Showroom 2/3DOF Flight sim first build

Yesterday I fabricated the bars to connect the motors to the platform using some tube that was laying around the workshop, I was planning on using some solid 20mm bar but I think the tube is lighter.


Installed on the rig.


excited to see how it performs I gave it a little go in DCS, as to be expected movement was all over the place and nothing like it should be, but my main concern was the motor / gearbox did not seem strong enough, one more so than the other, being 24 volt motors and 60:1 boxes I thought these would be more that up for the task.

It would struggle to push the rig back up unless you unweighted that side to encourage it to lift. when testing the motors I was able to stall the motors with my hands that raised concerns then.

I brought the power supply and sabertooth from a member on here in the classified, Not sure about the make of the power supply.

Edit - you just posted specs and even at dataplate rating, I’d say that power supply isn’t big enough. The motors are rated 23A nominal, 50A peak and that power supply is only 21A peak. That’s not too far out of spec for “nominal” but way out for peak loads. It’s even worse if that’s your only supply. Just off the cuff, I’d go with two supplies at twice that rating for those motors. They will only pull what they need. I think that motor controller runs two motors with one supply feed? If so, you may need a much bigger single supply but then you need to make sure the motor draws don’t exceed what the motor controller can handle.

I agree with @noorbeast. Just to ask the obvious question, you are running the 24V motors with a 24V power supply? Have you measured the voltage at the motors to see what they are actually getting? It’s odd that one motor is stronger than the other and is why I’m wondering about voltage drop in the wiring if the wires are unequal length and too thin of gauge. Connections and solder joints can also be sources of high resistance and voltage drops along the way between power supplies, motor controllers, and the motors themselves. I was looking back at the photos and the wiring looks a little light but at 24V your currents would be half what I’m used to (my rig is at 12V but I see up to around 25A per motor on my full frame rig). My supplies are each 600W with one for each motor. A little overspec (not by a lot, though) for my rig but you want your supply to be able to deliver whatever the motor controllers demand or else voltage will sag and torque will drop.

I can’t make out the power supply specs. What are its specifications and do you use just one for both motors or one for each motor? If you are severely limited by the power supply(ies), that could also explain being able to turn those output shafts by hand.

And one last thing is those rudder pedals are very nice but also very heavy. Cantilevered out like that on a full-frame rig will add lots of inertia that that your motors will need to overcome for snappy performance. You said you balanced the rig so it’s not having to dead lift them, but they still take force to move. The more weight that is cantilevered out can increase motor requirements but that doesn’t sound like the issue for low motor torque.

Apologies if you already considered this stuff but we don’t know your electrical background. The workmanship looks great and I love that crew seat!

One other thing why it may be so easy to turn your motor outputs, are the motors buzzing? Power supplies frequently protect themselves when severely overloaded by crowbarring out. They kind of shut down. You would need to know how that supply behaves in overload conditions but it may be “off” for the most part.

Thank you @Zed for the reply very appreciated and helpful, my electrical background is rather basic so any pointers in the right direction is more than welcome.

I only have that one power supply for both motors, so your assessment would seem correct and I should probably upgrade and use two larger power supplies, any suggestions ? also how would I wire the two power supplies to the one sabertooth or would I need another.

The power cables used are 1.5mm2 I presumed that would be adequate, but please correct me if I'm wrong, they have also been cut the same length.

The rudder pedals was a big worry for me from the start, they are a heavy lump but I really didn't want to use anything else, hence why iv taken every step to be able to use them.

Hey @Typhoon56, I hope it helps but I do think this is the issue.

Is that a Sabertooth 2x32 controller? If so it’s rated at 32A per motor with peak currents to 64A per motor. I’m not familiar with the Sabertooth controllers but that should be good I think. Your power supply may be just way undersized since the motors show 50A peak.

The simple answer is a 100A, 24V supply but you may be able to go lower. Since your pedal set is heavy, for heave and surge both motors would act together and would be trying to move that weight so current draws may be fairly high. Note all the hedging. I don’t have experience with those motors or controllers, but that would tend to indicate closer to 100A than not to keep them far from stall or near stall currents crowbarring out your power supply.

Thing is, they may not actually need that much current in practice depending on leverage and tuning. I wouldn’t be too worried about undersizing the supply except for those beautiful pedals. I haven’t tried them but heard they are great. But the weight is what concerns me. It doesn’t hurt to oversize the supply except for the money it costs. The motors and controller will only use what they need. To be safe you could go 100A but others here may have more insight.

