When you’re building advanced rockets as BPS.Space are, an unreliable launchpad is the something you really don’t want to be struggling with. [Joe Barnard] is working on a model rocket that can land vertically under its own power, like the Falcon 9, and has upgraded his launchpad in the process. A lot of thought and hard-earned experience has gone into its design, and the video after the break is a fascinating look the engineering process.
[Joe]’s rockets don’t use guide rods and fins for stabilization in the way most amateur rockets do, but instead have thrust vectoring motor mounts and reaction wheels for active stabilization during launch and flight. The rockets are clamped to the launchpad right up to ignition, and then need to release quickly and reliably. His previous clamps looked very cool, but suffered from high friction forces during release, and the integrated covers prevented easy inspection. These were replaced by much simpler spring-loaded clamp held in place by a small locking bar, which is knocked out by a servo to release the clamp. It also has no static friction, since it moves up and away from the clamping surfaces on the rocket.
The launch pad also features a ATSAMD21 based launch computer named Impulse, which at the most basic level controls the igniter, clamps, buzzer and indicator lights. It also has a number of inputs and outputs to allow for expansion. [Joe] experienced a number of inexplicable failures of rocketry electronics in the past, but believes he has finally tracked down the culprit: Tennessee humidity. He has since started conformal coating all his electronics.
The launchpad itself is made from plywood, so to protect it from the hot exhaust it has in integrated flame trench. This was made from 1 inch steel plumbing components, and directs most of the exhaust out of one side of the platform. It can also be reconfigured to allow a three core rocket like a Falcon Heavy to be launched.
It’s incredible to see how far BPS.Space has come in the past four years, with the engineering complexity and video production quality increasing in leaps and bounds. Earlier this year we covered on of [Joe]’s other projects, a silo-launched rocket named Thoomp.
This is certainly an interesting build. Personally I would have had the release hooks on a single mechanism with just one actuator for all of them to ensure that they are released “all at the same time – every time”.
He’s got active thrust vectoring guidance, and the time offset will be less than the opening time, and probably much better, so I think he made the right choice.
Every mechanical linkage you can get rid of is a win for ease of construction and repair, and sometimes cost too. They’re fussier than electronics as far as I’ve seen, except for maybe some of the truly excellent ones refined over many generations.
A HUGELY overcomplex design, like most of his stuff. A much simpler, but not as “cool” or as similar to the Apollo Saturn rocket hold-downs, but just as functional design also avoiding the corrosion issue from motor exhaust residue: Place holes in the 3D printed base of the rocket. Plungers of simple solenoids insert into holes which pull back into their 3D printed enclosure at launch, the metal plunger having a 3D printed “hatch cover” the same OD as the plunger epoxied to its end to protect the tip of the plunger from exhaust residue.
I agree. A four-solenoids solution would already be way better in my opinion too. Would keep the mechanical complexity down as per Daniel Dunn’s comment but still drastically simplify & robustify the design.
Here’s a question for people who know more about model rocketry than I. Would a sealed launch tube be better than a launch pad?
Perhaps – but then your rocket needs to be able to take the heat and pressure of its own exhaust all along the bottom and if it jams you have a pipe bomb in the making (most model rockets won’t put out enough for either of these to be a major problem but the big off the shelf ones probably do)…
Seems to me like a plausible but awkward idea – if you want that sort of launch a plane ol’ launch rail is what you want – the exhaust dissipates into the air safely, a jam just leaves the rocket on the rail – all round safer and easier to engineer the rocket.
Yes, it gives more force for the launch, but subjects thin gas to higher temperatures and pressures, is harder to inspect, and creates complexities for fins.
Unless one has to hold down the rocket even after it’s thrust is exceeding it’s weight, it is worth checking out the Soyuz launch pad mechanism:
Suspend the rocket somewhere along it’s length on four hinged arms with counter weights. As soon as the thrust exceeds the rockets weight, the rocket starts to lift itself from the arms, they swing back on their own to get clear of the launcher. No electronics or actuators needed.
Of course this limits the allowable launch acceleration, as the arms need some time to swing out of the way, so probably not ideal for model rockets. Maybe the mechanism could be augmented with an additional trigger/spring mechanism, like the one shown in the BPS.Space design?
https://youtu.be/NYv89dC7rn0?t=89
I like this idea, and if you need faster response a spring does seem the way to go for me. The only reason for the electronic control pad I can see is to selectively hold the rocket down deliberately – perhaps testing a burn duration or thrust vectoring or total output (but I don’t think this pad would take that for long anyway).
On big rockets, I believe it’s common to bring to motors up to full thrust before releasing?
Not sure if that’s about the possibility of an abort if one fails, or if it’s about the mechanics of how turbos work and stuff, or about not needing to sync multiple rocket engines perfectly.
Doesn’t seem an issue with model rockets, unless you’ve got multiple engines.
Indeed, there are safety reasons and efficiency reasons why you might hold the rocket down while firing. Doesn’t really apply to small solid fuel models so much though.. The old rocket engines took a very long time (relatively) to hit their expected launch thrust so keeping them locked down to that point just makes sense and ensures they launch with full control authority.
Doesn’t seem like a hard system to add a hold on if you want to either – just a simple solenoid powered latch if you so desire. But keeping it extra simple and electronics free makes it cheap and durable. Which as a hobby project seems like a winner.
Maybe this is to simplistic, but why not have the release mechanism held by a thread that is a few inches below the rocket motor. If the motor lights, it will immediately burn thru the thread and release the rocket automatically.
Forgot to say this is a neat project!!!
Isn’t explosive bolts the standard solution to avoid issues with releasing? Those small servos aren’t the most reliable things, and if one fails or is slow to release, you presumably risk the thrust of the rocket flipping it over for a horizontal launch?