MAGracing Forum

Following are detailed instructions for building a short and narrow 1/32 scale chassis, using Chassis Kit CK1 which can be purchased at
https://www.shapeways.com/product/QXW7Q ... d=60568679 .

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 1/32 small body, are covered in these instructions.

Part 1: Introduction

This kit is comprised of Base Frame BF1, Frontend Kit FK1a, and Motor Pod MP1a. If there is any demand, I can make the three components available separately, but it will cost less to buy them together as Chassis Kit CK1. The wheelbase of CK1 is adjustable from 2.80” to 3.40”. The chassis is only 1.85” wide. The frontend has 1 degree of positive toe and 2 degrees of negative camber. This eliminates frontend shimmy at high speeds, even when using the original stock front wheels. The lack of shimmy improves handling and lane change reliability.

CK1 is intended to be used with the original stock front stub axles and wheels, a stock rear axle and wheels, as well as stock gears. It is assumed that you also have 3 critical components, a motor, a steering coil, and a printed circuit board (PCB) for the chassis. 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 when brand new. Even so, the chassis exhibits no frontend shimmy at any speed. CK1 is ideal for someone who has a magracer but would like to marry it to a smaller, more detailed body, and doesn’t want to go to the expense of buying new wheels, tires, and axles.

If you have a favorite small 1/32 slot car, that you want to convert to a magracer, and you want to use all 4 wheels, tires, rear axle, and of course the body, you probably should buy the following components separately: BF1, FK1b, and MP1b. The later two items are intended for 3/32” (.0938”) (2.38mm) axles. Buying the 3 components separately will cost a little more but you are likely to get better results.

The only difference between FK1a and FK1b is the size of the holes in the stub axle carriers (steering knuckles). In FK1b, the knuckles have larger holes, to accommodate 3/32” stainless steel rivets, or 2.5mm diameter stainless steel machine screws, for front axles. You will have to clean out the nylon powder in the holes in FK1a or FK1b and perhaps enlarge them slightly. Of course larger diameter stub axles can be used in FK1a, but that will require the bores in the knuckles to be made significantly larger, which greatly increases the likelihood that the holes will not be aligned precisely. MP1b also has larger holes to accommodate bigger rear axles. The bores in the axle support post still have to be reamed out just slightly to get a perfect fit.

I do not recommend trying to change the diameter of the bore in a wheel hub unless you have a lot of experience at this. Most of my attempts have failed. The exception was enlarging the bore in front wheels 2 to 3 thousandths of an inch so they would spin freely on the front stub axles.

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, a small pair of scissors, and a fine tooth saw, most, but not all 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 a body. That kind of tool is
not needed, and should not be used, to build the chassis. A digital caliper may also come in handy during assembly and mounting the body but is not required.



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:
.0595" (1.51mm) #53
.0625" (1.59mm) 1/16"
.0670" (1.70mm) #51
.0700" (1.78mm) #50
.0730" (1.85mm) #49
.0750" (1.90mm)
.0760" (1.93mm) #48
.0781" (1.98mm) 5/64"
.0820" (2.08mm) #45
.0860" (2.18mm) #44

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

Download the attached pdf file to see a table of additional hardware and components needed to complete a car.

Part 4: Separating Plastic Parts

The picture below shows what you'll receive from Shapeways.




1. Using a sharp knife or sprue cutter, separate the base frame from the motor pod.

2. Remove any remaining sprue or burrs on the frame or pod by sliding the rough edge of each piece across a piece of fine sandpaper placed on a smooth flat surface.

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

4. 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. If that doesn’t work, try reducing the depth of the tongue, and thus the overall width of the pod, by sanding each side just a little.



5. Using a sharp knife or a sprue cutter, carefully separate the 6 pieces of the frontend kit. 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 of the frontend 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.


6. Remove any remaining sprue or burrs with a sharp hobby knife, emery board, and fine sandpaper.

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. Now press a 5mm diameter neodymium magnet into the hole in the end of the battery box, for the pos (+) terminal. To do so, 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 1.25mm - 3.0mm 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.

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. With a pair of small scissors, trim off the corners of paper on the end of the steering 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. Press down on the top of the coil until the bottom of the plastic coil bobbin is flush with the bottom of the frame. Now tighten the screw to hold the coil in place.

6. Now attach the PCB to the frame using a #1 pan head screw 3/16” long. 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 antenna wire is under the board and runs between the back of the coil and the wall of the battery box. Also make sure that one corner of the board is under the nub located on the wall of the battery box. Be careful not to over tighten the screw. 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. You may want to remove this white socket to provide more room for the cockpit. See photo 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

1. Determine the correct orientation of the polarity of the two neodymium 5mm dia x 3mm thick magnets to be glued into the box on the tie rod. 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, simultaneously 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 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.

• 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.

2. Ream out the hole farthest from the kingpins, in each of the stub axle carriers (steering knuckles) using a #50 (.070”) (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 bit. Do not use a bit larger than #50. Just run a #50 bit back and forth through the hole from both sides. Continue reaming out the hole from both the top and bottom until it is just the right size. 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 photos below.





