MAGracing Forum

Following are detailed instructions for building a 1:32 scale magracing chassis, using Chassis Kit CK4, which can be purchased at
https://www.shapeways.com/product/227CC ... d=60846518

The kit is available in white or black. It is designed to fit most LMP race car bodies with the motor mounted so that the shaft of the motor is perpendicular to the rear axle, NOT parallel to the rear axle. This requires a crown gear on the axle to mesh with the pinion gear on the motor.

Inspect the product when you receive it. Make sure that the pins/posts at each end of the tie rod and and at the end of the guide arm are not missing. If the product is twisted or warped when you receive it, lay it on a flat smooth surface for 12 hours. If the printing is still not flat, place a light weight book on it for another 12 hours. If the printing is deffective, contact Shapeways at https://www.shapeways.com/contact/conta ... peways.com

Please conatct me via PM with any questions or problems concerning assembly or operation of your chassis. Also, let me know about any suggestions you have for improving the instructions or the chassis kit.

Assembling the chassis and mounting it to a body, are covered in these instructions.

Part 1: Introduction

This kit is comprised of a Base Frame, Frontend Kit, and Motor Pod. The wheelbase of CK4 is adjustable from 3.20” to 3.55”. The frame is 1.95” wide. The frontend has 1 degree of positive toe and 3 degrees of negative camber. This eliminates frontend shimmy at high speeds. The lack of shimmy improves handling and lane change reliability.

Unlike the original stock magracer, the battery is mounted between the front and rear wheels on the right side and the battery is loaded from the top, instead of the bottom. This requires removing and replacing  the body which takes about an additional 10 seconds, compared to a battery change for an original magracer.

CK4 is intended to be used with 3/32” (2.38mm) diameter front and rear axles, along with wheels and tires typically found on 1/32 slot cars. Before beginning to assemble the kit, it is important that you obtain the wheels you will use in front and the wheels you will use in back. Also procure the axle that is appropriate for the rear wheels you have chosen, paying attention to how the wheels will be attached to the axle. Some wheels are simply pressed onto the axle, while others are attached with a set screw, through a protruding wheel hub.

It is especially important to obtain the best fitting front stub axles for your chosen wheels. The front wheels of most slot cars are fixed to the front axle and do not spin on the axle. Instead the axle spins in some kind of bearing, and the axle and wheel spin together. In the case of the original stock magracing chassis, the frontend is designed for the front wheels to spin on the front stub axles, which are fixed and do not spin in the stub axle carriers (steering knuckles).

In the case of my chassis you can set it up either way. If you have front wheels and stub axles produced by Fly or Scalextric (and many other brands I suspect), you can enlarge the bore in the steering knuckles so that the stub axles spin freely in those holes. In that case, plan to connect the front wheels, stub axles, and steering knuckles the same as Fly or Scalextric. This looks better since you won't have the head of a rivet or screw showing on the outside of the wheel. The plastic stub axles common to Fly slot cars work well after the heads are reduced easily by sanding..

If you don't have any stub axles from a slot car, in most cases, 3/32” diameter Stainless Steel Flat Head Solid Rivets 1/2" long should work very well as stub axles, once the length and head are modified. The exact length (under the head) should be about .21" longer than the length of hole in the hub of the wheel plus the thickness of any spacers you may use to obtain the desired front track. If the wheel is made out of plastic, and the hub is too long, you can easily reduce the length of the hub by sanding off some of the hub protruding beyond the inside edge of the wheel. The 3/32" diameter rivets I purchased from McMaster-Carr measure .095", a little over 3/32".

An alternative stub axle is a 2.5mm diameter Stainless Steel Metric Pan Head Phillips Machine Screws with fine thread. The 2.5mm Machine Screws I bought measure .096", slightly under 2.5mm. The machine screws work well if your front wheels have holes going all of the way through the hub and you attach the wheels to the steering knuckles so that the wheels spin on the axles. In this case, one advantage of the machine screw is that it is easy to adjust the gap between the hub of the wheel and the side of the steering knuckle. It is also easy to remove the screw and thus the wheel. It also eliminates the need to modify the head, but the head shows.  

