MAGracing Forum

Following are detailed instructions for building a large 1/32 scale chassis, using Chassis Kit CK2, which can be purchased at
https://www.shapeways.com/product/LUTD9 ... racing-car

The kit is available in white or black. 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 large 1/32 body, are covered in these instructions.

Part 1: Introduction

This kit is comprised of Base Frame BF2, Frontend Kit FK2, and Motor Pod MP2. The wheelbase of CK2 is adjustable from 3.20” to 3.80”. The frame is 2.05” wide. The frontend has 1 degree of positive toe and 2 degrees of negative camber. This eliminates frontend shimmy at high speeds. The lack of shimmy improves handling and lane change reliability.

CK2 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. This opens up unlimited possibilities for magracing. 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.

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 front end. 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. How about the head lights? Determine and record the wheelbase and front track that you want. In most cases you will want a front track that is shorter (narrower) than the one of your slot car.

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 attach the front wheels to the steering knuckles, the same as Fly or Scalextric. This looks better since you won't have the head of a rivet or screw showing. 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.

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. The exact length (under the head) should be about .21" longer than the length of the bore in the hub of the wheel. If the wheel is made out of plastic, and the hub is too long, you can reduce the length of the hub by sanding off some of the hub protruding beyond the inside edge of the wheel. This is typical. Another alternative stub axle is 2.5mm diameter Stainless Steel Metric Pan Head Phillips Machine Screws with fine thread. The 3/32" rivets I purchased from McMaster-Carr measure .095", a little over 3/32". The 2.5mm Machine Screws measure .096", slightly under 2.5mm. 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. However, screws may wear out the holes in the wheels or steering knuckles sooner, (Which one depends on how the screws are attached).

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 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 off the shelf. As of November 2016, they aren’t available on eBay either.

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. 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, if you choose to attach the stub axles so they don't spin. That should not be a problem with the right drill bit. If you are using the 30 tooth rear axle gear from a stock magracer, you’ll have to enlarge the bore, to be able to press it onto a 3/32” rear axle. CK2 allows you to use slightly larger and slightly smaller diameter spur gears. You may want to use the spur gear that came on your axle. Of course, changing the gear ratio changes 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.

Please contact me by PM if you have any questions or problems concerning assembly or operation of your chassis. Also, contact me 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. If you find a mistake in the instructions or have a suggestion for improving them, please let me know.

Part 2: Tools Required to Complete a Car

In addition to soldering gear, drill bits, and a fine tooth saw 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 is handy for removing mounting posts or other obstructions inside a body and disassembling the interior of a body. A digital caliper may also come in handy during assembly and mounting the body.



The sandpaper is 220 & 600 grit. The hex socket is 4mm. The diameter of the fishtail router bit with 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 USD 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 CK2.

Part 4: Separating Plastic Parts

The picture below shows CK2 in white, as received from Shapeways. It is also available in black.



1. Using a sprue cutter, separate all 9 pieces in the kit.

2. Remove any remaining sprue or burrs on the frame and the 2 pieces 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, round off slightly the top edge of the tail end of the frame, where the motor pod slides into the frame. Slide the bottom surfaces of the 2 small pieces across a very fine piece (400 - 600 grit) of sandpaper laying on a flat smooth surface. The bottom of both of these pieces must be 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, slide the bottom of the tie rod across a very fine piece (400 - 600 grit) of 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, try to round them up a tiny bit with an emery board. Do NOT shorten the pins. The stub axle carriers (steering knuckles) are symmetrical and the 3D model for the left one is identical to the right one. The negative camber is achieved by producing the holes for the king pins at both ends of the upper suspension beam, just a little inboard of the corresponding holes in the lower suspension beam.


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 as well as the groove on the inside of the motor pod.

6. Carefully slide the motor mounting plate onto the motor pod as shown below. The plate should slide easily onto the motor pod. Do not try to force it on. If it does not slide easily, smooth the bottom of the plate, by sliding it across a piece of super fine sandpaper (600 grit) placed on a smooth flat surface. Later the motor will be glued to this plate. This sliding plate allows for precise meshing of the gears.



7. 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 pod, by sliding it across a piece of super fine sandpaper (600 grit) placed on a smooth flat surface.



