Active Modelling

Following on from Sweaty Dave’s excellent series on modelling railways, here’s a missive on what I term “active modelling”.
Radio Control stuff is now awesome. Forget 12 hour charging times and a 4 hour trip to the modelling shop to buy a small specific bolt or screw. You can buy everything you need online.

I first started out with a small RC car in my teens. The Tamiya Boomerang:

I do recall I got it as an unusually generous Christmas present, so my Christmas Day was spent reading manuals and pulling plastic off the sprues. Then sanding the sharp bits off with P100 and then down to P400 sandpaper.

Assembly was quite the challenge, the Boomerang was a full 4WD car with a single engine so it had two gearboxes with full differentials. Differential gears have little to do with OldTrout’s writings (although I am sure she could indeed describe the motion of each gear in turn to mathematical precision. Instead they are gears within gears that allow that the wheel on the outside of the corner may need to travel faster than the wheel on the inside.

This explains it better than I could.

Each gear that connects to the wheel has a feedback mechanism to the central driving gear. While building these gearboxes I was less than impressed at the faffing about, although once built I took one apart again just to examine the operation so I could understand it. I had a shiny shiny new toy and still couldn’t play with it. By Boxing Day I had built the thing, and had a healthy appreciation of differential gearbox assembly, and reading the Zen like JapEnglish instructions. The instructions were good, and correct, as I recall but a little terse.

So, once built, I was off racing. Back then the rechargeable batteries were pretty rubbish, a trickle charge was all they could manage. I had a charger that would feed a gentle charge for a timed 12 hours to the battery, and then it was off to race it for five minutes or so.

Then – a 12 hour wait.

After a couple of months and the saving of pocket money for domestic jobs and Saturday job wages, I bought a new uprated battery; 6v to 7.2v. This burned out the plastic gearbox bearings so I then saved up and bought steel bearings. This then lead to the savage accident of driving into a kerb whilst overpowered. Smashed to pieces.

I uprated the chassis by impact adhesiving a thin veneer of aluminium across the base of the car. This then lead to further speed related accidents, so I kept raiding my Dad’s workshop for spare bits of metal to uprate the car to withstand the poor quality of my driving.

Then came the Demon upgrade for the Boomerang (no link available sadly, think they went to the wall). I had to work all summer to afford it but…

It was, to borrow a phrase, pure fukkin’ magic. Every plastic bearing from gearbox to wheel mounts was replaced with steel proper ball races. No other RC car of my friends could come close to mine on the dirt tracks. I once raced a proper car down the road, on the pavement and -literally- undertook it.

By which I mean I lost control of the car on the pavement and ended up driving underneath the car on the road, regained control and shot out ahead of the car before it then turned off the road.

Great days indeed.

Wavy lines for 30 years gone by

So as I got older and into my second childhood I cast about for some RC cars as a hobby. I bought one, with a 7.1v battery and what was called a “brushless motor”. At the time, having more money than sense I just read on t’Internet the brushless motors were awesome and that was it. They are really rather good as it happens, very high torque and good power efficiency. Brushless motors explained.

The car arrived the day after I ordered it, ready assembled (RTR – Ready To Race) and with no maintenance instructions. It was good, but not as good as those I had seen elsewhere.

So I bought a Vantage, which was a lovely little car. Until I broke it and broke it again, then replaced pretty much everything with custom forged aluminium and carbon fibre. And a monster uprated 11.1v battery.

The difference was amazing. Going out to the local BMX track I managed to actually fly the thing. Yes, fly. As the car reaches the apogee of flight, you can (on 4WD vehicles, certainly) put it into reverse to keep the front of the car up to ensure a level landing. You can also twist the front steering wheels to snake the car in the air too.

There was quite a lot of building, rebuilding, and yet rebuilding going on here, but the difference being was I had no idea how the car was put together. I had to pretty much disassemble the thing and work out how to put it back together again. You could buy new fully assembled gearboxes, all properly lubed and with the undoing of a few bolts, you’d be back racing again.

The point I am making is – previously the modelling experience was borne of waiting, engineering and practical experience. The RTR out of the box experience is almost instant and just requires money. I am sure there is a lesson in there for society, somewhere.

So, after a time, the Vantage got a little boring. So I bought a Vorza. I liked it so much I bought another, mostly so I had one still on the road while the other was being rebuilt.

They will do ~70 MPH with a little uprating, and they are far too much fun to be described as a simple “toy”. Batteries charge in a half hour and they will deliver (when paired) 22.2 volts at about 50 amps. Through a brushless motor.

Brushless motors are a modern miracle. Instead of having to rotate the static magnetic spindle, it is all done through electromagnetism and some super clever electronics. They spin up super quick, deliver a massive power curve and are pretty efficient as far as energy usage goes. Acceleration is fierce and because the motor is electromagnetic, it can be used to brake too.

I lost control of one of my uprated Vorza’s and went to hospital with a suspected broken shin. It had just chipped the bone, luckily, but that is the amount of kinetic energy these little monsters can deliver to the unwary or stupid. Nailed on both counts.

The Vantage was still flying nicely though; not quite like this though.

However, I got a little bored. So I had a go with some of the little minidrones you can get out there, ones for indoors. Too easy to fly, they have autocompensating gyros and load balancing circuitry so each motor on the corner gets just the right amount of juice to maintain level flight.

