Crius MultiWii Lite Review
MultiWii is perhaps one of the most well known Open Source multicopter projects. All its hardware and software is open source. Originally based on sensors taken from gutted Nintendo Wii controllers, this project has come a long way – and these days you don’t need to cannibalize a WiiMote or Nunchuk controller anymore. You get a board like the Crius in this review, and you’re set. But how well does it work and how difficult is it to set up? That’s what we’re looking into in this review.
There are several versions of this particular hardware available. The “Lite” version comes with a 3D Mems Gyro and a 3D accelerometer as well as offering support for a 2-axis camera gimbal stabilizing system, while the “SE” version offers a barometric sensor and compass. Crius also supports optional GPS navigation by plugging in a GPS antenna. In this review we’re taking a look at the Lite version.
MultiWii is one of the most versatile, but also one of the most difficult systems to get working. With the other boards we reviewed so far, things were mostly plug and play with little (if any) configuration necessary. MultiWii is a different beast altogether.
The Crius board does not come with USB connectivity or any other means of changing parameters, you need to purchase either a little LCD module, or a USB FTDI module, or a bluetooth module. There’s a great app available for Android, which allows wireless setup and monitoring, provided you purchase the bluetooth module. This way you actually don’t need a PC at all! However, if you want to change from a quad to a hexacopter or an octocopter, you will need to download the MultiWii sourcecode, comment in a line in the file config.h, recompile the code and upload the new firmware to the Crius. That sounds intimidating, but actually flashing a new firmware is the easy part – it’s the finetuning of the controller board parameters that will no doubt make you pull your hair.
Before you do anything else, read up on the Newbies Guide to Setting Up CRIUS MultiWii SE board v4-22-12 , this gives pretty much all the basics needed for getting the board up and running. Upgrading from the included Version 1.9 of MultiWii to the new v2.0 is highly recommended and quite easy.
The optional LCD module can be used to change values in the field, and it’s quite handy for tuning the controller parameters – but you cannot change everything with it. For example, defining which channel enables auto-level, GPS return to home or altitude hold functions must be done with a PC over USB, or via Bluetooth using your Android phone. For that matter, the LCD module is much less useful than the bluetooth module. In order to be able to use the LCD you have to enable the LCD setup mode by pushing the pitch stick forward and holding right rudder, select values with pitch up and down, increment/decrement values with left and right aileron, and save your changes by moving pitch forward and holding left rudder. With the android app you get a much more comfortable user interface with a simple SAVE button, and you don’t have to enter any special modes to change parameters.
The Crius board is shown here with the FTDI USB interface installed. Note how the connector height causes the board to be bent downwards by being sandwiched inbetween the quadcopter’s frame. It’s a shame the USB interface doesn’t come standard on the Crius board itself.
The optional USB FTDI interface gives you the much needed USB connectivity to your PC. This board sits rather loosely on the connector, it’s obviously not meant to be installed permanently. It’s unclear why the Crius doesn’t include that right on the board instead of requiring a silly extra component which, as you can see in the image, can be a pain to install in your finished multicopter.
On the plus side, the FTDI Board does not need special drivers under Windows 7, it’s supported out of the box. And unlike the Rabbit FC setup program, MultiWii does not need Windows XP to work. There’s a central program available for configuring your MultiWii compatible controller board, and it works just fine for the Crius.
One thing we noticed with MultiWii version 1.9 that came pre-flashed on the board was that the roll and pitch indicators in the PC program were off by 90 degrees. Upgrading to 2.0 and using the 2.0 PC software fixed that. (Check the newbie guide PDF linked above for instructions on how to upgrade to 2.0)
Getting Airborne
The first attempts at flying were unsuccessful. As it turned out, the RCTimer 30A ESCs are simply not compatible with the Crius board, regardless what motor timing was used for the ESCs. Calibrating throttle range and all the helpful hints from the various forums didn’t help either. Each time the quad got into the air, one or more of the motors would just cut out. So we installed the controller in a different frame with four Turnigy Plush 30A ESCs, and lo and behold, it was hovering just fine.
However, now we had to deal with the infamous “PID tuning game” that every MultiWii newcomer learns to hate. Basically, you have to tune three values, P, I and D, for both roll and pitch (yaw isn’t so sensitive, the defaults work fine there) until the multicopter is neither too unstable, nor exhibits a tendency to flip or oscillate. And here’s our hint for making this work:
Forget all suggested values they tell you in forums, your values will be different. Start with P=2.0, I=0.020 and D=10 and slightly increase “P” in steps of 0.1 until the quad oscillates, which means you got too far. Then increase “I” in steps of 0.002 until you notice excessive counter-movements after quick taps of the roll/yaw stick. After that increase “D” in steps of 1 until you notice the quad becoming unstable, which is again a sign to back off again. After you got “D” up a bit, you can increase “P” a bit more still. If the quad starts oscillating, flips when applying sudden power, or otherwise reacts jumpy, your PID values are too high, and if it’s hard to control and feels mushy then they’re too low.
