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Mad Ax

Pole Trailer to Rigid Conversion

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i have 2 mfu sets and i think they have the support legs in the kit if they are their you are more than welcome to have a set but i would have to find the boxs and check what is inside

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@topforcein thanks for the offer.  Please have a look if you have a moment, anything is appreciated, although if memory serves the MFUs don't come with trailer legs.  The standard spring-loaded legs are usually part of a trailer kit and the motorised legs are an accessory.  Will be interested if you have a set, tho :)

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ok i have managed to find these if i remember i swoped them from the flat bed trailer when i installed the motorized legs.

if they will do for what you need then they are yours.;)

 

IMG_20200516_163622.jpg

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I spent a bit of Sunday morning on the trailer.  First thing was to investigate the cheap Etronix micro servos I'd ordered from Wheelspin to see if I could modify them.

Here's one servo with the case removed:

P5310025.jpg

Behind the output shaft is a little potentiometer.  This is what tells the brains of the servo how far around it's gone, so the servo will shut off at full swing and will return to centre.  We want this servo to spin indefinitely and not have a centre, so we need the servo to think it's always in the centre.

P5310026.jpg

Unclipped from the housing, we see that the pot is working as a voltage divider.  Working with a multimetre, we see that with the pot in the centre position the voltage is around 2.7KOhms from red to black and 2.7KOhms from red to white.  So if we desolder the pot and solder in a 2.7KOhm resistor between white and red and another between red and black, we are hardwiring the servo to think it's in the centre position.

Jobbed

P5310028.jpg

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It's a bit tricky to get heatshrink over the resistors when soldering at this scale, so to insulate after wiring, I used hot glue.  Actually I used a bit too much here and had to cut some away to get it back into the case.

P5310031.jpg

Next problem was the housing itself.  It had this lug on top to act as a mechanical stop to prevent the servo swinging too far.  I didn't notice this at first and my power-run with the servo connected resulted in the lid being spat across the worktop.  Fortunately no damage was done.

This was a pain to remove as it's right up in the casing.  I need a set of vertical snips (I'm not sure what they're call, the sort that have their jaws perpendicular to the handle like nail clippers).

P5310032.jpg

The problem after this was reassembling the whole package.  In theory I could have cut the bottom off the output shaft and left the pot neatly in place (it was a more uniform shape and fitted better into the packaging than my soldered and glued resistors) but it was very sensitive and a tiny little movement would have the servo spinning away to itself and out of control.

P5310033.jpg

Job jobbed

P5310034.jpg

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Next thing to do is start hacking away at the trailer legs.  These are not Tamiya motorised legs, these are the standard spring-loaded legs that come with any Tamiya trailer kit.

This lug in the upper part of the leg body holds the top of the spring.  It needs to be removed.

P5310035.jpg

Like this:

P5310036.jpg

The micro servo is then exactly the right size to fix into the housing, provided we cut off the mounting lug

P5310037.jpg

And the stanchion itself needs to be shortened

P5310039.jpg

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This lug inna leg also needs to be removed

P5310041.jpg

Neat!

P5310040.jpg

And that is about as far as I got before I realised I needed more parts.

Basically, the top of the servo is going to turn a threaded rod.  The bottom of the rod will go into a nut connected to the stanchion.  As the servo turns, the stanchion will go up and down.  At present there's no end-stop switch to stop it moving (that would need more wiring inside the servo) and the plan to get the rod connected into the output shaft is based mostly on hopes and dreams and less on glue, locknuts and a modified servo horn to act as a compressor.  It might work just fine or might be the undoing (literally) of this particular plan.  If that fails then there are some small 6V motors with threaded rod already attached, and while they are probably neat enough to mount inside the leg with very little outwards modification, they cost more than the micro servos and need a separate servo board or motor driver to operate, thus adding to the electronical complexery.

