Advice on 2 DoF geometry

[Graham]

Hello everyone,

I'm a new user here, just thinking about building a 2DoF racing sim. I have plenty of experience building and fabricating things, mechanical design, electronics, programming, trigonometry and so on, I don't see anything that would present any special difficulty, but I'm new to the world of sims so some advice or discussion about what I have in mind would help make sure my design was theoretically sound.

I'd like my sim to have reasonably realistic levels of g simulation, so I was thinking that having full roll and pitch of ±20° would be about right without making it too excessive. This only allows a static g of 1.34. This does seem to be more than most people end up with though, so that's my first discussion point - what angles are sensible? What do other people work to?

Assuming these sort of angles are OK, I need to consider how to drive these mechanically. I was thinking of using these motors: https://www.motiondynamics.com.au/worm-drive-motor-12v-24v-200w-180-rpm-20nm-torque.html which have 20Nm of torque. To achieve the ±20°, my thoughts are to use an offset from the pivot point to the point of attachment of the rod arms of about 300mm, and a crank throw of about 110mm, which yields the necessary 20° at the extremes of the crank travel. This gives a force available to the motion platform of around 180N in the centre position, which I think is the worst case position - as the crank rotates to the extremes the force available increases as the motion available decreases. The question is: is this enough force? I want my build to include the wheel, pedals and monitors as well as seat and driver, so that's going to be quite a lot of weight to be moving around - as a rough ballpark maybe 120kg. Of course the weight will be statically balanced with the CoG over the pivot, so the dynamic forces needed will be a lot lower than this, but it's not clear to me that 180N is enough - I don't know enough about mechanical design to calculate whether that's OK, so any help with that would be gratefully received.

I notice that a lot of builds connect the motion rods symmetrically to two points behind the seat/platform with pitch and roll effectively mixed. Thinking about this design, it seems to me that it means that at extremes of roll (for example) there would be no pitch available, and vice versa, so the combined angles achievable would be much less than the full 20°. To avoid that, I was thinking that making each axis completely independent so that each motor drove only pitch and roll alone, would be better. To do that, the mechanical arrangement would need to link at 90° from the pivot point, one to the side and one to the rear (say). I've noticed only a few designs that do it this way. What are the pros and cons of this vs. the more common symmetrical/mixed pitch/roll arrangement?

I hope these questions are clear - if not I can explain further or upload some diagrams to show what I mean, but hopefully they'll make sense to builders that already have some experience. Thanks very much for any help or advice you can offer.

[theSteeg]

Hey Graham

Hows your build going?

Ive been wondering about all your points, and would like to find out what you've experienced

Karl