Sunday, October 26, 2014

SLH 6047 Scorpion review

The Why

Every time I buy a toy grade 'copter, I feel like I need to justify it. In this case, I was adding an RF module to my Devo 10 running deviationTx, and wanted something cheap to test it with, rather than risking the more expensive models I was planning on using this for.

The SLH 6047 used the new module, and wasn't just another toy quad. Or even a helicopter. So it was something new to try. Filling two purposes and having a good review from Flyin' Ryan1 made it an easy choice.

The What

What's unusual about the Scorpion is obvious when you look at it:


It's got six engines on three booms, with a coax pair on each boom. The lower engine is inverted.

Some folks call this a tricopter, because it's got three booms. Others call it a hexacopter, because it's got six engines. I don't feel either is right, because it doesn't fly like a tricopter or a hexacopter, but will go with hexa because it could be called a hexarotor.

The Review

So, let's look at the thing.

First impressions.

To me, the pictures make this look a lot bigger than it really is. It's a small 'copter, being barely bigger than the Nano QX:


Part of what makes it look large is that it also looks solid. This, unlike the size, is not an illusion. This thing is rock solid, and has a feeling and weight to match.
It's been through numerous crashes at speed and the only thing that's broken is a propeller. Unfortunately, it was the same orange one that was broken when it arrived2, so I've had to use the black spare, which is what's in the pictures.

In investigating replacement propellers, you can use standard multirotor propellers for the top ones. However, the bottom ones are pusher props, which are much harder to find in that size. Something to keep in mind if you plan on flying one a lot.

The flying

Coax multirotors tend to be stable but with poor efficiency. They have lots of lift for their size, which the scorpion needs because of its weight.

What that translates to is trouble overcoming its own inertia. It seems slow to respond to the sticks, and tends to keep going once you get it moving. The controller it comes with makes this worse, but I want to talk about that at length, so see further down.

This thing has been around for nearly two years. The technology in these things is changing fast enough that that's several generations old, and it shows. It doesn't even fly well compared to better toy quads of that era.

In summary, I can only recommend this if you want something other than yet another small quad.

The controller

It's been quite a while since I've looked at a toy RTF controller, and this one is much nicer than those. SLH gets credit for making it configurable enough to fly lots of different aircraft. All four channels can be reversed. You can also configure whether or not it beeps at you. Nice.

Toy controller problems

That said, it's still very much a toy RTF controller. While it has two rates, you can't set what they are. Nor can you alter the control curves in any other way. The fact that this aircraft is slow to respond is made worse because the controller seems to have a dead band near the center of the cyclic controls. Could be a quality issue with the one I got, or it could be designed that way so the toy-grade gimbals have a properly neutral center stick.

A hobby grade controller

Since the point of buying this was to test a new RF module in my hobby-grade controller, flying it with that was one of the first things I did.
This immediately brought a lot of new features to the table. A real throttle hold switch, to help reduce damage to the 'copter and bystanders during crashes. The dual rates are a switch, not a button, so it's possible to tell by feel if it's in low rate mode. Ditto for the flip functionality. Of course, all three have inverse video icons on the screen which are much easier to see than the dual rate symbols on the RTF controller. There is no indication that flips are enabled on the RTF controller, but it seems to time out quickly. And the RTF controller has no throttle hold, so that doesn't need an indicator.

More importantly, the dead band issue is gone. Getting rid of that makes the thing fly much better. Even better, I can apply some expo to the high rate curve, which makes flying it a lot saner. I feel that this justifies my avoiding 'copters that I can't fly with a hobby-grade controller.

The rant

It's not obvious if all you use is toy grade RTF controllers, but the controller is the important part of an RC aircraft system. It is the connection with your aircraft. So it having problems will also mean you will have problems with your aircraft . Similarly, if the controller is improved, say with better gimbals, or faster response, or whatever, then you'll have improved control of your aircraft, and an improved flying experience.

On the other side, getting the system set up properly is a critical part of an enjoyable flight. Large parts of the setup of a modern 'copter happen on the controller. Much of the functionality showing up on flight control boards can be done in the controller with a good enough controller. So again, a better controller means a better flight experience.

In summary, if you're just flying the toy-grade RTF controllers, you're cheating yourself out of a better rc experience.

  1. If you fly small 'copters and aren't familiar with his reviews, you should check him out. 
  2. Fortunately, it was fullfilled by Amazon. They couldn't send a replacement prop, but gave me $10 credit instead. 

