jes's build log

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jes
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Re: jes's build log

Post by jes »

Well my spool of Taulman 910 arrived and I've been doing a bit of learning.

The seller suggested I dry it out in the oven before I even use it, but I was keen to press forward so I didn't bother. The first few test prints came out great apart from bed adhesion. They would curl up from the bed at the corners. For reference I have an Anycubic i3 Mega with Ultrabase on the bed. So far the best defence I have against the 910 curling up is adding a 10mm brim to the bottom layer.

After I was happy with how the filament was printing I tried printing a chassis half but after about the bottom 3mm of layers it started popping and hissing. I let it finish the print but the surface finish was very poor. I then dried the filament out in the oven at 80 deg. C and it has been fine since then.

Happily, the nylon is about 20% lighter than the PETG which has allowed me to add an extra perimeter to the wall thickness without adding any weight.

This is what I currently have assembled:

Image

I don't consider this presentable. Also the wedge is slightly too tight at the moment so it doesn't automatically pivot downwards. If I can't solve this problem by increasing the clearance then I'll have it pivot on some small bearings.

The bottom chassis half in that pic is the one that was printed before drying the filament out with only 1 perimeter, and the top one is with dried filament and 2 perimeters, you can see the bottom half looks a bit misty and furry. Unfortunately the top half also had much worse performance on overhangs (e.g just above the top of the wedge), I think possibly because I had 2 perimeters instead of just 1, it was more prone to curl up at the corners. Both halves were printed in the orientation of the bottom half.

I'm currently experimenting with printing a chassis half the other way up with support material under the bridges in the middle, and with printing at 245 instead of 260, and with using a raft instead of a brim (like any good scientist, I change about 4 things at a time...). Will report back on how it goes.

The other thing I'm struggling with is how to invert the control when the robot is upside down. The FlySky FS-i6 controller has a setting to invert each channel, but this is a global setting and can't be conditional on the position of one of the switches. It also allows you to set a "dual rate" curve for each channel based on the position of a switch, but it won't allow you to set a negative rate, the lowest it will go is totally flat. Ideally I'd like to be able to flick one of the switches and have that switch decide whether or not the throttle is reversed. Anyone know how to do this? The best plan I've got so far is to leave the menu open on the screen that allows you to invert channels and then invert it using the menu if I get flipped upside down, but that comes with a risk of fat-fingering the menu and inverting the wrong channel.

At the rate this is progressing I expect to be ready by the end of the month, and as such have signed up for AntFreeze 7 :)

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Kyro
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Re: jes's build log

Post by Kyro »

regarding the flipping a switch to invert controls, it cannot be done on the flysky.

but honestly, its better to learn how to drive inverted anyway.

when inverted its only forward and reverse that is wrong, left and right remain the same. reversing the channels (2 of them) would likely reverse the steering which is worse than forward and reverse being wrong.

the flysky however is great for when you use your own mixing... i have a tutorial on setting up drive, quick and easy.
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jes
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Re: jes's build log

Post by jes »

Sorry, wasn't clear, it has a setting to allow you to invert each channel individually. I tried inverting the stick I'm using for the throttle and it does exactly what I want, it's just that the only way to control it is with the menu interface rather than the control switches.

It's a real shame the controller can't do it, it has all the hardware required, just a small software change would solve it.

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Re: jes's build log

Post by razerdave »

You can do a hardware hack to invert your controls with the flick of a switch, a DpDT switch wired up in the correct fashion would give you the desired result, but it would have to be 2 switches, but you’d get used to clicking the 2 together in time :). I’ll get a diagram when I’m on a computer.

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jes
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Re: jes's build log

Post by jes »

That's a great idea! I think just 1 switch would do to invert 1 channel.

Something like this? If previously the "bottom" of the pot was 0v and the top was 5v, we can add a DPDT switch that allows you to swap them over.

Image

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jes
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Re: jes's build log

Post by jes »

I opened it up, identified the connections for the stick I'm using, cut the potentiometer pins, and soldered wires to each side of each cut. They're the 4 thin grey wires in the picture below.

I'd suggest being careful with the little PCB on the back of the pot as it is only held in place by the pins on the pot, and once you cut 2 of them there is only 1 pin holding that PCB in place. If you were more cautious than me you might consider adding a dob of hot glue to stop it from moving around.

Image

I don't have a suitable switch on hand at the moment, so I twisted the wires together in both orientations (first the same as before, and then crossed over) and can confirm that it inverts the channel as expected. I tested it by looking at the "Display" mode and observing that the channel moves in the opposite direction.

I don't yet know where I'm going to put the switch when it arrives, possibly throw away the "VrB" knob and put it there, there isn't a great deal of space to be putting new holes in the front. Maybe the top or the sides, but then I'd be concerned about it getting knocked during transport.

The only bit I didn't expect is that the midpoint on the joystick is not exactly the midpoint on the pot, which means when you swap the ends over, the midpoint on the joystick is no longer the zero point on the channel. It doesn't change by that much though, I expect I can trim it so that with the stick centred the robot is not moving in both modes. Failing that, a bit of creep while running inverted is not a big deal.

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MarkR
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Re: jes's build log

Post by MarkR »

That is an exceptionally creative hack. Well done.

I like it a lot.

Mark
Robots: Betsie - RaspberryPi controlled flipper bot with gyro stablisation - too clever for her own good?
Stacie - tidy flipper; 4wd driven by hair bands

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Kyro
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Re: jes's build log

Post by Kyro »

why not just use one of the current switches?

out of all 4, i use just 1 of them and the throttle hold option. this i use backwards though and flipping it engages full throttle so i have a fast flip or immediate spin up by flicking it, i use shock cord to make it return to the upright position.

that way it would do what you want while looking exactly the same on the outside
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jes
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Re: jes's build log

Post by jes »

The current switches are all SPDT so I'd have to use 2 of them, but it'd certainly be an option. I might even put the DPDT switch in the place of one of the existing switches, still haven't decided.

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Kyro
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Re: jes's build log

Post by Kyro »

well a DPDT switch is basically 2 SPDT switches so using 2 would work... they are relatively cheap on feebay though so replacing 1 is a cheap option.

i had never considered a hardware mod to achieve inverting drive...
Team Rocket
Esper(4wd flipper)
Mantis (4wd grab 'n' lift)
Dominus (Vert SPINNAAH)
Breakout(modular cluster)
Remembering Rex (antweight cassius)
Fennec (4wd flea) former world champion

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