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Full auto sling-x-bow: New approach

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Old 01-12-2017, 11:28 PM   #21
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how heavy is the weapon?

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Old 01-21-2017, 12:32 AM   #22
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Why not use two drills to add more even torque (just a thought it's been some time since my physics class in high school)? You could even have them controlled by a microcontroller, with a switch on the trigger for easier control.

You could also perhaps get more powerful electric motors mounted more permanently. Maybe the electric motors that hybrid vehicles use? Or just electric high torque motors that are powerful enough to increase the speed.

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Old 01-21-2017, 02:24 AM   #23
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He's showing off what he made, I don't think he ever asked for suggestions for improving. It seems every time he's post a weapon, there's a dozen people that come on here with ideas on how it could be improved. I could understand if he'd asked for help, but can we just enjoy what he's made?
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Old 01-21-2017, 02:38 AM   #24
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"He's showing off what he made, I don't think he ever asked for suggestions for improving."
"but can we just enjoy what he's made?"

Both are possible. Better engendered discussion than blind acceptance.
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Old 01-25-2017, 08:00 AM   #25
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Unless your absolutely certain that you have an improvement that will work I think people should not suggest things because it means he has to read so many comments
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Old 01-26-2017, 02:36 PM   #26
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do you think that an ebike geared hub will have enough torque to crank up the bands? ? If yes you can integrate the hub into the crank gear and obtain a slender profile.

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Old 01-28-2017, 06:05 PM   #27
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Default Full auto sling-x-bow: New approach

Could this possibly speed up your mechanism. The speeded up section of the gear could be for releasing of the trigger. I know adding another gear would obviously increase friction but still it's an interesting idea itself. maybe it could work if you could keep the friction down.

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Old 07-06-2017, 05:50 AM   #28
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Have you tried using a cordless impact driver instead of a cordless drill?

I started doing some research on high torque drills and noticed that cordless impact drivers have much higher torque than cordless drills.
For example, I found this 20V Max Lithium 1/2 in. Cordless Xtreme Torque Impact Wrench at Harbor Freight that has 1200 ft. lbs (1627 Nm) of breakaway torque. Since the gear wheel only has teeth on half of it, maybe this would be a well suited application.

Now assuming a factor of safety of 4.0 to protect the motor from over heating, you have 400 ft. lbs (542 Nm) of torque to design with.
Assuming a gear radius of 3 inches (76 mm) you should be able to pull back a force of 1600 lbs (7117 N). That is some serious power,
and would take a lot of rubber to get that much resistance, but even 300lb or 400lb draw weight would be able to fire regular hunting crossbow bolts.
One thing I'm not sure about is the RPMs, they say the impact drivers have variable speed too, so I'm not sure if the impact driver would spin too fast to operate correctly or if careful trigger pulling to get the best speed would be required.

I really like your design and plan to make one of my own soon in my spare time.
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Old 07-07-2017, 12:56 AM   #29
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I'm skeptical. Those 'breakaway torque'-figures are values generated by the internal hammer mechanism of an impact wrench. This means rapid high energy impulses, not continuous torque that is required to drive the gear set.
My guess is, an impact wrench would destroy the mechanism in very short order.
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Old 07-08-2017, 10:20 AM   #30
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Belargo got it right. To make things worse impact drivers can't cope with counter force, they are designed to loosen/tighten nuts and bolts. Between the "hammer blows" there is zero torque and the slingshot bands would drive the wheel backwards.

Conclusion: Impact drivers are useless for the purpose.

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