Thursday, October 16, 2014

Why PayPal sucks


Every so often I run into someone who uses PayPal on a regular basis, and has never had a problem working with it. While I believe they are entitled to their opinions, and have no problems with them choosing to use PayPal, I think they ought to have all the facts. So I've written up my experience and what I've discovered about the company. But one person's experiences may not be indicative, so you can read other people's problems with PayPal.

Understanding PayPal

What PayPal is - and isn't

PayPal's early attraction to the consumer is that they don't give your credit card info to merchants, which provides an extra level of security. That used to be unique, and them being first has made them very popular. These days Google, Apple and Amazon all have similar services, or have at least announced them. There are also a slew of others, possibly even Microsoft, but none of them have made an impression on me. All of these services are free to you for making purchases. Which means that, as with any free web service, you are not the customer, you are the product. In this case, it's easy to tell who the customer is - it's the merchant you're buying from, who is paying for an easy way to get customer payments.
One difference between PayPal and the other three is that the other three all have store fronts of their own. PayPal doesn't. That means that you are, at least when buying from their store front, a customer of those other three. So they will treat you like a customer. You can also see how the vendors are customers there, because the vendors pay a premium in order to have products show up in those three stores. It's worth pointing out that, unlike those four, when you make a purchase using a credit card, you are a customer of the bank. The merchant is a customer of the credit card company, not the bank.
Another difference between PayPal and the other three is that PayPal wants to hang on to money for you, which lets you spend it from your account instead of your credit card, sort of like a checking account at a bank.
It's important to know that, even though PayPal acts like a bank issuing a debit card from your perspective, it is not a bank. It isn't bound by the laws covering banks or debit cards, and you get none of the legal protection you'd have with a real debit card.

How PayPal makes money

Looking at how all these entities make money helps explain their behavior. Apple, Google and Amazon make money primarily by selling you things from their storefront, and have moved into the payment processing market to get a slice of the money from other sales as well. Banks make money by charging you interest on money you borrow, or by making interest on the money they hold for you for a debit card, and also by charging a variety of fees. PayPal makes money on payment processing fees, and by making interest any money they convince you to let them hold.

PayPal's behavior

So let's look at how PayPal has treated its users.

General behavior

Another difference between PayPal and the other three payment processing companies: PayPal has lost a series of class action lawsuits brought by its users for figuratively stealing their money. PayPal has a habit of doing everything they legally can to keep earning interest on money that people have trusted them with. Making it hard to contact them, freezing account withdrawals (but not deposits!) for suspicious behavior, then having hard to find and even harder to meet requirements to unfreeze them, and so on. That's what's caused those lawsuits.
While PayPal has improved things a bit (you can now call their mis-named customer service department), this is mostly because they have been forced to as part of various settlements, not because of a change of attitude. The lawsuits didn't stop until they changed their terms of service to say you could not sue them about these things.

My experiences

I opened a PayPal account over a decade ago, with an email address I still use. They doubled billed me for a purchase. I eventually found an email address (there was no phone number to be found on their web site at the time, one of the things the lawsuits forced them to change), and asked about this, and was told "Just have your bank reverse the charge." I did. PayPal ran the extra charge again. I reversed the charged again, and PayPal did a bank transfer to get the money. This happened another time or two - I forget the details, because it's been over a decade. Eventually, I got my money back, but they froze the account for "suspicious activity" - which state it's still in. They also took the money back from the eBay vendor, claiming I said the merchandise was never delivered, making it look like I ripped off the merchant, when it was in fact PayPal that had done so.
That old account still exists, and is permanently locked. This means that, should I make a purchase with PayPal and forget - or not have the option because my account with the vendor uses it - to use an alternate email address, I risk refunds winding up in that locked account. It's happened, but not reliably.
So having recently started buying from (only when there is no reasonable alternative) merchants that only accept PayPal, I've had the dubious pleasure of using PayPal's "customer service". While I can now reliably get someone on the phone to talk to, they are just as reliably useless. Fortunately, there is usually a supervisor available, who is only mostly useless. If you've got a representative from your bank on the line to talk to them, you can actually get them to give you your money back. But nothing short of that has ever gotten PayPal to release money they owed me once it's held.
Maybe things would be better if I had a PayPal account, and let them make interest from my money. But this seems silly when I can get a free credit card with no fees, no interest charges for 30 days - much longer than PayPal will extend me any credit, I get a small percentage of my purchases back as a reward, gives me the legal protection of using a bank issued credit card, and comes from a company that treats me like a customer instead of a product.


Yes, merchants that use PayPal - or sell on eBay, which is another rant - are usually cheaper than Amazon or those that take real credit cards. But understand that there is a reason for that: customers that make payments from a PayPal account have given up the legal protections they would have from using a bank credit card, which is how PayPal can charge less than the credit card companies.
This doesn't matter so long as things go fine, but the real measure of a company is in how they behave when customers are unhappy. By my experience, and that of many others, PayPal is doesn't measure up.