If you want to use stock magracer axles and wheels contact me by PM. Stock front axles have a diameter of 1/16” (.0625”) and rear axles have a diameter of 2mm (.079”). You should be aware of the fact that the stock front plastic wheels have tapered bores. They measure .0635” on the inside of the hub which is very good for the .0625” diameter axle. But the bore diameter is at least .008” larger on the outside. Consequently the front wheels wobble on the stub axles even when brand new.

It is assumed that you have 3 critical stock components, a motor with pinion gear, a steering coil, and a printed circuit board (PCB) for the chassis. These components are not available separately new off the shelf. As of December 2016 I can’t find them anywhere. Used stock magracer chassis are available which can be cannibalized.

I do not recommend trying to reduce the diameter of the bore in a wheel hub unless you have a lot of experience at this. Most of my attempts have failed. If you choose to attach the stub axles to the knuckles, so the axles don't spin, you may have to enlarge the bore in the front wheels from a slot car by 2 to 3 thousandths of an inch, so they will spin freely on the front stub axles, That should not be a problem with the right drill bit.

CK4 requires a crown gear on the rear axle. I recommend that you first try the gear that came on the axle, if you are converting a slot car. Keep in mind that the gear ratio and tire diameter affect the top speed and acceleration.

My experience suggests that which body is mounted on the chassis has little effect on top speed. However, the body has a very large effect on the overall performance of cars running on my track. My track has several banked corners, bumps, and an S curve where the bank changes from right to left. The body greatly affects handling and cornering. Changing the body will almost always affect best lap times because the body affects handling, cornering, and acceleration slightly. The body may not make as much difference if your track is smooth and flat with no banks or twists in the roadway. Heavier bodies reduce run time on a fully charged battery. Heavier bodies may also cause a motor to overheat sooner. If you run your chassis without a body and then with a body, you'll see a difference in performance.

If you are converting a slot car to a magnetically guided car, before disassembling the slot car note how the wheels are located relative to the wheel wells of the body. Pay close attention to the frontend. If you build your magracer with the same front track (measured outside to outside) will the tires clear the wheel wells when turning? Probably not. Will they clear the head lights? Determine and write down the wheelbase and front track, (measured outside to outside), that you think will work best. In most cases you will want a front track that is shorter (narrower) than the one of your slot car.

Contact me by PM if you are interested in buying a small packet of screws, nuts, magnets, and washer/spacers. Some of those which are needed in this custom chassis are not used in a standard chassis. Also please contact me with any questions or problems concerning assembly.

Part 2: Tools Required to Complete a Car

In addition to soldering gear and several drill bits, most of the tools and materials shown in the photo below, are needed to build the chassis. A small electric rotary tool like a Dremel with a router bit is handy for removing obstructions inside a body and disassembling the interior of a body. A digital caliper is very useful building the chassis and mounting the body. It is required for very accurate work and is highly recommended.



The sandpaper is #220 & #600 grit. The hex socket is 4mm. The diameter of the fishtail router bit with yellow/green collar is about .09". It is very useful in a Dremel tool for removing material
on the inside of a plastic body. The block of wood measures 3/4" x 1 1/2" x 3".

The drill bits required are as follows:
.0670" (1.70mm) #51
.0700" (1.78mm) #50
.0730" (1.85mm) #49
.0750" (1.90mm)
.0760" (1.93mm) #48
.0781" (1.98mm) 5/64"
.0935" (2.37mm) #42
.0938" (2.38mm) 3/32"
.0960" (2.44mm) #41
.0980" (2.50mm) #40
.0995" (2.53mm) #39 Needed only for 2.50mm stub axles.
.1015" (2.58mm) #38 May be needed for 2.50mm stub axles.

These can be purchased new or used from DrillBitsUnlimted.com . They sell sets and individual drill bits and router bits. I have found their used carbide drill bits to work well. I paid $0.83 each. You can buy 10 bits for less than $10.00 plus shipping. Here are the URLs:
http://drillbitsunlimited.com/Drill-Siz ... 32971.aspx for .0380” to .0787”
http://drillbitsunlimited.com/Drill-Siz ... 32972.aspx for .0810” to .1180”

Please contact me by PM, if you find a mistake in the instructions or have a suggestion for improving them.