Anyhoo - I had to stop because the micro servo shaft only takes a 2mm thread and I didn't have any 2mm threaded rod in stock.  Some is on order and will hopefully be here before next weekend.

Watch this space.

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Got a bit more work done yesterday.  My M2 threaded rod turned up in the week, so I was able to get started straight away by screwing it into the servo output.

P6070105.jpg

I took one of the included servo horns and pushed it over the splines, the idea being this should (in theory) clamp down on the spline and prevent it from opening out.

P6070106.jpg

Next I added a nut and torqued it up to act like a locknut, hopefully preventing the rod from unscrewing.  Time will tell if this is successful.  If not I will either need a new solution entirely or I will have to get a metal geared servo that I can use threadlock or a locking nut on.

P6070107.jpg

I used a dremel and craft knife to cut the horn away so it was just a round boss.  No pics of that.

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Here the whole assembly is lined up.  Now I need to add a captive nut somewhere in that stanchion.

P6070108.jpg

As it needs to be an M2 nut, it is quite small, so I figured I was best to reduce the size in the leg by adding layers of plasticard.

P6070109.jpg

P6070110.jpg

The final slice of plasticard had to be forced in, thereby trapping the nut in place

P6070111.jpg

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Here it be

P6070112.jpg

Next, I added some hot glue to secure the nut.  Hot glue isn't really perfect for this - two-part epoxy would have been better - but I wasn't sure how I could clue the nut without getting epoxy in the thread.  I figured I might be able to do it if I greased a screw and threaded it through the nut - in theory the grease will stop the epoxy from sticking to the thread but in practice the greasy will probably spread onto the nut and stop that from being captivated also.

P6070113.jpg

From the back, there is hardly any glue on the nut.  That won't do.

P6070114.jpg

That's...  er...  Well, there's glue on the nut now, but there's also glue all over the thread.

P6070115.jpg

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OK, so with the stanchion in the freezer to cure the glue, I turned my attention to the backplate.  This needs to be cut open to clear the servo.

P6070116.jpg

Like that

P6070117.jpg

Stanchion fully cured.  Now let's see if we can drill that glue out...

P6070118.jpg

In the end I used a 2mm and then 3mm drill bit, turned by hand, to mill some of the glue away, then used an M2 machine screw to turn through the thread a few fimes

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OK, final thing installed:

P6070119.jpg

It actually does work.  The nut isn't fixed very securely and the leg will move around, but that might be a bonus as the threaded rod isn't exactly straight either.  A little flex will allow it to take up the uneven rotation without ripping out of its location.

Final badboy assempled:

P6070120.jpg

So - does it work?

Well, surprisingly, yes.  This was only supposed to be a cheap way of proving a point, and it does have its flaws.  The servos seem fast enough when operating a horn but they take quite a while to lift the legs.  This does have its advantages though - low speed = more lifting force, and just a single leg was strong enough to list the not-insignificant weight of the trailer.  There will be two legs on the final installation, so the servos will be more than up to the job.  Whether the hot glue will survive the test of time is another matter.

Also there is no stopper on the thread.  I was worried that a stopper would cause the rod to unthread from the servo, or thread in harder and strip the plastic.  This would be harder to fix on the layout than threading on a leg that has come off.

I will be operating two servos at once.  There is no guarantee they will both turn at the same speed.  They are the same brand and will be operated from the same radio channel, so in theory they will turn the same, but there are various factors that could cause one to run faster or slower than the other.  There won't be an easy way to re-balance the legs if they get out of sync.  My alternative build idea was to use those cheap 6v motor & gearbox assemblies from banggood, as they have more torque and stronger M3 threaded outputs that won't unscrew, but they are not as cheap as the servos and they come with no way to control the speed.  I would either have to cannibalise a servo to control them or use a cheap ESC.  But even then, unless I was to make a balancing gear or use a single motor for both legs (both of which are beyond my ability to design and make), they are probably more likely to run at different speeds than a pair of modified servos.

