The ratio I found was 2.5 parts CWF and 1 part water. Thins it down so you do not have to sand as much, and it smooths out nicely, and is dry enough to not warp balsa...
YMMV
Tau Zero Leonora Christine
- Thread starter BigMacDaddy
- Start date
Help Support The Rocketry Forum:
YMMV
I think I will stick with 24mm on this because of the current design / motor mount. I did not really think about it before my question but all the 3D printed parts would need to be made larger for 29mm. Also not sure the cardstock nosecone would be great with higher power. Fins have pretty big tabs and deep mounting slots so I think they would be ok on launches but landings are a bit more risky. Maybe bigger engine in an upscale in the future...
So with only the 18" parachute opened (24" 2nd chute stuck closed) the rocket landed somewhat hard and a fin popped off. Ironically, I had built this initial prototype with quite small fin tabs and did not necessarily glue them tremendously well so the fin just popped out of its slot and I can glue it in again.
I had planned the new model with much more internal support and larger tabs (basically tabs would have 3D printed full size slots so the tab would be have lots of surface area for glue and lots of sideways support internally.
However, I am worried that these fins will always be somewhat vulnerable. Thus I was considering designing the slots so that the fins could be inserted on a slight forward angle and pushed back and "locked" in position without glue (basically using a plywood bulge/tab). This would allow the fins to fold forward and pop out of the rocket on landing (which it would hopefully do before breaking).
What do you guys think -- worth exploring / trying this?
I had planned the new model with much more internal support and larger tabs (basically tabs would have 3D printed full size slots so the tab would be have lots of surface area for glue and lots of sideways support internally.
However, I am worried that these fins will always be somewhat vulnerable. Thus I was considering designing the slots so that the fins could be inserted on a slight forward angle and pushed back and "locked" in position without glue (basically using a plywood bulge/tab). This would allow the fins to fold forward and pop out of the rocket on landing (which it would hopefully do before breaking).
What do you guys think -- worth exploring / trying this?
I have seen this idea discussed here a number of times, but I can't think of any examples of someone having actually tried it. It sounds interesting. Those fins were always destined to be a vulnerability, that was obvious from the first drawing. Sure do look cool though.
In theory it seems like it might work. I don't know how hard it will be to engineer it so that the fins are very secure in flight but able to pop forward on landing. With your 3D-printing wizardry I wouldn't bet against your ability to make it something work.
I do worry about stupid stuff like losing the fins after landing... if you do this it would probably be good to include a few extra fins in the kit.
Is the area where the fin attaches to the motor mount accessible from the rear? It looks to me like the rear unscrews or something. I had considered putting in some thin 1/16" balsa strips, one on each side of where the fin attaches, sort of like a guide to place the fin and provide more strength once glued in.
But, if there is some way to provide for a strong mechanical connection between the fin and motor mount/tube such that that broken fins can be popped out and replaced easily, that would be far preferable. Even if one papers the fins with cardstock, I can see them breaking off frequently.
But, if there is some way to provide for a strong mechanical connection between the fin and motor mount/tube such that that broken fins can be popped out and replaced easily, that would be far preferable. Even if one papers the fins with cardstock, I can see them breaking off frequently.
Maybe try something like the pivots on the M1147 model maybe?
With the pivot on the front of the fins which would allow a forward pivot when it hits the ground to dissipate the force.
With the pivot on the front of the fins which would allow a forward pivot when it hits the ground to dissipate the force.
Thanks -- yeah, they look more or less like the pictures (although those are actually even a bit thinner and even longer in some pictures). I am thinking about something like locking shelf brackets but don't want a tap that is too complex or long since that will be a fragile spot. On the plus side it would be pretty easy to use one fin as a template to cut a new fin but I can probably include an extra fin or two.
I thought about doing something with pins but I am afraid that it might make a weak mount point plus it is kinda complex. The M1147 does provide inspiration -- in that model I also had an internal lip that the fin detail fit against.
Maybe something like this (forward / top is on top) -- The 3D printed detail is only 2mm wide and sandwiched on both sides by solid 3D printed faces so should be plenty strong. I do think reinforcing those tabs with CA glue would be a good idea.
It is accessible from the rear and the fin tabs reach the motor tube. I thought about trying to do something from the rear to lock in the fins. Replaceability was a key goal I was going for. Much harder to dig a glued in fin tab out than one that is not glued.
The 2mm plywood used here is quite durable so with a proper parachute they should not break on reasonably soft ground.
I think you're overthinking it. Overthinking stuff is a thing with which I have a great deal of experience, so I know the signs.
