9v Battery not supplying enough current or mechanical advantage too low?

Projects General Guidance
1

I've built a simple circuit that activates a motor when a momentary switch is closed, disengages the motor once the switch opens again. There are random delays and timers involved which is why I didn't simply connect the switch to the motor.
It's a 12V motor I scavenged from an old optical drive, together with the gear set.

The purpose of the circuit is to reset a hinged target once it's been knocked down. I plan to add a scoring system, but that's a story for another day.

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Functionally and programatically, everything works fine, the problem I'm having is related to the output of the motor. I tested the motor directly connected to the 9V battery and the output is more than enough, in fact, it spins too fast for my application (I can use PWM to bring it down if needed).
Once I connect everything as shown in the diagram, the motor stalls when trying to push the target back up i.e. too little torque. This is exacerbated by the fact that the target is relatively heavy, and it has to be, since I'll be shooting it with steel BBs.

I took current readings with and without the circuit connected:

  • Current draw motor only: ~110mA (I should've probaly taken a stall current reading as well)
  • Current draw with complete circuit: ~160mA
  • Stall current with complete circuit: ~200mA

All 3 readings are total current draw from the battery, not probing somewhere random in the circuit.

So my question(s) is this, is my circuit unoptimised or is the battery too weak OR is my gearing inefficient? Would a 9V motor provide more torque?
How would I achieve the best mechanical advantage? I don't mind the motor spinning 10 times slower if it meant more torque.

Some pics of the build here, and a video of a previous itteration here (never mind the ending, I made a funny for a reddit)
A lot changed since that version, heavier target, different set of gears, different circuit, different construction, etc.

Just a side note, i'd like to test with 9V DC coming from the wall, but I don't have one, only 5V and 12V. My next project that I'm still sourcing parts for is to build a bench power supply with 9V DC output, but I don't want to go ahead an do that only to find that the problem may be elsewhere.

Thanks for taking the time to read.

2

Those little oblong 9V batteries really can't supply much current.

You'll need something beefier for your loaded motor. A 9v DC wall wart would be a good option. If it has to be batteries try 6xAA or larger.

3

Please read the forum guides about posting images - a lot better than links in most cases.
Many helpers won't even opem the external links - so it's to your benefit.

4

lastchancename:
Please read the forum guides about posting images

Well i did try, hence my explination on the first link shrug I'll have a look when I'm in front of a PC again.

Fixed.

5

GypsumFantastic:
Those little oblong 9V batteries really can't supply much current.

You'll need something beefier for your loaded motor. A 9v DC wall wart would be a good option. If it has to be batteries try 6xAA or larger.

Is there no possible combination of 9V to motor spec to gear ratios that could work in this situation? How would a 9V moter compare?

I would really prefer using a 9V battery, but if there's no other way then that's that.

6

You have to gear down to gain mechanical advantage. Use full 12v and slow it down by gearing. Do you have access to any geared motors? You can also use pulleys and belts if that's easier. The concept is that the motor spins faster than the target mechanism multiplying torque. A large servo could work here also if designed correctly (depending on the weight of the target).... prob not with 1/2 plate.

Note I don't really like 9v alkaline batteries much. Sure they give you 9 volts but they're only rated for about 500 mAH. I would use a little lead acid rechargeable 12v for a project like yours and you can plink all day! Better yet use a $5, 6v lead acid that gives you 4500 mAH and maybe use a different motor.

I like the part the target falls off on your video... :smiley:

7

wolframore:
You have to gear down to gain mechanical advantage. Use full 12v and slow it down by gearing.

I understand the concept, but I think I'm losing a lot of that advantage where the spinning arm makes contact with the target. I'm not sure on how to make this more efficient. The plate is not all that heavy, it takes barely any force if I push it with my hand, but that's linear motion as apposed to rotational. As a side note, I've tried using the rack and pinion setup from the optical drive (obviously hacked up so only the least amount of material remains to do the job) and that works fine, but this adds complexity since I need an H-bridge to reverse the slide again.

wolframore:
Do you have access to any geared motors? You can also use pulleys and belts if that's easier.

Nope, all I have are optical drive motors. There is also the worm gear motor that moves the laser, I tihnk it's a stepper motor, I need to read up on how to use those.

wolframore:
Better yet use a $5, 6v lead acid that gives you 4500 mAH and maybe use a different motor.

This sounds good, I'll look into it, my local electronics store has a range of these batteries. I'll just need to look for a suitable motor then.

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I just did some pricing

  • 4.5Ah Lead acid = $10
  • charger = waaaay too much, like >$100
  • 6V high torque motor = $3

So much for a shoe-string budget...
I'll probably get the 6V motor and go with 4 or more AA rechargable. I was planning on making about 5 of these connected to my Nano so I could set up some reaction time training. I guess I'll have to change the scope a bit.

Oh one other thing I didn't mention is that I'm using a Nano, I don't want to feed it 12V on VIN, I head it drastically shortens it's lifespan. Maybe I'll add a regulation circuit... I need to rethink this whole design.

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9v batts + Arduino != a good time

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You can get a 12v trickle charger at harbor freight for next to nothing. Then you have a rechargeable battery that will practically last forever

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I'm not in the US, but I think I found an affordable one locally, in the range of about $10.

12

Cool... that works... Do what you like but a target should be enjoyed all day at low cost. 9 volt batteries get pricey and work for a low current project but not for motors.

Here's a cheap gear motor with low RPM and voltages you can choose - meanwhile you can use the current setup on 12v just fine or maybe you don't need this once you get the voltage up...

cheap gear motor

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maybe a stupid idea, but might be worth thinking about: rather than hinging the target plate at the bottom (where less effort is required to knock down, but more effort is required to reset), hinge the target plate on the side, where less effort would be required to reset.

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you'll never know til you try... but the target going down flat is has a good effect... it knocks down!

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I've considered hinging it at the top, but never at the side, omg, you may be onto something... How have I never though of this before.
I do kinda like the idea of having them fall down though, but a side hinge makes a lot of sense.

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I only ever made the hanging targets that spin... i like this auto reset idea... i think you should put a microphone on it so when it hears a hit it activates after a short delay. I have also seen these reset with a rope but this is more fun!