Jump to content
Mad Ax

King Blackfoot Pro-Mod

Recommended Posts

Great work @Mad Ax it’s great to see your ideas come to life.

Sorry to hear about the storm damage, I hope you get it sorted soon and that the damage is easy to resolve. 

Share this post


Link to post
Share on other sites

Great work so far!

I literally just bought a set of Blitzer arms and hub carriers last weekend to experiment with them on an old Super Blackfoot. This is good motivation to get that on the build list and develop an integrated mount for those front arms... 

  • Like 1

Share this post


Link to post
Share on other sites

Updates!  I spent most of last Sunday on a lazy motorcycle ride to the estuary coast, but I had a bit of time when I got home to start on the steering for the KBF.

These arrived from the Riders of Jaz.  Uprights for the Blitzer Beetle.  The Blitzer uses the same uprights as the KBF, and my KBF now has a Blitzer front end anyway, so it should all go straight on.

sm_P2270071.jpg

Naturally, "should all go straight on" must come with some caveats, the first being, it won't go straight on.

It fits well enough:

sm_P2270072.jpg

but the provided screw isn't long enough to go through the hub, plus there's nothing for the screw to bite into, so it could wind its way out, if it wanted to

sm_P2270073.jpg

The second problem was that the bearings wouldn't go over the shafts.  The first problem could be down to lazy parts fulfilment, the second is likely down to poor quality control.

The shafts have a dark coating on them, because naturally, dark coloured shafts are better than shiny ones.  A little bit of metal polish on some blue roll and the aid of a cordless drill on high speed setting, and the black stuff came off, just enough to let the bearings slip over.  Although one of them has since got stuck on, so I'll have to strip the hub down to slide it off and give it a bit more polishing.

sm_P2270074.jpg

  • Like 1

Share this post


Link to post
Share on other sites

Now fitted, with a longer screw installed.  Annoyingly my long screw selection is either too long or too short; next time I place a screw order I must remember to tick the "Just Right" option.

sm_P2270075.jpg

Too long isn't really a problem, because it doesn't interfere with the wheels.

sm_P2270076.jpg

This pic shows the bearing stuck in place, but what it means to show is the steering arm fouling on the bottom arm.  This probably occurs because a) the Jazrider uprights have two options for ball stud placement, making the end of the arm wider, and 2) I've set up the KBF with more suspension lift than would be normal for a Blitzer.  There doesn't really seem to be a solution for this - bending the steering arm would probably weaken it, and likewise cutting into the bottom arm would introduce an obvious point of failure.

sm_P2270077.jpg

sm_P2270078.jpg

sm_P2270079.jpg

For now, I'm going to pretend this isn't a problem.  Under sag, the suspension should be compressed enough to get a full range of steering, and it's unlikely I'll have the traction to use full lock when the front is unloaded anyway.  The servo might even be strong enough to pull the suspension up anyway, which isn't ideal, but as it lifts the inside wheel only, it might act as a kind of active anti-roll.

  • Like 1

Share this post


Link to post
Share on other sites

These next few photos are a bit clumsy, but they show a nice angle on the steering link.  This is with the link connected directly to the steering arm and the cranks mounted on top of the chassis.

sm_P2270080.jpg

The problem here is clearance - the cranks are too far inboard.  Moving them outward won't really help as the angle is right on the limit of what the Tamiya rod ends can manage.

sm_P2270081.jpg

Also the geometry isn't great.  It's OK when fully unloaded, but gets worse as the suspension compresses.  What we really want is for the link to be exactly the same length as the upper suspension link.

sm_P2270082.jpg

With that in mind, I cut a new steering link that is the same length as the top link, then marked the position on the piece of scrap metal that I was using for a steering rack.

sm_P2270083.jpg

sm_P2270084.jpg

  • Like 2

Share this post


Link to post
Share on other sites

This setup, along with a taller ball stud, gives us a kinder angle on the steering link, plus eliminates any bump steer

sm_P2270085.jpg

sm_P2270088.jpg

sm_P2270089.jpg

sm_P2270090.jpg

  • Like 3

Share this post


Link to post
Share on other sites

So, the next plan is to transfer this geometry onto the other side and trim down my scrap metal to make a symmetrical mockup of the rack, cut it down to size, and test the Ackermann angles.  It might be that I need to refine the stud position on the rack so that the inner wheel gets more steering than the outer one, although I might be lucky and discover it's mostly right already.  I'm also considering the possibility of re-making the uprights from some plain aluminium bar stock, assuming I can drill it accurately enough, so I can get rid of the need for tall ball studs (they tend to bend easier) and reduce the interference with the bottom arm.