Friday, October 3, 2014

Introduction to Open Source Transmitter Firmware

Open source

What is open source

If you're not familiar with it, open source software (or books, movies, hardware, etc.) is software for which the source is freely available, and redistribution is allowed. The Open Source Initiative web site has a detailed definition and discussion.

In practices, this means that anyone can take the source, modify it to better meet their needs, and contribute those changes back to the project, or create a new project based on their changes. The latter is known as forking the project, and the new project is a fork of the old one. Because the source is visible to the users, the engineering processes are also often visible to the users - you can see the problem reports, changes to the source, etc.

The opposite of open source software is closed source, or proprietary, software. The source is not available, and the engineering processes are usually not visible to the end users.

Why you would use open source firmware

The second paragraph above contains the primary reason you'd want to use open source firmware in a transmitter: you can modify it to better meet your needs.

For instance, someone noticed that the popular Devo 7E transmitter - which the open source firmware deviationTx runs on - had unused control lines on the micro-controller it used. So they added two switches to the hardware, and support for the two switches to the software. That wouldn't have been possible if the source hadn't been available.

To compare it to models, open source firmware is like having kit, whereas proprietary source is like the all-in-one electronics boards used in micro and nano-sized aircraft.

So suppose you added a spotlight with servos to point it to your scale aircraft. If you can't control the servos, they have no purpose. With a kit, you can just plug the servos into spare channels on your receiver. If the receiver doesn't have enough channels, you can replace it with one with more channels. If you have all-in-one electronics, you may not know if you have enough channels, and even if you do, there may not be any way to access them. On the transmitter side, proprietary firmware should let you tie those channels to controls on the transmitter. Open source firmware lets you program a switch to move those channels in a search pattern.

Like the kit, open source firmware doesn't mean anything is possible. The kit may not have space for a receiver with enough channels, or the model may not be able to lift what you want to add. Your controller may not have enough memory for the modifications you want to make, or it may not be fast enough to do what you want as well as keeping up the channel communications.

Why you would trust open source firmware

If you're not familiar with open source software, you may now by wondering why you would trust your expensive model to software written by a bunch of amateur programmers in their spare time. The answer is - that's not the case.

Many - if not most - of the developers working on open source software are professional software developers. Or possibly students. Working on open source projects is not looked down on by most companies, and is an accepted way to develop new skills or learn about new software tools. In some companies - most notably if the engineers still have some say in the screening process, or the company is using open source software - contributions to open source software are a requirement.

Which brings up the spare time question. Open source is used in many commercial products - DVD players, DVR's, printers, etc. Apple's operating systems (but not the user interface code) are based on open source software, and many components are still open source. Microsoft uses open source in their operating systems. The Android phone and tablet operating systems are open source, which is why forks like Amazon Fire can be created. And there are at least two commercial transmitters based on open source firmware: the Turnigy 9XR and 9XR Pro, and the FrSky Taranis.

Professional developers work on these products as their job. In some cases, the people contributing to them do so as their job, because their employer uses that software in some capacity.

It may be hard to believe, but we enjoy programming. I'm sure the people who work for large hobby companies don't stop building and flying models just because they are now getting paid to do that. Personally, I'd rather use software written by someone was doing it as a labor of love than someone who was just trying to earn a paycheck. In at least one study, open source was shown to have better quality than closed source.

The fact that the open source projects have publicly readable problem reports means I can check them for issues with my model, and possible fixes - and if there's a patch for the software, I can apply it to my copy! This just isn't possible with proprietary software.

And finally, the authors of the open source firmware all trust all their aircraft with it.

The firmware


That anyone can fork an open source project can cause a problem in that it makes lots of forks possible.

One popular open source firmware family - I'm going to call it the TH9X family, because it was initially written for the FlySky TH9X transmitter - has more forks than I can count. Many of them exist because the author wanted to experiment with radically different interfaces, but most of the popular ones - based on activity in their forums and source repositories - are very similar.

On the other hand, the deviationTx software is also very popular, but there aren't a lot of forks of it, and most of them have actually been incorporated into the main distribution.

I wrote an overview of the choices a while back.


The choices for hardware range for cheap clones of the original FlySky TH9X to relatively high end transmitters like the Walkera Devo 12S. I also wrote an overview of those. The only real change is the release of the Turnigy 9XR Pro. That has gotten mediocre reviews, whereas the Taranis has generally good reviews since this was published. The Taranis is generally considered the better buy for the price - at least once you factor in the cost of buying the things the Taranis comes with that the 9XR Pro doesn't.

