Hoddem's DIY Linear Actuator

I got a little further on the rig design. Digging through my extrusion I am able to double up the side rails and front and rear cross section which should significantly increase the rigidity of the frame. I have done this before with end connectors and t-nuts and lots of access holes. It is a pain, but it can be done and creates a very solid single connection.



I'm still debating on 3 vs 4 actuators. I'm pretty much sold on 3, but I don't like the front actuator so far out. The pitch pivot point will essentially be the steering wheel. A single actuator in the rear will prevent the seat from sliding unless I extend the frame a good amount (6" plus). with a single rear actuator I could move the front side actuators to about where the steering column is. I have the actuators mounted as high as physically possible right now and honestly I still don't think its high enough. I have a couple of ideas I am rolling around right now.

1. Build a sub-frame that will elevate the whole chassis and allow the actuators to be mounted even higher without the frame bottoming out. This would also give me a large space to house all of my electronics.

2. Flip the actuators upside down and make pivot points similar to a typical 6dof build. This would be a lot more challenging, but I could get an effect similar to this.


My current frame design is very similar to the sim lab P1, both in extrusion size and footprint. I will proceed with my mock up chassis for now, I have it in my head that I will be getting a new seat and I don't want to cut any aluminum just in case the new seat requires more or less frame space. The seat I am looking at is the NRG Prisma, its less than $300 shipped and SRG gave it high marks.

For what it's worth I built a 4 corner all metal sfx style rig and I want to change it to a 3 inverted actuator setup like the last pic you posted. My two top reasons are actuator weight off the rig(20 lbs a piece, thats 80 lbs moving around right now) and center of rotation closer to my center of gravity. The frame will not be as simple though and there will have to be a moving frame and a floor frame.

I don't think I will do the change though until motion cancellation works (or maybe better to say until I can get it to work). The center of rotation only matters for larger movements. Larger movements in vr are crap without cancellation.

@cfischer which Vr headset are you using. I’m still rocking the oculus rift which I understand has no motion canceling. I would like to get the index, assuming it actually works with motion rigs.

I’m thinking I could just flip my actuators upside down and set them right on the encoder cover. I would just need some framing to hold them in place. I’m wondering if I’m over thinking it though and venturing back to the more traditional linear actuator requirements.

that is one massive power supply base.. wow..

Hi @Hoddem you may have saved me some money was about to place order for 40 x 80 extrusion and noted that you mentioned Flexing with 40 x 80 or was your 4o x 40 . just need reassuring before i flexed the plastic so going straight in for 40 x 120 Cheers

I’m using 1.5x3” but it’s the equivalent of 40x80. I just finished tightening everything down with a ratchet and the stiffness is considerably better, but it still flexes. 40x120 should be plenty stiff. I see that sim lab uses 40x160, I’m sure that is rock solid. I will probably continue with my plan to double the rails to make them 1.5x6”. I also have to think about weight, there isn’t much to my rig right now and it’s already pretty heavy.

I was able to get 3 actuators up and running with my modified 600w server power supply and my kids power wheel battery rewired to 24v.
this is using the default 3 actuator configuration posted by @Thanos in another thread.

Here I am using the curve generator to test the different forces.



More testing running each actuator individually, no speed limits and the auto tune settings. These actuators can be pretty aggressive if I cut them loose.



The motion is pretty shaky, I was able to clean it up a bit by taking the serial baud rate to the max, maxing out send rate and setting a speed limit on the actuator.

Here is the final test of the day, Heave only at 100% so full stroke. I tweaked the stock tune slightly, added a speed limit of about 75%. It is much smoother, but I still need to work on the tune more. All of this testing is unloaded right now, as you can see at the end of the video I tripped the power supply and I am only running on batteries. I will either need another set of power supplies or better batteries.



I'm curious for anyone that is running SFX-100 with servos if the motion is perfectly smooth or not. I won't be happy with my setup until I can run through the heave cycle with no shaking or dips. I'm assuming that the ST90 servos would do that no problem.

