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Mini-Giant: Evolution
It wasn't long after Venom Racing released the 1/20th scale Mini Giant electric MT in 2004 that curious and inventive owners began doing conversions with cantilever suspension, tube frames, bigger wheels, etc. It's no wonder -- with solid axles and a multilink suspension in stock form, the VMG screamed, "To the rocks... I must crawl!"
Well, that was all fine & dandy, but what did it leave for me to do? I'm the guy who made a rally car out of an E-Maxx for cryin' out loud! Searching for a unique direction to go with the Mini 'G, I decided to go for a "tough truck" setup -- something much lower than a monster truck for better high-speed handling over rough terrain, without going the full 4WD stadium truck/racer route.
What followed was over two years of stop-and-go work as I cycled between excitement and frustration. Progress led always to a brain-twisting challenge, which led to frustration, a break, a moment of inspiration, and more progress. Never did I imagine that such a small project vehicle would take such a large and drawn-out effort to complete. Then, on July 17, 2006, it was all done.
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The only parts that remain mostly factory-stock on the vehicle are the axles, transmission, and integrated electronics combo (receiver + ESC). Everything else was either custom-fitted or hand-made.
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Videos:
Project Log:
7/17/06: First up, I had to get the front bumper taken care of, as I'd been looking forward to for over a month. It took another 2 hours to design & build this piece, but fortunately it came out nice & sturdy. Carbon fiber side plates are connected by thick-wall 3/16" aluminum tubes with all-thread going through them. Locknuts are used on both sides. I would rather have used drilled & tapped solid rod with button-head screws inserted from either side for a bit more tidiness, but I lack a proper set of equipment to pull that off.
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Next, it was time to finish the body mounts. After painting up a new Trinity "Red Bullet" (Volkswagen Touareg race truck) shell, I found that I could mount a body much lower than originally expected, and the front mounts would need to be reworked. It didn't take long to realize that I'd need to come up with a completely different mounting strategy. I ended up using music wire brackets that slide tightly into deep holes drilled into the shock towers. At the end of each bracket, a piece of Lexan is securely atached, and a few strips of adhesive-backed Velcro are attached to that. Larger pads of Velcro are then used inside the body, under the rear roof and hood. One more piece of velcro is then added under the roof to hold a Lexan antenna spool. The simplest way to remove the body is to detach the Velcro at the front, and then pull the whole thing up and to the rear, which pulls the rear body mount out at the base. I can then remove the front mount to take cleaner photos of the chassis! The mounts won't come out with the body on, though, because they're inserted at nearly 90 degree angles to eachother.
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So there you have it. My most difficult project to date is finally done. It's quick, agile, and more stable than could ever have been expected from something that started out as a Mini Giant. Mission accomplished.
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7/6/06: Quiet as I kept it, a couple weeks ago I actually got the truck fully running free with a full battery charge and mounted electronics. It took about two hours to route all of the wiring, and what a painful process it was. When you look at the pictures, it's easy to not realize just how tiny the whole thing is. The wheelbase is under 6 inches, and the chassis is just over 3 1/2" wide. Into that area, squeeze 4-link suspension, two battery pack segments, the transmission & motor, driveshafts, shocks, shock towers, and servo. Follow? Now, add in the 3 wires of the battery pack, the servo line, and motor wires, and don't forget to tack on connectors for the battery bridge, battery to ESC, and ESC to motor, and don't forget the power switch & antenna. Madness!
At any rate, she ran, and ran well. Damn well. Better than I ever would have hoped, actually. On carpet it will flip onto its back instantaneously, starting in either forward or reverse. On linoleum, it does 4-wheel drifts. It can do a 360-degree turn inside of three feet, and when it is near the limits of lateral traction it will intermittently lean over on two wheels and touch right back down. Steering and throttle response are both immediate and linear. It has some speed, too. And then I hit something.