Part 3: Other Components and Parts Required

Click on the attached pdf file to view a table of additional hardware and components needed to complete a car using Chassis Kit CK4.

Part 4: Separating Plastic Parts

The picture below shows version 3 of CK4 in white, available after 11/21/2016.



1. Using a sprue cutter, separate all 8 pieces in the kit.

2. Remove any remaining sprue or burrs on the frame and the motor pod attached to the rear, by sliding the rough edge of each piece across a piece of fine sandpaper placed on a smooth flat surface. Using an emery board or sanding stick, round off slightly the top edge of the tail end of the frame, where the motor pod slides into the frame. Slide the bottom surface of the motor pod across a piece of very fine ( #600 grit) sandpaper laying on a flat smooth surface. The bottom of the motor pod must be very smooth.

3. Be especially careful handling pieces with small pins so as not to bend or break them.

4. Remove any sprue or burrs on the 6 pieces of the frontend with a sprue cutter, sharp hobby knife, emery board, and fine sandpaper, paying close attention to 3 pieces. In the case of the tie rod, which has a pin at each end and a box in the middle, slide the bottom of the tie rod across a piece of very fine (# 600 grit) sandpaper laying on a flat smooth surface. This piece has to be smooth on the bottom. Be careful not to bend or break the pins on this piece. In the case of the 2 steering knuckles, the diameter of the pins is important. If they are out of round (which is unlikely), try to round them up a tiny bit with an emery board. Do NOT shorten the pins.

5. With the point of a very thin nail, clean out any nylon powder residue in both grooves on each side of the tail end of the frame, and also along the tongue on the outside of the motor pod.

6. Place the the frame on a smooth flat surface. Carefully and gently, slide the motor pod onto the tail end of the base frame. The pod should slide easily onto the frame. Do not try to force it on. If it does not slide easily, smooth the bottom of the motor pod some more, by sliding it across a piece of super fine sandpaper (#600 grit) placed on a smooth flat surface. If needed, also slide both long edges of the motor pod across a piece of super fine sandpaper (#600 grit) placed on a smooth flat surface. This will reduce the width of the bottom of the motor pod. Be careful not to remove too much of the tongue along these edges of the motor pod. See photo below of version 2 which is almost identical to version 3 of CK4.




Please contact me by PM, if you find a mistake in the instructions or have a suggestion for
improving them.

Part 5: Attaching Parts to Frame

1. Place the frame on a smooth flat surface. Using the flat blade of a screwdriver, press two 3mm dia x 2mm thick neodymium magnets into the holes on both sides of the chassis. Make sure that the polarity of both magnets is orientated the same. Both magnets must be orientated the same way, either both with the positive (+) pole facing up, or both with the negative (-) pole facing up. Sometimes it takes a lot of force to press the magnets into the holes. Press the magnet down so that the bottom of the magnet is flush with the bottom surface of the collar around the magnet. Do not press them so deep as to protrude below the surface of the collar around the magnets on the bottom of the frame.

2. The hole in the side of the battery compartment will fit a 4mm x 3mm thick magnet. If after operating your chassis for a few hours, you find that the positive (+) end of the battery is popping up, you may want to put a magnet into this hole to hold the battery in place. It probably won’t be needed and that magnet may interfere with the magnets in the box on the nearby tie-rod.

3. Before mounting the steering coil, smooth that portion of the base frame that the tie rod will slide across. This is a strip about ½” wide, running the full width of the frame, in front of the steering coil. The fine side of an emery board followed with some #600 sandpaper works well for smoothing this. Also, smooth the bottom of the tie rod. Sliding the bottom surface of the tie rod, back and forth over a piece of #600 sandpaper on top of a smooth flat surface, works well. This step is very important.

4. Now mount the coil. Place the frame on a smooth flat surface. With the mounting screw partially inserted into the back of the coil, carefully insert the coil into the pocket in the frame. Make sure that the lead wires are visible on top so they can be soldered to the printed circuit board (PCB) later, if they are not already attached. Press down on the top of the coil until the bottom of the plastic coil bobbin is flush with the bottom of the mounting bracket. Now tighten the screw to hold the coil in place.

