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Need help with a Torque issue (suggest motors or another method)

I'm purposely being vague because this is my next robot and I believe this to be my last issue to work through. I have the circuit working on a breadboard and this is the last piece in the physical build.


Blue plastic "gear" 



Gear on motor pushing on red peg


Side view of gear on peg


What I need is something that can push the peg down and then let go. The motor is supposed to spin the blue gear which pushes down the peg. When the gear turns shallow again it lets the peg pop back out. As long as the motor turns is is supposed to continually push the peg down and then let go. The problem is the motor doesn't have enough torque when supplied with 9volts. If I turn it by hand it works perfectly. Any ideas on a new motor or another method I can use. The problem is ground clearance isn't much since I am using the solarbotics black plastic wheel and this is on the bottom of the bot between the front axles. I do have some linear gears which I could try to hook up to a gear mounted on a servo, but I doubt that would be enough torque either. Any ideas for motors (I need 4 so cheap is preferred under $5 each) or another method?  Each robot has 2 pegs and I would like each peg to be controlled individually, but to make it would I would consider if they worked at the same time.

Thanks for the help! I was hoping to finish the build tonight so I could work on soldering the circuit, but alas lady luck is not on my side!

And yes Frits those ARE paint sticks and that IS a ton of hot glue!


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Is that a setting on your camera? ;-)

The use of a "cam" for tensioning a peg (a cam follower) and quickly releasing it again, is a good choice. But you need to estimate if this motor can produce enough power to push the peg this far down/up in just one rotation.

Just to be clear: a cam is not the same as a gear. You're probably using a gear motor there: a motor with a gear reduction attached or built in. Make sure that the linear motion of the peg is well aligned towards the shaft (axle) of the cam.


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First off: if you're using a 9v battery, stop.  Use AA's or AAA's instead.  6 of them if you want 9 volts.  9v batteries don't produce nearly as much current, which translates to torque when you're running it through a motor. 

Also ... if that's not enough to make it work, try another method.  You're probably losing a lot of energy in friction, which doesn't really need to happen.  Try to come up with a way to reduce the friction between the gear and the peg.

Another option for linear motion is a solenoid, but you'll have to rebuild some of your project and change the programming.  If you're willing to do that, then you might as well look into other forms of making linear motion.  Worm gears are pretty cool, I hear, as are rack-and-pinion setups.  But these might make it difficult to quickly release the peg, like what happens with your gear.

I hadnt thought about the problem possibly being the 9volt battery. I'll grab some AAs and see what it can do. It may be the motors. I'll dig through my previous orders and see what the torque rating is on them. I was hoping to avoid solenoids and rack gears because they would require more room than I have. I do have worm and rack gears, but when I dry fitted them I would need to do somethign with all my axles to give more room. I'll play later tonight or Friday and see if batteries will do the job.