Very large seven segment displays

[Mr RB]

I would use a small DC motor to rotate each segment. You don't need a spring, just drive the motor in either polarity to rotate, and use a resistor in series with the motor to give current limiting in each stable end position. They only need 50mA, maybe 100mA.

 

[Sangoma]

I would use a small DC motor to rotate each segment. You don't need a spring, just drive the motor in either polarity to rotate, and use a resistor in series with the motor to give current limiting in each stable end position. They only need 50mA, maybe 100mA.

Probably have a startup torque that is too low with sufficiently limited current, and low holding power to keep the display in the desired position if the power was removed. Even at 100mA, the slightest resistance on the hinge would cause it to stick or move erratically.

 

[dr pepper]

I See what you mean there roman an improved version of my idea, a pin to stop the segment with either rotation ought to do that.
And you could probably use the motor itself as one of the hinges if you speayed it black to hide it, with just a simple wire hinge at the other end.
A burst of pwm will give it the go to get it moving with a narrow pulse to hold it.

 

[Mr RB]

Yeah power should not be a problem. If the motor driver voltage is high enough and a decent current limit there will be plenty of speed and torque to "flip" the segment. 100mA on those small motors will give significant torque, especially since the load is balanced and should require very little torque to move.

Then when the segment stops and motor stalls the current limit will drop the voltage very low but keep the current on, so the segment will be held securely by the motor current in stall condition, but total motor power will be low as the motor voltage will be low (so it will be safe and not cook the motors).

Basically this is just using the motors as "rotary solenoids" with a current limit.

You could also drop the current X mS after the event (as Dr Pepper said), to reduce motor heat further but I'm not sure that would be necessary.

You can buy tiny 8-pin hbridges perfect for driving small DC motors <1A.

 

[dr pepper]

My local supplier does a 4.5v motor for 85 pence.

**broken link removed** From This Range

 

[Divan]

After taking everything into consideration I think the DC motor with H-bridge driver is my best option. There is a farnell distributor in Cape Town, but I'm still waiting on a quote for the motors, hopefully it won't be too expensive. Once I get the components I'll build a digit and post some pictures on here.

Thanks for everybody's help

 

[dr pepper]

Keep us posted, I'd like to build something like this too when theres time.

 

[Mr RB]

Ebay has tiny DC motors in bulk lots, very cheap.