In spite of my valliant efforts to secure the upper link mounts on the axles, they still managed to develop enough freedom to rotate around the vertical bolt that holds each down. The design was doomed. I need to come up with something that wouldn't go anywhere, no matter what type of force was applied to it, so I decided to go back to a 3-link design. The pictures below explain it all. I measured & drafted everything out on paper and then made new miniature Delrin thingamablobs that would accept three lengths of all-threaded. The two longer rods would receive the ball cups from the links they were replacing, and the other, a real shorty, would take a cut-down Kyosho ball cup (3.5mm I believe) to co over a stud I'd bolt directly into each axle at the factory stock location I'd been trying to repurpose.
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It worked. The new assemblies fit just right and the axles now stay located exactly where they're supposed to be. If only I had done this long ago! Live & learn...
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That's how the truck looks tonight. The front body mounts are on and the rears have been bent and are awaiting installation. The antenna will probably be mounted internally on a thin strip that will be Velcro'd to the inside of the body to keep it out of the way. Don't quote me on that, though -- at least not just yet. I actually have a brand new body that's being masked off for painting, but I haven't decided yet whether to use it or an older option.
Oh, and I still need to make that front bumper...
6/10/06: Finally some serious progress! I hardly know where to start, I've done so much in the past couple of weeks. I suppose the biggest news has to do with my bigest fear and mental block -- the battery straps. They're done! Both sides are well secured with easy-to-use Velcro straps, and the cells sit as low and cozy as possible in deep recesses. Just as important, closing the straps very tightly is easy and straightforward. Over the 5-cell hump, double-sided Velcro is used and one end passes through a slit in the other to allow you to pull them against eachother before flipping them down. On the 2-cell side, a very wide and strong hook piece has a tab shape that you pull down firmly in the middle, and two thin, flexible hook strips (actually double-sided because it's what was convenient) get flipped up on either side. No longer did I need the vertical plate I had installed on the 5-cell side, so I axed it. Oh, and the battery pack itself is all soldered up, as you can see. It's just waiting for a micro bullet connector as a quick-disconnect point for the bridge wire.
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Now, if you look at any of the older pictures carefully, you'll notice something quite odd. Is your mind playing tricks with you? Are these newer photos flipped? No, that can't be. Well, I'll spoil it for ya. I flipped the entire chassis around. It needs to be this way in order to not drive backwards! Yeah, I messed up when I did the original layout, forgetting that with a modified motor, you can't just flip the wires around to change its direction of travel and expect it to perform well. Found that out when I ran the truck around on the floor for the first time!
Another thing I found out the hard way is that the steering was all wrong. With the knuckles flipped as they are, a normal direct linkage gives negative Ackermann (e.g., in a left turn, the right wheel will turn more than the left, and that ain't right). So, I had to run the right linkage to the left side of the servo horn, and vice-versa.
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It looks funky, but it works well. Too well, in fact. With the proper Ackermann and the flipped midsection of the truck, I encountered some serious binding of the inside tire against the chassis. To escape this, I lengthened the front suspension and inserted a Mini-T dogbone that's been heavily modified at the ends to fit. While I had everything apart for this, I dyed the ball ends to a nice blood red color that goes well with the rest of the chassis, giving the whole thing much more of a "factory" look. I also went ahead and built a whole new upper chassis plate from scratch, as I was always bugged by some asymmetry issues.
With the batteries situated and the steering working, I figured it was about time I build a home for the electronics. They'll be perched over the rear axle as planned from the start, double-taped to a spiffy new carbon fiber & delrin platform.
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I gave up letting myself feel like I was on the home stretch over a year ago, so I'll spare myself an excited quote about "the last things" to do. *Next* up will be the body mounts and routing all of the wires. As the steering is uncomfortably exposed again, I'll probably look into building a new bumper as well.
5/20/06: Alright, geometry problem solved. I went ahead and made two new upper axle-link mounts so as not to leave the front end out of the party, even though there wasn't any binding there. The link angles are now much, much better.
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In other small details today, I trimmed the front inner steering ball studs and removed their basically unnecessary locknuts so that I could put the stock front bumper plate back on. The locknuts were moved over to the battery strap mounts so as not to have a net loss of red bling.
