Now I have something "new" to me... and a new project

[rjs987]

Just bought a Uni-Go trailer from a member. He stopped by yesterday to drop it off while he just happened to be in the area.
Since there are NO sources from where to buy a hitch for the AK 550 I'll be making one. I've made up the electrical harness for a few bikes (GW and ST1100) before and designed one for a few others so this part won't be difficult at all. The hard part is the hard parts of the hitch framing. The AK 550 doesn't really have any handy bolt-on locations for something like this and the bike frame is all aluminum squared C channel. So it will be a clamp-on design.

I'll be using 1 x 1 square stainless steel tubing and square "U-bolts" on the rear frame inside the body and exit to the rear at a downward angle. There will be a bend at the rear of the tubing so the Uni-Go receiver ends up vertical.

This trailer has a vinyl cover over the front plate and I can feel the extra mounting holes behind it for adjusting the draw bar up or down as needed. I expect the end result with line up approximately as shown here. Excuse the mess. I don't have the luxury of an epoxied floor and designer cabinets for my stuff.



For those unfamiliar with this model here is a photo with a typical bag of chips thrown in for scale. Hopefully I won't go throwing in twice as much as I usually have when I go camping. But it will be nice to fill a large shopping cart at Costco without wondering how I'll get it home.

 

[Sadlsor]

Wonder if some unknown-to-me scooter forum (which would be all of them, actually) has some ideas.
Surely some other wingnut, er, scooter enthusiast, has attempted a similar solution for similar reasons.

 

[rjs987]

I'm one of those, er, enthusiasts who is a member on 3 of those scooter forums.
No real ideas other than what I've come up with so far from them. Though they have made a few helpful suggestions. And the market share of the AK 550 is small enough in the USA that I'm being considered the trail-blazer on this.

Here is the beginning of what I am planning. Worked on the left side of the bike today.
Left side under the seat with the storage box removed. Too bad I really can't just tie it with string like this but I'll be using square U-bolts on the 2 frame members shown here. This bike has an all aluminum frame and I really don't want to disturb the integrity of the frame by drilling holes in it. Using all stainless steel square tubes.



I'll be putting a bend in that tube to follow the mud flap angle and then mount the receiver near the bottom of the mud flap. Will be doing the same on the right side.

 

[rjs987]

There is an outside chance I'll have this setup ready by the end of February. Then I can bring home leftovers from the RTE at Scooters. More likely I'll not be done until at least the end of March or maybe even April. I definitely intend to be pulling this rig down to FerrySTOC.

 

[the Ferret]

Interesting. sometimes it's good to be the trail blazer. other times not so much lol. Please keep posting your progress.

 

[Sadlsor]

@rjs987 don't know if you've seen this on ADVrider.
Someone there may have some ideas for ya to bounce around...

Scooters and trailers

 

[rjs987]

@Sadlsor , Yep, saw that thread. I even have a few posts in there (same alias as here). Most of those ideas are different kinds of trailers. There are about as many different ways to make a hitch as there are bikes and scooters that pull them. I already have the trailer so I am making a hitch designed to pull that one.

 

[SMSW]

I don't understand how you are securing the square tube under the fairing. Of course, I know what squared off U bolts are, but there does not seem to be much space to use a couple. Some thoughts....

* The tubing you are using is pretty thick. I wonder if it needs to be this stout. Extra wall thickness simply adds weight without contributing much of an advantage.
* Your hole in the fairing for the square tube is very nice, but it does not leave any room for flexing or movement of your hitch. While I don't expect 3/16"(?) wall tubing to flex much, I would think there will be some movement of the hitch as you ride and hit bumps, etc.
* How will you join the two sides (assuming you are doing this on the right and left sides of the scooter)? If you weld it, I'd think everything should be the same material, and you might be looking at TIG welding. Or bolting it up.

Looks good, keep us in the loop.

P.S. I'd suggest you dump the cotton rope and use one of the newer climbing style ropes...something like a nylon core with an aramid sheath. It's stronger....

 

[rjs987]

Today I tackled cutting the hole on the right side.
I started by making a template matching the panel on the left side lining up with the panel seams and tracing the hole on card stock. Then I cut out the hole, flipped it over, and taped it to the right side. I used a scratch awl to mark the outline of the hole and then started in with the 1001+ times of scoring the line with my utility knife and I was through. I put both square tubes in place and verified that it all lines up perfectly. Same angle out the back and same level.

Then I leveled the bike. I did this with the help of the guy I bought the trailer from. I put a bag of rubber mulch on the passenger seat (to compensate for my riding gear and what I pack under the seat) and sat on the bike to load the suspension. My friend placed a small level on the luggage rack and put a block under one end until the bubble showed level. I took note of the block and level so I could repeat as needed. Turns out that putting the front wheel on a 2x4 block set flat and with the bike on the center stand then the bike is level as when the suspension is loaded for riding.