I'm not sure if I'll have time for all that this weekend, as I won't have as much time as usual in the workshop on Sunday.

  • Like 1

Share this post


Link to post
Share on other sites

It's been nearly a month since I've updated this thread, and a lot of work has been done.

Way back on 6th March, started work on the proper geometry for the steering rack.  I cut down my scrap metal piece to make a more realistic shape so I could test the steering and Ackerman angles.

I don't know how to measure this properly, but it looks about right to me:

sm_P3060036.jpg

sm_P3060037.jpg

sm_P3060038.jpg

then I transferred the holes onto some 3mm FR4 sheet and used a flange nut to mark a radius for cutting a nice smooth corner.

sm_P3060039.jpg

sm_P3060040.jpg

Share this post


Link to post
Share on other sites

My FR4 rack is thicker than my old dummy metal piece, so I was having clearance issues with the bulkhead.

sm_P3060041.jpg

I flipped the rack upside down and re-drilled the holes.  They had to be a little further back.

sm_P3060042.jpg

ah, that's better

sm_P3060043.jpg

Share this post


Link to post
Share on other sites

After that, I turned my attention to the steering knuckles.  I was looking forward to trying these Jazrider options, but the clearance issue with the bottom arm is a killer.  There's nothing for it - I'll have to fabricate my own.

This is 10mm square section alloy bar.

sm_P3060044.jpg

I drilled the bar as accurately as I could

sm_P3060046.jpg

then punched the axle stub out of the old, deformed knuckles with a hammer and drift

sm_P3060047.jpg

This is a snug fit.  Unlike the weak Frog knuckle design, the screw-thru-the-axle arrangement here is much stronger

sm_P3060048.jpg

  • Like 1

Share this post


Link to post
Share on other sites

Fitted to the uprights.  I had to use 3 washers underneath to take out any play.  We could call this a "tuning option" if we were being generous.

sm_P3060049.jpg

sm_P3060050.jpg

Next trick was to file the corner off the back of the new knuckle, so it will clear the bottom arm.  This was only a prototype, for the finished article I drilled the hole for the ball stud first.

sm_P3060051.jpg

Prototype fitted, with wheel.  The wheel doesn't rub at all.

sm_P3060052.jpg

This is only a rough example, as it was hard to make recess for the screw head after filing the corner off the bar, but I decided it would be better to use a screw-through-the-knuckle for the ball nut, instead of tapping a thread.

sm_P3060053.jpg

  • Like 1

Share this post


Link to post
Share on other sites

Plenty of clearance on full extension now

sm_P3060054.jpg

extra thread won't exist on the final version

sm_P3060055.jpg

most importantly, with the spacer under the ball nut, the steering link angle matches that of the top arm, which is exactly what we want to eliminate bump steer

sm_P3060056.jpg

sm_P3060057.jpg

Share this post


Link to post
Share on other sites

The tricky part was making two final versions with identical screw spacing.  Getting two holes lined up is easy enough - just clamp the bars together and drill through them as one.  That becomes the reference for all the other holes.

The next set of holes needed to be at right angles to the first.  The best was I could figure that out was to put some screws into the threads and press them up against a known vertical angle on the drill vice.  The screw heads on these stainless screws aren't perfect but I rotated both to find the smallest side.  It was close enough for me.

sm_P3060058.jpg

Two bars cut and drilled

sm_P3060059.jpg

I had to recess the underside of the ball nut screw holes, so the screw head wouldn't interfere with the bottom arm, but I had to not drill all the way through.  I used the drill press with the bed positioned so it would only go so far up before it reached its stops.  That should mean that both knuckles have the same recess depth and no risk of drilling through.

