Build notes and observations


#1

I’m going to keep some notes in this thread while I build the motor unit. I’m building in my small spare time now so this might take a while. Kudos to those that can finish it all in a week. Might be a month for me. I think of this as a bit of a beta test situation so if I sound critical please take it as constructive criticism. I’m super excited to get to the point where I can fly it! It reminds me of the early days of the home PC market, where you ordered a box of parts, followed some photocopied instructions, and hopefully ended up with a working machine. Much like Legos, the building is part of the fun.

One thing I noticed right away is that one of the swingarms didn’t slip onto the pivot point while the other one did. Probably just tolerance stacking in my parts set. Nothing a dremel and some fine sanding couldn’t handle on the pivot arm hole couldn’t solve. Always test fit your parts before final assembly. It gets rid of the great finish on the parts, but since it’s the inside of a hinge so I don’t mind. I’ll add some dry film lube later to handle any roughness and protect against corrosion (on aluminum?).

So far, I’ve assembled one of the lower legs. The plastic end pieces that the cage will slide into are too big and definitely need sanding. Dremel to the rescue again! It’s necessary to sand them just to get it into the slots on the CF sections. I had some difficulty deciding if there was a particular side that should face the inside: the side with the holes or the solid side. After watching the build video I noticed that it was the side with the holes that faces inside. If I had looked at the part more closely I would have noticed the curve on the part and figured it out from there. In one of the parts bags there are little dimple springs (I don’t know what they should be called) that seem like they go inside the plastic parts art the end of the legs and arms. The dimple part would extend past the hole and help lock in the cage hoop sections.

Trouble with that theory is that there are no holes in the cage sections. Should I drill the holes myself? Also, the width of the plastic part makes it impossible to use one of the standoffs that sandwiches the plastic bit at the end of the leg. I used the dremel (I see a trend developing) to sand in a channel in the plastic bit so that the standoff can fit with the holes in the CF panels. In future parts I would say that the CF panels should be made wider so the screw hole can be moved outward and the standoff can fit.

That would also solve another problem. With the head of the screw so close to the plastic bit there is not enough clearance for the aluminum cage section to slide all the way into the plastic bit. I’m probably going to drill a notch into the end of the section so that there is clearance for the screw head.

The black plastic bits are too short to fit 2 of those dimple springs but that doesn’t seem to be a problem. The legs would sandwich that cage section so it would never get removed. It just needs to fit one spring for the outer cage part. However, unlike the red plastic bits, the black plastic bits don’t seem to have the channel for the spring cut all the way through. If I had a drill press I could fix that, but since I don’t it’s going to get interesting.


#2

That standoff on the leg isn’t needed because there is one on the other side. Also, there are two versions of those standoff’s. The other ones don’t have the hex shape so they are much smaller and would fit.

The buttons aren’t needed. Paul doesn’t use them and I haven’t been using them either so don’t drill holes in the cage. You can always do that later if you really think they need it.


#3

In the video OpenPPG 22 v3.1 Build Video (part 1) [ https://youtu.be/kEDDKatQQ3E ] I can see at 3:04 that there is a bolt on the in side of the standoff. I can take it off, but it’s definitely in the video. From the image it also looks like the cage section would not fit under the bolt head.


#4

I think my kit it short on 20mm stand offs. I started to assemble one of the motor mounts and the video says to use 20mm stand offs. The motor box itself doesn’t have any stand offs in the little hardware bag. The bag with the 20mm stand off’s that came in the kit has only 10 left so that’s not enough for 4 motors. I used 9 for each of the legs so that means the kit came with 28. Even if I recover the “extra” stand off on the in side of the legs that’'s still not enough for 4 motor mounts.


#5

Ya your kit should have came with 35. Iv been know to miss count but that is not even close. Ill get some more over to you.

BTW for anyone else who thinks they are missing hardware this is what the kits should have hardware wise.3


#6

Thanks for sending the short stand offs. No particular hurry needed so don’t overnight it or anything like that.

I did take some time to assemble the complete leg portion of the frame. Didn’t seem to run into anything of note there. I did remove the bolt/standoff on the in side of the cage coupling/spacer/3D printed plastic bit on the end of the legs so that the short cage section would fit flush. The legs seem flexible enough to add or remove the cage section without much fuss, but I like how strong it feels in the direction of flight (crash?). I do wonder if the rigidity will make it more brittle compared to the aluminum tubing in most designs. I don’t have any experience with carbon fiber beyond small prop dings.

I also started on one of the motor arms. The only thing of note in the arm assembly was the bolts used on the red aluminum hinge block. In the video you can see that the screws used are different color. On the “front” from the direction of flight I used the longer less silvery ones (M4x12) and the “rear” I used the short shinier ones (M4x8). The longer ones didn’t seem to fit in the rear screw holes and I have 8 total of the M4x8 ones so the math seemed to add up.