As to the wire gauge, there are tables online that show gauge, length, and current. You can also look at wire resistance for the length you need and using Ohm’s law figure out what the voltage drop would be over the length of wire you are using. I’d not go more than a couple of volts so at 25A (close to nominal current rating), I think you want to keep the wire resistance below 40 milliohm per conductor since those add since both conductors are carrying the current. So if the wires (2 conductors) are 4 feet long (8 feet of wire at 0.010 ohm/foot), you need 10 milliohm per foot or less. And you can fudge that a bit. It just reduces motor torque which affects how responsive your rig will be. Using the 4 foot, 2 conductors, for 8 feet total, at 0.010 ohm/foot, at 50A stall current, you’ll be losing 4V (as heat - I^2R - or 100W) just in the wires and the motor will only see 20V - which also means the motor won’t pull the full 50A. Also, those peak currents won’t be the norm. But since you could see close to them on fast movements, you want to consider the impact at those currents. Resting currents if balanced should be much lower or even zero. Hopefully that makes sense.

Maybe wire that’s 0.005 ohm/foot or less would be better. You don’t want to dump so much heat in the wiring. 12 gauge wire is about 0.002 ohm/foot so 12 gauge (AWG) or larger gauge seems reasonable. That will drop waste heat at stall current to about 20W. And remember both conductors count since they are in series. Shorter wire runs also lower the voltage drop in the wiring.

Hope that helps...

@Zed iv already started trawling the forum for power supply ideas and looking what's available in the UK, thanks for the advice again.

I suppose I could also look down the route of two 12V batteries.

You could but just remember, depending on the kind of batteries, you can have hydrogen buildup, if they are flooded lead-acid, you may have spills, you have to charge them, etc.

And you may be able to go with a lower rating power supply. A 21A is apparently too small, but a 50A may not be, again, depending on how your motors are loaded. My supplies are rated at 50A (at 12V for 600W) each but I could possibly have used lower. I don’t usually see much more than 25A and they are fused at 35A IIRC. Haven’t popped a fuse yet so I could possibly have gone with smaller supplies. Unfortunately, with ratings like your motors have, you may need a big supply and it’s tough to know in advance. You have 240V mains I believe so at 100A/24V, that’s 10A at 240V on the mains. But again, that’s peak and you may not even hit it. If you do, it would just be for a moment. Flying also tends to be pretty gentle except for bumps and such so average currents should be low.

I forgot you asked about multiple power supplies in parallel. You can also do that with some important caveats. The supplies have to be tolerant of being run in parallel. Some just work, others need master/slave designation, isolation diodes, etc. It might be easier to use a motor controller per power supply but that would mean buying another controller too. The Sabertooth probably has a current limit setting (but that’s a guess) so that’s another way to maybe use a smaller supply that would otherwise be overloaded, but the sacrifice once again is torque.

(Edited for more longwindedness ;-)

I had the same issue as you and ended up using 12v car batteries. Never had the issue again . Used a wheelchair battery charger to keep them topped up. Works like a dream.

Thanks for the reply @Retro77 , I'm going to try using a couple of 12V server power supply first then if that fails I will go down the battery route.

That's exactly what I used at first. They tripped into protect mode all the time.

For the price I thought it worth a go , I'm going to up the gauge and shorten my wiring and fit a KBPC5010 Bridge DIODE as well, try all I can.

For sure .I'm interested to see if it works for you . Update your progress

so had a busy morning assembling my server power supply after a bit of faffing (removed DC chassis ground ) I got my required 24 volts out, happy with that I wired the rest including adding a KBPC5010 Bridge DIODE seemed like a logical thing to do , also larger gauge wire.



once connected to my rig, I powered it up, turned my back and next thing I smell is burring, the 50A breaker had tripped and I found the ground wired between the sabertooth and arduino had burned out.



what would cause this to happen ? when I put a meter between s1 and the GND I see 16 volts, I don't believe this is correct .

Also I cannot find my Arduino on my PC now is this because I have cooked it ?

Thanks Lee

Hmm. You can probably take those resistors off of your sabertooth .They caused me nothing but grief. Not sure if that's the issue but somewhere to start . Your positive you isolated the grounds on your power supplies? How do you have the sabertooth setup internally? I power my Arduino with the usb cable. I noticed an additional cable? 5v?