You can't decide if you should go with the XRP Off-Road mod or the XRP Boat mod? You shouldn't be asked tough questions like that. The answer is I want both! Let me present the solution: the XRP Amphibious Mod.
Designed with big off-road wheels and some floating aid to give you enough buoyancy to get your quite heavy XRP almost everywhere. Your XRP has by default only 2 motors. But if you want you can also upgrade your XRP to the XRP Mecanum Frame that offers you 2 different sizes and the possibility to use 4 motors for better transmission, especially on water by using 4 driving wheels.
This kit requires the latest chassis which is currently V1.5.3MF. This version offers a hole next to the motor shafts, so you can connect wheels outside the frame. For older Versions you would have to modify your chassis. I do provide a XRP Axis Hole Finder For Older Frames, that will help you to drill the hole in the correct position, have a look at my models.
And the mandatory note: Electronics and water are no friends! Protect your electronics well. Use zip lock bags, tape, etc. They might become permanently damaged if they come in contact with water!
The buoyancy will be good enough to keep your XRP floating. But this highly depends on your print settings for all parts and how heavy they are.
Buoyancy is key. The volume your print has is the weight it can keep above the water. One tire has about 570g buoyancy. So 4 tires will be able to keep 2280g floating. Sounds good enough, but … we got a lot to subtract and the biggest portion is that 2280g mean that it would basically completely be submerged but slightly breaking the water surface. So we can't put 2280g onto it. The motors are on the same height as the axis and we don't want them to be submerged. That means we're aiming more for only submerging between ¼ and ⅓ of our vehicle. So even with 4 tires we're back to 570g-760g. Let's see what we got to lift:
approximately weight in grams | buoyancy in grams | |
XRP Frame | 140 | 0 |
Battery Pack | 100 | 0 |
Motors | 60 | 0 |
Controller | 50 | 0 |
Rims | 100 | 0 |
Tires | 270 | 2280 |
Buoyancy Aid | 130 | 1220 |
That sums up to about 850g of load and 3500g of buoyancy. But we only want it to be submerged between ¼ and ⅓. So the weight for that targeted depth is between 900g and 1200g.
It's just an estimation, because it will differ with specific print settings and filament. Your slicer will show you the Volume in mm^2, just shift the point 3 digits to the left and you'll have the buoyancy. It will also show you the weight once you sliced it. I would see both values as an approximate value. It also depends on how well you did set up your printer and filament.
371,771mm^2 => 371g buoyancy, 57.79g own weight => 313g net buoyancy for your build.
The ¼ to ⅓ is also regarding the entire vehicle and also just an estimation. Obviously if you would bind an air balloon on top of the XRP, this would theoretically increase the buoyancy a lot, but with being above the motors this would not benefit our purpose at all. So most of the floating aid has to be underneath the motors to get them above water level.
Additionally
Also, sorry for the big floating aid print, I'm aware this will not fit every printer. But the XRP is a quite bulky platform with about 350g tare weight. The rest is physics. Hence also the foam anchors alternative.
Also feel free to mix it with the XRP Mecanum frames that offers you 4 motor slots, then you can go with 4 drive wheels (with fins) to be even more amphibious.
The orientation in the files is my recommended print orientation based on strength, print quality and required support. No support or brims are needed, but if you know your printer has issues with print bed adhesion you might want to use it for smaller parts like the safety rings or anchors.
For some parts the orientation will not result in perfect strength, but it will be sufficient to do their job in this build. E.g. the axis. They will drive your XRP without problems, but you will have to handle them with care. Especially when you put the tires on or put the front mount to the XRP. Always uninstall the axis from your frame if you're working on them. If you would mount the tires on the rims while they are mounted to your XRP the stress would increase big time and the axis might break. You can also increase the infill for the axis for better strength. I'm printing them with 25% cross hatch. But if you know you're not careful, go with 40% infill and 4 walls, this will make them much stronger. Same printing recommendation goes for the front mount. 2 walls, 25% cross hatch will be sufficient but you can also upgrade them to 4 walls, 40% infill to make them even stronger.
For everything else that's not necessarily under stress, I would recommend trying to reduce the infill, walls, top and bottom surface to a minimum to keep the weight low. But those settings will heavily rely on your printer and the filament. Some parts need to be watertight but more on that in a bit. The Tires and floating aids watertightness is key how long you can stay in the water. If you only want to be able to cross some puddles you might not care too much about small leaks. But if you want to stay longer on the water it really needs to be waterproof. Adjust your seam settings so they're not possibly an issue and leaving gaps.
For the tires I did use the Lightning infill pattern with a 15% infill density. This pattern can more or less be seen as “no infill” but printing support for a flawless print. I had good results with just 2 walls. I did print them with TPU. But for some scenarios another material also might make sense. E.g. on the Beach also hard materials might work fine. But in this case don't forget to merge the tire with the rim before printing it. But with TPU I had no issues at all, they've been perfectly watertight from the very beginning without any fine tuning with the default TPU profile.
