Question 6DOF motor choices - 25:1 to 50:1 ?

Hi guys,

Im shopping around for motors for the 6DOF rig Im planning on building.
The FAQ - Motor List helped me find some motors. Ive seen some worn gear motor 25:1 and 50:1.
I'd just would some input on which motor, 25:1 or 50:1, would be better choice for a 6DOF.

Thanks

DK

I am pretty sure the size and torque of the intended motor will help decide which gearbox to use. With a larger motor, a lower ratio gearbox can be used which I would assume increases fidelity. There are other factors as well, such as the CTC length of your actuator and the angle of the connecting rods.

Not to high jack your thread, but I have similar questions too as I am exploring building a 3DOF with components that can be added to in the future to make 6DOF. I would like to know what motor size and gearbox would be appropriate for about 500lbs mass (With a fixed or known actuator CTC length and rod angles). I have been messing with the SimCalc program to get figures in the ball park but I don't know if that will translate to a 3DOF or 6DOF configuration.

Do you plan on using DC or AC motors?

Good luck with your quest and hopefully we can educate each other.

mdp

i ended up using wheelchair motors !

@mprofitt Im planning on using these motors:
http://www.ebay.com/itm/371596157992?ul_noapp=true

@Gadget999 Do you have pics or link on them? I'd like to check them out.

they are 24v wheelchair motors - check out my build for more details, they seem to be working great

https://www.xsimulator.net/community/threads/formula-3-simulator.9118/page-2

It's actually quite expensive if you're simulating an airplane or a car.
In my opinion for the automobile it takes between 40 and 80 rpm in output of gearbox...

@momoclic The motors im planning on using are 80 rpm. Im just a little confused on which gear ratio would be best for a racing sim, 25:1 or 50:1?

In fact, it depends on whether you are simulating an airplane or a car.
In my opinion for the automobile it takes between 40 and 80 rpm in output of gearbox...

Our goal is not the reduction ratio!
Our objective is the sensation of acceleration. The slower the speed at the exit, the less violent the accelerations will be.

This does not only depend on the reduction ratio, but also on the speed of the motor.

In addition you don't indicate which type of motorization you intend to use AC or DC with which control system, nor the torque you need...

A gear unit is not chosen according to the reduction it provides but according to the need it must satisfy

so what are the trade offs. take a 50:1 at 4500rpm (90rpm) or 25:1 at 2250rpm (90rpm). do you get better startup torque at 50:1? Faster direction changes at 25:1? or gear lash, is 50:1 better? Faster motors seem cheaper than more powerful ones, are there significant benefits to 25:1?

Well said as in real life everything is a matter of compromise!

It all depends on its objective and the means that you are able to put into it.
Once again we start by defining the objective (target) and once we know where we will be able to choose calculations to support it. I repeat myself, it is a question of method.

Example 3DOF heave effect:

Personally, I always leave from need. Here the load: (Pilot weight + mobile structure and equipment) x 1,5

Example (70 +50) * 1.5 = 180 kg

180 x 9,81 = 1766 N

We divide by the number of engines

1766 / 3 = 590 N per motor

Therefore, the motor must provide a torque (Nm) capable of lifting this load at the end of the crank handle.

I want a 100mm stroke on 120° of rotation (60° = 0.866), which will ensure that I will travel at the maximum speed 100mm in 1/3 of a second.

Crank spacing 100 / 0.866 / 2 = 58 mm

So my actual motor torque requirement is C (Nm) = F (N) x r (m)

590 x 0.058 = 34.2 Nm

I use worm gear motors with non-reversible worm gears, efficiency of about 0.5, so my actual power requirement has to be doubled.

P (watt) = C (Nm) w (radian/s)

A 60 rpm w = 2Pi radian/s i. e. 6,283 radians/s

6.283 x 34.2 x 2 = 430 watts useful

On this it is necessary to take into account the electric efficiency of the motor we will take 0,7

430 / 0.7 = 615 watts

So it is possible to make a 3DOF wave effect simu with a maximum load of 120 kg and a vertical stroke of +-50mm with three gearmotors rotating at 60 rpm of 615 watts each.

Any gearmotor with a rotation speed of 60 rpm and an output torque of at least 35 Nm will do the trick, for my example, regardless of the reduction ratio.


This is an almost universal approach to power calculation, but not all the requirements of a simulator have been taken into account here.

with our sim designs we can compensate for the 25:1 or 50:1 by adjusting the length of the crank arm

typically a 50:1 mtor will have more torque and will accelerate slower than a 25:1 - by making your crank arm longer the sm can be made to accelerate faster

if you used a 25:1 motor you could increase torque and reduce speed by making the crank arm shorter

thanks guys! Specially @momoclic for the explanation!

Hi, I was reading through this and really appreciate the detail that @momoclic provided.

I was looking into this topic as I am a very hefty male and was wondering what motor would work best for me.

To be sure I understand correctly. In my situation I weigh 160Kg.

For a 2 DOF (using your example including vehicle weight and lever arm lenght) I would need a 1600W motor@60RM@90NM.

If you would be so kind to confirm this I would appreciate it.

Thank you very much,

Unfortunately it's not that simple. A 2DOF and a 3DOF operate on totally different principles. This involves different calculations.
The 3DOF's heave effect raises the load vertically, requiring powerful motors. On a 2DOF generally it is a universal joint that carries the load. The forces are calculated according to the lever arms used ...

I invite you to read my tutorial on building a 3DOF explanations are detailed:
https://www.xsimulator.net/communit...ulator-building-tutorial-3dof-heave-axis.9249 /

On the link site in French you will find detailed explanations for 2DOF, but unfortunately I have not translated them. Help you google translation, that's how I do since I do not speak your language.

This example needs added to the FAQ. Excellent description of the calculation process.

Just to muddy the waters even more... The specifications given for motors are not all equal - some relate to 5 minutes of operation while others may be continuous - some are from countries were they just seem to make it up . I trusted none of them and instead did my own testing before investing more into further motors and equipment. Unless you are using known good motors that have been proven to work in the type of sim that you are building then it can be a lottery. Same goes for motor drivers and other equipment.