Linear actuator using ClearPath Integrated Servo System @ 72V DC

Hi Dirty, Ive been browsing over the figures on torque (.09 N- > 2.8 N) and now I'm confused; at those figures it doesn't seem like it would be strong enough to pull your pants down????

Would you care to enlighten me, on why this product was chosen!

Retards Jerry.

Why are you using a belt and sensor?
Can't you use the builtin ClearPath positioning system or am I missing something?
That's the main advantage of those servos.

They are controlled in open loop from arduino. Even as steps using pulses, they are not going to be real time controlled as they buffer the pulses and must execute all motion in sequence before executing new position...

Hmm...they have 900W steady. Plenty Power anyway. And don´t forget the transmision (2.8 Nm @ 1:50 =125 Nm !!!)

Funny you were answering exactly now I am just writing something... gimme an hour or two.

Hey

sorry for the late reply. Took me forever. Been away for a while. But still quite active in the workshop! I am happy to be able to say I’m well ahead of schedule on this project which is a rare occurrence in my life

Here’s how I calculated:
The motors generate 0.9N of force @ a radius of 1m (continuous)
=900N @1mm
=112N @8mm (since the ballscrew has 16mm diameter = 8mm radius)

When the ballscrew does a full rotation it moves 50,27mm along the circumference of the screw while it pushes the ball nut 5mm forward. That is like a gear ratio of 10:1 leading to a push force of 1130N.

That’s ~113Kg of lifting capacity (continuous) or 350Kg (peak) per actuator. Can you imagine what happens when 6 actuators each apply 3500N of force (total of 21000N) on a 85Kg payload!?! This thing will initially accelerate upwards at 14G. I don’t know what kind of pants you’re wearing, but I’d be more concerned for my balls flying off when this beast springs into action.

All that said, please… if there is an error in my calculations, let me know! I might have gotten those numbers wrong somewhere along the road.

I’m still in Egypt (windsurfing) and for some reason I cannot access my cloud drive, but I will post a link to the excel sheet I’m using for you to check my calculations when I’m back. I’d REALLY appreciate some feedback.

To answer your question:
I chose those motors because they are very powerful and they can be driven directly by the AMC1280. All they need is a speed demand signal. No arduinos, no PID, no Kangaroos, no soldering (almost), no break resistors, no capacitors, no nothing!

Every thing I DON'T have, is a thing I don't need to understand, maintain, buy, fix, worry about or replace ...like EVER!

oh,... and to be brutally honest to myself I should probably admit that I bought those motors while I was under the wrongful assumption that I could even ditch the belt and position sensors and just rely on the motors internal position sensing, but that turned out to be not the case as @Thanos pointed out.

...more pictures (and videos) coming!

Dirty

...at least a picture.

Here finally a link to the Excel sheet I'm using:
https://1drv.ms/u/s!Arc3cFJctWW3hLwoP8yclU9zrvmo0Q

Hey @pmvcda

Well,…. Initially I was planning on building an actuator with a simple MY1020 and an Arduino. Therefore the belt and pot was a necessary evil and I designed the actuators with those in mind. When I switched to the Clearpath motors, I thought that I could leave everything out if I used them in „Follow Position Demand“ mode. Unfortunately, that wasn’t quite as easy as I would’ve liked it to be….

First @Thanos informed me about this issue with the motors having to finish every move before being able to execute a new move and recommended using the motors in „Follow Speed Demand“ mode together with the AEAT-6012 as a sensor.

Then I briefly considered using the motors internal sensor (like you do in your project) but those motors aren’t meant to be used in this way and my technical skills are definitely not sufficient to hack into the motors internal workings, so I looked into the AEAT-6012s.

They provide 12bit resolution (4096 steps) and I have ~10 turns per full stroke leaving me with ~40.960 steps for the 380mm of travel. That’s a resolution of 0,0092mm per step. Less than 1/100 of a mm. I know that this is a theoretical value, but at least I can be reasonably certain that the position sensing will not be the bottle neck when it comes to the accuracy of the rig.

Here a couple of pics of how I will mount the belt and sensor.
Instead of the T-shape belt run I planned earlier, I can now use this L-shape design.


