[in progress] 6DOF compact and small footprint

Hi everyone,

I did a ton of research and looked at many designs. I wanted a small footprint 6dof simulator. I didn't want to use actuators (to much noise in my opinion and would make the footprint larger as far as I could see from other designs). Please see the pictures of my small prototype with 6 small servo's. I also made a design in sketchup. I do not have decided on which motors, drivers, poti's and PSU to use for this project, and perhaps I can get some help with choosing these. I already have a DC motor so I could start some simple testing with a motor driver and a potentiometer (yet to order at least 1 of both). Then I can write some code and do tests see how everything works because all of this is still new to me. I am a programmer for many years so I think it shouldn't be a big issue to start from scratch (not planning on using SMC3 or any of that). I have done research on PID (pretty complicated in my opinion but learned a lot already), and will have to learn more about this during writing the code and testing things. Will see how that goes . When all of that is working nicely I will proceed with building the frame (I will build it from wood for now). Maybe at a later time I will re-create a frame with different material.

Of course I have a couple of question which I could use some help with.
When it comes to the weight of the platform, I am a tall person and weigh around 95kg.
Wooden frame that needs to be lifted by the motors is in total (LxHxW): 3798mm x 38mm x 89mm
The wood per 2700mm weighs around 4109 gram. So in total the frame would weigh around: 5.8kg
I do not have pedals nor steering wheel yet, but I do have a VR headset so there won't be a monitor mounted or anything. I assume steering wheel will be around 2kg, and pedals around 1kg. The chair which I don't have yet would be around 8kg.

So to summarize all of that the total load would be around 111kg

So correct me if I am wrong,
but with the above it would mean each motor would require a torque of 9 N.m:
= 111kg x 5cm CTC lever
Note: 1kgF.cm = 0.0981 N.m in SI units

I am not sure if my calculations are right, if someone could confirm it would be much appreciated

I am also planning on using gas struts (see below picture):



Any advice on what motors, drivers and potentiometers to use would be much appreciated.

I have seen that controller, but I am trying to keep things on a budget (even though I have the money for it myself, I am trying to keep it as low cost as possible but still a 6dof because I want to create it for friends if it works well).

Right now I am trying to figure out what DC motor would be a perfect fit for my design (to keep cost down).

I had already looked at those designs you linked. I think almost all 6dof designs that I have seen on this form are much bulkier and require more powerful motors than mine. My design is similar to that of dofreality, but slightly smaller footprint.

I also believe that because of the higher connection points onto the base the motor would require a little less force to move the base (but correct me if I am wrong).

ps. I updated my calculations on weight of frame due to incorrect weight of wood, it was 270cm while I used mm in my math (I already had a feeling the weight was of). So total weight is around 110kg. What do you think about torque calculation? Is it accurate?

Unfortunately DC motors are not cheap if you want them handle large loads, for 6dof you will need to be able to handle dynamic load of up to 300kg if your load calculation is 110kg (approximately 3 times the load). If you buy motors that can handle exactly the load, you will be running the system near stall conditions which means overheating drivers and cabling and higher risk of fire.

I am not to sure about this, when I look at ac motors they are much more expensive. I have seen 100 dollar motors with 20Nm which should be fine depending on CTC. That's why I am asking if anyone can recommend some DC motors for my design. I think if I can know what dofreality is using I can use any similar motor for my project amd see how it works out.

I think you didn't account for the cost of power supply and DC drive and possibly additional batteries/capacitors for back emf. Plus the cost of thick wiring able to handle 100A (in stall conditions) to avoid overheating). Been there doing all these back in 2007!!! 2020 now I don't want to look back in outdated and inefficient methods we had to relay upon. Back then servos cost 3000usd just for the motor, but now you can get one for 200usd!!! Isn't amazing how technology advances?

