Motor help

Erik Friesen

We have been using these motors - http://www.hobbypartz.com/86ma64-2215-740kv.html

We want quite a few, but with a shortened shaft. Hobbypartz/exceedrc are unable to do this for us. Any ideas out there where we can get an equivalent semi custom motor?

jdolecki

Why cant you cut the shaft yourself?

Use like a dremel tool wheel and it's cutoff wheel.

Just curious.

Erik Friesen

The shaft is hardened steel. It really needs to be removed from the motor, as grinding the shaft creates enough heat to make the bearing questionable. I don't want to do 100 motors this way.

Spiral_72

At $13 apiece, it'd be a shame to spend the money / time getting the motors modified. Is this something you could post a design for? I over think / over complicate things all the time. Maybe there's an alternative to cutting the shaft that another look might help point out. Maybe drill a deeper hole in the connecting part?

I've worked on a few of these. Sometime the shaft is "easily" replaceable; Easily being a term used loosely. This means that you might be able to remove the shaft for cutting, times a hundred of course

Also, if you made a jig from an aluminum block that would clamp and seal the motor away from your cutting operation the aluminum will wick away heat rapidly.... With a jig, that would make your modifications go much faster..... said without knowing the final shaft length you need. It seems reasonable you could cut one a minute like this.... after spending 6hrs making the fixture of course. What I imagine would be based on a shaft support: http://www.mcmaster.com/#shaft-supports/=h4ty44 but 1/8" DIA is pretty small. That sounds like something Stock Drive Products might have: http://www.sdp-si.com/

Erik Friesen

I don't want to post my complete design. Its rather complicated with pretty close tolerances. The shaft would stick outside the enclosure if not cut off.

To remove the shaft, a c clip has to be removed. They apparently use some type of bearing preloader or something, because it is very difficult to get the c clip back in place. I am experimenting with no c clip in place, I am unclear if the bearings need it to operate properly. I am using the face of the motor to drive the magnetic drive for the pump.

erco

+1 to Spiral's suggestion. A quick aluminum jig to clamp around the shaft (and use as a spacer) in a metal cutoff saw (abrasive disk) and you'll make quick work of 100 motors without disassembling or overheating your motor. Free fireworks (sparks) are a bonus.

I'd be surprised if it takes more than 10 minutes to make a jig like that with a chunk of aluminum, a drill press and a bandsaw.

More like 5 minutes. GO!

T Chap

For a 100 systems that is a big hassle to be grinding. Assuming you can in fact remove the shaft and replace it, if it were me I would call MisumiUSA.com and spec the revised shaft, have them in less than 7 days.

Mark_T

Erik Friesen wrote: »

The shaft is hardened steel. It really needs to be removed from the motor, as grinding the shaft creates enough heat to make the bearing questionable. I don't want to do 100 motors this way.

And you can't risk cutting debris getting into the bearing either... Besides the shaft will spin. Usually motor shafts are replaced by pushing them out of the armature with the right tool (apparently this is commonly done with RC electric motors).

In the UK the steel alloy used for shafts is called silver steel. Its a tool-grade steel that can't be easily machined.

Erik Friesen

I can cut it myself. I have done 10 of them, and its a pain. The way I want it is to not have to mess with it. Sigh.. I guess we don't get everything we want.

Fine metal shavings in an unsealed bearing is not good news for a motor that runs 1100 hours a year.

idbruce

Erik

I utilize motors quite often, and I often machine the shafts to some degree, by either shortening the shafts or milling flats for set screws. I would have to agree with some of the other folks and just cut the darn things. For that matter, cut one and test it for an extended period of time to see if the machining procedure caused any problems to the bearing.

As for the machining procedure, here is what I would do just to shorten the shaft.

1. Layout a motor mount from aluminum angle stock with very tight clearances around the shaft to prevent unnecessary debris from entering the motor or bearing surfaces. Additionally make 2 or 4 mounting holes to bolt the motor mount to a work surface.
2. Layout a chuck holder from aluminum angle stock being inline with the center of the motor shaft. The chuck will keep the motor shaft from spinning and act as a heat sink. Additionally make 2 or 4 mounting holes to bolt the chuck holder to a work surface.
3. Attach motor to bolted down motor mount.
4. Attach chuck and chuck holder to motor shaft, shim any slight discrepancies, and fasten chuck holder to the work surface.
5. Cut shaft with a Dremel cutoff.
6. Unfasten chuck holder from work surface and move out of the way.
7. Run motor and dress up cut shaft with an appropriate file, however, hardened shafts will damage a file.

