T_Y's Build Log

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LimaHotel
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Re: T_Y's Build Log

Post by LimaHotel » Mon Sep 09, 2019 7:43 pm

That looks really good - I'm sorry I won't be at the Sheffield aws!
I need to move that weekend is the problem. That's when my halls here expire and I move to wherever my first placement school is. Which they still haven't confirmed. :roll:
But ye, has the plow /wedge had any effect on the gear slippage? That was the primary reason for the change wasn't it?
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T_Y
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Re: T_Y's Build Log

Post by T_Y » Mon Sep 09, 2019 10:45 pm

It was actually more to do with having the forks there and the opponent being sandwiched between them and the axe. I actually now think that the gear slippage is to do with the servo horn (which is screwed to the larger gear) actually flexing under the torque when such a case happens. I'm going to pick up a metal servo horn to replace it and hopefully that should reduce gear slippage (I don't think I'll remove it entirely with this servo!). In the meantime I can try to be a bit more gentle on the throttle stick and that should help with slippage.
Thomas

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T_Y
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Re: T_Y's Build Log

Post by T_Y » Sat Oct 05, 2019 11:42 pm

Realised I didn't update this for AWS59.

Not much to say really, as usual an incredible day even if I didn't win any fights. After a chat with GeorgeR, I ordered some 0.5mm grade 5 titanium to upgrade the shield on Percussive Maintenance 2 - I had a whiteboard against Vampire where the alu shield stood up okay for a bit, until its blade got a good bit point and tore the shield off the hinge! I noticed that the bite happened on the bend, and I think because the shield is almost upright, there was little in the way of deflection happening. I don't think the hinge is worth using, at least in PLA+ form, so I'm just going to direct mount the Ti shield onto the front, with a small gap to allow it to flex a bit for now. I might revisit this in the future and try to make a polycarbonate hinge instead.

The rebuild of HYTTIOAOA is progressing, I've transferred the internals into the new shell along with another KingMax servo, so it should be much quicker on the lift. I'll make the front wedge out of 1mm aluminium, with the sides wrapped down in front of the cheeks to give it extra protection. Hopefully, the lower angle on the wedge should reduce the chance of a good bit happening.

Another idea that I want to try for AWS60 is to build a mechanum wheel bot, so a lot of the work this next month is going to be designing that! I think I should be able to cram all the electronics in there - I don't think an Arduino Pro Mini has enough analogue pins for all the control needed , so I might need to fit two of them inside, plus the motor drivers. I'll have to check the specifications to be sure though.
Thomas

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MarkR
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Re: T_Y's Build Log

Post by MarkR » Sun Oct 06, 2019 10:38 am

YES! Definitely build a mecanum wheel bot!

Of course it will be necessary to drive all four wheels independently, ideally with either stepper motors or shaft encoders, so that the speed can be set precisely. I've no idea where small/light mecanum wheels can be got, I looked (briefly) at 3d printing them, but I don't think it would be easy because of the high level of detail required for correct operation.

I think I'd probably use steppers, I've seen a load of N20-size steppers (fit the same gearboxes as N20) on Aliexpress etc, but I've not tried them.

You need a lot of output pins to drive all the steppers, 2x gpio per channels, so 8 pins, but maybe do-able on some stock Arduino or use a custom board (+ include stepper driver chips)?

But if you get it working, massive credit will be due.
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EddieJ
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Re: T_Y's Build Log

Post by EddieJ » Sun Oct 06, 2019 11:27 am

Do you want some mechanum wheels? I designed some antweight ones for another over complex project, but haven't got around to building anything yet.
Can cast you an extra set if you dont mind covering postage cost? :)
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T_Y
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Re: T_Y's Build Log

Post by T_Y » Sun Oct 06, 2019 4:07 pm

I think I'd probably use steppers, I've seen a load of N20-size steppers (fit the same gearboxes as N20) on Aliexpress etc, but I've not tried them.
I didn't realise you could get stepper motors smaller than those cube ones you always see, that'll be something to explore - I was going to use N20s I had lying around for the prototype, which won't be as accurate. Do you know if you can overvolt stepper motors in the same way as N20s?
Do you want some mechanum wheels? I designed some antweight ones for another over complex project, but haven't got around to building anything yet. Can cast you an extra set if you dont mind covering postage cost?
That would be amazing, I was going to design and 3D print them so that would save a lot of effort! I'd be happy to cover postage. If you don't mind me asking, what are the dimensions of the wheels and are they designed to fit on 3mm D shafts?
Thomas

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MarkR
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Re: T_Y's Build Log

Post by MarkR » Sun Oct 06, 2019 7:03 pm

I think you have to be a bit careful overvolting steppers because the way stepper drivers behave, they pull current when the motor is not moving, the "holding current", which can possibly overheat the motor quite quickly. Of course that might be fixable in software / firmware, or as some option in the stepper driver.

So unlike a DC motor, a stepper can have current flowing when not moving, not stalled or anything, just holding position, it's used in 3d printers, etc, to resist movement when not driving. It's worth a try though, I can't imagine a big deal overvolting a 6V motor to 8V (2S pack or whatever).
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EddieJ
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Re: T_Y's Build Log

Post by EddieJ » Mon Oct 07, 2019 10:51 am

Yea to fit 3mm shafts and 23mm diameter, will lock to axel - i would have liked smaller but each roller has to have a M1 axle, and making any smaller rollers and they will have next to 0 grip.

Have it roughed out at the moment, I will finish it off by blending all the elements together, making the struts more sturdy etc, and start 3d printing this month so you can get a set :D

Image
Image

Good luck with the fancy electronics, no idea about that! Hats off to you guys :P
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T_Y
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Re: T_Y's Build Log

Post by T_Y » Wed Oct 09, 2019 7:06 pm

@MarkR Ah right, fair enough. For the prototype, I think I'll stick to N20s, I already know which motor drivers to use and how to connect it all up (also, I think I'd need 4 separate driver boards for the steppers as opposed to the drv8833 I use for DC motors, which do 2 separate channels on one board).

@EddieJ Thanks a lot! How wide are the wheels?

Controlling the wheels should be alright, I just need to wrap my head around how to convert the logic for wheel direction/combinations into Arduino-readable stuff. Re-using code for some of my other bots will be helpful!
Thomas

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T_Y
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Re: T_Y's Build Log

Post by T_Y » Mon Oct 14, 2019 10:44 pm

Quick update, HYTTIOAOA is now complete, aside from the aluminium wedge. For that, I'm waiting for the aluminium servo horn to arrive (should be soon), as the plastic one currently attached is slightly shorter.

In the meantime, I've been procrastinating about the mechanum wheel bot. While browsing the Sketchup model library, I found a mechanum wheel model, so I'm going to have a go at modifying that and see if I can print it off.

@EddieJ I might not need you to send me a set of wheels in the end, depending on how this goes. Sorry about any inconvenience.
Thomas

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