Crumbs! (And Friends) - Team Manuva's Antweight Build Log

[Mr Manuva27]

So BotFest was due to happen a few months ago, but was unfortunately cancelled due to lockdown. I had redesigned Crumbs! to improve the lifter as the servo driven one didn't have enough power.

I always wanted to build a 4-bar lifter but kept it under wraps until the event. When it was cancelled, I lost a lot of motivation to work on it and it sat in my Fusion360 files for a few months, until last weekend!

The arm is now powered by a 100rpm N20 rather than a servo, plus a 300mAh 2S battery.

It needs reprinting at a thinner layer thickness before it is truly combat ready, plus superglueing a stainless steel beak (leftover from BDR) to the front arm. Regardless, I'm super happy with it.

Hopefully events get back to normal sooner rather than later so I can take it for a proper test run!

[Ocracoke]

Yeah, I hope I get to see this soon, love the arm action! I've been cleaning out the shed here and found the BotFest arena in there, sitting there ready to go.

[McMullet]

Looking great Andy, I'm also working on an antweight 4-bar lifter (very much languishing in work-in-progress CAD though).

Do you have a way to stop the motor when the lifter gets to the end of its travel? I was planning on using a servo to stop it damaging itself, but it doesn't seem like a great power-to-weight ratio whereas that is super fast, looks more like a flipper than a lifter.

[Mr Manuva27]

Yeah, I hope I get to see this soon, love the arm action! I've been cleaning out the shed here and found the BotFest arena in there, sitting there ready to go.

Thanks! Really pleased with how the arm movement came out. I still need to adjust the horns at the back so it can self right, but aside from that it's perfect. Fingers crossed we get the all clear to fight again soon.

Do you have a way to stop the motor when the lifter gets to the end of its travel?

I do! It's called the floor . Because my transmitter has both sticks on spring return, just a quick burst of the motor is enough to get full extension. Don't think it's enough to burn the motor out, but proof of the pudding shall be in the eating.

I was planning on using a servo to stop it damaging itself, but it doesn't seem like a great power-to-weight ratio whereas that is super fast, looks more like a flipper than a lifter.

Servo should be fine. It's worth noting that a 4-bar arm requires different force depending which end is powered. The "crank" (rear arm) takes less force to lift than the "rocker" arm (front). If you're worrying about a servo not having enough power, you'll be better off linking it to the back arm. It should be sufficient. I'm only using an N20 because I'm using a Malenki Nano ESC, which works better for motors than servos.

If you're making a 4-bar, I recommend the AskAaron blog and geometry calculator/excel sheet for it. Took lots of trial and error, but was worth it in the end.

http://runamok.tech/AskAaron/lifter_FAQ.html

[McMullet]

I've spent FAR too long playing with the spreadsheet. Happy with that part, just messing around with the infinite design space of 3D printing now...

I do! It's called the floor . Because my transmitter has both sticks on spring return, just a quick burst of the motor is enough to get full extension. Don't think it's enough to burn the motor out, but proof of the pudding shall be in the eating.

That's a good point. I was assuming I'd just stupidly hold the stick down with the motor stalled but in reality I'd probably be able to let go after a second or so... N20s look like a better power to weight than a servo.