Anyway - that's all for now.  I suppose I have to make my second motorised leg, then get both installed on the trailer and to a test-run.

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Updates: Ax's Big Workshop Day dawned dry and bright, and I was keen to get cracking on the pole trailer build so I can get the great behemoth off my workbench and work on something else.

The first thing I needed to do was drill out both chassis rails to accept the support legs, then cut holes in them to accept the micro servos.  This meant stripping down the chassis rails all over again.

Here's my right chassis rail, with the support leg holes drilled, and my left chassis rail, without.

P6140026.jpg

Rails bolted together for accuracy, holes drilled in the drill press, then a larger bit used in a slow hand drill to smooth off the nasty edges.

P6140027.jpg

Next job: bolt up the backplate of the support leg, which has the cutout for the servo, and draw around it.  Then using a Dremel, cut out the lines.  As my Dremel wheels are too big to cut the smaller lines, I had to drill a series of holes then file them through with a needle file.

P6140029.jpg

Bolt up the other chassis rail, draw through the hole, and repeat

P6140031.jpg

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Then use a file to neaten up the hole

P6140034.jpg

Now I turn my attention to the other support leg.  My prototype used an M2 nut jammed between some plasticard strips and fixed with hot glue, but I had a different idea for this side.  First I cut a piece of plasticard that was a tight tolerance fit in the support leg, where I wanted the nut to go.  I didn't trim the top yet, I just marked it for cutting later.

P6140035.jpg

Then I put a dob of grease onto the threaded bar in the servo and loosely assembled everything.  When I slid the stanchion into the tube, the end of the bar put a greasy mark on the plastic where the nut needs to go.  Then remove plasticard, and drill hole.

P6140036.jpg

Then I used some Uhu glue to secure the back of the nut in place.  I added a machine screw to hold it all in place for a moment.

P6140038.jpg

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Then I used some hot glue to secure the nut.  This time I used some heatshrink tube to protect the thread of the screw and stop it from getting sealed in.  The glue wasn't hot enough to shrink the material, which is good.

P6140040.jpg

I refitted the plasticard into the stanchion, then added more hot glue on both sides.  I threaded in a length of M2 rod and used more heatshrink tube to keep the threads clear.

P6140041.jpg

This is actually a prime use case for two-part epoxy.  I didn't use epoxy before because I wanted something non-permanent.  I knew I would end up with some on the threads, which would render the entire project useless and possibly mean sacrificing the legs altogether.  However this time I used something to cover the threads, so I could have just used epoxy without too many worries.  Epoxy is also easier to sand after it has dried to get a smooth action on the leg, whereas hot glue remains squidgy and tends to stop the legs a little.  Anyway, I know for next time - if I ever have to rebuild these legs (the prototype leg doesn't feel strong and might break at any time) I will rebuild using epoxy.

Here's the finished stanchion with the hot glue cut away so it slides smoothly

P6140043.jpg

P6140044.jpg

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With both legs assembled, bolting them to the trailer was easy

P6140045.jpg

After that, I needed to set up the Beier unit and wire everything up.  For a quick test I used both outputs from the IR unit, controlled directly by Proportional Input #6 in the Beier SFR-1.  This is hooked to Ch5 on the radio which in turn is bound to a rotary switch.  A 3-way toggle would have been nicer but I already use that to control the Tamiya gearbox directly from the radio (I don't have need to go via the Beier unit to do this, I never use the gearbox while driving, I just select the appropriate ratio for the layout before I start up).  I can replace the rotary with a 3-way switch later if I really want to, or I can go the full pig and build one of those crazy multi-function breakout boxes.

I had to make up a couple of extension cables to do this.  Later I'll probably turn them into a Y-lead and run from a single output.  I don't actually need 2 outputs on this trailer but it seems a shame to waste one anyway.

P6140048.jpg

P6140049.jpg

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So, does it work?