Bruce

EDIT: Additionally, I would make the cut off in several passes to eliminate bearing lubrication breakdown
EDIT: As opposed to a chuck and chuck holder, you could also machine a shaft clamp to act as a heat sink and to keep the shaft from spinning.
EDIT: A little effort put into machining the proper tooling can go a long way into simplifying a tedious and painful task.

erco

One more time: no dremel, that's bush league for 100 cuts. You'll spend more time replacing broken disks than cutting. A shop-grade metal cutoff saw with a thin abrasive wheel is the right tool for the job, clamping the motor shaft in an easily made aluminum jig which sets the cutting length and keeps the small amount of grinding debris out of the motor. A minute per motor or less once you get going.

http://images.search.yahoo.com/search/images;_ylt=A0oG7t_L3oxPoEwAKidXNyoA?p=abrasive+metal+cutoff+saws&fr=yfp-t-521-s&fr2=piv-web

idbruce

erco

Okay, I agree that a shop grade metal cutoff saw with a thin abrasive wheel would be the right tool for the job, providing that it would be several cuts instead of one pass, to avoid heat build up.

Bruce

Gadgetman

Also, cut grooves in the aluminium clamp to increase surface area.
Then get some good thermal paste and add a little bit in the clamp to further increase the thermal transfer.

LoopyByteloose

After you are finished cutting, clean the bearing with something like pressurized freon that is used in electronics as a NO residue cleaner.

Cutting should be water or oil cooled if you do not to reduce the steel's properties.

Frankly, the hobby part market is generally what you see is what you get. And with motors, I suspect that a company would want an order of thousands before they would fill to a custom specification.

Regarding assembly and disassembly, there may just be a learning curve about getting the c-clip into place. Preloading is usually an issue with big motors - 100s of horsepower, not these tiny items. But there may be a spring metal washer (appears to be bent, but that is as it should be) that takes up end play. I'd not try to leave out a c-clip or any parts.

BTW, $13USD per motor is a bargain price. These brushless motors can easily cost 10x that. Some brushless suppliers sell replacement shafts. If you can locate one of suitable dimensions that would be ideal, but again I suspect that this would be a special order and cost more than $13 per unit.

http://servocity.com/html/shafts__rod___tubing.html <== Try hear for shafts if you need replacements.

Spiral_72

Erik Friesen wrote: »

I don't want to post my complete design. Its rather complicated with pretty close tolerances. The shaft would stick outside the enclosure if not cut off.

To remove the shaft, a c clip has to be removed. They apparently use some type of bearing preloader or something, because it is very difficult to get the c clip back in place. I am experimenting with no c clip in place, I am unclear if the bearings need it to operate properly. I am using the face of the motor to drive the magnetic drive for the pump.

Wow you cut that close didn't you? I know a couple redneck machine shops that would love to do this for $200, maybe you have some in your area?

Can you use off-the-shelf female-male or female-female standoffs to lift the motor off the floor and keep the stock length shaft?

Somewhat off topic: Consider moving fresh air around the motor to cool it. Them babies will get hot spinning stationary with no prop on the end. The cooler you keep it, the longer the bearings will last...... but you probably already thought of all that.

Erik Friesen

This is all close tolerance, around .005" , I can't do standoffs. The limitation is that we are targeting an existing application with a limited space, so height is at a premium.

The point here is, I would like to ask the manufacturer how many I have to do to get this done. I have no link the manufacturer, and the link doesn't feel it can't be done for any price.

LoopyByteloose

I suspect the link you have is a distributor that buys OEM and puts their own lable on the brand. They certain are some of the lowest prices I've seen for brushless 3 phase and they may have bought on a one-time basis in a significant quantity. The actual manufacturer may be making big brand name products and these are going 'out the backdoor' in a different color and to be later labled. All these things are the 'ways of the world'. So unless you source the manufacturer - not the distributor, and ofter a big enough quantity purchase, you are just going to have to modify the units yourself with any subsequent hazards of defects and waste.

Economies of scale require manufacturing runs of 10,000. If you are not a player at that level, you are generally ignored.

erco

Blow compressed air on the shaft as you cut it; that will cool it and carry the "swarf" away so the motor doesn't get "bollixed".