Possible problem with the Dynamotor (and maybe a solution too…)

[David DeCristoforo]

I posted in my last "Monster lathe" update that the Dynamotor was not performing as expected and had, in fact, "ceased to function". I had not done anything that could have been considered to be outside the parameters of "normal use". My expectation when it comes to a motor is that when you flip the switch, the motor should start spinning. Pretty "cut and dried".

At first, this motor was performing in this manner although it seemed to take longer to "spin up" than one would typically expect. The problem appeared when I had mounted a fairly heavy blank on the spindle. Then, the motor would attempt to start but "stall out". I had to give the blank or the spindle a "nudge" to get it spinning. Once the motor came up to speed, it performed well. But apparently a frequent cycle of starting and stopping caused something to fail and the motor eventually refused to spin up, even with the "push start".

When I spoke to the rep at Dynamotor, he was most cooperative and had a new motor shipped out immediately. We had a brief discussion about why the motor might have failed. I am shipping this motor back for them to examine but two theories were proposed. The first is that the motor was faulty or possibly damaged in some way during shipping. Possible but somewhat unlikely. The electronics in this motor are much more delicate than anything found in a more conventional motor.

More likely (and a bit more "ominous") is the lack of sufficient starting torque. These are two pole motors. My understanding of electronics is limited but I do understand that a two pole motor has half the starting torque of the more common four pole motors. Why they decided to make these two pole motors is not something I understand at this point but it may have to do with the technology used to construct the variable speed circuitry. I will find out more…

If the starting torque of the motor is the culprit, these motors would not be the best choice for something like a lathe which, with a large blank mounted, would need the increased starting torque of a four pole motor. The motors might better work for machines that did not need to spin up a heavy load from a dead stop.

If this indeed turns out to be the issue, I would much rather can the whole idea and go with a conventional three phase motor and VFD setup. I think, if my "budget" would allow it, I would go that way in a heartbeat. However, the funds simply do not exist at this point.

Here's what I'm thinking as a "workaround". The motor would need to run continuously and be able to start with little or no load. That would mean some sort of clutch arrangement. So I am letting my brain loose on some kind of "quick release" for the tensioning pulley I rigged up for the main drive belt. That way, the motor could run at speed with the jackshaft turning all the time and I would start and stop the spindle with the "clutch". As I mentioned before, once I had the blank spinning, the motor seemed to have plenty of power. Anyone with an idea of how this might be rigged up is welcome to offer suggestions. I'm thinking it might require a couple of trys to get it to work without being cumbersome.

[Tony Wheeler]

there are two things I can think of off the top of my head. First would to get a longer belt and/or relocate the motor and mount a idler pulley that could be disingauged (sp) with a handle or I don't know if these would handle it or not but you could get a electric clutch from a lawn motor and use it with a swtich like on the mower. I don't know that if this would take the torque or not. But, my mower deck is 60 inches with three large blades so it might be a chance that it would work. I have used the idler pulley set up on a three phase converter that I made for my friends metal lathe. In that case I used a 110 motor to spin the 3 phase motor up to operating speed then give it 220 power and it wi make 3 phase to run the lathe then kick the idler pulley loose and the 3 phase motor run without the assist from the other motor.

[Jamie Donaldson]

I believe you have a motor that is not suited for the application unless some other deficiency is to blame. I would not try to construct a work-around that would be a performance compromise, with potential failure always on the horizon with an expensive repair/replace out of warrantee period motor. In a production situation, the machine should be matched to perform the task requirements, not amending the task to suit the deficiencies of a particular machine.

[Sid Matheny]

The Dynamotor sound a lot like the Nova DVR-XP motor but with some added problems. The DVR-XP is direct drive with the spindle as the rotor. This page gives a little info on the XP setup.
http://www.teknatool.com/products/La...ova%20_DVR.htm

Not that this helps you any but just a thought on my part.

Sid

[Harry Robinette]

I think I would use a starter motor, any motor could get the piece moving then turn-on the main motor and off the starter.
Just a thought.

[Mike Golka]

Maybe an electromagnetic clutch like used on auto airconditioner pumps.

[Phil Harris]

It seems like there should be some kind of centrifical clutch that would engage when an optimum rpm is reached. I know that the motor on my motorhome's generator reaches its operating rpm before it's clutch starts the generator spinning.

