low speed, high torque - 250RPM @ 12Nm

[tjagiello]

Hi everyone,

can someone recommend a motor solution to achieve 250RPM at 12Nm ? I'm looking for an off-the-shelf solution and the least amount of parts / devices involved. Torque requirement is momentary, I don't need 12Nm constant running torque, more like peak torque for 1000ms or so.

Regards,
Tom

 

[KllrWolf]

The Hp equivalence would be about 1/2 Hp. More information is needed to actually decide a motor setup. These are the basic questions you need to look at to narrow down the many designs out there on the market.

AC or DC?
What voltage?
Does it start and stop or run continously?
Is there a size/weight restriction?

 

[tjagiello]

Hi KllrWolf,

thanks for taking the time to reply. Here's more info, which I should've included in the original post:

- AC or DC, doesn't matter, but I'd rather have a quieter motor, which I think steers this into DC direction.

- with DC it would be preferably 24VDC, although 12VDC and 48VDC is also ok. As for AC this would have to be single phase 230VAC.

- start / stop action. On for roughly 10s at a time, but might have to work in short bursts through the day, so a lot of on/off cycles

- size needs to be limited in order to fit into a space of 120mm (D) x 160mm (W) x 280mm (H). I guess that automatically limits the weight.

Regards,
Tom

 

[itsmoked]

There are scads of DC motors with integral gear boxes.

I'd look to the robot stores:

http://www.robotmarketplace.com/products/motors_geared.html

Keith Cress
kcress -

http://www.flaminsystems.com

 

[mikekilroy]

couple more points to narrow it down:

cost objective?
250rpm +/- how much?
How to control? Just tell it to go and then stop after 10 sec?

You can do this with a gearbox on motor or direct drive. You said "min parts, quiet...."


Top of the line, quietest, smoothest prob is direct drive servo motor and 230v 1ph input servo drive; cost around $ 3000.00

cheapest for 1 off prob ebay gearmotor, no drive, $ 20.00

Lots of in between stuff.

 

[tjagiello]

Gents,

again, thanks for taking the time to reply.

I've looked at the robot stuff, actually I have a robot brushed DC geared motor, which can do 2.3Nm max at 480RPM and I can squeeze a 2.5:1 ratio done via HTD 5mm pitch 15mm wide. What this means is I get around 6Nm at around 200RPM, which is close to what I need, but a bit low on torque. Although on the other hand I'd need momentary torque of 12Nm, mostly to start the thing as the resistance is the biggest on startup, so this combo might be able to work. I'll test it over the weekend and see how I get on.

The main downside with DC brushed motors for robots is the fact that they are brushed, so need maintenance. Brushless would be better, but of course they need a dedicated driver and things get complicated quite quickly.

Cost objective: I'd like to keep it below $500 for the whole drive, so all parts, like drivers, PSUs if needed etc.

Speed: 200-250RPM, I wouldn't want to go higher than this.

Control: just press / switch a button and it runs, press / switch it again and it stops. Basic wired in switch will do for control.

I've looked at DC brushless servos, but prices are a bit skyhigh. I've found a Leadshine servo with a controller for $350, this will of course need a gearbox and a PSU, which means I'd need $500+ for this. It will give me speed control, which I don't really need, so there's monies paid for functionality which isn't needed.

Regards,
Tom

 

[ScottyUK]

Parvalux have a wide range of small gearmotors.

http://www.parvalux.com/downloads

 

[zekeman]

Your cost will depend on how fast you need to perform the task, how often, the type of load you are driving and the motor life desired.
So, why don't you tell us EXACTLY what you are doing and then you can get meaningful answers.
Otherwise you will only be getting the best guess from the contributors.
Not a good idea; you may be buying a Cadillac when a Ford would do.

 

[ozmosis]

Using the basics given, try this company. As you are using nM and mm, you are possibly in Europe so Parvalux are a decent start:

http://www.parvalux.com/index.php?id=66

 

[tjagiello]

Gents,

thank you for all the help so far. A bit more detailed info on the requirements, to answer zekeman's questions

1. how fast you need to perform the task

I thought 250RPM covers this, this will effectively limit the speed of operation

2. how often

This varies, I'd say every few minutes, run cycle would be 10-20s.

3. type of load

Covered by torque required, 12Nm max, this is static torque needed to get the machine moving. Once it's running, the load shouldn't be more than 4-5Nm.

4. motor life desired

As long as possible, which is why I'm looking at brushless design, as it's almost maintenance free.

The motor will be used in a small version of a precise conical mill, material ground will determine the load. From the tests I've done, hand cranking the shaft via a torque wrench, the maximum torque requirement I've had was around 10Nm.