For the floating aid, I tired 2 different PLA+ and one PETG. I'm not saying it's sinking like a stone, but when completely submerging it for a test, all of them did leak. I tried to fix that by just painting them. This actually revealed all the leaks with small bubbles or holes and what shall I say… it's all over the place. It's not like the edge, the roundings, the sidewalls, stuff that looked suspicious. Even walls that seemed to be printed flawlessly well… I tried more walls, increasing the temperature, increasing the flow rate, etc. Nothing made it really waterproof. I think TPU might work. I didn't try that tho. But I got the cheapest filler from my local hardware store for 2 bucks, nothing fancy, it just said stone, plaster, gypsum, concrete, didn't even mention plastic especially. I did just put it on the print and smeared it around with some gloves, let it sit for a bit and painted it again. No bubbles anymore. This added about 20g of material per floating aid. So if you want to print it be aware that it might need some post processing. My print recommendation would be Lightning infill with 15% infill density and 2 walls. Add for all zip tie mounts and clips modifier blocks to add more infill for them, I did go with 100% because it's just small areas anyway. For the clip that is in the middle of the print you need to connect it to the other side, otherwise you can't press the clip into the rail because it will just bend and maybe break the top surface. I did use 25% Rectilinear infill pattern. For custom infill there will be no support generation, so you need to take care that your infill pattern will bridge itself. This might also be up to the orientation of your item on the build plate, so try different options and have a look at the slicers preview if it works for you. Here's my preview.
Note: The zip tie mounts are another example of not the best strength regarding printing. They are fragile, but the other option would have been to make the holes thru the floating aid. This would be way stronger but also would decrease the buoyancy as well as make the print even more error-prone, hence introduce more possible leaks. And they will be sufficient for their task anyway.
I think I would recommend the foam board version, except if you like post processing 3d prints and don't mind that, it can also be a satisfying task and look awesome if done well and with a love for details.
It's good to figure out if your parts are watertight. Along with that you easily can check the buoyancy and the weight of your parts. Get a bowl that's big enough so you can completely submerge your print. Fill it with water. Enough to submerge your part, not so much that it would overflow. Weight your part first and write it down. Then put the bowl on a scale and zero it out by pressing tar. Now submerge your print.
Your scale will increase by the weight of the volume you're submerging. If your scale tells you now 100g than that's how much this part can elevate. Deduct the weight of your print and you'll get the net buoyancy aka “what you can add and it still stays afloat”.
Keep it a bit like that under water to test if it's watertight. When you now remove the part the scale should be pretty much at 0 again. The weight you're missing is somewhere, that can be some drops on the surface, but if it's a lot shake your part and hope you don't hear the water inside your part. If so, let's try to fix it…
First you need to get the water out of your part. Shake it to get most water out of your print. Maybe you can even spot where the water is coming out. When this is done let it sit and dry for a bit. Then you can try to fix it with gapfiller or coat it with paint. This will also depend on the flaw. if it has a big visible hole, you might even patch it with some tape or plastic wrap. Anyway, try to figure out what the issue was. you might be able to improve your next print. Maybe it's the seam, try different settings. Maybe it's the walls, try to adjust the flow rate, decrease the layer height, etc.
If you did go with the fully 3d printed floating aid you can skip this.
Cut a foam board to your need. Either use a box cutter or my hot wire foam cutter. Everything that fits under the XRP will do the trick. Have some clearance between the XRP and the floor. Otherwise it would always get stuck on land. Use some anchors so you can easily attach the foam with zip ties to your XRP. There are also Zip Tie Clips for the XRP, in case you can't mount the zip tie on the XRP itself on that spot. You can use the provided nails to attach multiple foam parts together.
Time to assemble your vehicle. Mount the front mounts onto the XRP.
Pull the tires onto the rims while the rims are not installed on the XRP. I would recommend not touching the axis at all during that process. Only touch the tire and the rim. Put all wheels thru their holes and use the safety rings to hold them in place.
Put the floating aid under the xrp and mount them. Don't tie the zip ties too strong, it doesn't need a lot of force to hold it in place. Be careful with them. You don't want to break them off or rip the anchors out of the foam. There's no force needed.
If you did print the anchor arm, mount it with a zip tie and attach some rope. You can then use it as an anchor or tie it to the shore.
You're done. Ensure the floating aid is well connected, place it gently on the water and hold it until you see it floats and all sensitive compontes are above water level. Do just a small test drive, stay close to it to ensure nothing gets lose and it sinks.
Once you verified the integrety you can have some fun. :)
The author marked this model as their own original creation.