Some of the photos which follow are of prior versions of CK4. A current version is used where needed for clarity.




5. Now attach the PCB to the frame with one #1 screw. If the coil is already wired to the PCB, attach the coil to the frame and then attach the PCB to the frame. Make sure that the red antenna wire runs under the PCB. Note that most PCBs have a white rectangular socket with 7 pins located between the bank of 4 dip switches and the screw used to attach the PCB to the frame. I removed this white socket to provide more room for the cockpit. See photo below.



6. Make a bronze connector for the positive (+) end of the battery compartment. From a coil of bronze spring strip 0.2mm x 5mm, (available at http://www.greenweld.co.uk ) cut a piece .81” long. Form it into a “U” with the short leg just long enough to reach the outside bottom surface of the battery compartment, about .34". See photos below.
.




7. Now make a bronze connector for the other end of the battery compartment. If you intend to use protected batteries, from a coil of bronze spring strip, cut a piece .70” long. If you are going to use the shorter unprotected batteries, cut it .73" long. The leg that goes over the top, of the end wall of the compartment, should be shorter than the one that wraps around the bottom edge. Ideally, the end of the leg that wraps around the bottom will make contact with the end of the battery about .05” above the center of the battery. [When loading the battery into the compartment, place the negative (-) end into the compartment first. Then press the positive (+) end down. This prevents damage to the connector at the neg (-) end.] See photos above.

8. Solder wires from the PCB to the bronze connectors for the battery as indicated by the photos above and below. Do NOT solder wires to the bronze connectors when the connectors are touching the plastic battery box. The heat from your soldering iron will melt the plastic.

9. Now attach the bronze connectors at both ends of the battery box as illustrated by the photos below.







Please contact me by PM, if you find a mistake in the instructions or have a suggestion for improving them.

Part 6: Assembling Frontend Kit

Be careful working with any of the frontend parts with small pins/posts. The diameter of these pins is specified to be .070" in the 3D model. When printed by Shapeways the diameters usually range from .064" to .067". Most of these pins fit into a hole and must rotate freely. The holes have a specified diameter of .072". When printed they usually range from .068" to .070". To get the pins and corresponding holes to fit precisely, you have to enlarge most holes to fit the pins. It is best to enlarge the holes in small incremental steps rather than in one fell swoop.

1. Determine the correct orientation of the polarity of the two neodymium 4mm dia x 3mm thick magnets to be glued into the box on the tie rod. (Note that these magnets have a smaller diameter than the ones used in an original magracer.) It is important that the polarity of both magnets is oriented correctly, when glued into the box.

• A. If you have an operational stock magracer:

• • 1. Place 2 magnets side by side on the blade of a screwdriver as depicted in the photo below.

• • 2. Now with your thumb and index finger, take a hold of the magnet box on your stock magracer, and place the magnets stuck to the screwdriver against the back of the magnet box. If the magnets are oriented properly on the screwdriver, they will quickly snap toward the magnets in the stock magracer and easily line up as shown in the photo below.

• • 3. If they don’t want to line up easily, the magnets on the screwdriver are not oriented properly. Change the orientation and try again.
    
    4. Once they are oriented properly, mark the exposed faces of the 2 magnets on the screwdriver with a black permanent felt tip pen. Also mark the top edge of one of the magnets to distinguish between left and right as shown in the photo below.

• • 5. Now that you have determined the correct orientation for the magnets, glue them into the box on the tie rod. Make certain that they are both oriented the same way in the box as in the stock magracer, with the black faces facing as depicted in the photo below. Be careful not to switch the left and right magnets. When gluing the magnets in place, make sure that they are firmly pressed to the back of the box and into the cxorners. CA glue such as Krazy Glue or Supper Glue works well for this. Two part epoxy adhesive also works. When the glue is dry inspect the bottom of the tie rod. Remove any glue that may have oozed out on the bottom edge of the magnets or box.

Tie rod oriented rightside up.


Tie rod oriented upside down.

• B. If you do not have an operational magracer:

• • 1. You‘re in trouble

• • 2. Not really! If you have a stock tie rod with magnets installed, use that as your model for comparison, and follow the instructions above.