And then I bought my first 6 channel helicopter.

They arrive, with a transmitter, charger and a battery. Unfortunately, this is like getting a full blooded stallion with ginger up its’ jacksy for your first horse riding lesson.

They are cruel beasts, inherently unstable and affected by their downwash at low heights. You can get trainer kits which prop the heli up so the wash from the blades doesn’t affect takeoff and landing, but seriously, who bothers with that?

Those that have unlimited funds and patience for the new parts to arrive. Or the naive and stupid. I get full marks on all counts. Again.

You start by trying to control the liftoff, which in turn needs some yaw control and quite a little more control besides. These were all unfamiliar terms to me when I started, so here’s the science bit:

YAW – roundy roundy of the helicopter
COLLECTIVE – Uppy downy
CYCLIC – Forwardy backwardsy sidewaysy

If only someone had explained these in such simple terms!

YAW – this is really how quick the tail rotor turns. Unfortunately when an electric copter speeds up the main rotor blades, it wants to spin in concert with the inertia of the main body of the helicopter. The tail rotor will spin to counteract this, not really needed when the forces of being on the ground are in play but when taking off – quite important. Many helis have a chain link from the main rotor to the tail rotor – the faster you go, then the more the tail rotor spins.

COLLECTIVE – now this gets to the nub of the 6CH heli. Common and cheap models will have static collectives, or Fixed Collectives (FC’s or FP’s Fixed Pitch). What this means is that the blades will not alter the angle at which they strike the air as they rotate. If the angle of the blade changes, it can generate more or less lift depending on which direction the blade is angled at. 6CH helis can generate a lot of negative lift, it they are configured to.

CYCLIC – this is probably the most interesting, from a modelling point of view. The servos involved in a helicopter are pretty simple, they service the swashplate:

El Cnutador, Going Postal

This is a Fixed Collective helicopter so the swashplate is only used to alter the angle of the blades in relation to horizontal, rather than the angle they strike the air. Push forward on the cyclic and the servo will pull the swashplate down at the front. The blades will rotate higher at the rear of the heli and lower at the front. In the picture above you can see the black plastic bit over the red swashplate – this is fixed to the rotor axle that the blades hang off and will push them off horizontal as the blades rotate.

So for forward flight, as the blades rotate, they are encouraged to lift at the back to provide a motive force, effectively pushing the copter forwards.

And as such, for sideways, backwards and on.

For Collective Pitch helis the swashplate is controlled by 3 servo’s:

El Cnutador, Going Postal

The servos are connected to the swashplate thus, there a 3 of them and they act in concert. Left, right forward and backward are all the same as before with regards the swashplate, however for collective pitch the servos move up and down simultaneously which pushes the inner swashplate up. The difference is that the inner swashplate is linked to the blades, and can alter the pitch of the blade itself.

All this, I learned from having to rebuild the damn things. Mini copters are delicate little flowers; even a small burr on one of the rotor blades can degrade the lift effect enough so that at best, the bloody thing will just about take off, then immediately seek your sofa’s leg. A large part of the minicopter control lies entirely within the transmitter. In my experience, they are crude things ready to hide the complex from the idiotic.

When you pick up a transmitter (Tx) controller they have two joysticks protruding out of them. You can configure them in a number of different ways that the transmitter knows about; however I prefer Mode 2 which is left stick up and down controls throttle and yaw, right hand stick controls forwards and sideways cyclic.

So, we have – left hand controls speed of motor (and to a certain degree, what the collective pitch is doing. This is overall rotor speed and the up-y down-y with a forwards and backwards motion on the lever. And the turney round-y is managed by a left – right motion on the stick.

Right hand controls the cyclic pitch which is the lefty – righty – forwardy – backwardsy bit.

Easy so far, right?

However, the servo’s are not as quick to change, they have some heavy lifting to be done and sometimes need a little time to settle into place when flying – there is a little lag between moving the stick and seeing the heli move. This will make your take off even more exciting, as the copter lifts off the floor then drifts off (sometimes violently) to the side if the servo is not centred.

In my experience, exciting takeoffs lead to expensive repairs. What they don’t tell you in the manual, however, is that there’s a few handy things you can do on the copter, as well as on the transmitter.

D/R stands for Dual Rate and it means that you don’t have to worry so much about overcompensating for Tx stick movements. A huge 100% movement on the stick does not always mean a 100% move on the servo side; servo travel can be limited. Add it in to EXP or exponential movement and you may end up with a flyable heli. Ish. They are unstable when flying so even hovering requires constant adjustments.

The idea is that small movements on the control sticks make a small movement on the heli, until you get to the outer limits of the control stick travel. Easier to control at low speeds, which is quite important for indoor helicopters. Getting your heli set up right for a beginner is a big learning curve and takes time, crashes and the occasional broken light shade.

Once you’ve got the hang of a 6CH 3D helicopter, you can fly them like this guy. This pilot is really rather good at it; needless to say I am a long way off these skillz.

Lessons for a wannabe RC model enthusiast – it will take time to get your own garage of spare bits together. There are some useful guides on the net on repairs, tuning and so forth, plus the occasional holy flame war over which x is best.
If you break the same part within 3 months, next time buy two.
 

© El Cnutador 2018