppers is truly spectacular.

    Delta is a Taiwanese brand made in China. They are good quality with good support, excellent documentation and very good PC based set-up and tuning software
    at very reasonable prices. Reasonable is still not cheap......a 750W B2 series Delta servo, drive and 3m cables cost you $438USD plus shipping. So you can get great
    performance but they are still a premium over steppers. The price gap between the best steppers and good servos has narrowed over the years but servos are still more.

    Craig



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    Default Re: Has anyone used G Penny Nema 34s?

    Craig thats some nice performance. Do you have or are you going to run a build log? Although if you're like me you will be more about building than recording. But it would be nice to see your project when it's running.

    Your planetary gearbox will be generating a considerable amount of torque huh. I've only worked with a few myself they took 44000rpm down to 1380(approx) in a different industry.



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    Default Re: Has anyone used G Penny Nema 34s?

    Hi,
    Do you have or are you going to run a build log?
    I have posted a few pics of components as they have arrived and a few of progress to date....but not many recently. You are right....I tend to build and not worry about documenting
    the process.

    I am using two 32mm steel plates in an 'L' shape with the legs 1200 mm and 1600 mm long and 150 mm wide for the C frame. They weigh 98 kg each and I was lunking them around to mark them out
    and hurt my back. Lost a day off work and quite a few more days where I was very uncomfortable. I have taken a break for a month or so to give my back a chance to heal, aside from which I've got
    work (paying) coming out my ears.....and really struggling just to keep up.

    Your planetary gearbox will be generating a considerable amount of torque huh.
    Yes the planetary gearboxes are great. The steppers are 23 size and only about 80 oz.in, but through the gearbox the output is 705oz.in. Direct coupled to 20mm 5mm pitch screws
    results in stall thrusts well in excess of 1500kgf. Of course there is no such thing as a free lunch, I have the ballscrews tuned to 240rpm max which results in G0 rapids of only 1200mm/min.
    Given the axis travels are only 180mm on my mini-mill the slow rapids are not overly tedious. My new mill will have travels of 350mm and G0 rapids of 25m/min......a big step up in speed.

    The servos have rated torque of 2.4Nm ( 7.1Nm overload). Direct coupled to 32mm 5mm pitch screws, neglecting ballnut drag, results in continuous stall thrust of:

    (2.4/ 0.016) =150 N acting at 16mm radius
    screw mechanical advantage = (32 x PI)/5 =20.1

    Thrust (at 2.4Nm applied)= 150 x 20.1 =3015.4N or approx 300kgf.
    Using overload torque the stall thrust is 900kgf.

    Craig



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    Default Re: Has anyone used G Penny Nema 34s?

    Hi,
    sorry have mis-represnted the stall force of the stepper/gearbox/ballscew combo, it should be 480kgf or about 1000lbf.

    I had 1500kgf stuck in my brain because that is the force that applies in a crash situation.....and for a small machine is scary.

    Craig



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Has anyone used G Penny Nema 34s?

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Has anyone used G Penny Nema 34s?