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

Part 5: Attaching Components 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. At this point, you may want to press a 5mm diameter neodymium magnet into the hole in the end of the battery box, for the pos (+) terminal. (This can be done later, and you may never do it, if you decide to use spring metal strip instead of a magnet at the positive terminal of the battery.) To insert the magnet, place the side of the chassis with the larger hole for the pos (+) terminal, on a smooth flat surface. Place the magnet on the blade of a screwdriver and press the magnet into the hole. The magnet can be 1.50mm - 5.0mm thick depending upon the amount of clearance between the edge of the chassis and the sides of the body. If the magnet is loose in the hole, you can later glue it into place with CA glue.

3. Press a 5mm diameter magnet into the hole in the battery box near the left rear wheel. This can be 2.0mm - 3.0mm thick. Be careful not to break the chassis. This magnet will be needed to keep the battery from falling out of the battery box.

4. 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.

5. 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. Press down on the top of the coil until the bottom of the plastic coil bobbin is flush with the bottom of the frame. Do not press it down until it is flush with the bottom edge of the reinforcing rib. Now tighten the screw to hold the coil in place.



If the coil is already wired to the PCB, attach the coil to the frame and then attach the PCB to the frame, as shown below. I decided to use spring brass/bronze strip for battery connectors for this chassis instead of magnets. These connectors can be added at a later time. For tips on how to use spring bronze strip for connector see Part 5 of viewtopic.php?f=28&t=642


In case you're wondering, the red wire under the PCB is an antenna.

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 one of them into the box on the tie rod. Make certain that it is oriented the same way in the box as in the stock magracer, with the black face 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 bottom and back of the box. CA glue such as Krazy Glue or Supper Glue works well for this. Two part epoxy adhesive also works. After the glue has cured for the first magnet, glue the other one in place. If oriented correctly, the magnets will naturally attract one another.

• 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 to the bottom and back 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 #51 (.0670” diameter) (1.70mm) 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 bit or a #50 (.070") (1.78mm) bit. Do not use a bit larger than #50. Just run a #50 bit back and forth through the hole from both sides. 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. Also, smoothing the inside faces of both beams where they come in contact with the steering knuckles may help reduce friction between the beams and the knuckles. A #600 sanding stick should work well for this.



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 that protrudes beyond the inside edge of the wheel. Usually all of the protruding hub has to be removed. The distance between the front wheels 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 .003” 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 .002” 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.

• • 2. Reduce the diameter of the head of your stub axles to less than .135” (3.43mm) and the thickness to less than .035" (.89mm). If made of steel, grinding it down with a Dremel is pretty easy. If made of plastic, sanding is even easier.

Stainless steel rivets like the one on the left were used to make the stub axles. Original and final dimensions were:
Shaft diameter - 3/32", 3/32"
Shaft Length - 1/2", .335"
Head Diameter - .20", .133"
Head Height - .038", .038"

• • 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 + the depth of the hole in the wheel hub + .005" for a little side play.

• • 4. Verify that the stub axles spin freely in the steering knuckles, with the wheels attached. Also verify that the wheels do not wobble when spinning. Correct any problems before proceeding. I recommend that you glue your tires onto your wheels and then sand 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. You may eventually have to glue the wheel to the end of the stub axle. 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 1.50” - 1.60” 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.


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


The photo above is one of a frontend assembly using front slot car wheels and method b, with spinning 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. (Note that the photo below is of a prior version of CK2.)



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 tightly 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 will have to enlarge the holes in the base frame and lower beam to handle the bigger diameter screws. A 5/64” (.078") (1.98mm) 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 attached to the tie rod. This gap should be .005" - .0015". A sheet of computer paper is about .004" thick. 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. If need be, 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 PCB is mounted.

3. Locate the hole that is used to attach the PCB to the frame. Attach the PCB to the frame using a No. 1 pan head screw 3/16” long. Make sure that the antenna wire runs under the PCB and between the back of the coil and the wall of the battery box. If you use a larger diameter screw, you will have to enlarge the hole. Be careful not to over tighten the screw.

4. At this point your chassis should look like the one depicted below.



5. Now turn the chassis upside down and insert the pin on the guide arm into the notch in the tie rod while inserting the machine screw through the hole in the bottom suspension beam. See photo below.