I noticed that the motor itself has the OpenPPG logo on it. I thought that was a really nice touch.

I’m not sure how to mount the ESC though. Given the position I see them in in the video I think I can suss out the appropriate screw holes in the arm panel, but I can’t see in the video how they are attached. The cables are directly over the mounting holes in the ESC so I would think a nut would go in there with the screw coming from the arm panel side. However, none of the screws in the the kit seem appropriate for that task, and there are no nuts that would fit in there anyway. As a matter of curiosity, the ESC would cover a hole in the arm panel that seems too big for a screw hole. Is that an artifact of a prior version?

I put together the swingarm assemblies, but other than a reminder to make one right and one left I can’t think of anything I would add over the video.


#7

I haven’t made too much progress now. I attached all of the aluminum blocks to the “front” panel of the main frame. I got the new package of 20mm stand off’s and completed the 4 arms to the same level. Still need to attach the ESCs to the arm. Can someone post some details of how they are to be mounted and soldered? Also, regarding the motor rotation the assembly video says that if the motor is spinning the wrong way then inverting two wired will fix that. Do the motors have a “natural” direction; if I connect all the wires in the same order from all the ESCs to the motors will they all spin the same way? I would like to get it right the first time. I’m thinking that if I wire two “straight” and two “crossed” then that should work.

I’m hesitant about wiring everything without more detailed instructions. More details would be appreciated.

One of the arms ends was damaged when I received it. The box was pretty beat up but I didn’t notice any damage until I unwrapped the arm from the plastic. Not a big deal, a little q-bond fixed it.

Looking at the top of the frame where the harness will attach, I would recommend making that an aluminum block instead of just having a standoff for rigidity. Passing the nylon straps through the CF slots is would to wear on the straps


#8

Yes I agree a wiring diagram would be a great help and also instructions on how to attach the Harness


#9

Here’s the best way I found to do it. Please forgive the rough sketch, I’m following along in the middle of the AU outback till I get home and resume the build.

Un-mount your motors from the arms. Cut the ESC leads between 70 & 80mm from ESC body.
Join two of them as pictured in figure 1 and two as in figure 2.
Mont the 1’s and 2’s 180 degrees apart on the frame (opposite corners).
You will need to source your own M3 15mm screws and nuts to get he ESC on the arm. Perfect first go for me (almost never happens:) But double-check rotation of motors before mounting props.


#10

I sanded the edges all around the frame as much as I could and used a soft Dremel attachment - Do it outside, have a fan behind you and wear a dust mask.


#11

I recently received my Openppg kit as part of the second batch delivery. It’s the first time I’ve participated in an open source project, and I’d like to offer huge congratulations to those involved. It was a massive undertaking, and promises to improve with new versions. I have extensive experience with paramotoring with gas engines ( just finished flight number 3,200 over 21 years of flying). I have been working on assembling the Openppg kit for the past two days. I’ve really enjoyed it. I have the great fortune to have two flying friends that are also electrical engineers that have helped with the electrical parts. My feedback so far:

  • It would be nice to have a detailed, step by step video showing assembly procedures so that builders won’t have to guess where parts go. I appreciate the video Paul made, and it is helpful, but eventually as Paul mentioned a more detailed one will help even more. As an example, I had no idea where the CF part went that goes with mounting of the on/off switch. No mention of it in the video. Also, no mention of the holes in the cage connector printed parts and how to use the push pins with connecting to the hoop. I knew about them from other motor rigs I’ve owned, but others may not. The center section plate standoff locations aren’t mentioned in the video, but a very brief view of them is shown while the wiring is discussed.
  • A friend that has extensive experience with large RC helicopters strongly suggested using locktite for all screws mounting the motors. He said they are sure to vibrate loose without it. I’ll need to go back and do this.
  • My friend also said to not only balance each prop (using clear plastic tape), but also to balance the motors. They should be completely vibration free.
  • The on-off power switch failure problem will need to be addressed.
  • Leg hinge pins or stops are needed, and I see someone has already found a solution with a 3D printed version. It would be nice if they could be purchased and added as part of later versions of the kit.
  • No one so far has posted assembly times to be expected for those assembling their own kit. I took my time and spent about 10 hours assembling the lower legs and plates, cage arms, mounting the motors, installing the ESC’s and installing the hinges. We ( my two friends and I) have spent so far another 10 hours soldering all connections and shrink wrapping them, installing the props and hubs, testing/rewiring prop spin direction and wiring up the controller. We have yet to wire up the batteries for charging, finalized soldering/shrink wrapping for motor wiring, installing center CF plate section standoffs, hooking up the harness with a hang test and installing center CF rear plate. We will also need to determine how best to mount the four Bonka batteries to the center plate, but the ideas posted by others all look good.
  • As far as electrical knowledge necessary…wow, it was way beyond my ability! So glad I had help from expert electrical engineers. No way could I have done the wiring otherwise. It would be worth it for those not familiar with high powered electrical motors and batteries to buy the kit prebuilt. The power produced by these batteries is enough to power three typical family houses, so this is not an area for an amateur electrician to be experimenting.