The third photo above shows the side of the truck you hardly ever see. It still doesn't show the nicely rounded trough the two cells are sitting nicely in, but believe me, once I get the straps in, those batteries aren't going anywhere.
Time to order some more hardware!
5/19/06: Well look at that, a little battery holder. Some thin aluminum angle scrap, a very thin piece of Dragonplate, some 3mm hardware, and a trimmed Velcro strap make this side nearly complete. I will add recesses to the chassis to let the cells sit a little lower and even more secure than they already are.
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On the other side, you can't see this, but I've recessed the chassis for the other two cells and I just need to mount the straps for them.
I also did some investigation into my rear suspension geometry problem and solved half of it by raising the lower inner ball studs a bit. The last thing I should need to do back there is make my new upper link mount for the axle, which will move the mounting point down to be close to parallel with the driveshaft (finally).
4/29/06: Oil shocks arrived and are in. These are the set for the Trinity Clash. It's $9 US for a set of 4 -- an absolute steal. They arrived prebuilt and sealed inside of two bags, but absolutely bone dry on the outside -- no leakage.
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I installed them with some small plastic spacers (Losi shock downtravel limiters, to be exact) to push them out from the shock towers and keep them at less of an angle.
If you look on the left side of the photo, you'll see that I've changed my servo saver to a more appropriate-sized (and appropriately red!) mini Kimborough unit. Also, while on Trinity's Shopatron site looking for the shocks, I picked up a Clash motor heatsink, which clipped right on with no drama.
With the final shock setup in place, I can see that my upper suspension links are a bit short. The front works out alright, but the rear pulls the axle too far forward and the driveshaft gets pushed all the way in. I'm hopeful that a new rear upper mount will allow enough link length to fix this.
4/11/06: What can happen over the course of a year? Obviously not a lot if you've been watching this page the whole time. That's alright, though -- my mojo is back and better than ever, and I'm gonna get this sucker done! Here's how it looks after a few afternoons of new work:
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Ah, yes, front shocks at last! I've gotten more comfortable working with Delrin working and I think the year-old rear tower may be feeling a little jealous.
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I can't recount the number of times I walked into my workshop, stared at the front axle looking for a place to connect the shocks, and then gave up & put it away. The little carbon fiber extension off of the tabs the servo mount are perched on really saves the day. The front shocks are purposely more upright than the rears because I plan to put more weight on the front to help keep the nose down and maintain some steering under power. Oil shocks are on the way! What I'm really happy about is that even with the bottom of the chassis now sitting a mere 1/2" off the ground, the truck articulates to over 2 3/8", which is actually a tiny bit more than it did when bone stock!
Next up will be an ESC/RX mount, followed by body mounts. A new body is painted and waiting...
4/1/05: Progress has been slow as other things in life have kept my R/C work suppressed, but the Mini-Giant continues to get a little love from time to time. In this round, I attacked the tire issue. There were two problems with the modified Mini-T upgrade wheel/tire set. First, the modifications I made to the hubs to allow them to fit on the VMG axles weakened them and left a somewhat flimsy connection point. Second, the oversized Trinity tires and their moderately deep offset (pulling them closer to the chassis centerline) didn't work with my new chassis and I was going to have to look into extending the wheelbase. On top of that, the big meats required significant (and unsightly) trimming of the body for the sake of clearance.
So, I figured out a better solution. I went back to my stock VMG wheels and cut off the outer portions of both bead seats, leaving what had been the inner ridges at the outside. The picture explains it better than my words do. Onto these narrowed rims I was able to mount stock-sized Mini-T tires, in this case opting for Pro-Line Dirt Hawgs. Problems solved, plus I get a wider track as a bonus.
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You may be wondering how I got the narrow red design on there. The wheels were first died black. When I trimmed them, the white plastic underneath was exposed along the cut surfaces. I just fired up a new RIT dye bath and soaked the wheels in Scarlet Red to get the trick effect. I didn't have to worry about the remainder of the wheel surface changing color, as black doesn't really dye to any other color.
