Quote:
I have personally exploded a GT3-127T-12 GRN pulley spinning at 12,000RPM and stopping it and switched to the bullet-proof KRP pulley because I was concerned the size and weight of the aluminum pulley might distort it's shape permanently.
Then you designed it wrong. Plain and simple. No doubt about it. No argument can be made otherwise.
Quote:
I'm not denying that the GT2/GT3 is a better profile over the XL and definitely quieter at low RPM over the HTD and seem suitable for spindle driving up to 2.2KW where low mass/inertia are present but it's high mass/inertia that are belt killers.
No matter how much mass or inertia there is, if the motor cannot supply the torque to exceed the belt or the pulley capabilities then they won't break.
Quote:
In post #98 you state that aluminum pulleys are the norm and now you state that the posts here commonly use aluminum pulleys and this may be so but it doens't make it the industry norm, just the norm here, if you really want to split hairs, this is 100% incorrect as the majority of the machines I see on a daily basis are employing composite (GRN - glass reinforced nylon or KRP - kevlar reinforced polypropylene) pulleys but in reality, direct drive is the norm and I have yet to see a composite pulley fail before it's aluminum twin when used with 4,000RPM MAX servo motors.
Well lets see. We are in a thread about a low cost servo drive for hobbyists using hobby motors and being discussed by hobbyists. I think most everyone would figure that the posts were in relation to hobbyists and not in relation to industry.
Quote:
One of the links in his (macdowswe) post to hobby-king is for an SK3 6374-149kv, with a max voltage of 70VDC and the SK3 4250-350kv you point to has a max voltage of 19VDC, of course people overdrive these motors without thought or really understanding it's intended electrical design but I wouldn't advise or recommend it, I'd find a 24V BLDC motor and operate it at 24V.
Also, ODrive wont handle this current requirement as some other real time tests are reporting the motor is a gutless wonder if the current is restricted or limited and that it doesn't start to generate any power when the current is below 15A and this 1007W (not 1190W as advertised) is input power, since the motor is only 66% efficient output power is only 671W, 19V@53A and you think 24V@6A using ODrive to power it is going to fly?
Let me ask you what machine you think I am intending to use this on? I don't think I mentioned it, so you can't possibly look only at the motor specs and say with any intelligence whether it is or is not suitable. You can spout all the numbers you want but without knowing anything but motor parameters you are only blowing smoke.
Quote:
My china clone 6364-250kv hits 6,100RPM at 24V and draws 6A (noload) and peaks at 19A and gives 310W of output, this is almost suitable if it weren't for the peak current, the required forced-air cooling and the > $80.00 price tag.
Don't really care what you think is or isn't a good value. If I want to spend my money on something that you don't think is a good value, that is my choice.
Quote:
Out runner as a spindle motors is another example, I wont go into how wrong it is for the general hobbyist to make a AIO spindle from an out-runner motor without decent plans to follow or some serious knowledge in spindle loading forces and design criteria but they do it just the same.
I get a kick out of those that make a body, drop in a couple of cheap multi-purpose deep groove bearings and an ER16 or ER20 collet head and think they've got a MAC-DADDY spindle, only the smart guys will use a dual row angular contact bearing in the nose of the spindle for bi-directional thrust forces because they expect the thing to stand up to the abusive forces of cutting without eating the bearings or living more than 3 months.
Another useless diversion from the topic of this thread. Why are you discussing spindles.
Quote:
I've not applied my criteria to anyone else, I simply state if you have weight to move, small skinny belts are unwise to employ and you refuse to acknowledge this making claims that the belt wont stretch or break and this is unrealistic and hilarious.
Tell you what. You tell me how much a 15 mm wide GT3 belt drive will stretch and how much it will affect precision on an unknown machine with unknown mass, unknown inertia, and unknown desired performance..
You are basically saying that belt stretch will be too much without knowing anything about the end product and applying how you want your machines to work to everyone else.
Quote:
Because some yahoo has BT2-15 belts on his RF45 doesn't mean much if his acceleration/deceleration curves are so mild that the ramp-up/ramp-down speed prevent the motion from achieving >100IPM for a movement of less than 4in or ever moving faster than 200IPM.
The table travel is small, it's a dovetail machine and with the gibs tightened down it probably helps control runaway inertia by restricting movement and the table only weighs 47lbs but I couldn't call it a good quality machine that's prime for a CNC conversion without doing some serious reworking and dumping the dovetails for some unrestricted linear motion capabilities which very few do.
I've never seen an RF45 or even an RF45N2F (it has a larger table) move at more than 200IPM rapids and never cutting (a serious cut like 0.250in with a 1/2in, not a .025in pass with a 1/4in end mill) above 50IPM without noticing head deflection so it's not in my opinion a reasonable example of a real machine, it's a large toy.
Didn't you just say you just state that you don't apply your criteria to anyone else? Re-read the above snippet, particularly this part.
Quote:
but I couldn't call it a good quality machine that's prime for a CNC conversion without doing some serious reworking and dumping the dovetails for some unrestricted linear motion capabilities which very few do.
and this one too
Quote:
so it's not in my opinion a reasonable example of a real machine, it's a large toy.
That sure seems like applying YOUR criteria to me. Many people chose RF-45 type machines and other benchtop mills for conversion and are very happy with them FOR THEIR PURPOSES. Not for YOUR purposes.