Well, yes.  As I said last week, it's quite slow - it takes a while to wind the legs in and out.  I also need to trim some of the heatshrink tubing off the latest leg as it binds before it if fully retracted.  However both servos move at approximately the same speed and despite there being a long run from retracted to extended, they both touch down at more or less the same time.  Close enough to not be a problem, anyway.  Unfortunately if they do get out of sync there's no real solution but to unplug one of the servos and wind it on a receiver.  But never mind.

I did take a video yesterday but I'll have to trim and upload to Youtube, please be patient while I work out the pitfalls of home video editing.

Overall - how pleased am I?

With the Beier - totally.  There's still lots of work to do to get the rig exactly how I want it, but the trailer IR unit has been a peach to configure.  Having to buy a separate kingpin coupler for the IR receiver was a bit annoying, although I already knew in advance that Beier don't make one.  From what I understand, most Beier folk don't bother installing the IRs in the kingpin anyway but I didn't want a situation where my trailer would pick up stray signals from other rigs or have problems with my own connection cutting out in certain conditions.

With the remote legs - so-so.  I'm glad I put the effort in and I know my solution can be improved, but it's good enough.  It was a lot cheaper than a set of Tamiya remote legs but in retrospect, possibly no less messy.  The servos are still visible between the chassis rails, arguably less so than Tamiya's hulking great motor and gearbox assembly on the remote trailer leg kit, but the Tamiya unit doesn't have the servo wires poking out in a visible area.  I'll have to come up with a neat solution for that.  I'm not looking forward to it breaking, which I expect it will.  I'm not looking forward to the legs grounding out over the club flyover, which they probably will.  In fact that will probably be where they break.

I could have gone with a cheap 5v motor and gearbox assembly in each wheel, but "cheap" is still more than the cost of the servos and would need a cheap ESC to power them.  Overall it may have been neater and easier to install, as well as stronger and faster.  I'll have to look at that when I come to do my next trailer, depending on budget.

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I know your trying go cheap. But did you know about "LESU" support legs? Like an actuator in leg form. Just throwing that out there.

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Thanks for the heads up - I knew there would be some reasonable legs out there somewhere but wanted to see if I could make a solution myself before I spent the cash.

I probably spent nearly half the price of the LESU legs on servos for my solution, and I had to chop those up to make them fit.  Now they're too slow and potentially not very robust.

As and when I pick this project up again, I'll probably buy the LESU legs and be done with it.  You can throw too much money at a "cheap" solution.

Apart from the legs, this trailer is nearly almost done.  In the Before Times, I'd probably justify the extra cash to get this project finished ready for the trucking season, but I don't think there will be a trucking season this year, so it's not much of a priority.  I might spend the winter getting my other trailers overhauled on the remote chance we're allowed out to play in winter 2021 :lol:

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Just been reading through the section on the motorised legs, ingenious way of doing this. I did a similar thing with the blade on the front of my forestry machine, but on a slightly bigger scale (I had to use a 540 motor with reduction gearbox and 5mm threaded rod), as I wanted it to lift the front end of the machine off the ground with the blade. To limit the movement of the blade I turned a bit of thread off the threaded actuator rod at both ends, so that if the threaded component that ran on the thread came to the end of the thread if would not drop off the end, and it could not lift it up high enough to lock when retracting. 

If you could file a bit of the thread of either end of each actuator shaft (I know it's only 2mm and it might snap), when the legs are lifted they will synchronise in the fully retracted position as they run off the end of the thread, as the smooth part of the shaft will allow the motor to turn without moving the leg, allowing the other leg to catch up.

Likewise lowering the legs, as long as they hit the ground before they run off the far end of the thread, if one hits the ground before the other it will just spin on the unthreaded portion of the shaft until the other one catches up. When there is weight on both legs and you reverse the motors, they'll pick up on the threaded rod again, being roughly synchronised by the floor level.

 

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