• • 3. If you don't have anything with which to compare, you have a 50% of getting it right! Just glue 2 magnets in the box. Make sure that they are firmly pressed into the corners of the box. CA glue such as Krazy Glue or Supper Glue works well for this. If they are oriented the wrong way, the car will steer the wrong way. In that case just swap the coil wiring on the PCB and you're good to go.

Be careful handling the stub axle carriers (steering knuckles) and steering plate (tie rod) so as not to break or bend the pins.

2. Ream out the hole farthest from the kingpins, in each of the stub axle carriers (steering knuckles) using a #50 (.0700” diameter) (1.78mm) drill bit held in a pin vice (small handheld manual drill). (The steering knuckles are symmetrical and the 3D model for the left one is identical to the right one.) Now check to see if the pins at each end of the steering plate (tie rod) will fit into the holes that you just enlarged in the steering knuckles. An easy and safe way to do this is to first place the tie rod on a smooth flat surface, with the pins facing up. Then with the finger of one hand, hold down the tie rod. Now with the thumb and index finger of the other hand, (or a pair of tweezers) grasp a knuckle near the hole you enlarged. Slip the hole in the knuckle over the pin on the tie rod. Be very careful doing this so as to not break the pin off of the tie rod. A pair of tweezers comes in handy for this. Do NOT try to force the pin into the hole. Do the same with the other knuckle and pin.



3. The knuckles should rotate freely on the pins of the tie rod but without any play (without any slop). If they don’t rotate freely, ream out the hole a little more with the same #50 (.0700") (1.78mm) bit. Do not use a bit larger than #50. The best hole diameter is usually about .003” larger than the pin diameter. When the knuckle is held as shown, the tie rod should should swing freely and come to rest as depicted in the photo below.



4. Now put the upper and lower suspension beams together. Simultaneously ream out the holes at the end of the beams with a .075” diameter(1.90mm) bit. See photo below.



5. After that, with the upper and lower beams still held together, ream out the hole in the lower beam that is used to attach the guide arm to the beams. Use a 5/64” diameter (.0781) (1.98mm) drill bit held in a pin vice to do this. See photo below.



6. Now separate the upper and lower suspension plates (beams) and check to see if the king pins of the steering knuckles fit into the corresponding holes at the end of the lower suspension beam. An easy way to do this is to first place the lower beam on a smooth flat surface. With the steering knuckles attached to the tie rod, place the pin of one of the knuckles, into one of the holes at the end of the lower beam. Do the same with the other knuckle. Label the knuckles Left and Right so you can put them back together the same way.



7. Now place the upper beam over the lower beam and knuckles, being careful to align the pins of the knuckles with the holes in the upper beam. Press the lower and upper beams together. The knuckles, with the tie rod attached, should rotate freely between the beams when the beams are squeezed together in the middle. If they don’t, remove the knuckles, put the upper and lower beams back together again, and ream out the holes again at both ends simultaneously with a #48 (.760”) (1.93mm) bit and try again. When reaming out the holes at the ends of the beams, only do so when both beams are held together so that the holes in the upper and lower beams can be reamed out simultaneously to maintain the proper alignment.



8. Determine how wide your front wheels (including the hub) have to be to fit your body appropriately. Measure the width of your body at the front wheel wells. In the example here, the body is 2.42” wide at the front wheel wells. Now measure the distance between the steering knuckles. It should be about 1.71” as seen below in the photo. Subtract the 1.71” from 2.42” to obtain .71”. Now divide by 2 to get .355”. Subtract side clearance of .005” from .355” to arrive at .350”. This is the ideal width of the front wheels including the hubs (with tire mounted).



9. If the original wheel (with the hub) is too wide, reduce the length of the hub as needed. This is common. If the wheel is made of plastic, it is easy to shorten the hub by sliding the hub back and forth over #200 sandpaper. If it is too short, you will have to put a spacer between the end of the hub and the steering knuckle to increase the front track. The photo below shows 2 aluminum wheels, one with the hub shortened by sliding it back and forth over a piece of #120 grit sandpaper on a smooth flat surface.