3 dual channel motor drivers will cost you £150
6 gear motors could cost £100 to £150 each new

you may be able to use dc gear motors from wheelchairs or mobility scooters - often available 2nd hand

these gear motors are £50 each

https://www.xsimulator.net/community/threads/my-best-attempt-at-a-racing-sim.15171/

Sure... power supplies? Batteries? 8AWG cabling?

a car battery is about £40
server power supplies can be bought for about £20

jump leads are good for transmitting power, 12 metres of cable costs about £12

First I want to welcome you aboard. This is a great hobby. I have built 3 sims and I am about half way on to my 4th build. Things have come a long way in the last 3 years and for the better.. 6dof is very ambitious.
May I suggest this. You can start with a simpler set-up. A 2dof rig. If you spend the money on high grade components you will be able to reuse these on a more complex 3-4-or 6dof rigs. Using the expensive AC closed loop servos is where it is at. And that fellow in the previous post (Thanos) has developed a pretty incredible controller for this type of motor. It will serve you well for anything from 2 dof to 6dof right out of the box.
Good luck in your build and have fun..
Its been great for me..
Tom P

Hi
If you are a EU member, you can go BLDC to
If you want dofreality specs, look on ebay with bldc motor nema23, and you have a motor and driver for €90.00
from Germany. I belive the store is act motors.
On AlieE you will find plenty of planetary gearboxes nema23 for less than €60.00.
You can use PMVCDA brusshless 6 dof as guide.
The avantage of this is ,its doublle the lifetime a fuw times from brushed dc, less backlash than a wormgearbox,
More efficient 90% in place of 55% with a i-50 ratio wormgearbox, no jithering because they are rolling
just my two cents
sorry for the bad english
regards Ad

I agree that the easiest way to do things would be to go with @Thanos method. But I am not going to. Instead I have contacted the supplier of dofreality motors and asked about their thought on what motors would be a good fit for such project. I got the email from @Mike Melga here: https://www.xsimulator.net/community/threads/newbie-starting-my-rig.15004/page-3#post-204762

Motor specifications:
24v
No Load - 2000rpm +/- 10%
Rated Power : 220w
Rated Speed: 1500 rpm +/- 10%
Rated Torque: 1.4Nm

Gear Ratio: 1:25
Rated Speed: 60 rpm +/- 10%
Rated Torque: 26 Nm

@T R Para I agree on this, but I just really want a 6dof. If I won't succeed, I will have 6 motors so I can scale down to 3 motors for a 3dof system and build 2 of them. One for myself and one for a friend.

Thanks all for the feedback and info/tips! I will (have to) learn a lot from this project since it's my first. This is also kind of the reason I don't want to go with a plug and play system that @Thanos recommended. I like to learn and do things myself Anyway we will see how it goes! I will keep you posted

After trying three types of 24 v dc motors I turned to industrial servos because of backlash in gear motors .......If your simulator doesn’t need to be very accurate it maynot be a problem but for precise moves it definitely is .

Hi @accelero, thanks for the heads up . Do you have any info on those previous motors and the ones you are currently using? Do you have a thread of your simulator? Are you using it for racing or flight? I am planning on using it for racing, and perhaps for flight just for some times, but mostly racing. How bad was the backlash? I believe this depends on what ratio you use too and what type of gearbox and not the motor itself?

I don’t want to give negative points on any seller or factory......Very little backlash on wiper motors from Germany 1 mm at the end of 40 mm lever but big one for Chinese stuff more than 4 mm .......( either 120 w or 400 w pieces) this multiplied by four with a 4 motor rig is far to much ....those were cheap which was a good point few years ago, I have learnt a lot about simulation with that stuff
Actually I use a platform for other purpose than racing or flying but I am still following projects with a lot of interest....learning from this community is of great value

A planetary gearbox with 25 arcmin backlash gives 0.29 mm backlash with a 40 mm lever

Hi
About backlash, as long you stay under 1G there is no backlash
There is only backlash when you go to far off balance en wants to fall over.
Dofreality uses a big footprint and a lowerd COG with smal movement, there for it wont fall over.
With youre small footprint you go to far off balance soon and you wil feel a lot of backlash

Backlash doesn't even matter if using arduino with 256 positions feedback using ADC and simple potentiometers. 256 positions for 180 degrees rotation travel... or 1024 positions if you use 10bit resolution perhaps.

Servomotors can deliver 16bit resolution at 180 degrees rotation (65535 positions) btw...

Hi Thanos
Youre system is the best way to go!
The only problem i have with it , a 200watt and 400watt motor cost more than a 750watt motor
I have a 220v 25 amp head fuse in my home and must pay €2500.00 to get 380v in my home