First Build, Wood 2DOF

Evening Kings,

I'm ready to get started, full of loosely thought out plans. The idea is a simple seat mover, a la DOF Reality H2. I'm going with the amazon motors, 24v / 50:1 / 35nm, run off a battery, IBT2, not sure if i'm going to do potentiometers or hall effect sensors, not 100% on how to execute the CTC levers but I have Ideas. More to follow on all that, first I want to finalize the design and fabricate most everything then do all the motors and electronics. Attached are my first rough drafts and SimCalc results. Excuse my Blender skills, just learning. I guess my first question is do you see any glaring errors? I think I'm getting the most I can out of the design.

Not certain about the pitch and roll degrees, while I've read Norbeast say less is more in VR as long as it is quick, is 9-10 degrees enough? I am limited by my U-joint to about 15-17 degrees so I was hoping for 14-15, I believe the H2 is 20. But if more experience says 10 is enough, I'm good with that.

I am also wondering if the seat should be flipped around so the motors are in the back and not in the way. Thoughts please, especially on the SimCalc numbers. I'm not married to anything in the design except simplicity. Thanks in advance

PS Inspired by RomanDesign and Joe Cortexion(I don't now how you @ people on here)

@noorbeast Thanks for the tip. Tracking on the possible motor interference, they can/should lay down.
In regards to the knee mount, my first instinct had been to tuck them back in a true compact design like your(really nice looking rig BTW)It would definitely be easier to get in and out. But I didn't like the numbers I saw in Simcalc, more likely I didn't understand them. I just took another crack at it and...it seems better.
Picture the motors laid down.

Moving the mounts to the 12 and 12 position still maintain near max efficiency, seemingly good force? and more pitch and roll than the knee mount. I like this. Are the lower torque values good or bad?

In reference to Simcalc numbers, how do the pitch torque and roll torque values effect the rig? Is higher or lower better?

The leverage is based on the length of the lever arm and the distance of the attachment to the center of rotation. So the attachment under the seat (your second post) has less leverage than at the wheel. I found that 70mm was fine but at 80mm I started to have problems.

My rig is very stiff at the front. The back with the seat not so much. So front is a better solution for me. You do have to be careful about interference with the motors. You should maybe add the pedals into your rendering.

My first prototype had a single 4x6 as the backbone. My early videos showed me how much that support beam was flexing. It worked I just hated the flex. Hence the two 4x6. Of source I am moving the wheel and pedals which is a quite a bit of weight,

Encoder: I use “multi-turn” Hall effect devices. There is no coupling. They are hard to center but I made a simple mod to add in an offset in SMC3. I would be happy to post a STL file for the mount. Very important to precisely center the magnet behind the sensor.

Attachment of levers: When what I have fails and I have to redo it I will get them welded. I don’t own a welder but it’s pretty easy to take the shafts and your lever arm to a friend to have them welded. My welder friends seemed to think it would not be an issue. I use 1/8 steel for lever arms.

Thanks @Joe Cortexian Please do post your STLs when you get a chance. I would also be curious to see your SimCalc numbers if you had them handy. When you say 70 and 80mm, do you mean CTC length?

I didn’t use SimCalc. I mean the distance from the center of the motor shaft to the center of the Heim joint (the swirly thing at the end of the rod for future google searchs).

I don’t have the STL handy at the moment but one other note is that you need to scrape a resister off the sensor module so that it outputs analog. You can’t use the digital outputs because it’s too slow like 10 times slower than analog.

Makes sense. I imagine the number will vary based on design geometry, motor strength, etc, but would you say there is a too low value?

If they are too long the system stops working because you are asking too much of the motors and electronics. If they are too short it may not move far enough to suit you.

Mine failed now and then at 80 mm with the failure being that the ibt-2 cut out. Now it fails rarely but is fixed by cutting power to just the ibt-2. I have a new driver on order which would likely fix this. In any case it’s good enough now.

So 70 mm gives me a theoretical motion of 14o mm but it’s actually closer to 100 mm. That translates (for my configuration) to pitch of +-9 degrees and roll is +- 13 degrees.

I did several experiments to determine the optimal length so you may not want to weld it to begin with or drill four holes at 50 60 70 and 80 mm to determine where it starts failing.

I got the idea today from another post, for initial set up and testing, no weight, I will 3D print them, once I find the sweet spot, I will either CNC them from aluminum(not sure if that will work) or like you suggested, get someone to weld an arm on the shaft.