Questions about antweights - servos, switch placement, armour

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Isioviel
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Location: Oxford, UK

Questions about antweights - servos, switch placement, armour

Post by Isioviel » Fri Dec 01, 2017 10:08 am

Hi everyone,

I’ve been lurking on this forum for a few months now whilst building my first antweight – your posts have been amazingly helpful, thank you!

I’ve finally got the electronics all working (I definitely didn’t take the most efficient route…) but could do with a little advice on the mechanics.

Servos:
I’m building a lifter – will a 9g microservo be strong enough? From the datasheet it looks like it will be fine, but they seem so flimsy, and I don't have the weight allowance left for a standard servo. Do I need to buy a better quality microservo to stop it feeling flimsy, or am I just overestimating the strain it will be under?

Switch placement:
How accessible does a switch need to be? Does it need to be immediately accessible, or can I put it under a hatch of some kind? Do I even need a switch as long as it's easy to access and remove the battery?

Armour:
I have some HDPE (an Ikea chopping board!) I originally planned to use, but it seems unnecessarily thick. I've seen a few posts mentioning 3d printing armour in ABS - is this strong enough to protect the electronics, or best used in combination with something else?
I am basically incapable of sawing in a straight line, so best case scenario (if I can't do it with scissors) is to 3d print or lasercut something, as I have access to the machines through work - so any recommendations for materials and thickness would be amazing.

Finally, all my electronics, except the motors, are temporarily held down with duct tape or adhesive foam - what's the recommended way of attaching things to your antweights?

Below is a photo of it in the testing phase (it's all soldered up now!).

Thanks in advance for your help :)
antweight.jpg
antweight.jpg (32.67 KiB) Viewed 447 times

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Lincoln
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Re: Questions about antweights - servos, switch placement, armour

Post by Lincoln » Fri Dec 01, 2017 6:00 pm

firstly, Welcome to the great community of antweight robots.

obviously if the servo will work for antweights will depend on exactly which servo you buy. in my experience those 9g servos are usually not up to the abuse, but if you find one with enough power, probably about 2 kgcm will do, then it should work for a lifter.

i would say that a switch is not necessary by the rules. but a quick way of removing power is. this can be a switch, removable link, or the battery plug. as long as it is a few seconds to access and not minutes.

3d printing can be incredibly strong, and also very weak. it's all about the design and the direction it is printed.
for example, one of my robots was pretty much entirely 3d printed, and some bits survived with a scratch and others broke apart.
sa7 flipper.png
sa7 flipper.png (19.56 KiB) Viewed 431 times
for example the flipper was printed vertically like this, when hit with a horizontal spinner it broke apart along the layer lines quite easily despite being over 3mm thick.
sa7.png
sa7.png (75.86 KiB) Viewed 431 times
on the other hand the main body which was printed this way up,got some scratches around the sides and back and only broke at the front after the flipper had broken allowing the spinner to get at the exposed edge.

if you are going to 3d print your robot, you could also go with a fairly common design of 3d printing the internal structure and bolting on 1mm polycarbonate panels for amour. and to attach components you can design little holders and clips to hold the components to the 3d printed chassis.

if you have any more questions or i forgot to answer one then just ask and someone will help.
Team RobotMad, home of the Smart robots, and very mean pots :)
Chris and Lincoln Barnes

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Isioviel
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Location: Oxford, UK

Re: Questions about antweights - servos, switch placement, armour

Post by Isioviel » Sun Dec 03, 2017 10:15 pm

Thanks Lincoln, for the welcome and for the advice - I'm excited to be getting started!

I might build it all up using a microservo for now, but leave a little extra room around it, then I can pick the best servo with whatever remaining weight limit I have at the end. Hobbyking are selling a slightly more powerful 10g one (https://hobbyking.com/en_us/turnigytm-t ... c-10g.html, so that might be a good bet.

Glad to hear 3d printing isn't a bad call - I'll print a couple of designs / orientations, then bash them around a bit to see what's the strongest. It'll probably take me a few goes to perfect my design anyway, to make sure I can easily turn off the power & also access the battery for charging (it didn't really occur to me before I started how difficult it would be to cram so many components into such a small space!), so I may as well put the failed designs to a good use!

Thanks again, that was all massively helpful!

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peterwaller
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Re: Questions about antweights - servos, switch placement, armour

Post by peterwaller » Mon Dec 04, 2017 7:16 pm

The other thing you can try to strengthen 3D printed designs is to try other materials.
I use Nylon (Alloy 910) and Poycarbonate (Polymaker PC Max).
The nylon is more flexible and therefore more able to withstand impacts but both are stronger with better inter layer adhesion.
While both can still be damaged by spinners they don't normally shatter or suffer catastrophic failure.

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