Peter's Projects

Jib, Dolly, Remote-Control Pan/Tilt

2007-06-23T17:58:00.000-07:00

I've recently built a jib using laser-cut parts and hardware from Home Depot. The jib can extend to a total length of about 16 feet. It uses circular wood discs at the pivot points to provide smooth, stable motion.

The jib can be used with a remote-control pan/tilt head, also built mostly with laser-cut parts. The pan/tilt head uses heavy-duty RC servos attached to external gear boxes. Both servos are modified to rotate continuously. The pan-tilt head can be supported from below or hung from above (the jib supports both options). To do this, the camera part is rotated 180 degrees.

The camera attaches using a custom mounting plate. Future camera rigs will use the same mounting system, so the camera can quickly be moved from one device to another.

The jib can ride on a laser-cut dolly that I built laser year. This dolly can ride on professional dolly track, including curved track. We used the jib with the dolly on a rooftop in Manhattan for a shoot a week ago.

I hope to return to the helicopter project this summer.

Balloon Rig, etc.

2006-10-30T11:53:00.000-08:00

I've been continuing to work on the helicopter almost every day (design, lasercut, build, and repeat).

The new wireless video transmitter/receiver works quite well.

I lasercut some structural components so that I have a single hand-held controller (including the video receiver, LCD TV monitor, battery, and radio transmitter).

I've set up a microcontroller to manipulate the signals between the radio-control receiver and the motor controllers. (The microcontroller takes in PWM servo signals and outputs modified PWM servo signals.)

I've done two shoots using a balloon rig. First I shot in a park. A week later I shot on a rooftop in Manhattan.

Now that I'm done with the balloon rig, I'll go back to focusing on the helicopter. Hopefully soon I'll determine whether I should be using 2, 3, or 4 rotors.

Weighing Video Cameras

2006-09-10T21:57:00.000-07:00

I had wanted to use a Panasonic DVC30 camera onboard the helicopter. This camera is quite similar to the DVX100, a good camera that I use rather often. The DVC30 can shoot 30P (30 progressive frames per second), which is close enough to the 24P mode commonly used on the DVX100. The DVC30 has the advantage of weighing about half as much as the DVX100.

Unfortunately, in the context of this project, the DVC30 still weighs a lot: around 1100g with a battery and tape. In order to lift that much, along with motor batteries, servos, and structural components, my recent electrical designs have required four motors and weighed nearly 10 pounds. Keeping 10 pounds in the air for 10 minutes requires an unreasonable amount of battery power.

So, I decided to look for a lighter camera. One option is the Panasonic SDR-S100, which records to SD memory cards and has reasonably good image quality. (It has 3 CCDs and a Leica lens, like most good Panasonic models.) It weighs just 282g, including the memory card and battery.

After building a spreadsheet of the weights of all the Panasonic consumer 3 CCD cameras and reading a number of reviews, I'm going to aim for the GS300. It has better image quality than the S100 and costs half as much, but weighs twice as much: 550g. Running through the numbers, I think I may be able to fly a 550g camera using a minimalist 2 motor design.

Because of the trouble and expense of renting helium tanks, I'm designing the new version without balloons.

Wireless Video

2006-09-04T23:08:00.000-07:00

A couple weeks ago I tested my 1.7 GHz transmitter/receiver and found that they did not work well enough to be usable. The problem appeared to be interference (which isn't surprising in New York), but could have also been some kind of device failure or mis-configuration.

I had selected 1.7 GHz specifically to avoid interference. Most wireless video transmitters operate at 2.4 GHz, but using that frequency in an urban environment would be foolish (given the proliferation of wireless ethernet, microwave ovens, and other devices at that frequency).

Other common wireless video frequencies include 5.8 GHz, 1.2 GHz, and 900 MHz. I would choose 5.8 GHz (since it's not a very crowded frequency), but that frequency is obstructed by many materials and is not good for non-stationary transmitters. (This table provides a useful summary.) So, I'm left with 1.2 GHz and 900 MHz.

After looking at various websites offering 1.2 GHz and 900 MHz wireless video systems, I've settled on this transmitter and receiver.

If that doesn't work, I suppose I'll try 1.2 GHz or a more powerful 900 MHz transmitter. (or a tether!)

User Interface

2006-09-02T22:22:00.000-07:00

The original plan was to use a laptop for the helicopter control console. The laptop would run a program that sends commands to a wireless serial link and displays video from a wireless video link (via a pcmcia video input device).

After some further thought, I've decide it would be better to use an R/C controller. This would be easier to hold while walking and less conspicuous (which may be a big deal when filming in difficult or shady locations). The R/C controller provides finer control than a keyboard and has built-in trim controls (for making extra-fine adjustments).

Also, the R/C controller provides simple, reliable, long-range radio transmission (which would be questionable using an inexpensive wireless serial link).

In order to do this, the airborne microcontroller will need to decode the signals from the R/C receiver and translate them into commands to send to the motors and servos. (The mapping between the controls and the motors/servos is simple but not direct.) Preliminary research suggests that this will be fairly easy.

(It's amazing how complicated and expensive R/C controllers can get. This one costs $2200.)

For the video display, I've ordered a small 12V LCD TV that I'll attach to the transmitter. This will be more reliable than feeding the video signal through a laptop.

The only disadvantage of not using a laptop for the control console is that the laptop would have been able to display status info coming down from the wireless serial link. Perhaps I'll still use a wireless serial link for debugging.