Quote:
Oh, again my mistake, when I say REAL machine, I am referring to a smaller version of a REAL larger machine such as a CadetMate 6030 or CadetMate 7040 where the only different is the physical size of the machine.
So despite all your bickering, your choice of a new (click to buy) BLDC motor, aluminum to make a new body, new bearings from VXB, 4150 steel for a new shaft, a new encoder from a source with an endless supply for others to buy them, a new fan, connectors and terminals of appropriate size and current rating, hardware to assemble it will cost more than I can produce a 48V or 60V 500W servo motor with a 2500PPR quadrature encoder that wont have any heat issues or require any external cooling.
Lets see some more application of your criteria.
First, apparently the only REAL machines are machines that match your idea of performance, that being performance equal to an industrial VMC with only smaller work envelope.
Now about the motor in question:
Aluminum to make a new body - Why? I see no reason to for MY potential application. A new body is YOUR criteria
new bearings from VXB - Why? I see no reason for new bearings until the ones it comes with start to go. YOUR criteria again.
4150 steel for a new shaft - I see no reason for a new shaft for the motor. YOUR criteria again.
a new encoder from a source with an endless supply for others to buy them - Umm what the hell is this. Any servo is going to need an encoder - Red herring
a new fan - I have a box of surplus fans that will work fine. A new fan is YOUR criteria again.
connectors and terminals of appropriate size and current rating - Once again, any motor is going to need these. Red herring
Quote:
it will cost more than I can produce a 48V or 60V 500W servo motor with a 2500PPR quadrature encoder that wont have any heat issues or require any external cooling
And you are going to sell these to everyone? Your can produce it, but others can't, so this is again YOUR criteria. BTW, this is the ODrive thread, so you might want to consider a 24V motor since the ODrive has a 24V bus. Your 48V or 60V motors might under-perform
Quote:
Oh, I've got a novel idea, why don't you create a kit and sell it to the users here, I'm sure they would be happy to buy your parts and buy the hobbyking motor and assemble it themselves as a cheap solution.
I've got a novel idea. If you approach is so much better why don't YOU put together a kit of your motor and sell it to everyone as the cheaper solution. When you do this then the above comment might bear some weight. Until then it is a hot air.
Quote:
I've ordered your 4250-350kv motor from hobbyking, when it arrives I'll connect it to my dyno and can then better comment on it but I doubt it's going to provide any eye opening results.
Now if you want to talk about spindles, your 4250-350kv wont cut it as a spindle motor if you need some serious power with RPM, with the help of a friend I've made my own 0-12,000RPM 220V 3-PH asynchronous servo spindle motor with an output rating of 3HP in a really small size (90mm x 90mm x 260mm) belt driving a BT20 ATC spindle and while cheaper than purchasing a commercial product, if you don't have access to precision lathes and mills and balancing equipment to do the work I wouldn't recommend it (you can have it balanced at a electric motor repair shop if you can do everything else) and I have yet to see a BLDC solution that can come close for the same or less money and nothing in a small size that doesn't have heat issues.
I don't want to talk about spindles. I want to talk about servo drives in a servo drive thread, so I could care less.
Quote:
Because someone does a CNC conversion on a machine such as an RF45, it doesn't mean a whole lot when in the conversion process they plan to create limitation in movement speed to save a buck, you only see people posting about their builds if they're either doing it right or doing it cheap.
You can't have it both ways if you expect it to be duplicated by another person (because you have motors doesn't make it cheap for the next guy who doesn't) and people tend to follow the most successful build they can afford to follow, replacing the leadscrews and dovetails with linear rails and precision ground ballscrews on an RF45 is the correct way to do it but it sure isn't the cheap way to do it.
More application of YOUR criteria. What you are discussing is a trade study. If a person limits performance to save money does not mean their build is invalid. Maybe to you it is, but you aren't everyone and your criteria isn't everyones.
Quote:
replacing the leadscrews and dovetails with linear rails and precision ground ballscrews on an RF45 is the correct way to do it but it sure isn't the cheap way to do it.
By YOUR criteria it is the right way. Someone else may say that dovetails an rolled ballscrews are good enough for what they want to do with the mill, and that decision would be the right way to do it.
Quote:
Now ODrive is being created to support single ended encoder signals and there is a difference between transistor and transmitter outputs and even with transistor outputs there are two types, NPN (most common) and PNP and they respond differently, personally I prefer a quadrature differential line transmission type but as long as a dependable source for the specified encoder (new) is provided I have no issues using it but encoder flexibility is currently limited to single ended transistor output encoders so making a decent servo motor available at a cheap price with such an encoder isn't a consideration I'd be willing to make.
Now you want to talk about flexibility and how everyone is different and can decide how they want to build things and this is false, this option is nonexistant with respect to encoders and ODrive, people are buying the board, and they can't just connect any encoder because line receivers are not employed and the device is set up and tested with the OP's encoder on hand so flexibility is limited to the type currently employed and tested so now people have no choice in the encoder they can use if they can't make or buy a board that gives them the connections for the encoder in the motors they bought or made.
You must tell them they can use any encoder they want as long as it's a single ended transistor output type.
Everyone can still decide how they want to build things, If ODrive can only use one encoder type then if I want to use ODrive I can use the one type encoder specified, or I could devise a way to use another type or I could choose to not use ODrive. Still a choice. Personally since the encoder that has been tested is a $10 piece, I have made MY decision that this isn't an issue for me. The fact that you don't like this style encoder and think there are better choices is up to you but has absolutely no effect on me.