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 How to calculate battery life on steppers? 
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Joined: Wed Mar 16, 2011 2:58 pm
Posts: 1348
Location: Denver, Colorado
Post How to calculate battery life on steppers?
Hey folks.

Maybe somebody can help me with this. Im not having much luck figuring this out.

I have an 8.5 amp-hour battery, 12volts.

say im driving 12v to a stepper, with a "2.5 Amps Current Per Phase" 1.8 Degree steps

How do i determine how long the battery can power that stepper? Im strictly speaking power consumption vs power supply (All other factors such as microcontroller and driver are thrown out the window for this question)

[*]260 Oz In. Hybrid
1.8° /200 Steps Per Rev.
2.5 Amps Current Per Phase
4-wire Bi-polar
NEMA 23 Frame

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Thu Jul 14, 2011 8:44 am
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Joined: Wed Mar 16, 2011 2:58 pm
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Location: Denver, Colorado
Post Re: How to calculate battery life on steppers?
Anybody? Bueller?..... Bueller?...

;)

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Fri Jul 15, 2011 10:55 am
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Joined: Wed Jan 14, 2009 8:34 pm
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Post Re: How to calculate battery life on steppers?
It will depend on how you're driving it; full-stepping, micro-stepping, employ different numbers of phases over the course of the driving cycle.

http://en.wikipedia.org/wiki/Stepper_mo ... olar_motor

scroll down to 'Phase current waveforms'

8.5A Hr / 2.5A = 3.4Hr = 3hr 24m if one phase consumes current constantly.

I don't know the requirements of your application but you can potentially save a lot of power by using shoot-move-shoot and cutting power to the stepper when it's idle - especially if you have something like a wormgear to stop things from moving about. This won't work perfectly with micro-stepping as the motor will collapse into one of its 200 positions when you deny it power, so it requires full-stepping. If the motor's only running for 0.1s every 10s then you can improve energy efficiency by a factor of 100. I do this, switching power with a power mosfet via a uC.

Perhaps the experts will provide further guidance...

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Fri Jul 15, 2011 1:10 pm
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Joined: Wed Mar 16, 2011 2:58 pm
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Location: Denver, Colorado
Post Re: How to calculate battery life on steppers?
Awesome thank you!

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Fri Jul 15, 2011 3:48 pm
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Joined: Thu Mar 10, 2011 11:38 pm
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Location: Exmouth, Western Australia
Post Re: How to calculate battery life on steppers?
As Astronomerroyal says, if you don't need to keep the motors permanently powered to apply holding torque, if you have a large ratio gearbox or worm-gear drive for example, you can switch off the motors between movements to save power. My rather primitive panning table uses a stepper motor to friction-drive a round wooden disk with a rubber band round the edge. The software I use to control it is set up to power up the motors only for the few milliseconds it takes to make the required number of steps. The table stays firmly in position without power to the motor.
I've done quite a few hours of timelapse in recent weeks but I'm still using the same 8 x AA batteries for powering the stepper motor and the camera control that I started with.

I was wondering what the possibility was of doing this with a microstepped motor. Looks like it will settle to one of the 200 standard positions. Obviously a choice to be made here between a huge gear ratio on a non-microstepped motor and microstepping with continuous power drain on larger batteries. A larger gear ratio would allow the use of a smaller motor as well. I think that would be my preferred route.

Kit


Fri Jul 15, 2011 7:07 pm
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Joined: Fri Feb 22, 2013 9:31 am
Posts: 70
Post Re: How to calculate battery life on steppers?
Hey there,
I'm feeding my brains with energy-saving self-blocking anti-backlash high-strength high reduction ratio options myself, these days...

My first approach was to use split-disc gears + electromagnetic stepper brakes. No good (see point 1, below). Plus, they require the brakes, pretty expensive and adding to the project's complexity.

My second approach was to use timing pulleys and belts + electromagnetic stepper brakes. No good for me at least, since most manufacturers only produce a very limited variety of pitch diameters (generally max. 1:7), while I need at least 1:9-10 or more. Plus, they require the brakes, pretty expensive and adding to the project's complexity.

The no-brainer here seems to be the self-locking worm gears.
So far, I encountered several types of anti-backlash worm gears:

1. split gear, mono-block worm (as weak as it's strongest springs - fit only for non-strength applications)
2. mono-block gear, split worm (much stronger, but the gap between the worms can create jolts and micro-jumps)
3. conical worm (adjustable axially, but because of it's conical shape requires 2 separate adjustments)
4. dual lead worm (cylindrical worm, with teeth gradually thicker - adjustable axially, apparently the most ideal solution)

I'm currently sending out quotation requests, as nobody seems to retail these babies...

Your thoughts?


Fri Feb 22, 2013 4:10 pm
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Joined: Wed Nov 11, 2009 10:45 am
Posts: 1685
Location: Merritt Island, Florida, Estates Unitas
Post Re: How to calculate battery life on steppers?
Check out strain wave gearing or "harmonic drive". Zero backlash because two sets of gearteeth on opposite sides are always in mesh.

Here's a nice video showing how it works.

http://www.youtube.com/watch?v=bzRh672peNk

Type "harmonic drive" in ebay and you're good to go.


Sat Feb 23, 2013 10:15 am
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Joined: Fri Feb 22, 2013 9:31 am
Posts: 70
Post Re: How to calculate battery life on steppers?
sciencelookers wrote:
Check out strain wave gearing or "harmonic drive". Zero backlash because two sets of gearteeth on opposite sides are always in mesh.

Here's a nice video showing how it works.

http://www.youtube.com/watch?v=bzRh672peNk

Type "harmonic drive" in ebay and you're good to go.


Hey, man, thank you for the link! I had heard about it but never understood it until I saw this video, so thanks! Anyway, as soon as I win the lottery, I'm all over the harmonic drives. Did you see how much they cost? I'm a DIY guy, not some bored rich fella ;)

Besides that, there's also the pretty interesting "ball worm transmission" - take a looky here: http://urobotics.urology.jhu.edu/projects/BW/

But all these are either proofs of concept or extremely expensive. I can barely get quotes and specs for regular worm gears... And find it almost impossible to get quotes for the (finer) dual lead worm gears (too exotic/rare/special?)... so I try to keep my feet on the ground for now...


Sat Feb 23, 2013 10:46 am
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