Showroom **RIP** - 6DOF project using 12v DC Motors, Sabertooth 2x60's (was MM's) and Arduinos + OSW

.25?? are you sure?

I don't know think they maybe the wrong type is there only wire wound that will work for this kinda thing ? @SeatTime what pots did you end up using on yours ?

@SeatTime, @SilentChill for your DIY actuators, is it 100% necessary to have an internal system to prevent nut rotation?

I figure that the actuator design could be simplified quite a bit for any application where the shaft is already prevented from rotating (which is the case for nearly all designs of motion simulator).

So long as both ends of the actuator are fixed to the base & platform using universal joints the UJs should transfer the reaction torque to the platform and prevent the nut & shaft from rotating.

I was just thinking that being able to do away with the anti-rotation mechanism would reduce the cost, complexity and drag.
...You'd need decent UJs though (that don't have any slop), but that's not too much of an issue.

Which anti rotation device are you talking about ?

Hi @SilentChill well done that man always shifting the goalpost and never doing things by half measure Massive congratulation on taking the plunge with this next evoloution of your sim building .. goes with out saying i'll be watching this space as well... Nicely done ,,By the way the anti rotation method I used in my design is the square block which holds the main support shaft..it keeps the leadscrew nut from rotating so you end up with the desired push pull operation from the leadscrew , not telling you guys how to suck eggs just another take on an issue that has many solutions .... Congrats mate

@SilentChill, The part of the actuator which stops the ball-nut spinning around as the motor torque pushes it up the screw.

Usually one or more steels bars runing parallel to the ballscrew with a linear bearing or bushing running along it which is attached to the ball-nut.
The thing to stop the ball-nut spinning around as the motor pushes it up the screw.

With CNCs this is often one or more steels bar which runs parallel to the ballscrew with a linear bearing or bushing running along it which is attached to the ball-nut.

@wannabeaflyer2 Does that method introduce any play when changing direction?

Hi @DEADBEEF the block is designed to have 0.5mm maximum clearance from the surface of the openbuild extrusions so there will be some play but minimal and not enough to impact on operation or feedback sensor... well at least in my theory so far its ok but tge real test will be duration and max loading testing to come cheers

nice work with this project

Hi @SilentChill thought I'd pass on some experience gained using these PM90 motors--------THEY ARE BLOODY POWERFULL" LOL fingers clear at all times and powered up by 12v battery in thier state unloaded they over run when hooked up to the leadscrew, (4000 rpm remember ) so allow a decent run on gap at both ends of the travel during testing I'd recommend Fitting limit switches early on even during testing , the speed and power can easily catch you unawares and can do some big time mechanical damage ( so far easily lift in excess of 40 + KGs at speed ) so serious care required during test and setup phase .. Just a heads up for when you get to the testing point good buddy

Hi @SilentChill thought I'd pass on some experience gained using these PM90 motors--------"THEY ARE BLOODY POWERFULL" LOL fingers clear at all times

noticed that when testing and powered up by 12v battery and in their unloaded state , when hooked up to the leadscrew, (4000 rpm remember ) they will overun due to inertia I guess, so allow a decent run on gap at both ends of the travel during testing I'd recommend Fitting limit switches early on even during testing , the speed and power can easily catch you unawares and can do some big time mechanical damage ( so far easily lift in excess of 40 + KGs at speed per actuator) so serious care required during test and setup phase .. Just a heads up for when you get to the testing point good buddy

Agree, the sims we work on can do some serious damage if care is not taken. Anything with the power capable of throwing around the weight of a human + equipment is not something that should not be treated lightly - especially in regard to safety. I do not have any issues with overrun, even with the rig unloaded, although I'm using a AMC1280USB controller which seems to have a very good PID. I have fitted limit switches from day one, as if anything goes wrong - pot failure etc - things can quickly end in tears. Recommend start your testing with low power settings and then ramp things up once you know everything is working fine.

Hi guys my bad for not being clear, I meant to say testing without controller connected, so far @SeatTime your 100% correct these units dont have overun issues when linked to a controller, my comments were based around just connecting 12volt battery to drive the actuator up and down manually to verify that it works as expected , cheers seatime you lead the way and now followers are growing, lol you got us going this actuator trend and its looking great

I do use a internal anti-rotation shaft and linear ball slider, but also use a coupler at the bottom of the actuator that stops any rotational movement, as inertia will still causes the actuator to twist. The top coupler is free to move in any direction. Have m

OK, I used a electric battery drill to test mine, high risk to operate your motors in the actuator without a controller . Depending on how you have you limits setup, even if the motor is shut down, inertia could drive it straight past the limits and re-energise . Be careful.

Love it haha that is something I would do just to test it slap full power on the mofo

I will take care when I get any where near ready to build the things. Lots of parts in transit.

@SeatTime and @wannabeaflyer2 what type of multi turn pots did you get ?

Hi @SilentChill I used these http://www.ebay.co.uk/itm/121839695...49&var=420832724718&ssPageName=STRK:MEBIDX:IT not sure how long they will last in use ..pay your money takes your choice sort o deal .. at < £5 I had to try just to see if the system worked , ideally l would have loved to use my 180° or some 360° hall effect sensors as the signal is digital and if my understanding is correct these are less prone to noise pickup.. but had problems sorting out the gear ration to use these ....The gears would have had to have been somey=thing in excess of 120mm diameter Do'h ( think homer simpson LOL ) so im using GT2.5 Belt and pulleys at to achieve ratio 1:1 where 350mm travel equates to approx. 10 Revolutions at the pot ...well that was the plan at least :-0 ..

why dont you try out the rotary encoders?

Hi @Jamshaid would have loved to be able to use rotary encoders with this arrangement but currently I don't think simtools supports this feedback option as yet ( I may well be wrong in that assumption ) , they relitevly cheap so would make life so much easier in some instances but the Arduino code would need to be in place to deal with this type of encoder and I think that processing slows down the Feedback part of the ard coding, .. I tested rotary optical encoders on another project ( Sabertooth 2x32 & Kangeroo module ) and was getting decent results before I had issues with the Kangaroo Controller modules i was using at that time ( self inflicted DIY newbie problems ) ..:-(

Any type of motor feedback has nothing to do with simtools - its all with the controller software. I played around with encoders at one stage when I was using three Arduinos for my 6DOF, but found just reading one encoder loaded the Arduino quite a bit. As I was running two motors per Arduino and had lots of other stuff to worry about, decided in the end to keep it simple and use pots - 7 months and still going strong. Nothing stopping anyone else from giving it a go though. I used some good quality pots from Element 14.

Can't comment on their use with Arduinos, but they work pretty reliably with a Sabertooth / Kangaroo combo.

The only real drawback I can think of is that they require a startup routine so the controller knows where the endstops are. This must be carried out each time the controller is powered down.
Obviously you can avoid this by just not powering down the controller between sessions. I've not directly measured the current draw of a kangaroo, but it can't be much.

I've not attempted to DIY a linear actuator yet, although these recent projects by SeatTime, etc. make me very tempted (I already drew up some plans for a 6DOF LinAc design I'd like to build one day).

To me the lack of moving parts of a rotary encoder based feedback system would be particularly attractive. Printing an encoder wheel onto a transparency and gluing it to the end of a shaft coupler (or whatever) just seems like so much less hassle than gearing systems and multi-turn pots. If you're already using Sabertooths, encoder feedback will likely be cheaper to implement and more reliable in the long run as well. Not to mention that it'll also work with any length screw without adaptation.