8. Now disassemble the beams, knuckles, and tie rod, being careful not to bend or break any pins.

9. At this point the appropriate instructions depend upon whether you intend to have your front wheels a) spin on fixed stub axles, like a stock magracer or b) not spin on stub axles which themselves spin in the steering knuckles, as is common for some 1/32 slot cars. Avoid pinching the king pins on the steering knuckles, so that you do not bend or break one. A pair of tweezers comes in handy here.

• a) If you intend to have your front wheels spin on fixed stub axles, like a stock magracer

• • 1. Make sure that your stub axles are the appropriate length. The distance between the front wheels can be reduced by shortening the wheel hub. The distance can be increased slightly by putting a spacer on the stub axle between the wheel hub and the steering knuckle.

• • 2. Verify that your wheels spin freely, without wobble on your stub axles. If not, correct before proceeding. I recommend that you glue your tires onto your wheels and then sand as needed to make them perfectly round. The diameter of the hole in the wheel should be about .002” larger than the diameter of the stub axle.

• • 3. Locate the hole for the stub axle in each steering knuckle. Ream out those holes so that they are about .001” smaller in diameter than the stub axles. If you are using 3/32 stainless steel rivets for stub axles (which measure .095”) , a 3/32” (2.38mm) drill bit should work fine. If you are using 2.50mm machine screws for stub axles , (which measure .096”) a #41 (.0960”) (2.44mm) drill bit will probably be okay.

• • 4. From the outside of the wheel, slide a 3/32” or 2.5 mm stub axle through the bore of a front wheel. Now place a washer/spacer on the protruding axle, if needed to increase the distance between the front wheels. Then, if a rivet, press the end of the stub axle into the hole in the Left or Right steering knuckle, as appropriate. If a machine screw, screw it into the appropriate knuckle. Leave about .005” of side play so that the wheels will spin freely on the stub axles.

• b) If you intend to have your front wheels NOT spin on stub axles

• • 1. Locate the hole for the stub axle in each steering knuckle. Ream out those holes so that they are about .004” larger in diameter than the stub axles. If you are using 3/32 stainless steel rivets for stub axles (which measure .095”) , a #40 (.0980”) (2.50mm) drill bit should work well. For 2.50mm machine screws, try a #39 (.0995") (2.53mm) drill bit, then #38 if needed. When enlarging the hole, do it in steps starting with a 3/32" bit and gradually increasing the diameter as needed. Beware, don’t squeeze the pins on the knuckles when reaming out these holes.

• • 2. Reduce the diameter of the head of your stub axles to less than .125” (3.18mm) and the head thickness to less than .035" (.89mm). Grinding steel rivets down with a Dremel is fairly easy but time consuming. The head diameter can be quickly reduced by spinning the head against a file using an electrically powered drill. The plastic stub axles that come with many Fly slot cars work very well. It is very easy to change the length and head dimensions of these by sanding.

The 3/32" diameter stainless steel rivet on the left was used to make the stub axle on the right. The length, head diameter, and head thickness were all reduced. The stub axle will be presssed into the wheel. Then the plastic wheel insert will be pressed on to the wheel.


A stainless steel rivet like the one on the left was used to make the stub axle on the right to fit the wheel, after the width of the wheel and tire had been reduced by sanding.

• • 3. Make sure that your stub axles are the appropriate length. The distance between the front wheels can be reduced by shortening the wheel hub. The distance can be increased slightly by putting a spacer on the stub axle between the wheel hub and the steering knuckle. Assuming you are not using any spacers to increase the front track, the length of the stub axles under the head should be equal to the length of the hole in the steering knuckle (.205”), + the depth of the hole in the wheel hub + .005" for a little side play.

• • 4. Verify that your wheels do not wobble when spinning on a 3/32" axle or drill bit. Also verify that the stub axles spin freely in the steering knuckles, first without, and then with the wheels attached. Also . Correct any problems before proceeding. Consider gluing your tires onto your wheels and then sanding as needed to make them perfectly round.