4. Now put the upper and lower suspension beams together. Simultaneously ream out the holes at the end of the beams with a 1.90mm (.0748”) 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 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”) bit. 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. Verify that your front wheels spin freely on the stock front stub axles. If not, correct this before proceeding.

9. Now disassemble the beams, knuckles, and tie rod. Put a stock stub axle through the bore of a front wheel and press the axle into a hole in the steering knuckle. Ream out the hole first with a #53 (.0595”) (1.51mm) drill bit, which should be large enough for the .0625” diameter axle. Leave about .005” of clearance between the hub of the wheel and the side of the knuckle, so the wheels 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. If you have trouble keeping these pieces together, you may want to put a small, very thin piece of double faced tape in the middle of the lower beam, before placing the upper beam on top. Press the upper and lower beams together with the steering knuckles and wheels attached and set this aside.



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. 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. If the magnet seems too large to press into the hole, dip the end of the guide arm in hot water to soften the plastic and try again.

12. Now thread a stainless steel pan head machine screw, 2mm dia x 14mm long, through the other hole in the guide arm. Tighten until snug. The head of the screw should be flush with or recessed below the bottom edge of the guide arm. Be sure not to over tighten this screw. Doing so will strip the threads cut by the screw and cause the screw to spin freely in the hole of the guide arm. If this happens use a drop of CA glue to prevent the screw from spinning in the 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.

14. Attach the guide arm to the suspension beams with a stainless steel Nylon-Insert Locknut, which fits the machine screw that is attached to the guide arm. Take care inserting the pin on the end of the guide arm, into the slot in the tie rod. Use a screwdriver to prevent the screw from turning while the nut is tightened or loosened. When the beams of this assembly are held in a vertical orientation, and rotated back and worth, the tie rod should move freely allowing the wheels to turn left and right freely. A frontend assembly is pictured below.



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. Ream out the holes in the suspension beams, with a 5/64” (.078") (1.98mm) drill bit. Now with the same bit, ream out the corresponding holes in the base frame.

2. Attach the frontend assembly (with wheels) to the base frame using 2 screws, by inserting the screws through the holes from the bottom. 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. Pan head machine screws 2mm x 10mm long work fine without using nuts. No. 2 pan head screws ⅜” long also work. Stainless steel screws work best but regular steel will also work. These screws do not need to protrude through the upper suspension beam.

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



4. Now 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 in the U.S. is .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. This coil must be adjusted and mounted securely in the frame before the motor is wired to the PCB.

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. If you are reaming the holes with a hand-held pin vice, make the diameter of the holes in the axle supports .003” -.006” larger than the diameter of the rear axle. A 2mm diameter axle normally needs .082” - .085” holes in the axle supports. A #45 (.082’) (2.08mm) bit should work.You may need the slightly larger #44 bit. If a long bit is available, ream out holes in both axle supports simultaneously to minimize any misalignment of the holes. 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 the 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. Relocate the 30 tooth spur gear on the axle if needed. 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 through the hub of the gear to attach the right wheel and the correct amount extends through 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 through the hubs of both wheels. The amount extending beyond the hub of the gear on the right side should be the same as the amount extending beyond the collar/spacer on the left axle support.

4. 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.



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

6. 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.



7. 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.

8. Now slide the 2mm rear axle through the axle support posts on the pod with a 30 tooth spur gear mounted on the axle.

9. Make a shim .042”-.043” thick by .75” wide and 1.0” - 1.5” long. A business card or index card along with some tape can be used to make a shim.

10. Place the pod on a small block of wood, deck of playing cards, or similar object with the spur gearing hanging over the edge.

11. Now place the motor on the pod with the shim placed between the motor housing and axle. Make sure that the + terminal of the motor is located in the upper righthand corner when looking at the black end of the motor. The shim will be used to perfectly align the motor with the axle. Snug the motor up against the shim and rotate the axle to see if the gears mesh properly. If not, adjust the thickness of the shim.



12. Before gluing the motor to the pod, scratch up the bottom of the motor with sandpaper to improve adhesion. Glue the motor onto the pod. When the glue is dry, the motor should be centered on the pod with one side of the motor snugged up against the shim and axle. Five-minute two part epoxy glue works well for this. It is slow to cure, compared to CA glue. This allows plenty of time to precisely locate the motor. I prefer CA glue, such as Krazy Glue, but beware, it permits about 1 second for adjustment. Be careful with any glue or you’ll end up gluing the shim in place. Remove the shim after the glue has set.



13. When the glue is cured, firmly press the right rear wheel onto the axle until it contacts the spur gear. If need be, first slide a washer/spacer on to the axle.

14. Slide the axle through the bores in the axle supports of the motor pod. If needed, slide a washer/spacer over the axle and then press the left wheel onto the axle leaving about .003” of side-to-side play/slop.

15. Now slide the motor pod onto the frame. If vertical clearance under the body is extremely limited, first run one or both wires from the motor through the holes in the battery box as shown below. This requires very flexible wire.



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 doing any wiring, 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. A Dremel tool is handy for this. You may also find that part of the car interior prevents you from positioning the body properly, compared to the front and rear wheels. Before cutting out part 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, 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 fasten the 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. 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. The consequence of this is that these wires cross over one another when attached to the PCB.

8. Solder the wires from the motor to the PCB as shown in the photo below.



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