2DOF Seat Mover - First Build

Hey all,

I hope you are well.

I asked a question about a build in another section, but guess it's time to start on the actual build!

This will be my first attempt, I was looking to buy the NLR V3, but have decided to go DIY instead. I have been reading a lot this past week and would really appreciate your input in anything I have missed, or have advice for.

So, the build will be based on the Arduino UNo R3, which I have already had shipped. I have 2x BTS 7960s on the way too. The next part will be confirming aluminium profile sizes and getting them ordered, along with motors and pots. So far I am looking at;

2x 250W 24V 75Rpm Low Speed Brush Motor, 44Mm Longer Shaft, 17Mm Shaft Diameter
2x Mean Well LRS-350
2x HEXEH DC 5V Hall Angle Sensor Non contact Industrial 0-360 Degree Rotation Sensor

I have been following these threads mainly;
https://www.xsimulator.net/community/threads/my-project-2dof.13425/

https://www.xsimulator.net/communit...IOkgy61axSkrcg6EbI_aem_iDbS_PVI9aK711trnyAX0Q



My questions start with, do I need 2x PSU?

I have been running simcalc but until I get the motors and frame here, I cannot be 100% on my results.

I would really appreciate your input guys, want to get this right the first time if I can, I am UK-based if that helps for locating parts.

Look forward to hearing from you, Kris

Thanks @noorbeast, My apologies too, been busy with work.

I think I need to understand the angle more, so that's 80 degrees, from rest angle (rest angle 90 degrees to lever?) So 80 up, 80 down if that makes sense?

On the IBTs, I can turn down the voltage? I have seen they need thermal paste etc to keep them cool.

Happy to run 2x PSU, sooner be safe than sorry!

From the threads I have been reading the 24v motors and pots seems to be quite common for the type of build I am looking to replicate, would you say the items I stated were appropriate?

I do apologise, this is a new front for me so lack of knowledge, but reading as much as I can. I normally build custom PCs, so it's a whole new world. For fun, here's one I built for Intel.

Thanks @noorbeast that makes sense now. Il order in the PSUs too, the motors look ok? Seem to be quite popular, just so many variants/brands but assume they are all the same?

Yeah I cant seem to find more info anywhere on them but they do look the same as what other people have used.

Well, its moving along!

I've just ordered the aluminium profile. motors, hall sensors, GT2 Belt (200mm) and also managed to sort a great Universal Joint from a Land Rover specialist, 2x flanges plus the centre bearing for around £24!

Parts starting to arrive and Ive also 3D printed the hall sensor brackets today. Be about 2 weeks before the motors get here. Aluminium profile and universal joint should be here before the weekend.

Is it worth removing the IBT2 heatsinks and applying thermal paste, believe I have read they don't come with any applied?

My experience with the IBT2's is that they do not have any thermal compound applied. Also, that they are utilizing the anodization on the heatsink as an electrical isolation barrier. If I remember correctly, you don't want the tabs of the two drivers to be electrically connected. When I used them, I applied an electrically isolating thermal pad.

My other two observations about them are that they do not like 100% duty cycle on the PWM signal and that they should have a voltage suppressor if you are running them at 24V. Turning the voltage down on the supply will help, but I would still recommend something like a TVS diode.

If you haven't gotten those Meanwell supplies yet, I would recommend the LRS-350N2 versions. They are made to better supply the current spikes that motor drive applications can pull. Other than that, they are pretty much identical to the regular LRS supplies.

Thanks for the advice @Gefahren il take a look at the heat sinks, I have loads of thermal pads here from building PCs so should have some that will work. Il check out the PSUs too.

Aluminium has arrived, just waiting on connectors and the universal joint now to see some progress

Well since I am at a loose end Ive applied thermal pads to IBTs, now I wait some more for parts

@Gefahren I've gone for the N2 version of the power supplies, they will be here sometime during the week.

I also had the 4040 connector brackets turn up so the frame is assembled to start looking at the universal joint mount options. That will be here tomorrow and I am hoping the hole spacing will tie in nicely with the profiles.

Well, sadly Mouser has cancelled my order for the LRS 350N2 as I am not VAT registered etc. Any other alternatives to look at that you would recommend?

The regular LRS-350's are still a good choice, the N2's just had that extra surge power. They also make an LRS-600 which would most likely allow you to just have one PSU.

I'm really not familiar with how all that VAT stuff works from a consumer standpoint, so I don't know where to direct you for purchasing.

Thanks bud, I'm struggling to source the 600 in the UK though. It would be nice to run a single unit to keep things more compact.

I miscalculated a couple of aluminium pieces, so the replacements are on their way.

Next is to source 40t pulleys with a 17mm bore which I am struggling with, I assume as long as the ratio is 2 to 1 ie, 60/30 60/32 etc or better that will be ok if needed?

The more total teeth the pulleys have, the more teeth are engaged at one time. That means the torque it can transfer is higher before the belt jumps, within the limits of the belt and the pulleys. I suppose however that doesn't really matter much since you are just driving the position sensors.

I think you said your axis is moving +/-40°, so if you drive your sensors 2:1 then they are only moving +/-80° which means you are losing about half your resolution. Or are you using 0-180° sensors?

Hi bud, Ive gone with the 360 hall sesnsors that a lot of people here seem to use. Yes, my motion will be +/- 40 as recommended by @noorbeast

What I meant was if you've got 360° sensors and your axis is only moving 80° (+/-40°) then why not use a 4:1 ratio driving the sensors? That way you could use 320° or 89% of your sensor's resolution.

For example, my current seat has an approximately 3.51:1 ratio between the sensor and the gearbox output shaft. My gearboxes are only moving thru 90° of rotation (+/-45°) which means the sensor goes thru ~316°. I'm using the analog 0-5V output from the sensor going into the 10-bit ADC in the Arduino. All the math works out to having 0.1° position resolution.

I'm not surprised your having trouble finding a 40T pulley with a 17mm bore. That's only going to have about a 1" diameter and after putting that big of a hole in it there won't be a lot of the pulley left.

Ah I understand that a bit better now. I have found some 70t pulleys with a 17mm bore, so if I go 70t and 16t 6mm bore on the hall sensors that should be about right so to not complete a full turn for safety limit?