Three Questions

Question 1: Does the torque of stepper motors (Bi-Polar) increase when switch to half step mode?

Question 2: I have a phototransistor that I would like to use for a back door alarm system.. when the door is opened a beam of IR light, which is other wise always on the phototransistor, is broken.. resulting in a siren buzzer to trip. I want either sheild the phototransistor from all non-IR light... any suggestions? are there any premade IR recievers out there I can use?

Why are most IR recievers tagged with XXkhz ? Can these take a solid beam of IR or does the light need to be in pulses?

Question 3: What do you guys think about the unbelievable shooting at Virginia Tech? It was in an engineering complex.

My answers to:

Question 1: Don't know, but I'm very curious to know myself. Any spec sheet I've seen for a stepper motor has not made any reference to a decrease/increase in torque when half-stepping - I've just seen graphs for various supply voltages and revs/pulses per second. I haven't used steppers enough to give a proper answer.

Question 2: I wouldn't use a light that needs to be on all the time for a door alarm. What happens if for any reason the light goes out by accident? I think it'd be easier (and less obvious to the intruder) to rig up a momentary switch that closes when the door's opened by someone who shouldn't be there. Since you can have current for a really loud siren go through your switch, this would reduce you overall components than using a sensor/relay combination. Maybe you have your reasons for using the IR, that's just my two cents.

Question 3: Only just heard about it an hour ago, and I'm going to check out the details in a minute. Sounds like an absolute shame.

The Source sells IR transmitter/receivers as a pair in a pack - is that good enough?

The stated spec for stepper torque is as good as it gets. If you're running close to the limit, you're better off ramping the motor up from stop. Also down, if the mass is large.

The IR receivers at rated in KHz because the control signal is usually pulsed at some frequency, using the IR as a carrier.

Understand the crazy more-or-less erased himself. Makes it hard to know what the motivation might have been, or how this was supposed to get even with someone. May just be like Indonesians running amok.

May just be like Indonesians running amok.

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What do you mean by that?

Does the torque of stepper motors (Bi-Polar) increase when switch to half step mode?

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I think every second step is a weaker one (maybe 2/3 of normal torque) because of the current distribution in the coils The other steps have normal torque.

but I'm very curious to know myself

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If you are still intrested..

HALF STEP

Half step simply means that the motor is rotating at 400 steps per revolution. In this mode, one winding is energized and then two windings are energized alternately, causing the rotor to rotate at half the distance, or 0.9º's. (The same effect can be achieved by operating in full step mode with a 400 step per revolution motor). Half stepping is a more practical solution however, in industrial applications. Although it provides slightly less torque, half step mode reduces the amount "jumpiness" inherent in running in a full step mode.

I have used stepper motor with half stepping as well, but I couldn't feel any improvement in the torque, that is a small stepper motor.

dch222 said:

I think every second step is a weaker one (maybe 2/3 of normal torque) because of the current distribution in the coils The other steps have normal torque.

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Maybe every first step is the weaker one? Because more magnetic field is created? Maybe the second step is weaker because the power dissipated to two coils. Some reference books show that the torque is higher for half stepping.

Without incresing the resolution, I think 2 coils are turned on everytime would give higher torque, something like this:
0011
0110
1100
1001 and so on
So the stepper motor doesn't need two different current to be used, just use higher current by increasing the collector current and reducing the base current. Does this make sence?

That's standard full stepping with two coils energized
Half stepping would be.
1100
0100
0110

The steps where only one coil is energized are going to be lower torque than the steps where two coils are energized obviously.

Sceadwian said:

That's standard full stepping with two coils energized
Half stepping would be.
1100
0100
0110

The steps where only one coil is energized are going to be lower torque than the steps where two coils are energized obviously.

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Oh ya, you're right. I was confused