Linear Actuator Build - Yes...another one

Hi all.

Firstly I must thank @SeatTime and @wannabeaflyer2 for their inspiration and extensive work on this style of actuator. Hopefully if I can get the prototype working I can build 5 more. Once working I will pull it apart and paint/powder coat the parts.

I have spent the past month doing design on AutoCAD in 3D (I am ok at the basics), then after receiving the parts from the Laser Cutters and eBay I have assembled the prototype. I love laser cutting as it is actually inexpensive and give awesome accuracy.

The next step is the electronics which are not my strong point. At this stage I am using MM's and Arduino to do the testing and will decide after testing if that is the way I go.







I am also building the cyclic, collective and pedals for a Helicopter simulator. These are the prototypes.

The collective has a rotating throttle. I have added a small gas strut to give it some feel and also so it will return to home if it is let go like a real one.

The pedal uprights will be made from a heavier material or be reinforced.

I am planning to start on the cyclic tomorrow. It also has gas struts to give some weight to the movement.

Great stuff this thanks for sharing and keep up the great work

Hello , great work, I really like the pot position, much cleaner than the other solutions that I found.
Can you provide some information about your motors? Can't seem to find anything on internet about it.

Great job !!, where do you buy your laser cutted parts ?

Great work so far, in every little detail, and nice pics, really clear and self explaining.
I'd like to know something about those motors too

Thanks for sharing

keep posting man , a real pleasure to see your pics well done

Great Stuff!
I thought to do about the same with pots and my actuators, but they were meant to be short throw in the beginning, now that they have 350mm throw, I think i will need too much reductions to do the same.

Great work matey excellent craft work there

Nice Work . I actually tried and moved away from the high speed belts/pots gearing and metal linear bearing (its in my thread) - but if you not too sensitive to noise then thats Ok. Also note the metal balls in the linear bearing can wear the carbon shaft. What are you going to use to stop the main shaft twisting under load?
The helicopter controls are brilliant.

i'll add to what the other guys are saying , really great to see another linear actuator and once again design changes which show there are many ways to achieve the same desired result , excellent workmanship and detailed photos ..this will be another one to watch ..

Hi @Blugreen nice idea regarding the feedback pot and gear train, could you share some details about the final gear ratio, of the setup you have i.e the number of teeth for each Gear required to cover the total linear actuator travel distance of X mm and Belt length used maybe ?

Thanks for all the comments and invaluable feedback. Imagine trying to do this sort of thing without the internet and forums like this.

@SeatTime - I followed your thread and agree that the top bearing will wear the carbon shaft. That is something I will change but isn't an issue for the prototype. There is another 12mm carbon shaft (not visible in photo) under the main shaft to stop the twisting.

@wannabeaflyer2 - I used the GT2 pulleys because I like the look of them and I could buy many different sizes on eBay. The belts are cheap also and I bought a selection of sizes. I wasn't sure of the measurements so drilled the holes for the 5mm shaft bearings in the plates where required. I used http://geargenerator.com/ to work out the gearing with what I found on eBay. I couldn't do the reduction that was required with a single pair due to space limitations so used 2 pairs. I have used a 10 turn pot (will be changed to a 3600deg Hall effects once all tested). With a motor speed of 4500rpm and a thread pitch of 5mm I have ended up with 380mm travel and 9.5 turns on the pot.

The motors are Motion Dynamics as per @SeatTime - https://www.motiondynamics.com.au/12v-350w-4500-rpm-straight-dc-motor.html

I used a local laser cutter. I had them cut the main disks and also a selection of misc parts that fitted on the threaded rods that I could use for the gearing mounts etc. That way I get accurate parts for very little cost. From memory all the laser cut parts cost around $50. Most of that would have been in setup. If I get 6 sets it would be maybe $100 total. Getting a good deal help when you supply them with a flat quality DWG or DXF file so they don't have to spend any time on it.

I purchased 1x MM to test and it looks to be working. I tested it with an Arduino Uno and SMC3.

A question for the electronics gurus out there, how do I hook up the micro switches that I have top and bottom of the travel incase it drives to far? I would like if the drive hits a switch to stop motion in that direction but allow motion in the reverse direction. From memory you did something like this @SeatTime.

Again, thanks to all.

Mark

Hi @Blugreen one thing I learnt is that these units get quite a bit of inertia and so tend to overrun when limit switches are tripped ( especially the lower one ( due to weight etc) even with my limit switches the unit will usually end up with hard metal to metal clash stop ( not good for ballscrews) so you may need to factor the likely over run when setting limit switch location ...im thinking of putting some hard rubber spacer or coil spring at the lower end to minimise this for future..

the trick your after involve diodes across Switch terminals , I'll see if I can find a drawing / Photo to show you later , but it is possible ....found it

If you are using MM's all you have to do is wire the limit switches to the power for the Pot, when SMC3 loses the power of the pot the motors stop its that simple. Thats what I used before my tooths

Run the PWM signal through the limit switches so that the relevant signal is cut when the limited is reached. Which one? - something that you are going to have to measure and connect to suit your wiring.

I think a more elegant solution would be to use the limit switch to operate a relay which would switch enable on the h-bridge.
Run +5v or 12v through the limit switch to common and then normally closed contact to the relay. Mount relay between smc and h-bridge.
On the relay, use the com and normally open to switch whatever signal you want to disrupt(en1, in1, in2 or pot).
I would highly not recommend to do as seattime said, you want to avoid running control signals all around. More chance of picking unwanted interference, a 5v signal which is either on or off is less likely to be affected by interference.

Btw with 2 levels of limiting provided by SMC, motor limit and input limiting, how are you going to return the ball screw to the safe zone?
You would have to bypass all safeties to return power to the h-bridge or turn whole system off(safety) and manually turn the motor/screw.

Hi Guys on my sim the Limit switches trip the relays controlling the Power to my Sabertooths ,,effectively disconnecting them from the control system , the downside of this is that this allows momentum to back-drive some of the ballscrews further past the limit switches and hence they wont stop till the hit a mechanical hard stop ( not Ideal )

this method also has the disadvantage that I now need to manually drive the offending actuators back to the operating zone before each limit switch is tripped, then I can re-enable the power to the controller ..

its an inconvenience more than anything, as I'd rather have this than a massive stall current surge going to the controllers ..

Next mission is to find a better limit switch cut-off opton

How hard would be adding limit switches in the control loop? Like here for example:
http://motionsim.blogspot.com/2016/12/redesign-of-amc1280usb-motion.html

I see he has 12 limit switches inputs available!



Mike

The limit switches are there as a last resort when everything else fails to stop it for whatever reason. SMC3 uses its axis limits really well and if you set that up right you should never ever need to use your limit switches, SMC3 hard reverses the motors when the limits are reached on the software side and your limit switches should be just outside that range. I have not hit mine since I have had it all setup right and not rushing things like I always do.

Yea that would work fine, but like a few who do not use SMC3, you need to do something else to give the same outcome. @wannabeaflyer2 , as @Mmcool said, it looks like the 1280 has been upgraded with a mod for using limits with the sabertooth. Maybe worth investigating when more info is available for retrofitting it to the old cards that we use. As you need something to reverse the motors and stop them running into the ends of the ballscrew or actuator.