• • 5. Slide a 3/32” or 2.5 mm stub axle through the hole in the Left or Right steering knuckle, as appropriate. Now place a washer/spacer on the axle, if needed to increase the distance between the front wheels. If a rivet, press the end of the axle into the hub of a wheel. I do not recommend gluing wheels to the stub axles with CA glue because you probably won't be able to adjust or separate them. If using a machine screw, screw it into the hub. Leave about .005” (.127mm) of side play so that the wheels will spin freely.

10. Attach the knuckles, with the front axles and wheels, to the upper and lower suspension beams. An easy way to do this is to place the lower beam across a block of wood 1.5” wide and about ½” thick and 3” long. Place the bottom pin of each knuckle in a hole at the end of the beam. Then place the upper beam on top making sure to line up the pins of the knuckles with the holes in the beam. Press the upper and lower beams together with the steering knuckles and wheels attached and set this aside.


The photo above is one of a frontend assembly using front wheels from a SCX slot car and method b, with spinning stub axles made from stainless steel 3/32" rivets.


The photo above is one of a frontend assembly using front wheels and plastic stub axles from a Fly slot car. The stub axles spin in the steering knuckles.


The photo above is one of a frontend assembly using stock front magracer wheels and method a, with fixed 1/16" diameter stub axles.

Be careful handling the guide arm so as not to break or bend the pin.

11. Now press a neodymium 4mm dia x 3mm thick magnet into the guide arm. Make sure that the magnet is oriented so that the polarity is the same as that of the two 3mm dia x 2mm magnets pressed into the frame earlier. All 3 magnets must be orientated the same way, either all with the positive (+) pole facing up, or all with the negative (-) pole facing up. If oriented correctly, the magnet in the guide arm will be repelled by the magnets in the frame, so as to naturally center the magnet in the guide arm in the large hole in the frame, as depicted in the photo below. The bottom of the magnet should protrude about .010” - .015” below the bottom of the guide arm. A 4mm x 3.25mm magnet should also work.



12. Now thread a stainless steel pan head machine screw, 2mm dia x 14mm long, through the other hole in the guide arm. Just before snugging the head down on the guide arm, apply a drop of CA glue under the head. Now tighten until snug. The head of the screw should be flush with or recessed below the bottom edge of the guide arm. See photo below.



13. Now pick up the upper and lower beams with the attached wheels and carefully insert the pins of the tie rod into the holes in the knuckles. Do not attach the guide arm at this time.



Please contact me by PM, if you find a mistake in the instructions or have a suggestion for improving them.

Part 7: Completing Front of Chassis

1. Attach the frontend assembly (with wheels and tie rod) to the base frame using 2 screws, by inserting the screws through the holes from the bottom of the frame. These screws do not need to be long enough to protrude completely through the upper suspension beam. Stainless steel screws work best but regular steel will also work. While attaching the frontend assembly to the base frame, hold the frame and suspension beams together, so that the lower beam is tight against the spacer molded into the base frame. Stainless steel pan head machine screws 2mm x 10mm long work fine without using nuts. No. 2 pan head screws ⅜” long also work, but you may have to enlarge the holes in the base frame and lower beam (not the upper beam) to handle the bigger diameter screws. A #45 (.0820") (2.08mm) drill bit should work fine for enlarging the holes for No. 2 screws.

2. If need be, adjust the gap between the front of the coil and the 2 magnets glued to the tie rod. This gap should be .010" - .0015". The typical business card is about .013” thick, so it works well as a feeler gauge. If the gap is too large, loosen the screw holding the coil to the frame, slide the coil forward, insert the appropriately sized shim, and re-tighten the screw. If the gap is too small, you can remove the paper on the end of the coil to provide clearance between the coil and the magnets. You could also reduce the thickness of the rear face of the coil bobbin by sanding. This coil must be adjusted and mounted securely in the frame before the motor is glued to the frame. See photos below.



3. Turn the chassis upside down and insert the plastic pin on the guide arm between the magnets on the tie rod while inserting the machine screw through the hole in the bottom suspension beam. See photo below.



4. While holding the guide arm in place, turn the chassis over and secure the guide arm to the suspension beams with a Nylon-Insert Locknut, which fits the machine screw that is attached to the guide arm.

Please contact me by PM, if you find a mistake in the instructions or have a suggestion for improving them.

