This article was written and submitted by Yobear Jones. The photos, techniques and comments are that of the writer. We thank Yobear for his contribution and sharing his ideas here at Speed Inc.
Introduction
It’s not often that an opportunity comes along whereas you get the full support of a major manufacturer when it comes to modifying a product that it actually makes. This is the case of the Mega G Series 2. Although the chassis has been discontinued, A/FX wanted to see our approach to improving the chassis for a possible “Builder’s Class” in the upcoming kick start of the S.H.O.R.S. Series re-shaped to showcase Hardbody Racing.
Build 1
Instead of giving some long history speech about the history of the Mega G chassis, we are going to dive into what we are trying to build.
Our Goal is to basically make this chassis perform better. We’re going to use time tested theories and applications to work the chassis up in a way that are easy and cost effective, but will also make the chassis more durable and it from “Toy” status to serious performer.
At A Glance…
We are going to build two chassis. The first will be a functioning prototype and the second will be a refined version that will be the actual full blown racing chassis.
After receiving two complete rolling chassis from A/FX, we started by removing the factory wheels, pick up shoes and springs. It was determined by “others on line” that the chassis can be set for High and Low down force configurations. Here is basically how it is done:
So we will start from here by setting our chassis in the “Low” down force position. Using a Scale Engineering setup block with .012 rails, we first find tire heights front and rear. For this chassis we determined that a front tire of .335 worked well and a rear tire of .440 allowed the chassis to roll free but stick very well to the rails.
Next we turn our attention to the engine compartment. Unlike the chassis of the past from A/FX, the Mega G2 brush orientation is set east/west or what some would call Tyco timing. They used separate barrel tubes with a brush spring and brush combination like the Tyco electrical systems of the past, instead of the old standard of a north/south SG+ orientation using the standard “Endbell”. This set allows for the chassis to be thinner and have a lower profile. It works well for use because it allows you the option of using a standard A/FX armature made for the MG2 or a Tyco based armature. The first build will use a stock armature that came with the car. The second build will be with a Tyco based armature simply because of time tested durability and known performance of the Tyco armatures. After-market products for the MG2 chassis are sparse, so you will have to use the stock motor and traction magnets. So we will use the Scale Engineering Blue Bushings, better brush springs, the factory stock brush barrels and silver brushes for the first build.
The armature in the picture above was the original A/FX armature, but it was determined that commutator section was defective. So a Tyco armature can be chosen as an alternative if you have problems with the original armatures. The Tyco armature’s shaft needs to be modified to be closer to the actual factory armature shaft length.
Basically we just swapped the factory brushes and brush springs with the higher performance items and upgraded the factory bronze bushings for after-market plastic “Blue” bushings.
We kept the original gearing and broke the brushes in on a power supply set at 3 Volts for 8 hours. We also turned the Comm of the stock armature to ensure the brushes seat well for better performance. We also altered the pick up shoe geometry to account for the lower stance and to make sure they made excellent contact with the rails. We were unable to use the original factory pick up shoe springs,so the first build used a set of SG+ pick up springs.
Overall the car handling was greatly improved and it has great speed and durability.
Although the chassis performs very well, one has to wonder how well it could actually perform with a secondary power tap and more adjustability. Most used a “shunt” type set up to provide the secondary power supply tap. Here are some pictures of what a fellow builder added to his Mega G2. Not only did he add a shunt kit, he also fabricated a set of retainers to keep the pick up shoes on the brush barrels for his MG2 1.7 chassis.
Although effective, we were looking for something a tad less extravagant, but effective. For sometime this stymied us in the shop.
The Marvin Tap
Mike Marvin of New Jersey also wanted to address the secondary power tap issue. What he came up with was a stroke of builder’s genius. What Mike did was to make a small incision at the back of the pick up shoe spring box as seen in the picture below.
Then he added a set of Life-Like pick up shoe springs. The incision removed a tiny amount of chassis plastic to make a groove so the fly wire of the Life-Like spring was free to reach the brush barrel.