For now I will print all parts in PLA (a dream to print!) until I am through a few design iterations and found the right setup and everything works flawless. Then I will switch over to either NylonX or PETG for the "serial production".


Here you can see, that the new design I adopted from @bruce stephen 's recommendation allows me to have only one idler.


Dirty

To keep the end of the ballscrew from dangling around inside the rod, some form of spacer needs to keep it in place (centred). This spacer must also be able to let air pass through, because when the rod moves the air inside it must have somewhere to go.

Initially I used this star-shape design.


The problem is, that you need tight tolerances to prevent (noisy!) vibrations of the ballscrew but at the same time you need a little wiggle room to allow it to rotate on the ballscrew and to keep it from getting stuck inside the rod as it moves past the spacer.

This new spiral-design works a lot better!


It has an outside diameter about 0,2mm (1/100th inch) greater than the inside diameter of the rod. So you will need to flex-in those spiral arms a little to get it inside the rod, but then it will deliver
1. a nice and constant "springy" centering force to the ballscrew
2. will allow for ventilation and is
3. absolutely play-free.

I have made a before and after video from the same distance and there is an audible difference in noise level I will post those when I'm back home.

Dirty

Hi Dirty, and thanks for the reply, and explanation showing how new I am to this stuff.

Also thank you for the XL sheet, I may help me understand better.

So I wont be needing 6 of these after all!

https://www.aliexpress.com/store/pr...0a05-44e1-9604-9e3eedc75b9b&priceBeautifyAB=0

Regards Jerry

Hi Dirty, I have question if I may?

Can we add the weight of "motor and ballscrew inertia" into the equation?

It would be interesting to see the difference on the outcome.

Regards Jerry

I'd say the rotational moments of inertia of the ballscrew and motor axis (aka. "what it takes to get these small parts into motion") are negligible compared to the inertia of the platform/payload (aka. "what it takes to get this huge mass into motion!)

Keep in mind, when it comes to actuation speed or nominal static force of the actuators, inertia plays absolutely NO role. It is only important for acceleration.

If you wanna reduce weight, your platform and your "belly" are the most promising candidates

Holy smoke,... NO!!!!

In my opinion, those motors are total overkill! In fact, I think even my own motors at 6 x 1100W are overkill already.

If I had to come up with a catchy rule of thumb for the power requirements per motor (Preq) of a stewart-platform, it would be...

Preq[W]= 3 x upper-mass[Kg]

so,... with the platform at ~50Kg and the payload at ~100Kg, I'd say that you should use 3 x 150 = 450W of power per motor.
...something like this perhaps.

IF

But only if you take lead srews with 5 mm pitch

AND if the angle between the actuators and the floor is not too small You can see that problem in SilentChills Thread...

Hi Dirty, and MystAr, thank you for your input and explanation.

It is always appreciated.

Regards Jerry.

...I wouldn't necessarily come to that conclusion. Power is the ability to apply force along a path per unit of time. Or to apply torque at an RPM.
Power = Force x Distance / Time (translation)
= Force x Velocity (translation)
= Moment x 2π/s (rotation)

It's completely up to you if you want to turn that power into speed or force. You will have to trade in one for the other though. I guess we agree on that? If you use a 10mm screw vs. a 5mm screw you will trade force for speed, right? Now, it depends which of these factors is limiting in your case.

Most electric motors I came across run at a speed of somewhere around 3000-4000 rpm. With a 10mm screw and a 4000rpm motor, I agree, that there is a high chance that you will be limited by the torque of the motor if you use the 3W/Kg*motor formula. But it is an important distinction to make here: Torque is the limiting factor, not power!

If you simply recommend using a more powerful motor that has a higher rpm then you will still have the same problem.
But if you recommend using a more powerful motor that has a higher torque then you will save the day

Dirty

Hi Dirty, thanks for explaining the usage reasoning once again, I really appreciate the guidance you have given me.

Jerry

Hooray Hooray!!!!!! IT'S ALIVE!!!!!!

finally

this is the comparison I was talking about:


...so far, I'm simply jogging it up and down via the manufacturers software, but the very fact that something (anything!) is moving when I click a mouse button is simply amazing!

Can't believe it )))))))))))