Aluminium robot arm.

krolikbest · Joined: 02 Jan 2017 Posts: 112

Hi,

there is no questions. Want to show my latest project, still in progress:

https://www.youtube.com/watch?v=suFuSS_XOX4

Arduinos are working with Bascom code.

Regards,

Martin

albertsm · Joined: 09 Apr 2004 Posts: 5921 Location: Holland

Looks like a real robot arm. I mean not a small desk one. what are the plans for the arm when it is finished?

krolikbest · Joined: 02 Jan 2017 Posts: 112

Exactly. I'm going to use it in production proces like " take, move, put".
It's significant difference between making a toy on the desk using modelling servos and using industrial stepper/servos... and in spite of
long TODO list, slowly getting closer Smile

And thank you for nice comment:)

albertsm · Joined: 09 Apr 2004 Posts: 5921 Location: Holland

I will follow the project Very Happy

krolikbest · Joined: 02 Jan 2017 Posts: 112

Next step - with arms. still a lot to do... but it develops.
https://www.youtube.com/watch?v=nW0IslMvxqQ

six1 · Joined: 27 Feb 2009 Posts: 553

Looks Good Laughing

But i think, you have to slow down speed, if you reach the endpoint

krolikbest · Joined: 02 Jan 2017 Posts: 112

I know. This is caused by too small transmission ratio. I don't want to change setup of timer1 which is my square wave generator. Servos should work as fast as possible (to avoid jittering), transmission ratio e.g. 1:20 would fit my needs the best. Unfortunatelly have 1:6 and changing microstepping (greater) also isn't good solution for so small transmission ratio since stepper have too weak holding position capability. Currently I'm working on changing this ratio.

krolikbest · Joined: 02 Jan 2017 Posts: 112

So finally last chapter about my first robotic arm. You can see it there https://www.youtube.com/watch?v=FdPu8XA_B-Y.
Now I can say that:
- during this project, I came to the conclusion that atmega328 is a bit too weak to parallel generate pwm signal for servo and reading servo's encoder. The workaround seems to be simply, it'd be enough to generate pwm signal on the separate MCU and talk with uC readfing encopder's signal or.. the next idea is to use xmega with quadrature encoder read registry. It is very likely direction I will follow. So far have no experience in xmega thus i count on this forum! Any help how to configure or read quadrature encoders on xmega are more than welcome Smile

- my second project is under way: i'm going to buy scraped industrial robotic arm with removed motors. Only arm, it's about stiffness. Servos of my choice, electronic and application by me.

Regards,

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

The mega1284 may do it running at 20 MHz comes in a 40pin dip .
Regards Paul

albertsm · Joined: 09 Apr 2004 Posts: 5921 Location: Holland

thanks for the video. it looks like a professional robot arm. you are right that it is about sturdy but also about repeatability. that is why it is so expensive. yours look usable. but i do not know what the ultimate goal/application is.
i played with some toy arms. they are not really usable, only to play around.
you learned a lot with your project. Xmega is a good choice for most demanding projects. but of course you can also take 2 tiny, megaX or DB chips.

krolikbest · Joined: 02 Jan 2017 Posts: 112

initially indeed it was meant as a toy but with time I decided to develop fully scaled application that I could use in my next project (I'm going to buy scrapped robotic arm, probably old Fanuc arm). I decided to use hybrid steppers Nema34, torque =9 Nm*planetary gearbox1:10 => 90Nm, so need to generate very fast pwm signal. And now comes the question which uC to use to control position of the stepper and parallel generate pwm. Paulvk suggested atmega1284. I checked specs and it seems to be fine but on the other hand there are xmegas. Especially with encoder's register which suits my needs. The problem is however that I know less than little about xmegas Wink

Currently in Poland i can buy this: https://kamami.pl/minimoduly-avr/557590-xmega-exploree5-z-atxmega32e5.html.
Between Christams and New year i'm going to play a little with 1284. Maybe in January I'll come to some conclussion regarding this uC.
However any suggestions about xmega and setting the register for reading the encoder are welcome Smile

Regards,
Martin

JC · Joined: 15 Dec 2007 Posts: 586 Location: Cleveland, OH

What a great project!

All of the Xmegas are the same... Except the X32E series...
There are a few differences within it compared to the large pin Xmegas.

One point to remember with the X32E5 is that for many of the interrupts one has to clear the interrupt flag yourself, by your software, within the ISR code.
The ISR flag is not automatically cleared just by executing the ISR, (which it is in the older Megas and Tinies).

However, Bascom makes it easy to use the Xmegas and the new AVR DB series chips.

At times the extra speed of the Xmega, 32 MHz, is helpful.
I don't know if you are doing a lot of floating point calculations for the motions to move the arm, or if those are being done by the PC.

What a great project!
Thanks for posting the videos.

JC

krolikbest · Joined: 02 Jan 2017 Posts: 112

Thank you
acording to floating point operations - avoid them like plague. No, there is only integer operation in atmegas. The main calculations are made by PC, RPi actually.

Paulvk · Joined: 28 Jul 2006 Posts: 1257 Location: SYDNEY

I found the 1284 a very useable chip but the main reason I suggested it is because its 5 volt
20mhz and should require minimal circuit changes you may even be able to overclock it to 25mhz
Besides the electronics being great very nice machining work you have done.
Regards Paul

hgrueneis · Joined: 04 Apr 2009 Posts: 902 Location: A-4786 Brunnenthal

Paul,
I use a Xmega for a main Controller and have seven Atmega168 connected to it, that do the sampling of sensors and so on and outputs.
Have some of these run at 24MHz without problems. At VCC 5.0 volt and IF to the 3V Xmega.. If you supply 5.5 it can be clocked reliably higher.
For servo speed control I use a distance to endpoint percentage algorithm for speed up and slow down. Works well and does not need a license from Fuzzy Logic. Also used 1284s without problems (a great chip with lots of memory and ports).
Regards
Hubert.