Geared motors for 12/24V DC?

On Thu, 21 Oct 2004 02:15:03 +0200, "Q" calmly ranted:

should have something you can use.

There are usually a few for sale on eBay. Engineman1

I bought some here recently (USA unfortunately);

Electric wheelchairs/ mobility scooters will fit this bill perfectly. Find a local manufacturer/ service agent for these type of devices to see about purchasing stock, etc.

Could you put numbers to 'a "lot" of torque'?

Also, any clue how small they must be?

With the PM servo motors for the Bridgeport, I can get any RPM from 2000 RPM down to something like 0.01 RPM or better. And the torque is sufficient so they will turn over the drill-press vise holding the motor if I lock the shaft.

These are ones with a tach feedback generator sharing the shaft with the motor, so the servo amp can increase current until something

*does* turn. I'm driving mine with servo amps capable of +/- 40 V at +/- 20 A.

One benefit is that there would be *no* backlash, as there is no geartrain. But the size might be a bit much for your needs. They are about 5" (127mm) diameter, and about 12" (304.8 mm) long. And, of course, they are rather heavy. :-)

My suggestion is to look up various surplus catalogs, and eBay, as these tend to be rather expensive bought new.

Good Luck, DoN.

Since nobody else mentioned it, automotive power window motors might be a good candidate. They probably turn a bit faster than the

15 RPM you are looking for, but probably not too much faster.

Jon

"DoN. Nichols" skrev i en meddelelse news:cl7d1q$oat$ snipped-for-privacy@fuego.d-and-d.com...

Hmmm... not really, b ut I can tell you what I am going to do with them ( it might give you an idea )

Am trying to motorise ( and remote control ) a small cart that will weigh approx. 200 lbs when finished, and run off one or 2 car batteries.... The wheels are approx. 6" diameter ( from a lawnmower )

This part of building a 2 arm, mansized robot on a 500$ budget :-).. Am using an old PC for the control software and a wireless LAN link for the remote control via another computer..

As small as practically possible :-)

Unfortunately servo motors require a little more control than I have at the moment...

The idea I was planning on was to use some inductive sensors and some small nuts glued to the wheels for RPM feedback to the controller.... This doesnt need to be 100% accurate

+/- 40V is doable, but I'd need to build a rather noisy switched mode PSU to do this, and I am afraid it will interfere with the WLan..

My initial idea was to use some cheap cordless drills and just pull the motor and gear from them, but these things do not provide enough torque by themselves and do too many RPMs... I could get a small set of gears for this, but OTOH.. If I need to build some sort of gears anyways I might as well use a couple of starter motors from cars..

Problem is that I dont have a full machineshop at home, so it might be hard doing too many experiments..

The base of this thing is 500*500 mm, so that wouldnt be a problem..

Any links to the surplus places ?

Thanks for your help sofar

/peter

On Thu, 21 Oct 2004 12:45:54 +0200, "Q" calmly ranted:

$110 from

for a 24VDC transaxle ought to do it. $27.95 for a non-powered lawn mower transaxle from the same source.

Select the "power trans" tab, then the "transaxle" link.

Please take pictures during the build and make a web page so we can see the process/finished product, Q. Sounds fun.

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"Larry Jaques" skrev i en meddelelse news: snipped-for-privacy@4ax.com...

The transaxle idea is partially good and partially bad..

Good things: Its easy Bad things: I was planning on using one motor on each drive wheel ( and just

2 swivel castors for the rear end ) and use different speeds ( possibly even reverse one of the motors ) to do the steering..

I have some pictures of the control electronics ( computer interface and motor controllers) as they look so far ( I need to do a little hardware hacking to do some sort of RPM feedback on each wheel )..

Most of the hardware will be built in my 25 square meter living room, while the heavier stuff ( welding etc ) will be done at the maintenance dept. at the food processing facility where I work..

Before you start laughing I will tell you that I have NO formal training in the metalworking field, but have worked with electronics design for a few years.. Nowadays my dayjob isnt even closely related to this ( I make cheese )

I actually bought 2 cordless drills ( chinese junk for 15$ each ) and some gears, so I am going to try if this will work properly.. Trick is that I wont have to beef up the PWM controllers ( they can only source about 6 amps in the standard config )

I will post some pictures as soon as I get this working

/peter

Hmm ... what about how steep a grade will it need to climb?

But anyway -- this suggests that the backlash of a geartrain will not be a problem for you, and the extra torque will be a serious benefit.

A bit of a challenge.