sm_P3060060.jpg

et voila

sm_P3060061.jpg

Share this post


Link to post
Share on other sites

It would be another week before I had time to finish the knuckles.  Here is one fitted.

sm_P3130062.jpg

sm_P3130063.jpg

sm_P3130064.jpg

Loads of clearance here

sm_P3130065.jpg

sm_P3130066.jpg

  • Like 1

Share this post


Link to post
Share on other sites

Let's check those angles now

sm_P3130067.jpg

sm_P3130068.jpg

after that, it was time to work out where my steering servo was going to go.  I already had these plates made (2x 3mm allu plates fit nicely in the recess inside the chassis frame mouldings) but I needed to change the shape and size to get a servo in.

sm_P3130069.jpg

I figured a sheet of 3mm FR4 would be perfect.  Lighter than allu, at least.

sm_P3130070.jpg

sm_P3130071.jpg

sm_P3130072.jpg

Share this post


Link to post
Share on other sites

I kept the allu plate underneath to maintain the correct spacing for a tolerance fit in the frame mouldings.

sm_P3130073.jpg

sm_P3130074.jpg

sm_P3130075.jpg

sm_P3130076.jpg

Share this post


Link to post
Share on other sites

For the best clearance, I wanted to mount the servo up underneath the plate instead of on top.  My servo had some webs between the mounting lugs and the case top, so I filed slots into the plate to accommodate it.

sm_P3130077.jpg

sm_P3130078.jpg

Cut a slot out of the allu plate for the servo

sm_P3130079.jpg

Assembled servo plate

sm_P3130080.jpg

Fitted

sm_P3130082.jpg

  • Like 1

Share this post


Link to post
Share on other sites

As I anticipated, I had to file a notch out of the steering rack for the servo link.

sm_P3130084.jpg

sm_P3130083.jpg

Assembled

sm_P3130085.jpg

sm_P3130086.jpg

  • Like 1

Share this post


Link to post
Share on other sites

As you can see, I had a temporary loadout of electrics on the chassis, including battery.  I took the truck out for a run in the garden to see how it went.

Overall - it went very well.  Loads of traction with the progressive spring settings, possibly a little soft up front but it was very compliant in the bends, where the old truck would skip and understeer over everything.  If felt incredibly planted and, around my little patch of grass and patio, it was very nice to drive.  Things might be different in a bigger area or over rougher surfaces, but there's a lot of tuning options in this truck now.

There's heaps of play in the steering, however.  I think most of it is in the servo saver and the cheap old servo - the finished truck really should get a proper servo saver and better servo.  I have more investigation to do, but we're about to hit silly season and I still haven't rebuilt the M03 for round 1 of the Iconic Cup in just under 2 weeks time...

More to follow, including choosing a body.  I can't really afford to buy a new body for this truck, so I'm going to repurpose an old one of another favourite runner.  It should be an easy job, but I have to paint the NIP hard body for the other runner first, which could take some time...

  • Like 3

Share this post


Link to post
Share on other sites

Very cool, that's a lot of custom work but looks to be worth it.  You sir have much more patience and fabrication skill than I.  Nice to hear that it drives much better.  

Why use a saver at all?  I've pretty much stopped using savers on all of my crawlers, monsters, really everything when I think about it.  I still use them on the stock Tamiyas (Hoppers, Blackfoot, etc.) just because they're all stock and I don't feel like messing them, but with a truck like this I'd just ditch the saver for an aluminum arm.  Would probably steer even better and with hardly any weight on that front end I doubt you'd have any issues with breaking servos.  

  • Like 1

Share this post


Link to post
Share on other sites
19 hours ago, 87lc2 said:

Why use a saver at all?

To be honest, if I get a half-decent servo in there, I doubt I'll use a servo saver.  I have broken the odd metal gear servo over the years but they're way tougher than they were back in the 90s.  At the moment I'm right out of good servos and with limited budget to buy more, so it's running an old basic Acoms servo.  At some point I'll put some money into upgrading some basic stuff and then it will get a better one, but until then I'll have to run a servo saver to protect those plastic gears.  (That said, I've got enough plastic servos that I could just use it sacrificially) 

  • Like 1

Share this post


Link to post
Share on other sites

If using a plastic-geared servo savers are a must.  And I agree, servos now are worlds better than they were back in the day.  I wouldn't have dreamed of running without a saver with my old Clods and servos on axles, learned the hard way after I killed a few.   A good saver shouldn't hurt anything anyway.  I like the Kimbrough 124, but they go for about $8-10 these days when a cheap Amazon metal geared servo is around $15-20 and I've had good luck with them.  