With the frame tubes in place I measured the angle the frame tubes are offset from vertical. I have the adapter my friend used when the trailer was hitched up to his bike. It is a 31/59/90 triangle. I re-measured and found it was a bit off. Even though one or two degrees is not enough to really matter I know that if I start accurately in the plan the end result will be better. The Uni-Go receiver is bolted to the long side off the 90 deg angle leaving a 31 and 59 deg angle. I plan to weld the long side between the 31 and 59 deg angles to a 1/4 inch plate that will be attached to the ends of the hitch frame tubes. I measured the frame tube angle as it comes out of the bike at 86 deg from vertical. I'll have the 31 deg angle of the adapter pointing down. Therefore I will need to put a 55 deg bend in the frame tubes to end up with the Uni-Go receiver set vertically. The receiver must be vertical for the best result and stability of the trailer. Lots of geometry that I never thought I'd use. Just to verify I drew it all out on paper with a protractor. [corrected after measuring more than once].

While the frame tubes were set in place I test fitted the storage box to see if I measured right for clearance. I didn't... exactly.
I did measure right for where I originally intended the ends of the frame tubes to attach on the bike frame but then I moved that point forward some inches. That was enough so that each of the frame tubes are about 1/2 inch too wide at the very ends.

So on to plan B. And I actually did think up a plan B several days ago just in case. I'll be welding a length of 1" x 1/4" stainless steel flat bar to the outside of each frame tube and back down the square ends about 7 inches. This is best to maintain the clearance around the mud flap for the hitch frame tubes. The bend will be right at the top of the mud flap so the tubes need to clear each side.

Here are some pictures in a collection from today. One pic shows the bends and angles I need to make. The thick blue line is the bent frame tube and the thin blue line is the vertical reference (but obviously this is not really to scale).

trailer hitch project 2-6-2024

 

[Larry Fine]

That's way up in the air. I'd be concerned with being pushed over by the trailer.

It seem that around swing-arm or rear axle height would be preferable.

 

[rjs987]

I don't understand how you are securing the square tube under the fairing. Of course, I know what squared off U bolts are, but there does not seem to be much space to use a couple. Some thoughts....

* The tubing you are using is pretty thick. I wonder if it needs to be this stout. Extra wall thickness simply adds weight without contributing much of an advantage.
* Your hole in the fairing for the square tube is very nice, but it does not leave any room for flexing or movement of your hitch. While I don't expect 3/16"(?) wall tubing to flex much, I would think there will be some movement of the hitch as you ride and hit bumps, etc.
* How will you join the two sides (assuming you are doing this on the right and left sides of the scooter)? If you weld it, I'd think everything should be the same material, and you might be looking at TIG welding. Or bolting it up.

Looks good, keep us in the loop.

P.S. I'd suggest you dump the cotton rope and use one of the newer climbing style ropes...something like a nylon core with an aramid sheath. It's stronger....

Yeah, I think I will dump the rope.

I contacted Uni-Go HQ in Florida (where they are now). I told them what I was planning and they said to stick with the 1/8" side wall so that is what I am using. Otherwise I might have gone with a 1/16" side wall. The hitch frame for a Uni-Go, or any other mono-wheeled, trailer must be VERY rigid. I am guessing 1/16 inch wall thickness might flex just a bit too much which will result in trailer sway at speed.

I will likely need to slightly enlarge the holes in the panels anyway per the addition of the 1/4 inch bar welded onto the square tube as mentioned in my previous post. Otherwise it will be very hard to slide the tubes in place after they are bent as needed. I do expect some flex so the holes will definitely be "fixed" near the end of the build. But for now they help hold things in place.

I will be using a 4" x 12" x 1/4" thick plate either welded or bolted to the ends of the frame tubes. The adapter I got with the trailer (was used to mount the Uni-Go receiver to a standard ball hitch) will be welded to that plate. I showed some details of that in my previous post that I just put in.

Since I really don't want to tamper with the integrity of the aluminum bike frame by drilling bolt holes in places they are not already put by the factory I'll be using the square U-bolts to clamp the hitch frame tubes (and 1/4" flat bar on the end) to the bike frames in two place on each side of the bike. There is enough room with the change I am planning (1/4" bars) for the U-bolts to fit. I intend to drill holes in the flat bar at the front end of the hitch frame to pass the U-bolt legs through, which will wrap around the bike frame. That will ensure the hitch frame doesn't slide in the U-bolts. The stresses of this lightweight trailer are more side to side and up/down.

 

[Larry Fine]

The stresses of this lightweight trailer are more side to side and up/down.

And twisting for a one-wheeled trailer.

 

[rjs987]

That's way up in the air. I'd be concerned with being pushed over by the trailer.

It seem that around swing-arm or rear axle height would be preferable.

Per the one photo that shows the bend angles I'll be needing the Uni-Go receiver will be centered about 15.5-16.5 inches off the deck. That's just below the bottom edge of the mud flap. It is above the rear axle height. Uni-Go recommends the bottom of the receiver to be 11-14 inches off the deck and the receiver is 4 inches tall so 16 inches is at the upper end of that range.

The Uni-Go tow bar is adjustable up and down on the front of the trailer in 1.75 inch increments. It is a higher receiver than on the typical 2 wheeled trailer.

edit: actually the axle/swing arm on this bike is much lower than on the ST. The correct height for any hitch on a standard ball type coupler is where the draw bar of the trailer is level with level ground when the suspension is loaded normally. Higher or lower would result in some bad results and possibly ruin your whole day.