Count on that. I was ready to say you should move from balsa to plywood, and then I read the above and see that you're already using that. If the 2 mm plywood isn't strong enough then use 3 mm plywood. Use a single parachute to avoid one chute interfering with the other; if the 24 inch chute isn't enough by itself then go a size up. Good chute, strong fins, glue'm in tight, and push the button.
- Joined
- Aug 27, 2011
- Messages
- 11,594
- Reaction score
- 6,213
My theory on multiple chutes to same chassis:
It takes a certain amount of air flow to get a chute to deploy. If one chute opens first (which is close to inevitable) and it slows down the descent SUFFICIENTLY, there isn’t enough flow to open another chute. However, given the effect of the first chute, the second is likely superfluous. If first chute WASN’T sufficient, the second chute would open.
So no harm, no foul, and points for redundancy.
It takes a certain amount of air flow to get a chute to deploy. If one chute opens first (which is close to inevitable) and it slows down the descent SUFFICIENTLY, there isn’t enough flow to open another chute. However, given the effect of the first chute, the second is likely superfluous. If first chute WASN’T sufficient, the second chute would open.
So no harm, no foul, and points for redundancy.
- Joined
- Aug 27, 2011
- Messages
- 11,594
- Reaction score
- 6,213
Put three dowels on the tail sticking a couple inches past rocket nozzle. Paint them silver or black and call them antennas. They should hit before fins and take brunt of impact. Rig it so they are easy to replace if THEY break, maybe friction fit in some sort of receptacle.
Bonus points. On soft ground highly likely to (literally) stick the landing!
Made the notched fins and redesigned mounting slots in the 3D printed parts to allow the fins to be locked in place and removed (plus should allow them to pivot up if the model has a hard landing). I accidentally slotted my first prototype backwards (forgot which way is up) but got that corrected. Anyway, they seem to work pretty well -- but need to reinforce the tab with thin CA glue. They are a little less rigid than when fins are glued in place (not surprising) but it lets people glue them in place if they want or leave them free to move (I like to provide options).
Last edited:
Have you played around with smoothing the ABS parts? I looked into it, and aside from doing the acetone vapor steam bath method, or melting the supplied extra ABS scraps into acetone, the only thing I could think of is something like the BIN shellac based filler primer I have. But I have not been able to find ANY info about compatibility of shellac primers and ABS, so I'm pretty reluctant to try it.
I figure to sand down the parts as much as I can, then fill the remaining defects somehow, but haven't decided how yet.
I figure to sand down the parts as much as I can, then fill the remaining defects somehow, but haven't decided how yet.
With a large PLA (not ABS) part, I smoothed it out totally old school. Sand, prime, repeat. The printed part is a lot harder than balsa, so I started with courser sandpaper than I'm accustomed to, but other wise it's just the same old grind (so to speak).
I usually do a bit of sanding, fill any more significant vertical seams with ABS slurry or wood filler, and spray with filler-primer. That is usually enough for me. Wood filler is much easier to sand than ABS slurry but not sure if it will ever pop out or something (have not had that happen). I have heard others do a number of coats of filler primer with sanding between and get really smooth results.
For this model I decided to leave some surfaces with more district faces -- like the spheres and tubes. I also usually do not worry much about resolution / faces on the shoulders
I am also doing my best to increase the resolution of parts (more faces) and with the print orientation to try to get better prints. For example, I am testing printing larger BT-80 caps (short semi-circles) vertically instead of horizontally. Bit more assembly and need to fill a seam but much smoother overall finish. For example, bottom part is printed vertically.
I'm quite new to working with 3D parts, but I find Tamiya Basic Putty works well the Radical Rocketry prints. It's what I use on plastic nosecones and body tube spirals, so I have it on hand. It may not be the best filler and, as ever, YMMV.
I've taken the easier way out, and just sanded the parts. Some aren't even visible once the rocket is assembled, and so I don't bother unless needed for parts fit.
I've started construction of my Tau Zero, and will be posting in a separate construction post once I get further along. I took a lot of time try-fitting parts, measuring things, documenting the build steps, etc. The measurements in the .PDF should be taken as a rough guideline, and be prepared to modify as needed. A challenging build, but I think its going to look very nice once done.
I've started construction of my Tau Zero, and will be posting in a separate construction post once I get further along. I took a lot of time try-fitting parts, measuring things, documenting the build steps, etc. The measurements in the .PDF should be taken as a rough guideline, and be prepared to modify as needed. A challenging build, but I think its going to look very nice once done.
Similar threads