Pretty soon I'll be showing off my new body!
2/9/05: Got the rear shocks mounted!
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The tower is carved out of a single piece of Delrin, one of my favorite materials in all the world. Strong, easy to work with, and versatile. I'm expecting to do something similar up front, though perhaps not identical. Yes, I see the rear tire touching the chassis a tad. Nothing a Dremel won't fix!
1/9/05: Today I put something in the range of 5 hours into the truck, and this is what I have to show for it:
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Looks pretty decent and the suspension range of motion is very good, but I'm a bit annoyed by the high work/return ratio! The next big challenge is going to be mounting the shocks.
1/7/05: After a long sabbatical, I'm back at it. First, I've installed a Hitec HS-81 micro servo directly on the front axle with lightened (couldn't help myself) set of Swami mounts. Next, I've started mocking up my chassis layout and 4-link setup. The new chassis layout accomodates an asymmetrical 7-cell saddle pack which results in nearly perfect left/right weight balance and lowers the center of gravity of the truck to a degree that's never been attempted. I hope to make this the best-handling VMG out there!
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Since these photos were taken, I also set up the rear links & axle, and disassembled the mockup chassis to start laying out on drafting paper to create a final version out of either woven CF or graphite plate. Or should I continue with the theme and use red-inlaid CF...
6/20/04: Today I started letting out the stops. With a bit of careful Dremelling, I was able to convert some Mini-T rear wheels to work all around. I'm using Trinity's MonsTer off-road mounted treads, which are a good deal larger than stock Mini-T treads, but smaller than the Mini-Giant's chevrons. The new treads are also made from a softer rubber compound and have a more practical tread for riding on dirt. Pre-installed foam inserts help the ride as well. Unfortunately I ruined the hub of the second wheel while working on it, so while the truck looks great right now, it needs a replacement.
Also borrowing from the Mini-T world, I earlier found that a Team Losi "H2O" Hummer-styled shell would be a good fit. The paint scheme features a splattered Pactra Metallic Red with a slightly Fluorescent Red nose, all yielding to a a Spastix Chrome base. The somewhat mirror-like finish of the Spastix paint nicely complemen ts the blingin' wheels, though I may do a little trimming on the rims later to tweak the look. The body isn't fully trimmed yet, pending final placement. I've included a "before" picture with stock wheels & tires below, for comparison.
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I decided to bring the front shocks back inboard to make the truck look more clean and also to make way for some later steering mods. Still needing something soft and stylish to tide me over until Venom's oil shock set comes out, I dyed the white stock shock parts to a metallic black (an overdose of RIT "pearl gray" dye did the trick) and installed some new springs that I picked up at the local hardware store. I used 1 1/2" rear springs of 0.023" wire, and 1" fronts with very soft 0.016" wire. One small zip tie closed tightly around each shock body provided the needed preload spacing. Up front I also used short lengths of heat shrink tubing around the lower portions of the front shocks to take up a bit of slack inside of the springs.
Not obvious in any of these pictures is that I have installed a trick Venom Fireball 370 motor, plus a Venom Hex 7-cell battery pack to feed it. Even without charging the battery right out of the package (kids, don't try this at home), this setup is a real screamer!
6/1/04: This first modification was actually completed while I was writing my review of the truck. Given this platform with so much flexibility just waiting to be taken advantage of, I could not bear to leave things stock for even a single day. I moved the front shocks' lower mounting point to the tip of the bumper and relocated the rear shocks' upper mounts (requiring one new hole to be drilled into the chassis on each side).
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The dramatic increase in shock rake angle softens the suspension and boosts maximum articulation from the stock 2 5/16 " to a whopping 3 7/8 ". This photo says it all:
The only problem I encountered was a minor clearance issue with the front tires, and this was solved by pushing the inner tire beads over the inside ridges, slightly narrowing the tires and offsetting them to the outside (as clearly visible on the right front tire above).
Here's a bonus picture showing the parts the shocks are made of, for those who are interested:
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