I hope this information is helpful and is taken with the positive spirit it is intended. It is not meant to be critical of those designing the kit, just my observations as a pilot/builder with almost zero electric knowledge. As with most projects, now that we have assembled one kit we could probably assemble another one in half the time. Can’t wait to get the kit completed and fly it.


#12

My build update: A friend and I have completed all the wiring and installed the main center section plate to enclose the wiring. This took an additional 5 hours, so about 15 hours total for wiring, soldering and assembly of the frame/hoop. However, I have run into two baffling problems. First, the main hinges at the top of the leg sections do not have a locking mechanism. When the unit is assembled, the weight of the arms and motors makes it want to flop over either backwards or forwards. I see someone has produced a 3D printed hinge stop, but has anyone else solved this problem of locking the hinge at the proper angle so the hoop is perfectly straight and round? The second issue is the cage hoop alignment. When I connect all parts of the hoop and tightly secure the netting the hoop is not straight when viewed from the side. My hoop 3D connectors are all black, and in previous videos I see red ones. I had to do quite a bit of sanding to get them to fit into the oval holes. Perhaps I received the wrong type? I’m used to doing Power-off forward inflations since I have flown older Miniplanes and Sky Cruisers with flexible cage poles and hoops. I assume power forwards aren’t recommended with this design.


#13

The bolts through the hinges at the top of the legs need to be tightened so that the legs remain in position with friction but not so tight that you can’t move them. The stoppers that I designed help to get them to the right position but you still need to rely on friction to hold them.

Yeah, the side view of the hoop isn’t straight when the net is tight but that is mainly a cosmetic issue. I printed some hoop connectors that are slightly longer as well as printer friendly to get a better print and better fit to address this issue a little bit. If you sand your connectors too much the bending will be worse but that shouldn’t be an issue unless they are so loose that they are falling apart.


#14

You are correct there is no locking mechanize for the leg hings. They are designed to be friction fit so if they are moving to easily, just tighten the bolt up that runs through them.

Forward should be the same as any other, maybe if you can get a pic of whats holding you up from performing forwards it will help us understand.


#15

Ok, thanks, Gliderpilot. This was what I needed to know. I’ll just tighten the bolts so that they are tight enough to hold it upright with friction, but not tight enough to keep them from bending. Got it. I appreciate your feedback.


#16

I probably didn’t express myself correctly, it’s not my forward technique. It’s the integrity and strength of the hoop being laterally torqued that concerned me. I haven’t flown my unit yet. The connectors aren’t loose, They fit pretty snug. I don’t think I oversanded them. I was just wondering if there was a method to tighten up the hoop besides using the netting. Back in the day Paralite used to run a bungee cord through the center of the hoop, then the hoop sections didnt easily come apart and felt a bit more secure. Sorta like connecting aluminum tent poles if you are a camper familiar with how that works. The Paralite bungee system wouldn’t work on the Openppg rig because it folds up. I understand what I need to do now. Thanks for the quick reply, Paul.


#17

FYI for those interested in weight data. I weighed my fully assembled Openppg rig with an Air Conception harness attached. Without the batteries the weight was 29 lbs. This is exactly as Paul listed earlier in one of his videos.


#18

I made a little progress. I finished attaching the ESCs to the arms. I used M3-.5 nylon lock nuts from Home Depot. For bolts I used the longer bolts that came with the motors. The were too long so I cut them down with the Dremel to a little over half their original length. That seems to be long enough to engage the nylon in the nuts. They could have been a bit longer but I didn’t want them to extend beyond the nut. The cables directly above the nuts are already in contact. I didn’t want to vibrate a bolt into a power cable.

I still haven’t connected the ESCs to the motor though. My impression is that most people are soldering them directly. The motors came with connectors though, so why not use them? It would make reversing a motor direction almost trivial. Is there a concern that the connectors would lead to higher wire temperatures than direct solder?

I put 2 of the ESCs on the right and 2 on the left. My thinking is to put the ESC on the “high” side of the arm, which should put it into the wind flow more than the “low” side given a slight recline hang angle. Maybe it’s not a big difference since there will be a propeller pulling air across the arm, but it makes me feel better.

Regarding the power input to the ESC, is this where we use the XT90 connectors that came with the kit?