 

[rjs987]

And twisting for a one-wheeled trailer.

Thus the thicker sidewalls on the hitch frame.

 

[rjs987]

I was just thinking about the last few posts... I bought the trailer from Scott and he also supplied the adapter he had made for it. If all goes as planned I will actually end up with the Uni-Go receiver about 1.5 inches lower than where he had it. I will likely also lower the tow bar resulting in the front of the trailer being raised maybe 1/4 inch from where he had it when he was pulling it.

To give some perspective here is where the receiver is from the ground when Scott was pulling it on his bike.

 

[Upt' North]

Couldn't resist it Robert.
Now that's what you call a trailer.



Obviously, no help at all, especially if you like going around corners and occasionally exceed 30 mph.

 

[rjs987]

Yesterday before I started working on the bike I pulled the trailer next to the AK and using some jumper wire in the SAE connector for the BT, which is always on, I tested each of the lights on the trailer. Tail light, brake light, left turn and right turn lights as well as the convenience light inside the trailer. There was also a battery powered light inside stuck on with Velcro but I broke a tab off opening the back to replace the batteries. Those are cheap so I'll just replace that one. All lights worked as expected. There is even a light bar above the tail light that comes on only with the brakes. It is fairly bright so that will work. That will save me from adding one.

Also last night I dug through my collection of electrical wires and relays and connectors and found that I already have the connector I need for the trailer. There is a flat 5 pin connector on the trailer wire harness and I found the matching bike side connector in my stuff that has about 3.5 ft of cable. Plenty for this project. A really nice thing about this trailer harness that I had is that each of the wires has the function printed right on them every 6 inches or so.

Today I had a medical appointment so didn't work much on the bike. I did ride my AK to get the registration changed over and get new plates. I have to wait to get a custom personalized plate that I want. I also got a bike side plug cover for when I ride without the trailer.

 

[rjs987]

You all know that any project plans change more than once before completion of the project. Well, now we're on to plan C.
Met with a retired metal worker and welder tonight to discuss what I have figured out so far. He is actually the husband of one of my wife's female friends who was in that career.
He had a lot of insight that was helpful given that he was here and looking at the situation in person. I was hoping he would assist with any tube bending and/or welding. But he doesn't currently have the equipment for working with stainless steel bending or welding. He did say he really liked what I was coming up with so far but had some suggestions to consider.

He considered my plan for bending the tubes but stated that most shops would do better to put a V cut where a bend is needed, bend the tube and weld it at the resulting seam. He also said the shop would put a gusset at the bend to make it stronger. That does resolve the issue of the tube deforming at a curved bend. He told me that the old adapter I was thinking of using would add a bit of complication since it is mild steel and not stainless steel like all the new metal I am using. It can be welded but the weld is not as good and the mild steel would be subject to rust as time passes. He also had a really good idea that the hitch frame tubes can be slotted and the rear plate that the Uni-Go receiver is bolted to can be fitted into the slots and welded to make it even stronger at the end. He did encourage me to add in the hanger bar as I was considering. So based just on this much information and recommendation I came up with 2 alternate setups shown in these pics.
The first is simpler but not quite as elegant yet might be stronger with only one welded bend involved with a bigger gusset. The second is closer to the original frame shape I was thinking of but will require 2 bend/welds and gussets.

He thought my idea of using square U-bolts was good. I asked about the issue or possibility that putting a hole and using bolts in the OEM rear bike frame might damage the integrity of the cast aluminum. As he looked at the OEM rear bike frame he immediately assured me that the OEM frame is a bit over-built and well strengthened and that drilling a hole in the upper frame on each side and a hole on the lower frame on each side where the square tubing lays against the bike frame would be no issue at all. He said he likes to do a little overkill on his projects and would have no hesitation to use hardened (grade 8) M8 bolts and spacers to attach the hitch frame to a cast aluminum bike frame like this one. He also said that using bolts through the frame would be better than using U-bolts. I was also thinking that as well. So I think that is the direction I will go. It would make it much more secure and easier to attach. I would only need a spacer on the forward attachment point and not at the rear attachment point right at where the hitch frame goes through the plastic. Of course drilling the holes would require that I remove the rear side panels but that's OK.

As it has been so far this is a project that will require doing a little bit, test fitting, going back and doing a little more, repeat. That includes any metal bending or welding that I have done... a little at a time when I have the time.

 

[Sadlsor]

A wise man has many counselors.
If the counselors know what the heck they're doing, so much the better.
Excited to see the results.

 

[Upt' North]

I'm no metallurgist but I think the second version could actually turn out stronger with the extra gusseting to resist flexing of the new......I spose it's a subframe.
Plus like you say when you're not using the trailer it will fit in better in a cosmetic sort of way. The frame you're drilling through? Is it a subframe itself or the main frame?
I think it's great you're getting good input from folks who know what they're talking about, pity he couldn't take the job on for you.
Good luck.
Upt.