Part 8: Assembling Rear End

1. First enlarge the bores in the motor pod to fit your axle precisely. Make the diameter of the holes in the axle supports .004” -.006” larger than the diameter of the rear axle. A #40 (.098’) (2.50mm) bit should work fine for a 3/32" axle. If you have a long 3/32" bit, ream out holes in both axle supports simultaneously to minimize any misalignment of the holes. Then follow with a short #40 bit. To check for the correct clearance, slide an axle through the axle supports. Hold one end of the axle and swing the pod hanging from the axle. It should swing back and forth freely without any slop/play.

2. Now determine the appropriate length for your 3/32" rear axle and cut it shorter if needed. The length will probably be dependent upon the width of the body at the rear wheel wells and the width and style of the wheels.

3. If you haven't yet done so, carefully slide the motor pod on to the tail of the frame. The motor pod should slide easily onto the frame. Do not try to force it on. If it does not slide easily, smooth the bottom of the pod, by sliding it across a piece of super fine sandpaper (#600 grit) placed on a smooth flat surface. Also, sand lightly the top edge of the tail of the frame where the motor pod slides onto the frame.

4. Now slide your 3/32" rear axle through the right hand axle support post on the motor pod, then through the crown gear and then through the left hand axle support post.

5. Slide spacers on both ends of the axle to create the desired rear track. The amount of axle exposed at both ends should be the same. See photo below.



6. Now attach both wheels to the axle, leaving about .003” of side-to-side play/slop. The axle with wheels should spin freely. See photo below.



7. Slide the motor pod with wheels and axle to establish your desired wheelbase. Lock this wheelbase in place using a small screw and nut as shown in the photo below.



8. Verify that the weelbase fits the wheelwells of your body. Also verify that there is room for the crown gear. You may have to remove some of the ducting on an LMP blody and also some of the interior. Before removing any mounting post molded into the body, consider whether it may be useful to you in mounting the body to your new chassis. Once the motor is glued to the frame you won't be able to adjust the wheelbase.




9. If need be, attach an 8 tooth pinion gear to the motor shaft. To do this, press the gear part way onto the shaft. Then cut a jig from a piece of card about .010" thick and slip it around the shaft as depicted in the following photo. Now with the gear on a smooth flat surface press the motor down until it’s tight against the card jig. Remove the jig and you now have a perfect gap between the motor housing and the gear.



10. Solder 2 thin, and very fexible wires about 1.0" - 1.4" long to the terminals on the motor. Multistrand copper is best because it is very flexible.

11. Determine where the motor must be located so that the crown gear does not interfere with the body. Now glue the face of the motor, without the identifying numbers, onto the frame. Before doing so, scratch up that face of the motor with sandpaper to improve adhesion. The black end of the motor should be snugged up against the rib on front edge of the motor pod. This helps to maintain proper alignment of the motor shaft and the axle. Five-minute two part epoxy glue works well to glue the motor onto the frame. It is slow to cure, compared to CA glue. This allows plenty of time to precisely locate the motor. CA glue, such as Krazy Glue, also works, but permits about 2 seconds for adjustment.

12. When the glue is cured, fasten the crown gear to the axle so that it meshes properly with the pinon gear on the motor.

Please contact me by PM, if you find a mistake in the instructions or have a suggestion for improving them.

Part 9: Wiring PCB to Coil & Motor

1. If the wires from the coil are not yet soldered to the PCB, now is the time to do it. The wire emerging from near the back of the coil, should be soldered to the terminal on the PCB nearest the front of the coil (on the corner of the PCB). The wire coming from the front end of the coil, nearest the 2 magnets on the tie-rod, should be soldered to the terminal on the PCB that is next to the front most terminal. See photo below.

2. Connect the wires from the motor to the PCB as shown in the photo below. Note that the motor in the photo below is glued to the frame so that the identifying numbers on the motor are visible. When wired as shown, the negative (-) terminal on the motor is connected to the terminal on the PCB that is located on the corner of the PCB.




Top view of completed Chassis


Bottom view of completed chassis.

Please contact me by PM, if you find a mistake in the instructions or have a suggestion for improving them.