6. 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 .003” -.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 are using the stock 30 tooth spur gear from an existing magracer, enlarge the bore of the gear to 3/32". If not, obtain a 30 tooth spur gear, with the same pitch, for a 3/32" axle. A slightly larger diameter spur gear with more teeth, and the correct pitch, will also work but the top speed of the car will be slower and acceleration will be faster. The gear should be positioned on the axle so that when the gear is slid up against the collar on the right axle support, the correct amount extends beyond the hub of the gear to attach the right wheel and the correct amount extends beyond the collar/spacer on the left axle support to attach the left wheel. The correct amount is that which leaves both ends of the axle protruding the desired amount into or through the hubs of both wheels.

4. Now slide your 3/32" rear axle through the right hand axle support post on the motor pod, with a spur gear mounted on the axle. The spur gear should be located so that it rubs up against the spacer/collar on the right axle support post on the pod. Attach the right rear wheel to the axle. (In this case, I'm using the rear axle, wheels, and tires from a SCX slot car and a spur gear I happened to have on hand. The gear has a larger diameter and more teeth, so I know the top speed will be slower than a stock magracer.)

5. If needed, slide a spacer over the axle and/or shorten the wheel hub, and then attach the left wheel to the axle leaving about .003” of side-to-side play/slop. The axle with wheels should spin freely. See photo below.



6. 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.



7. Glue the motor onto the motor plate. Before doing so, scratch up the bottom of the motor with sandpaper to improve adhesion. The end of the motor with the pinion gear should be set back from the edge of the plate about .03" so that the pinion gear will mesh properly with the spur gear. (See photos below.) One side of the motor can be snugged up against one of the ribs on the plate to maintain proper alignment. Five-minute two part epoxy glue works well to glue the motor onto the plate. 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.







8. If needed, cut 2 pieces of insulated, thin, and very flexible wire about 3” long. Multistrand copper is best because it is very flexible.

9. Look at the black end of the motor and note that it is not symmetrical. In the photo below, the + terminal is in the upper righthand corner of the motor.



10. Solder each wire to one of the terminals on the motor. As depicted above, the wires will run to the left, so attach the wires accordingly.

11. Now slide the motor plate, with the motor glued to it, onto the pod until the pinon gears meshes perfectly with the spur gear. See photo below.



12. Now slide the pod onto the frame. If the vertical clearance between the cockpit and chassis is extremely limited, you might want to run one or both wires from the motor through holes in the battery box instead of over top of the battery box. This requires very flexible wire. Note that the wires used in these instructions and photos are not color coded.



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. Before connecting anymore wires, place the body over the chassis and slide the motor pod as needed to get the wheels to line up properly compared to the wheel wells. In order to do this, you may first have to remove some mounting posts molded into your body. Before removing any mounting posts, consider the possibility of using some to attach the body to your chassis. A Dremel tool is handy for removing these posts as well as other parts of the interior. Before removing most of the interior to get the body to fit correctly, consider the possibility of making a “photo cockpit”.

2. To make a photo cockpit, pop/pry the interior out of car. (A Dremel tool with a fishtail router bit would be helpful to loosen the interior at the points where it is attached.) Take a color photo of the interior from above and print it out on matte photo paper. Now remove the driver’s head from the stock interior. Poke a hole in the photo in the location of the head. Now glue the head in place on the photo. Trim the photo and tape or glue the photo, with the driver’s head attached, to the interior of your car.

3. After getting the wheelbase adjusted so that the wheels line up properly with the wheel wells, remove the body and set it aside.

4. If the excess tail of the frame doesn't show under the body, I suggest that you leave it on. But If you want to cut it off, now is the best time to do it. Draw a line at the end of the motor pod and across the the frame to indicate where the tail should be cut off.

5. Now cut off the excess tail of the frame. A fine tooth saw works well for this. (Even a hack saw blade will do. I do not recommend large scissors for this.) If you think you might want to lengthen the wheelbase sometime, you can leave a little extra on.

6.Verify that the motor pod is still located where you want it and that the gears still mesh properly. Now fasten the motor plate and pod in place with a pan head, machine screw, 2mm x 5-8mm long with matching nut. Stainless or regular steel will work fine for this.

7. Now solder the coil wires to the correct terminals on the PCB. 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.

8. Connect the wires from the motor to the PCB as shown in the photos below. The second photo is of an earlier version of CK2. If needed, route one or 2 wires through the holes in the battery box to minimize interference with the cockpit.




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