I am also noticing a fair amount of heat coming form my motors. It is barely noticeable when I am running the rig empty, but when I am sitting in it they heat up pretty fast.

Youre E30-400 motor and a 750ac motor have allmost the same power, but he is twice as fast and deliver half his torque
there is youre heat

I was going a little crazy with the shaking on my rig with the curve generator too. Mine looked exactly like yours. It took me a while to see that in game motion is perfectly smooth and high quality. For testing with the curve generator I was able to smooth the motion by applying lots of smoothing. I concluded in my mind that the curve generator program simply has low resolution motion data and the servo showed the flaws clearly.

Just for the record my actuators are all metal similar to sfx but they are 230mm long. So the shaking was crazy with a full stroke sign wave.

Are you using 5mm ball screws and the st90 motors. If so are you hitting full speed (3000rpm)? I’m hitting close to 4500rpm and I’m thinking it’s a bit much. I need to get my second set of power supplies up and running and start load testing.

I have been contemplating just getting the servos, but I’m almost certain they will bother me with the noise that some people can hear.

@Hoddem ,

Great work!

So it's you who's going to test Mover with 3 actuators?

I

I had no idea that it had 3 actuator support. Heck ya I’m going to test it.

It's still WIP with a new build to come out in the next two days
But I would love to have some feedback on this type of rigs.
When you want to try, say something so I can help on the setup.

will do, I’m not quite there yet but hope to be soon.

I setup two more power supplies so now I am running 1200w @ 24v. I also have 4 12v 9ah batteries wired up as a big 24v 18ah supply. It still isn’t enough, I suspect that my battery cannot handle the current spikes and it’s overloading my power supplies.

That being said I did some testing with the motor speed limited to 3000rpm which should mimic the servo pretty well. At the end of the video I pop my power supplies again but up to that point it was moving pretty good. The motion isn’t perfect as I can feel some lag coming from the actuators. In an actual race I’m not sure it would be noticeable with all of the forces mixed together.

Again this test is 100% heave speed limit of 3000rpm.




Motors didn’t get hot this time! Just a short test but I had actually played with it for a while before I took the video.

In summary
I NEED MORE POWER!

Side note, does anybody know why my profile picture has the starter banner?

Great work @Hoddem but I'm a little lost to why you would go 4DOF instead of 6DOF ? (edited as I dont want to upset touchy people)

I dunno each to there own and everyone has a reason I just don't get it

Totally understandable seeing I started this making an actuator for a 6dof setup.

Well I pretty much stalled out on that project and when I stumbled upon the SFX project I figured since I had almost all of the gear needed I could throw together 4 actuators and play with that for a while and maybe someday cannibalize those to make 6 actuators and a full 6dof rig. I figured I could throw this together quicker and cheaper then a full 6DOF setup and if I actually invest the time in iracing again then I will look into going 6DOF.

I took a long break from the forums, last I had heard you were having a ton of problems with oculus and your motion rig. Did you get that sorted out?

I now have a Reverb and motion cancellation still a problem but bearable.

My 6DOF still going strong but soon to be dismantled and sold off in bits as I am upgrading to a brushless more compact system.

With my rig I experimented with AASD20a servo drives and 80st-m04025 servo motors. I went this way because for the same price I could get lots more torque, a bit more power, while sacrificing a bit of top speed(2500 max). The ball screws are 300mm long 5mm pitch(theres my speed back). I don't think I have an easy way to measure max rpm but I also don't think I ever see max rpm in game. There are too many quick changes to see max rpm.

The whine is pretty stupid. Its a shame thanos didn't setup his controller for a different drive that doesnt switch the current in the audible frequency range. I do however understand the SFX guys popularized the AASD10A. Its a great cheap driver other than the whine. Oh and the fact that the Chinese cannot ship the motor power wire shielded is really stupid too. I replaced mine with shielded wire. Total PITA.
https://www.racedepartment.com/thre...controller-thread.168360/page-20#post-3047521


...by the way, your profile pic has a starter image on it because you started the thread.