OWLplane Catapult Launcher
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OWLplane Catapult Launcher
Throwing your models with a hand launch method, it is prone to human errors. If the thrust ratio is less than one, we have to put extra force into it. Especially, EDF jet engine, usually it does have about one thrust ratio or less, proper and correct way of throwing the plane is challenging. If EDF jet is designed to fly faster, the designer needs to reduce exit nozzle diameter, as a result, it will reduce the thrust ratio more. It gets harder to throw. Moreover, it limits the weight of the battery also, since we need to keep the ratio close to or above 1:1.
OWLplane offer a solution by utilizing a catapult launcher. Not only can the catapult throw the model with 10x of model AUW force but also, it ensures that the force is not breaking the model due to its significant pull force. OWLplane came up with the idea to use a launcher adapter for the model where it gets support from the fiber carbon spars which are the strongest parts. With the adapter, it is now safe to launch the model. If you have your own catapult launcher already, you may only print the adapter. The launcher adapter can be used also with any other catapult launchers.
If you would like the parts to be heat resistant from strong sunlight, you may want to print those with PETG filament or if possible with ABS/ASA filament. We printed the parts with PLA filament and all the videos made also use PLA filament and so far we do not see any degradation yet.
You may want to watch how the catapult works by clicking the following videos, enjoy !
Specification, Design and Requirement
Start with Watching the Following Videos :
Catapult Launcher Ropes :
3 segments are utilized to use for the launcher. Let say that they are segment A), B) and C). Only segment A) and C) utilize elastic ropes where segment B) employs non-elastic rope.
Here are the details :
- Rope A) is called an adapter rope. It is an elastic rope with length about 15-20cm long. It is really important to use elastic rope for segment A). During firing, the different length from (bottom side of rope B + rope C) – (rope A + top side of rope B + rope C) makes shock force. To absorb the force, rope A must use an elastic rope. It also maintain the hook in its place by creating a bit tension when positioning the model.
- Rope B) is made of two sub-segment and called middle rope. The first sub-segment is a top one. The length is ranging about 1.8m-2m long. When small model such as 50mm EDF jet, it uses 2m long rope where bigger model such as 70mm EDF jet it uses 1.8m long. Anyway, feel free to adjust the length of the rope. The second sub-segment is a bottom one. The length is about 2.85m. At the end toward the triggering parts, there is a metal ring (read “How to Create Firing Ring” section how to create one) . The metal ring is attached to the PVC firing stick when stretching out the C) segment rope (please watch how OWLplane Catapult Launcher work video). It is better to use/create longer middle rope B) so that it will have less difference (it means less shock force). At least 2.85m long rope for the bottom rope since it has been tested with no issue.
- Rope C) is made of bungee rope with diameter size of 8mm and length about 20m. The total length will be 10m since that rope will be doubled when installed to the launcher. It is possible to use different size and length but during the testing we have successfully used about 10x of OWLplane 70mm EDF jet AUW models. At the far end, OWLplane use crowbar stick to support the required force which is also about 10x of OWLplane 70mm EDF jet AUW models. Please use weight scale to make sure the pull force has reached targeted force. For 50mm EDF OWLplane jet, use 10kg-12kg where 70mm EDF OWLplane jet use 15kg to 17kg of force.
How to Create Firing Ring :
Catapult Launcher Model Adapter :
OWLplane Model Adapter Directory :
Catapult Launcher Pull Adapter :
Catapult Launcher Triggering Parts :
The triggering parts have a set of 3D printed parts and non-3D printed parts.
The 3D printed parts are shown in the table below. They are printed with GR4 profile code. The non-3D printed parts made of:
– 4x gear wheel stop set collar 9×4.1mm.
– 2x 4mm OD steel rod (custom the length as per your convenience) to extend the pedal.
– 1x short steel rode with 4/5mm OD.
– 1x long steel rode with 4/5mm OD.
– 1x PVC 1″ for pedal axis (20cm long is more than enough but feel free to custom it).
– 1x PVC 1″ for triggering stick (65mm long is more than enough feel free to custom the length).