Control responsiveness can be tweaked down to the smallest detail. Want more reaction speed depending on how far you push the sticks, while still having a docile hover behavior when the sticks are near center? No problem, MultiWii has a parameter for that. Indeed the amount of customization is MultiWii’s greatest blessing and course at the same time. It’s a great system for someone who has build quadcopters before and knows a good deal about setting up these devices, but for someone just starting out it can be a nightmare.
Get used to this sight. You’ll tweak quite a few numbers before the Crius board flies smoothly. But after this is done, flight performance is great.
A drawback of the Crius board, and MultiWii in general, is that you have to set up the normal flight mode first, before you even get to setting the parameters for the autolevel mode. And to make matters a bit more complicated, autolevel mode needs it’s own “trimming” setup on top of that, which involves hovering and observing where it drifts off to, landing, go into “trim mode”, move the sticks according to where you need to trim, exit trim mode, and try again. But you need autolevel to work in order to take advantage of things like the GPS return to home function, should you want to pursue that option.
The little LCD module can be quite useful for quickly fixing a wobble-inducing parameter, but in general the bluetooth module + android app is more comfortable.
Flight performance
Setting up the PID values can be tedious and RC enthusiasts used to plugging in a controller and just taking off are in for a rough awakening. On the plus side, once the parameters are set correctly, this is a very stable controller, and easily on par with the Rabbit board. Forward flight speeds of over 80kph are no problem, and it’s a real joy to fly.
While the Rabbit FC comes with the auto-level mode enabled by default and the “3D mode” as something you switch on when you feel adventurous, the Crius MultiWii Lite has no auto-leveling enabled by default – you have to assign that to a switch, and you need to get the normal flight mode stable first before you can tweak the auto-level mode. That said, once this has been done, auto-level works great.
Check out this video of the responsiveness of the Crius MultiWii Lite:
Verdict
We really liked the versatility and quality of this board. The bluetooth option and using an android app for setting up your multicopter is just plain cool, and flight performance and stability are top notch. The fact that a big community stands behind MultiWii and keeps updating the software and adding support for new capabilities is yet another big boon. Plus if you know how to set up the Crius, you’ll be pretty much at home with any MultiWii compatible board.
The big negative point about MultiWii in general is a certain amount of complexity during setup. Most people don’t even know what a PID loop is, and here you are tuning not just one, but actually three PID loops – four if you count yaw and the autolevel PID values. This is the one area where Rabbit FC is simply better: Most people will plug it in and it’ll work for them without much fuss.
The other negative thing is that MultiWii requires good ESCs that can work with its 400Hz ESC update rate. If one of your motors cuts out and your are sure your throttle range is set correctly, get Turnigy Plush ESCs instead. There’s a ton of problem reports on the various forums about people having trouble getting this board to work, and in most cases it’s simply badly tuned PID values or an incompatible ESC.
This is a flight controller for experts. If you haven’t uploaded an Arduino sketch to an Arduino controller before, you’re in for a learning experience. But if you’re experienced, or better yet, already familiar with MultiWii, the Crius board is a very capable and stable controller.
Sources
Crius MultiWii Lite + USB FTDI Module: http://www.goodluckbuy.com/mwc-multiwii-lite-4-axis-x-mode-flight-control-board-quadx-w-ftdi-basic-breakout-.html
Crius MultiWii SE + USB FTDI Module: http://www.goodluckbuy.com/mwc-multiwii-se-standard-edition-4-axis-flight-control-board-quadx-w-ftdi-basic-breakout-.html
Bluetooth Module: http://www.goodluckbuy.com/serial-bluetooth-rf-transceiver-module-rs232-w-backplane-enable-and-state-pin-1.html
This isn’t a review of the Crius board at all. Everything you mention about features and configurations are attributes of Multiwii and have nothing to do with the board it is running on. Therefor it’s a review of the Multiwii software.
Wingspinner
Things like the external FTDI board and the lack of an integrated USB connection are certainly not attributes of MultiWii.
The most important aspect is whether it flies well. It does, but it takes some effort to get there – in great part due to the way MultiWii works. Hence the details about MultiWii.
It says here: http://rctimer.com/index.php?gOo=goods_search_list.dwt&gcat=159&p=2 you can hook up an OSD to the Crius. Which OSD and what kind of connection?
There are many options. MultiWii supports output of all the data via serial connection. The release notes of MultiWii list these OSDs:
Rushduino:
more info here: http://www.multiwii.com/forum/viewtopic.php?f=8&t=922
mobiDrone:
more info here: http://www.multiwii.com/forum/viewtopic.php?f=8&t=1498
BTW Remzibi OSD is also compatible with the Crius SE, AFAIK.