Sounds like fun. What OS do you plan to use on each? (I would choose one of the free-source unix types, like OpenBSD or linux, just because I don't want to consider what a BSOD (Blue Screen Of Death) would do when you have 200 pounds moving at some serious velocity. :-)

O.K. They have to be able to fit inside a walnut shell, and capable of lifting 200 pounds at perhaps 10 MPH up a 20 degree slope. :-)

Not too difficult, with off-the-shelf servo amps (which can be run from 110 or 220 VAC (as the AeroTech ones going into my Bridgeport). Once you have that, you simply put in a DC voltage from -10V to +10V (or it can be from -5V to +5V if your computer is happier producing that). The speed will be directly proportional to the voltage. And with mine, set up for 2000 RPM at 10V input, if I take the input down to 0.0001V (I have some nice Power Designs power supplies which will do this happily), I have to put a piece of tape on the motor shaft to see it move -- and wait a while. :-) You could bypass the 115 VAC and the built-in power supply and generate +/- 40 VDC to power the amplifiers, and this would probably gain you some efficiency. But a switching-mode servo amp will be better at conserving power, even though it takes more money to purchase one. (The AeroTech ones which I have came from hamfests and from eBay auctions.

Hmm ... better if you put something like a steel gear on the back end of the motor, *before* it goes through the gear reduction. Otherwise, your speed control will be rather lumpy.

Hmm ... it might, indeed. But then again, a PWM controller is similar in operation principle, so it might generate as much RFI as the DC-DC converter for the +/- 40 VDC.

What is the maximum speed which you need? If it is not too high, you can use a worm gear to get a large speed reduction, and a large torque boost from the motors.

That does put you at a disadvantage. Most of us here are accustomed to having lots of machine tools ready to hand.

O.K. Though the "no backlash" benefit does not seem necessary for this.

As for the 500 x 500 mm, dimensions -- if you plan for a separate motor for each wheel, 300mm long motors might still be a problem. How sharply need this thing be able to turn? For somewhat less turning ability, perhaps one motor for the left wheels, and one for the right might do it.

Some others have already posted some. I tend to find useful things at hamfests, and flea markets, so I don't have the surplus places bookmarked. One which I used to get some things from (from a print catalog) was Herbach & Rademan (not sure that I have the spelling right any more). Someone else has already posted a link to that, I believe.

Best of luck, DoN.

P.S. It almost sounds as though you are building something like a "battlebot". :-) Even if not, you might do a web search on that term to find techniques which others have used for building those.

"Q" skrev i en meddelelse news:r8Ddd.59199$ snipped-for-privacy@news000.worldonline.dk...

I ended up getting a pair of cordless drills and doing some minor modifications to them

Larry asked for some pics of this project, so I threw some pics and text at

Feel free to point out bad spelling and grammar, or throw some ideas at me.. At this point I need some good ideas for the arms ( using off the shelf parts )

/peter

"DoN. Nichols" skrev i en meddelelse news:cl9g5u$p64$ snipped-for-privacy@fuego.d-and-d.com...

Well.... None, actually.. Ideally it will be used indoors, but I may need it to run over cables on the floor and such, but it shouldnt be a problem..

The torque is what I am after here.... As you may (not ?) have seen I threw a little more info on

... At first I tried with a cheap cordless drill, but my guesstimate was that this wouldnt have enough torque, so I decided to try adding a set of gears giving a 12/80 ratio after the cordless drill and this gave me plenty of torque ( I cant hold the wheel with the motor running at full speed )

Well... I think its possible by using stuff from the junkpile supplemented with new parts here and there..

Since this project is just a matter of killing time and taking up the challenge the demands for build quality arent that high :-)

So far I am looking at using Win2K since this is the I/O card only comes with drivers for Winblows based OS's, but judging from the testing BSODs arent a problem ( yet )

Something like that... And preferrably not cost more than a few bucks each :-)

110VAC is completely out as we use a 230/400 VAC powersystem over here.. 230VAC is possible, but not practical since this thing should be wireless.. And NO.. I am not putting a generator inside :-)

Same thing w. the PWM controllers I got my hands on.... Kewl thing about them is that they are pretty easy to beef up to pull more than the rated 6 amps or so..

That wont be a problem here.. I could add a second set of relays to disconnect the motors from the PWM controllers..

I am not convinced that heavy duty Servo controllers will be withing the budget of this project :-)

True, but the main purpose of the feedback is positioning, and just indicating that the wheels are turning

Agreed, but the harmonics from a PWM regulator operating at maybe 5KHz are less likely to interfere with Wlan compared to the harmonics of a SMPS operating at maybe 50 KHz ( most of the SMPS stuff I have worked with worked at around that freq. and required some serious effort to avoid interferance in various RF equipment )

I just need it to move faster than 3ft / minute :-) Worm gears are hard to find in the sizes needed here..