Share this post


Link to post
Share on other sites

Updates!!  It's been way too long, but I finally dragged this car out of the box to give it a refresh.  I didn't do any kind of bash meets in 2022, the Revival Monster Truck Race is ancient history, and I don't run stuff at home much, so there was no incentive to finish this off.

To be honest, I remembered the front end being a bit loose thanks to my home-made hubs, but I stuck a battery in it and went out on the lane and it handled very well indeed.  Especially since there was no oil in the shocks.  Super-smooth (if a bit bouncy) and the steering was right on the bubble.

With that in mind, I figured it was high time to stick a body on this beast ready for Tamiya Junkies and some big wheel track action.

Here's the chassis, as it came out of the box

sm_PA010435.jpeg

After a quick test-run, I put some HPI 40wt oil in the TXT dampers.  It felt like a good starting point, and I've got loads of it.  TBH it's useless if it's not right because I don't know how it compares to any other oil, but it'll be better than nothing.

sm_PA010436.jpeg

Then it was time to find a body.  I had a few things lying around that might work, including this very old Monster Beetle body that's been on 4 or 5 different cars since I've owned it and still never found a permanent location.  I think it needs to become a Huynhesque creation at some point, but not on this chassis.

sm_PA010437.jpeg

This was the runner body from my SRB, which now isn't a runner after I cannibalised it for parts at the Revival, and also has a nicely painted re-re Sand Scorcher body which is now slightly less nicely painted since the box fell 10ft off a storage floor and smashed open on my motorsickle, spewing parts everywhere.

I think this looks kinda cool on here, but ultimately I would pass on this one.

sm_PA010438.jpeg

Share this post


Link to post
Share on other sites

At the end of 2019, I bought a Mud Blaster 2 as a basis for my Fifty-Fifty project, which of course came with a lexan Brat body.  I had an original Mud Blaster back in the early 90s, so I wondered if it might be nice to put a Brat body on this truck, for old time's sake.

sm_PA010439.jpeg

Well, the wheelbase is right, and the ORV and the Brat were kinda made for each other.  So...  Why not?

I drilled out the rear shock towers to mount some body posts.

sm_PA010440.jpeg

sm_PA010443.jpeg

sm_PA010444.jpeg

Share this post


Link to post
Share on other sites

The front wasn't so easy.  I came up with this solution, but with hindsight, I wish I'd cut a GRP plate to go over the radio tray to move the body posts out a little.  I could even have utilised the pre-drilled holes in the Brat body, instead of cutting new ones.

sm_PA010445.jpeg

It all fits well enough

sm_PA010446.jpeg

Photos of finished body to follow - I finally got around to painting it earlier today and have just finalised the official truck name and new graphics, too.  Hoping to have some time to get it all decal'd up before I leave for Junkies on Friday morning.

Just before I sign off - I threw this body on at the weekend, as a temporary extra spare just in case the new one wasn't ready in time for the weekend.  This body originally came to me in an NIB Brat re-re around 15 years ago.  Way back then I also bought a used King Blackfoot as a restoration project (I even found an NIB KBF body back then, too!  Those were the days!), but then I hit hard times and had to sell some stuff, so the Brat body got a quick coat of paint before the whole thing was given to a friend as payment for some work he did for me.

Well, a few years back it was my birthday, and he gave it back to me :) Very, very, very used!  The KBF chassis is virtually wrecked, the body is badly ripped in places, and the tyres - my goodness, the tyres!  I guess he left it in a windowsill in full daylight or something, they've all split and perished and cracked open, there's nothing left of them.  Those tyres were new when I gave it to him!!

Anyway - at least here it has a temporary body on it, so if the new one isn't done, I have something to run it with :) 

sm_PA080486.jpeg

  • Like 2

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now

×
×
  • Create New...