Two Gas Engines

2006-08-28T16:58:00.000-07:00

Today I finished assembling the main helicopter structure and performed the break-in procedure for the second gas engine. The two gas engines are located near the center of the helicopter, so that if one stops running, the other can bring it down for a controlled landing.

On Friday, if I can successfully rent a helium tank, I may try doing a test flight. (The design still uses four helium-filled weather balloons.)

I'm increasingly concerned about the vibration of the gas engines, so I'm going to continue working on building an electric version of the helicopter.

One issue is with having both gas and electric helicopters is that different cameras would be suitable for the different versions. The electric one needs a very light camera, whereas the gas one can lift a heavier (higher-quality) camera.

Gas Engine

2006-08-22T18:43:00.000-07:00

Two weeks ago, I decided that I should try using a gas engine, because the batteries for the electric motor take too long to charge.

One week later, I had obtained an R/C airplane engine and all the accessories. After much trial and error, I was able to run the engine.

Today I built a new test rig that allows me to turn the engine from horizontal to vertical while it is running (this requires positioning the fuel tank, fuel lines, and carburetor on the axis of rotation). Using this rig, I determined that the engine can run and be started in a vertical orientation.

Photo of the rig. Detail. Accessories.

This contraption (including the 2.5 pound weight) can take off vertically. Of course, it's not a stable flying machine, so you have to hold on to it with one hand (which requires a certain amount of insanity).

The amount of lift and fuel consumption are both good.

The biggest problem is vibration. Every nut and bolt must be very tight; otherwise it will shake itself to pieces. (I bought some nut-locking glue, which I'll use on the final version.) Normally the engine is rigidly attached to a heavy airplane body, but for this helicopter, the engine should be the heaviest component, so there isn't much to damp the vibration.

Of course, this much vibration will be bad for recording video footage. I'll have to modify the helicopter body to isolate the camera as much as possible. Perhaps I can use a smaller engine to reduce the vibration.

The engine has other drawbacks: it is rather loud, it coats everything in fuel residue, it is a bit tricky to start, it requires many parts and accessories, and it requires draining the fuel tank and fuel lines after use.

Nonetheless, I think I'll continue to experiment with the engine.

One option would be to have two gas engines fixed in a vertical orientation and use two electric motors for forward motion and turning. Alternatively, I could place the engines on actuated pivots, as was the original design for the electric motors.

Next step: laser-cut an engine support structure.

Propeller Test

2006-08-07T20:11:00.000-07:00

I've finished the first round of propeller testing. The test system uses software to send commands to a serial servo controller, which is attached to the speed controller, which is attached to the motor and battery. I measured lift using a digital postal scale.

Photo of the test system. Photo of propellers.

I measured each propeller at 70% and 90% of max power. I expect 70% will correspond to hovering speed, leaving a reasonable margin for climbing, turning, and battery depletion.

I tested each prop in order, then recharged the battery and retested each prop in the reverse order. This should reduce the battery charge bias.

Results:

Prop Type/Size	Lift at 70%	Lift at 90%
APC 10x4.7	740g	900g
APC 11x3.8	800g	995g
APC 11x4.7	940g	1130g
EF 11x4.5	950g	1130g
APC 13x6	1085g	1335g
MA 13x6	1150g	1345g

Each prop is denoted with its manufacturer and two prop size numbers. The first number gives the prop diameter (in inches). The second number relates to the forward speed of the propeller. For the helicopter, I'd like high static lift, not a high top speed, so I want a low second number. (Though these experiments suggest that the second number shouldn't be too low.)

The best props from this set are the 13x6s. These provide over 1kg of lift at 70% power. The motor, gearbox, prop, electronics, and battery weigh a total of about 350g, so flying with these props should be reasonable. (Some of this lift may be due to the ground effect, though I tried to reduce that by raising the props up off the table top.)

I'm going to order more propellers near the best in this batch (e.g. 13x5 and 12x4). According to the motor specs, I shouldn't go above 13" diameter, so as not to overheat the motor.

Given the charge time for the LiPo batteries, I think I may try a gas-powered engine. More on that later.

Initial Parts List

2006-08-01T09:41:00.000-07:00

Here is a partial list of what I have so far:

I have most of the mechanical and structural components. I also have some microcontrollers (I'll probably use a BASIC stamp for the first prototype).

I have an assortment of 10" to 13" low-speed props. I need to buy a scale so I can measure the lift provided by each.

Helicopter Project Introduction

2006-07-29T21:40:00.000-07:00

The helicopter should be able to carry a small video camera. Video from the camera should be transmitted wirelessly to a ground operator and commands from the operator should be transmitted wirelessly to the helicopter.

A traditional RC helicopter has certain drawbacks I'd like to avoid: difficult control, high vibration, and dangerous rotors. A possible solution is to use multiple smaller rotors.

For my first prototype, I'm going to try two propellers (10" to 13" in diameter) and four helium weather balloons (each about 2'6" in diameter). The balloons will provide stability and protect the camera and propellers; they won't provide much lift. The propellers will be attached to 20-amp brushless motors with gearboxes, powered by LiPo (Lithium Polymer) batteries.

If the balloons turn out to be too much trouble, I may ditch them. I may also need to add more props.

I've ordered and received most of the components for the first prototype. Soon I'll post a parts list.

This project is partially funded by a grant from the MIT Council for the Arts.

Next step: testing the components and measuring the lift provided by the props.