Using it

The popular open source firmware choices have similar interfaces - and it's not at all like what you find on proprietary transmitters.

Closed source behavior

Every computerized closed source transmitter gave you roughly the same set of controls. The first four to six channels have their output from the specific controls, and that can't be changed. Beyond that, they are from specific controls, but you can move them around.

There are then specific controls for manipulating those channels in ways that depend on the aircraft type. You enable dual rates and/or expo on some of the channels, usually enabled by one of a few switches. You can set a throttle curve, and possibly have a throttle hold or throttle cut. On helicopters, you can set up pitch curves selected by flight mode. And so on.

You also usually get some small number of mixes which let you modify an output channel based on a control other than the primary one.

The goal is to make setting up the manufacturers receivers easy, and it generally does that. Which is why all of the proprietary transmitters I've seen do things this way. If you're aware of one that is radically different, please tell us about it in the comments!

Open source

The popular open source choices - most notably deviationTx, OpenTx (on the Taranis) and the TH9X variant on the Turnigy 9XR - all have similar interfaces.

The first difference with closed source comes from the fact that, while the radio protocols may be radically different, the actual RF module used in proprietary radios may well be the same, and the difference is in the way the bits are sent. So open source firmware may well let you choose a protocol. You might also be able to add an RF module, and the firmware will change modules depending on the protocol selection.

Second, the number of channels on a digital radio is just a matter of software, as each channel is a slot in the digital packet the transmitter sends to the receiver. Since the open source authors aren't making money selling the software, you can configure the number of channels for each model. The limits depend on the speed of the CPU and the protocol, not keeping the low-end models from taking sales from more expensive ones.

Third, this software typically either doesn't have mixes, or has many of them, depending on how you count.

Each channel is - or can be, depending on the firmware - a mix. Or several mixes. Each mix can use any input control (pretty much required to support multiple protocols), can be enabled by any switch, or none, can have it's own curve - including fixed values that ignore the input - and can be combined with the previous mixes in pretty much any way you'd like.

There are also virtual channels that aren't associated with a transmitter output. They can be used for creating values to be used in the output channels.

Channels can also be used as switches, with their value determining the state of the switch. Some versions layer in virtual switches, which can test channel values and use the value of other switches in determining their state. All of these can be used to enable or disable mixes.

This is by no means an exhaustive list of the features available in open source firmware - it's just a list of the features that are common among the popular versions.


The benefit of this model for transmitter software is that the firmware is very flexible. Some examples follow.

Since you can use a virtual switch for the throttle hold switch, you can create a sticky switch for the throttle hold, that doesn't turn off unless the throttle output is off. This means you can't accidentally spin the prop when you turn off the throttle hold.

The Blade 200SRX has a panic switch that enables auto-level and disables the cyclic controls. This can be done on the transmitter with open source firmware - at least if your aircraft has auto-level. Set the channel that controls auto-level to a value that turns it on, and use the same switch to enable the last mix for each cyclic channel to set the output value to the level mode. Or - since each output channel has a safety switch and safe value, not just the throttle - use that switch for the safety switch and set the appropriate safe value.


The downside to all this is that there's no guidance. There are no settings for elevons, you have to know now to set up the mixes. You have to know which channel controls the pitch, and set the curve on it, not via a pitch curve control.

The popular firmware is solving this in a variety of ways. Some have desktop software that looks more like the proprietary controls, and you can use it to create a model to download to your transmitter. Others have a traditional mode that looks like the proprietary firmware, and you have to enable advanced mode to get the full power of the firmware. These are still very much works in progress.

Legal issues

Since you're working with a radio transmitter, your government probably has some things to say about what you can and can't do.

Since the software doesn't change the RF behavior of the radio, but how the controls change the digital values in the RF signal, just changing the software shouldn't be a problem. But that could depend on whether the licensing is for the transmitter as a whole, or for the transmitter module that the transmitter is using.

Changing the protocol might also be a problem, depending on the country you're in.

Modifications that alter the RF behavior - adding a module, or changing the power output levels - almost certainly invalidate the license the transmitter was sold under.

In the US, you'll be ok so long as you keep the power under 1 watt on the 2.4GHz band and aren't planning on selling the thing, because that usage falls under the FCC Home-built transmitters clause.


Using open source firmware on your transmitter provides a lot of extra flexibility in how you control your aircraft, at the expense of making common but not simple tasks harder. It's not for everyone, but the only reason to avoid it if it's for you is that it might not be legal where you are.