[Faust M. Ruggiero]

All good solutions and all potentially throwing good money after bad. Buy the VW. :>)
faust

[Stephen Walker]

David,

If you know anyone who has a gas engine powered chipper/shredder, most of those have the type of engagement mechanism you're talking about. It is simply a moving idler pulley that is controled by a handle on the linkage. I'm thinking a couple of pieces of flat stock and a handful of nuts and bolts and you're there.

Steve

[Dick Strauss]

David,
You might take a look at the foot operated clutch that Del Stubbs used on his lathe featured in his Bowl Turning video.

[David DeCristoforo]

Some interesting thoughts. The idea of an electromagnetic clutch is delicious. But... more technology and more cost. A centrifugal clutch would be simple and cheap but, as far as I can tell they have an engagement speed of 2,000+ RPM which would preclude any low speed options. I have come up with a simple tensioner design that should be cheap and effective.


"...a couple of pieces of flat stock and a handful of nuts and bolts and you're there..."


That's my kind of thinking! I seem to have two possible thought processes. One is to take the "cost is no object" path and refuse to settle for anything less than the ultimate. This is my preferred approach but it only works if you have plenty of money and/or time to throw at it. The other is the "whatever I have that I can make work" line of thinking. That's the one I am on right now.


I should mention that my total investment in this is essentially zero. Almost everything I have used so far was "on hand" and/or 'repurposed" from something else. The main cost would, of course, be the motor and speed controller. But I did not buy this motor. The manufacturer sent it to me for the express purpose of evaluating it's performance in this type of application. They are still developing this product and are very interested in how the motor performs under various conditions. The only way to do that is to put the motors in the hands of people who will try them under "real world" conditions. So I am, in effect part of their R&D effort. This would fall into the category of "field testing".

[Reed Gray]

Just sounds like too much work, and I would not like a motor that doesn't turn off when it is not being put to work. I like the Nova DVR for torque, but not the speed change mechanism. Turning a dial is so much more convenient. I like the 3 phase motors with converters. I do have a Robust Sweet 16 which has a 3 phase motor and a 'vector drive' phase converter. It feels more like the DVR in that I can feel more torque being delivered, and may out torque my Beauty, though I do probably need to replace my belt. My biggest complaint about any lathe I have tried is that I can stall them all when roughing with gouges and scrapers with any bowl over about 10 to 12 inch diameter.

"I am on the Brute Squad."

"You are the Brute Squad!" from The Princess Bride.

robo hippy

[Rick Markham]

Hey maybe the replacement will work just fine. Heck you're Beta testing this thing, and it sounds like the company is interested in getting a working product. I'd let them work the bugs out, it might just be a computer board. I wouldn't change what you are doing David until you HAVE to. (I also understand that you are just thinking ahead) I realize it's frustrating being you want to just turn on that beast you've spent so much time on I'd give them a chance to iron out all the details. They might surprise you in short order! (I'll keep my fingers crossed for you)

[David DeCristoforo]

"...maybe the replacement will work just fine..."

I have not totally discounted the possibility that my motor go dropped on it's head somewhere along the line and one of it's gizoids got knocked out of whack. The main reason I am leaning toward the low starting torque theory is that, at first, the motor worked better but it's performance degraded. It had some trouble spinning up under load pretty much from the outset but I could get it going by "jogging" the blank. After a while, that would no longer get the motor spinning. Finally, it would would kind of toggle back and forth maybe an eighth of a turn and then just stop. It was only at the suggestion of the guy at Dynamotor that I even thought about the starting torque possibly being insufficient. I have worked up a very simple method of easily releasing and tightening the belt tension but I am going to wait and see if it is really needed before I cobble it up.

"I would not like a motor that doesn't turn off when it is not being put to work."

Turning the motor off under load is not an issue. In practice, letting the motor continue to spin when the belt is slackened should not be a problem. This is all assuming that the starting torque turns out to be the problem which, as Rick has pointed out, has yet to be determined.

[Mike Cruz]

DD, not sure what you budget is, but I have a local shop that I'm sure I can get you a used 2 or 3 hp Baldor 1725 rpm 3 phase motor for $75-100. I've bought one of each from the guy, both work great. He'll even change the bearings for $25. And the TECO FM50 is $150 for the 2 hp and $200 for the 3 hp. So, you could get a 2 hp motor (with new bearings) and VFD for $300 plus shipping. Just a thought. Not sure what your idea of cost was for a motor and VFD...