First time 2DOF advice

Just putting together the parts to make my first 2DOF sim.
Picked up 3 of these motors http://www.ebay.co.uk/itm/12V-DC-Mo...al_Components_Supplies_ET&hash=item58b2dc4233
with the aluminium 25:1 gears.
A pair of 40a 12v power supplies, 3 Pololu JRK 12V12, 3 hall effect position sensors, a load of square tubing, universal joint and an omp seat.

I just have a couple of questions for you guys, I notice that most of the sims have the motors at the rear, attaching at shoulder level but a couple on here have put them at the front near the feet. The distance to the universal joint pivot would seem to be similar for boths point, but is there an advantage to using one over the other?

I did get an extra motor with the idea of using it for a drift axis, but I may leave this until I get the main platform with 2dof working first. There doesn't seem to be many videos of a drift axis in use but rotating around the middle universal joint would make construction a lot easier (and probably correct for a flight sim) but for racing a forward pivot point would seem better, anyone used either and have a preference?

The position of the screen, some have it moving with the platform others have it fixed in front of the moving platform. For those that have built them, what is your preference and why?

Thanks.

I build the seat movers with rear position motors this is the optimum position for supporting the weight and achieving the ultra fast reactions and speeds I feel a race simulator must produce , 200kph down a track should shake like hell, wall impact should take your breath away, It really adds to the immersion factor.

Foot mounted motors work well too when moving the whole frame , but I still prefer the rear mount , have found over time it supports more weight and gives a better range of movement.
To me a racing sim shouldn't move completely as in a seat mover is more the style of what is actually going on inside a cockpit of a race car. Very hard to get that same style of motion once you have to deal with the inertia of the whole rig in motion. But for flight this style is a must.

The drift axis for racing , I prefer to pivot from the front, if using this for flight you can set a small % of axis to the Yaw force so you gain the feel of the rudder motion in the plane.
But again if you want to move the whole rig you should be rotating around its centre to give a better feel and when racing you can set this rotation to traction loss but only use a small % of its axis to gain a feel of the tyres sliding around.

With screen it comes down to design , if whole sim is moving I prefer to mount them up on the rig, but you must take into account when building and setting the pivot position the extra weight that will be added in front of the drivers weight, plus if you add 3x screens , you run into problems because the two outer screens can affect the weight transfer and you may find you need stronger motor to move it correctly. Weight balance is the key in building a good sim, where most mistakes are made. Now I use a seat mover so my screen is stationary with the seat mover and moves with the traction loss base as so does the seat mover on top.

Thanks for the feedback. I think going with rear mounted motors attaching at the shoulders seems the way to go.

Haven't decided on whether to go with a moving screen, I have an Oculus DK2 on its way which should be interesting to play with, so I might go with a static screen first and see how it all works. I can always add a mount for a screen later and move the pivot point.

The motors are rated at 23a @12v, do you think these would handle a platform mover with a 10kg screen on the front? I haven't estimated to total weight yet, but the seat is 10kg, I'm around 90, no idea on the platform yet but maybe 5-10kg for the wheel/pedals etc. so could be up around 150kg but most of the weight will be over the pivot point.

you may have to consider putting 50:1 or 60: 1 gear boxes on the motors with that weight, even if its balanced on a pivot.

Thanks, I'm going to go without a moving screen mount and see how well it works, if it looks like it's going to struggle then I'll look at a pair of 50:1 boxes for them.

Been playing with a couple of small motors, the hall effect position sensors and the JRK 12v12 to see how it all works, as I've never done a great deal with hardware in the past. So far so good, once tuned in the JRK utility they seem to perform as expected, hopefully that will translate to the full size motors!

if you do put a screen on it, remember you will have to re-balance it and move the pivot.

Ok, finally started construction of the frame, slow progress but I'm in no hurry

Finally received my Oculus DK2 which I've been playing with this week, I've found it nearly impossible to use without getting bad motion sickness from it, anything more than 20-30secs and I get a horrible nauseous feeling which takes some time to get rid of. Multiple fixed screens it is then!

Very slow progress, but started on the pedal mount.

wow, RealGear pedal set, you know what to do

They are, most pedals have always been a big disappointment to me, so I wanted to get as real a feel as possible, these should be pretty close.

A little work on the steering wheel mount, very sturdy, no flex even if I sit on it! Hopefully the gearing/lever length of the motors can be tweaked to make it all move.

nice, however, are all these adaptability mods going to add much more weight?

It probably adds a little weight, but not too much more than it would need to be rigid. I didn't want to have any flex in the steering or pedal mounts. I haven't weighed it all yet, but it's not as heavy as it looks.

I don't know how much the motors I have will cope with, I'll find out when it's all connected up and look at what alternatives there are if it doesn't work. I may need your advice on what I need to make it all move

Once you have all the top together then find its balance point , a lot of the weight will be held by it. Your body weight will balance off the weight of the front additions as long as your not moving the rig at great angles it will be fine, You wont get the sharp vibration movements that a seat mover can deliver thou, it will be cool to use a flight rig.

Not much of an update, got the throttle pedal mounted along with a few adjustment holes, plus a couple of bracing bars across the back to attach the motor mounts to.

Not had much time recently to get much done, but started to make a little more progress! I must be in the running for longest build thread with not much progress.

Anyway, finally mounted the motors, steering wheel and attached the levers.













It's not as heavy as it looks, but I think I'll need at least the 50:1 or 60:1 gearboxes rather that the 25:1 that the motors came with.

It will be nice to try and get it actually moving this year!

Nice work, what flying is it please?

Looking good mate.
Yes 50:1 min to move that with any hope of accuracy, pivot seems too far back, and not enough angle on the connecting rods will not help either, but very nice progress.