I have access to a full machineshop ( w. CNC milling etc. ), but part of the concept behind this project is building it using very basic tools.. So far the only electrical tools I used are a skilsaw ( cut the sheet of ply ) and a cordless drill..

Again.. I dont have any specific demands for this :-)

I looked at a few of the links posted and found some motors that'd do the trick, but the cost would be prohibitive compared to getting a pair of cheap chinese cordless drills, so thats what I did...

So far the best idea for a real purpose is renting it out as a bartender, but that might end up with the robot needing battleskills :-)

thanks for the input so far.... I will return with more dumb questions once I get the rest of the base done :-)

/peter

On Thu, 21 Oct 2004 19:49:26 +0200, "Q" calmly ranted:

Yes, individual/reversible/geared DC motors would work better.

That's always fun. Lugging things around, misplacing things in two different locations, etc. BTDT.

Who moved my cheese? (Great book, BTW)

Can I start laughing yet?

Thanks.

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On Fri, 22 Oct 2004 01:33:18 +0200, "Q" calmly ranted:

Cute. But I thought you said you wouldn't consider using BSOD for an OS. I've been playing with that particular "benefit" of Win2k all this week after adding memory, a vid card, and Mozilla 1.0 Preview which causes it.

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"Larry Jaques" skrev i en meddelelse news: snipped-for-privacy@4ax.com...

The BSOD is just the front page.. Click the picture and you get to the second index..

Besides.. the PC going in the robot is an older 500 mhz pentium something stripped down to the parts absolutely nescesary ( harddrive, RAM, COU, MOBO, small gfx card, Wlan and the USB interface ), so crashes shouldnt be that much of a problem...

/peter

O.K. The larger the wheels, the better for the cable climb. At least your needed torque just went way down. :-)

[ ... ]

That sounds close. If you get it strong enough so if you do manage to hold the wheel, the chassis tips up to allow the rotation, you have all that you will need. :-)

Agreed. It just slows the project down significantly.

Good enough.

[ ... ]

Wait 'til you start throwing around the RFI from the DC-DC converters. :-)

[ ... ]

But -- as I mentioned, you can bypass the input transformer and the rectifiers -- or just bypass the input transformer, and use the existing bridge rectifier -- if the diodes are fast enough. It will certainly reduce the required filter capacitor size.

[ ... ]

Yep -- just use them to drive larger transistors -- probably power MOSFETs -- to handle the additional current -- and add more heat sink, of course.

I wasn't talking about the ability to *stop* it, but rather to

*almost* stop it, and still have it move at a stable speed. :-) (That does depend on the tach generator built into the motor, of course.)

Hmm ... $15.00 each -- at hamfest prices. :-) They are obsolete technology. You certainly would not want to buy them at *new* price. :-)

O.K. But how closely can you space the nuts? That will limit the resolution you can achieve in your positioning. Working at the motor rotor, you get a lot more resolution.

Yep -- lots of higher harmonics. I don't know how much noise immunity the wireless ethernet may offer you, but obviously, near infinite retrys could wind up with commands arriving out of order.

Hmm ... there are ways to make them -- but again we are talking about the need for a machine shop. One technique is to put a large tap in the chuck and start it rotating, and to bring the wheel (turned to the proper OD, and mounted on a bearing) against the side of the tap. The tap will start rotating the workpiece as it cuts. When the thread gets deep enough, you wind up with an integer number of teeth around the wheel. You then drive it with a length of all-thread of the same diameter and pitch as the tap. Obviously, a proper hobbing machine will do the job more easily, as it will be rotating the workpiece under power too, so you are assured of the number of teeth which you intended. :-)

O.K. Note that I have seen some electric drills which have a worm gear cut on the shaft of the motor, and drive a matching gear at right angles to the motor's axis. (Usually, you will find this on right-angle drills, which tend to be more expensive, but if you can find some with things like broken handles or the sort, they would make good starting points.

[ ... ]

O.K. Sometimes you can find good motors and the like at hamfests -- as part of old computer printers which have been stripped apart.

[ ... ]

At least, self-defense skills. :-)

Feel free. You'll always find people with suggestions here.

Good Luck, DoN.

Wheelchair motors. M.K.

On Fri, 22 Oct 2004 04:37:59 +0200, "Q" calmly ranted:

By BSOD, I meant the Windows "Blue Screen of Death". Are you talking about Free BSD or some other OS? I'm not aware of any other use of that particular acronym.

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