The picture above is of the Life-Like pick up spring we cut down for the second build that sits much lower to the track than Mike’s original seen below that was set up very close to the factory stock tire heights. As you can see in the picture how the tap looks installed.
We installed the tap and tested the chassis on a power supply for 24 hours at 4.5 Volts and it performed flawlessly. But that’s on a chassis standing still. Our goal is to install the tap on our second build and test it in real world applications, but here is another angle of what we now call the Marvin Tap Version 1 or the MTv1.
Now it’s time to gather all the components we are going to use for the build and to start the build.
We pulled out the second chassis, stripped it of all its parts with the exception of the motor magnets and the traction magnets. As seen in the diagram in the beginning, we turned the traction magnets over to set the chassis up in the low down force position and tested for clearance on our Scale Engineering set up block and got a very pleasant surprise. As you see from the photos below of our first chassis and then the second chassis, the second chassis sits much lower on the same test tire set than the first chassis. Although it added a tad more down force, the chassis still rolled very free on the test block.
First we are going to add the armature. We are going to use an original Team On-Slot “Blue Puma” that we had in our armature parts box for several years, but never got around to using. The armature is a balanced and trued unit.
As you can tell by the picture, the Armature fits well. Normally we would install a higher performance bushing in the front, but because we are going to use a set of customized adjustable Wizzard brush barrels for Tyco, we are going with a hybrid set up with a performance bushing and a factory stock bushing. We reversed the bushing to check for alignment and spacing.
We are using two, .010 steel washers in the rear and an extra stock phenolic washer to make sure we have proper clearance in the rear of the armature. Unlike the G type armature, Tyco armatures do not have a built-in rear bronze boot, so proper spacing is important. We also want to try to keep the armature in its “natural” magnetic sweet spot in between the motor magnets. Once determined, we then add more shimming to the front of the armature for the front bushing. In this case a .010 bushing was a tad too tight, so we are going to go with a couple of .003 steel shims. Below is the corrected alignment and spacing for our build.
We have just enough free play in the armature so it can spin freely. We added a rear gear set to make sure our calculations are on point.
Adding the Brushes and the Brush Springs
This set up proved to be a tad difficult. Because we modified the brush barrel lengths so that they would fit the chassis length wise, we reduced the amount of space inside the barrel itself. We did not want to cut down the brush nor can we trim down the Allen screw. So that means we need to be creative in the brush spring area. We first tried to cut down a higher performance spring, but that proved to still be too stiff, so we reworked the stock brush springs and they proved to work a lot better.
We now have the silver brushes installed and the Marvin Tap in place, along with the pick up shoes. Now we do a break-in to set the brushes and make the added adjustments.
Because of the space in the rear of the Mega G chassis, your choice of gearing as limited. Viper or HC Slots makes a 23 tooth crown gear that is specifically designed for the MG platform. Another way is to play with your pinion gear choices, using a 7 or 8 tooth gear depending on the tracks that you race on.
We added an HC Slots rear axle for better performance and used the classic “SimmTek” building process to use the stock gear and spacer. Now we need to fit the body onto the chassis.
We tried several bodies and settled on a custom one built by John Peddy. We are not a fan of resin cast bodies. Although they look great, they tend to be like graham crackers during a race and end up in pieces. But John Peddy has come up with a very unique technique. His bodies are soft and supple and smooth. They are also flexible and I mean FLEXIBLE! They are thicker than a Rokar 240 or Porsche body, but are just as flexible. The one he designed for me is based off the McLaren F1 GTP and it fits perfectly with just some very mild messaging.
Just One Last Piece of House Cleaning
Before we close this chapter, there is one last bit of house cleaning to do. As with all builds, the tiniest thing cannot be overlooked, because it will be the one thing that can make the difference between a podium or ticked off. Check your pick up shoe geometry. Because we are using stock pick up shoes you will not be able to get the whole shoe flat on the rails. So get the best line you can on the hump of the shoe. That way your car will get the maximum amount of power in that contact patch.
We are now ready to go test this new A/FX-J.L.M. Racing McLaren F1 MG2 1.5 Chassis.