How to assembly the pedal:
Just watch assembly animation video and use 4x gear wheel stop set collar 9×4.1mm and 2x 4mm OD steel rod. Use hot-glue to attach the “TRIGGER-PEDAL-EXTENSION # GR4” into the “TRIGGER-PEDAL # GR4” with 2x 4mm OD rod.
How to make holes on triggering stick:
Complete your catapult launcher assembly including the triggering stick. Make sure the triggering stick touch the bottom of “TRIGGER-BASE # GR4″ part. Mark the stick with two dots near the pedal/”TRIGGER-PEDAL # GR4” arms for installing “TRIGGER-PIN 4-5mm OD ROD” both sides. At the same time, mark also the stick by inserting the marker using holes from “TRIGGER-GUIDE # GR4” both sides. Use 6mm drill bit to make the required holes.
Catapult Launcher Construction and Its 3DP Parts :
Only “3DP-KNEE-L # GR4” and “3DP-KNEE-R # GR4″ are 3D printed. The rest use PVC 1” pipes and connectors. The 3D printed parts are substitutions if do not want to cut top side of PVC knee, just print OWLplane “3DP-KNEE-L # GR4” and “3DP-KNEE-R # GR4” to use. Do not use PVC knee directly since it will block the model during the launching on the top side.
In summary :
- 6x PVC T-Joint.
- 2x or 4x PVC Knee (only 2 needed if using 3D printed parts).
- 1x “3DP-KNEE-L # GR4” and 1x ““3DP-KNEE-L # GR4” to replace 2x PVC Knee.
- 2x 150cm-PVC Pipes.
- 2x 40cm-PVC Pipes.
- 3x 25cm-PVC Pipes.
- 2x8cm-PVC Pipes.
- 6x15cm-PVC Pipes.
Total : 561cm, please add also firing stick 65cm and pedal axis 20cm.
Grand Total : 646cm.
Catapult Launcher Supporting Parts :
Two type of supports are used for the launcher. The first one is “BASE-LEG-SUPPORT” where you do not rope to install the support. It can accept “tent stakes” from the provided holes. Another type of support “BOTTOM-ROPE-SUPPORT” needs rope to install. In this case, it is more flexible to use since it is not constrained by the hole sizes. OWLplane use it with crowbar to get strong support. Feel free to use any type of supports and make sure the supports are strong enough to hold more than 10x of model AUW.
The following picture show tools/materials that can be used to support the catapult launcher construction.
Table of Contents
3DP Slicer Profile Suggestion
G-code are already provided for Bowden or DD extruder. In case you would like to slice by yourself, you may start with using GR4 profile code. Please take note that the GR4 does not have fan turned on and also support not enabled. Please read the following to get better result:
Hardware and Materials
- PVC-Pipe : read “Catapult Launcher Construction and Its 3DP Parts” above for more details and please add the triggering PVC pipe and pedal axis PVC pipe for the total pipes. Grand total : 646cm.
- PVC T-Joint : 6x.
- PVC Knee : 2x or 4x (if two, please print “3DP-KNEE-L and R # GR4” as replacement).
- 8mm OD – 500mm long for assembling “Catapult Launcher Model Adapter”.
- 5mm OD – 4x with 25mm for assembling “Catapult Launcher Model Adapter”.
- Tape for fixing 3D printed parts location for “Catapult Launcher Model Adapter”.
- 5mm diameter elastic rope for creating A) segment rope used for “Catapult Launcher Model Adapter”.
- Non-elastic rope to create segment B) with total length about 6m.
- 8mm diameter bungee rope with 20m long for creating C) segment rope.
- 2-2.5 OD rod for creating triggering ring.
- Tent stakes used for locking rod or supporting catapult launcher construction.
- 4mm/5mm OD rod with 55cm long used for triggering rod.
- Some carabiner (how many depending on your need at least one for connecting segment B) rope to segment A)). You may want to use velcro instead.
- 1x or more crowbar and combining with tent stakes can be used for supporting the catapult launcher.