Parvalux is good indeed, but a bit limited on speed with torque much higher than I need. I will however go through their offer in more detail, as I've only had a quick glance.

Regards,
Tom

 

[waross]

I will be surprised if 12 Nm keeps you happy.
Double or triple that may be better for grinding through the inevitable jam-ups. You may want to consider lowering the voltage/torque somewhat but using full voltage/torque to back out of bad jam-ups.
How much torque can the mill take before something breaks? Consider 50% to 75% of that as maximum drive torque. You may limit torque to a lower value in normal operation. But use full torque to back out of jam-ups.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[tjagiello]

Hi Bill,

10-12Nm is what I managed to measure on one occasion with a torque wrench and this was with a jam-up, so effectively the maximum torque required.

The shaft is 25mm, body is 15mm ali, should take quite a lot of abuse before things start falling apart.

To be honest it's hard to get a motor which can do 250RPM at 12Nm, so I'd guess it's even harder getting something with 20Nm+ at 250RPM.

Regards,
Tom

 

[zekeman]

"To be honest it's hard to get a motor which can do 250RPM at 12Nm, so I'd guess it's even harder getting something with 20Nm+ at 250RPM."

You don't need exactly 250 RPM and nor should you be thinking of a fixed RPM; you are talking a transient problem reuiring 12N-M with a time frame of speed ABOUT 250RPM.

It's really not that hard, especially for your rather loose spec on control.
For example, I looked at the Parvalux link you were given by "OSmosis"

Look at the data sheet on p12 of the brushless catalog and you will see the specs for the PBL-86-118 48VDC motor alone.

Follow down and you get rated speed of 3000RPM @ 1.1 N-M of torque.

For you application requiring 12 N-M, this means that adding a 10:1 gearhead would bring the torque to 11 N-M @ 300RPM. Since your duty cycle is small, you can easily achieve 12N-M and more at somewhere near 300RPM or slightly less. ( they offer GB ratios near 10:1).
If you aren't comfortable with this ( I am), then you could go to the next motor size, PBL86-145, 48 VDC with a rated torque of 1.4 N-M and you will have more torque overkill.
BTW, this is a UK company and what they offer is not unique; with a little bit of searching you should be able to find others. I don't have any since, the last time I designed something like this was 40 years ago.

In either case, you don't need need a fancy controller, only the basic commutating , since you have an open loop system, from your description.

 

[tjagiello]

Hi zekeman,

thanks for your input.

Your way of thinking is roughly the direction I was going in. Get a brushless DC motor / servo and couple that with a gearbox (was thinking planetary 10:1 or 15:1). The main problem was:

1. DC power supply - mostly due to the amount of current needed by the motor, especially peak current, which can reach 18A. Nominal is fine, normally is around 7-8A, most small-ish PSUs can do this, but if one wants to cover the whole range of current, which includes peak, it's going to be one beefy PSU. That creates a problem, as the space I have is rather limited.

2. motor driver - cost and size again. I'd happily stick with a simple controller, but googling for a solution brings mostly DIY devices. I know small RC BLDCs use ESC units, but these are quite often 12VDC, when I need 24VDC or 48VDC.

Regards,
Tom

 

[waross]

I would look for an AC gearhead, three phase motor at 1800 RPM and a single phase to three phase VFD. A gear reduction of around 7.5:1
If I could not find a suitable AC solution, then I would consider DC.

Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[zekeman]

I have to agree. The brushless design is too expensive and the power supply is too bulky.
I would start at the cheapest, 56C frame ( about 1/4 to 1/3 HP) single phase AC 1800 motor and marry the appropriate gearhead. I don't think you need VFD here.

 

[mikekilroy]

now that more facts are in, I too agree the best solution based on these facts may be the following:

1) 1HP 1800rpm 3ph motor (4nm) $ 235.12
NES1-007SB Hitachi VFD, 240 volt, 1 phase, 1 HP $212.00
3:1 timing belt/pulleys to load $ 50?

There. Got under your $500 mark

 

[KllrWolf]

With the toque requirement of only 12Nm max, it should only require about a 1/2 - 3/4 Hp motor (still with the other parts, of course). Of course I do not normally deal with motors this small, so there may be something I am missing that would require the larger HP.

 

[mikekilroy]

I'd say what you are missing is cost of a gear box. Of course you can use a higher speed (thus lower torque & hp) motor, but then you need to add the cost of a gearbox - probably around $ 400. MY method is to optimize cost by using 1hp motor with no gearbox, just a couple pulleys. If OP can handle really big pulleys then sure, go for it, but typically 3:1 is about max normal size for them.

 

[mikekilroy]

I forgot to put in that by adding the $ 400 gearbox, you saved about $20.00 on the smaller motor.... not much of A trade off.