[WIP] Moving Saw Arm Mechanism

[heyitsdisty]

Since TC11 concluded, I've been wanting to have another go at building some more Technic battlebots. Robot combat fans will probably be able to guess what I'm planning to build from the video above - but I could really use some input from the Technic community to help me make it more efficient/less sucky.

The video doesn't show it particularly well, but there's a motor driving a worm gear, which in turn drives a gear wheel, which in turn drives the sequence of gears connected to the pivoting arm, which drive the chain connected to the saw blade.

Most of the gears on the arm are attached with friction pins and serve as clutch gears, allowing the motor to drive the saw once the mechanism has fully extended/retracted.

So here's how I want to improve it:
 - I generally want to shrink the mechanism down, especially the width. It's 10 studs across and I definitely want it to be narrower.
 - Is there a way of modifying the mechanism so the saw starts spinning as soon as the motor switches on?
 - Ideally I'd want the saw to only spin in one direction (don't mind which one though). Am I right in thinking I can achieve this with a differential? And if so, how exactly?
 - The saw piece itself isn't ideal, since it only has a pin hole and it's a little too small for the MOC I'm planning. Are there any disc pieces out there with axle holes that could pass for a saw? They'd need to be available in grey/silver or similar too.
 - If there are any better mechanisms/techniques that'll achieve the same result (ie arm slowly moves but doesn't stall the motor when fully extended/retracted, saw blade moves fast, whole thing is run using only one motor), I'd be interested to hear about them.

Any advice you can offer will be much appreciated. Thanks!

Edited May 15, 2017 by heyitsdisty
Swapped Flickr-hosted video for YT-hosted video

[Leonardo da Bricki]

Try using half beams to make it narrow.

Not easily. If you used another chain to drive it directly, that is the best way.

Differential is used to split the drivetrain and allow one side to drive at a lesser speed, specifically when turning. So, it is not the best option to use.

Check the wide selection of Bionicle parts for some blades to use. I cannot think of a specific part at the moment.

Use the white clutch gear to make the extension easier.

That is all I have at the moment, hope this helps.

[Captainowie]

4 hours ago, Leonardo da Bricki said:

Differential is used to split the drivetrain and allow one side to drive at a lesser speed, specifically when turning. So, it is not the best option to use.

That's one use for it, sure. But you could certainly use a diff in this case too, with one output moving the arm back and forth, and the other output rotating the blade. As long as it takes more torque to rotate the blade than it does to move the arm, then when the motor turns forward, the arm moves out until it hits its stop, then the blade turns - the reverse happens when the motor turns backwards. You could possibly add in a ratchet if you didn't want to have the blade turning when the arm is retracting, but then you stall the motor when the arm retracts fully.

Owen.

[Leonardo da Bricki]

That's true. At the time though, I was thinking that it was too wide for what you wanted to use.