A " How To " Article on Building a HO Dyno

by David Parker    

I first met Dave Parker, by name and face, during this year's re-running of the 1969 Southern 500 at MOPAR Mountain. As I walked past his "Pit Tent" located above the race complex I noticed what seemed to be a dyno on his work bench. Dave was inside the Motorplex running some practice laps so I asked his tent city neighbor, Tom Bowman, just what did we have there? To my delight it was indeed a HO Scale Dyno and yes, Mr. Parker was selling them. Well, it seems he had sold all he had with him but not only did he offer to build one for those who asked for a rain-check at the event but also offered to write-up a how to for the DPR website ..... so without further ado, your step by step guide to make your own " Rocket City HO Speed / Checker Dyno "

 

 

 

Photos tell the tale as far as modifying the basic box.  First photo (Dyno photo 31) shows the additional parts needed (100 ohm pot, power jacks, SPST switch, and knob for the pot), all available at Radio Shack.

(Dyno 31)

(Dyno photo 32) shows the box split open, and the electronic panel removed.  This makes it easier to work on the top piece.  At this point, check the rollers and axles to make sure they spin true.  Swap out parts if they don't.

( Dyno 32 )

( Builders Note )The only parts that are needed to complete the dyno are the middle axle with the gear and rollers.  If the axle does not turn true (the middle gear wobbles) it can be swapped out with either of the other two axles.  If one or both of the rollers on that axle do not spin true (check against the edge of the opening to look for runout), they can be swapped with one of the other large rollers (although those rollers will need to be glued in place).

(Dyno photographs 33-35) show the top stripped down, then the cuts made to free the center piece, and finally the center piece moved to its new location.  The (Dyno photo 36) shows a mod I did this time around ... I glued some small styrene pieces to the center piece to help it sit flush in its new location, then glued the assembly in place.

         

                                                                 ( Dyno 33 )                                                                                   ( Dyno 34 )

 

 

         

                                                                                  ( Dyno 35 )                                                                                                   ( Dyno 36 ) 

 

The next shot (Dyno photo 37) shows the top view.  I added a 3 7/8 square piece of 1/8 in plexiglass (Home Depot) to provide a flat surface.  I secured it with two bolts (so I can remove it and clean out the junk after drilling the rest of the holes).  I drilled holes in the end and installed the power jacks, then drilled holes for the On/Off switch and the pot and installed them.  All that's left is to wire everthing together, add some power leads for the car, and reassemble the original hardware.

( Dyno 37 )

(Dyno photo 38)  In my opinion, this is the most critical step. After setting up the axle and rollers you have chosen to use, reinstall the assembly as shown.  Spin it a few times to ensure there is no rubbing anywhere.  I have found that sometimes moving the middle section results in minor rubs.  Listen and feel for contact, and use an Exacto to trim away plastic where necessary.  Reinstall the gear assembly, and make sure the white gears line up but do not bind.  Washers may be needed to move the assembly a little higher so the gears don't bind.  Once everything spins freely, you are ready to continue.

( Dyno 38 )

(Dyno Photo 39)  Run wires as shown.  I use stranded wire as it bends easier. And I just realized I missed photographing one step.  You'll need to drill holes for the guide pin and power braids.  Look at (Dyno Photo 42) as a reference.  Set a chassis (without guidepin) on the rollers so the wheels are in the center half of the roller.  Insert a small drill bit through the back hole where the guidepin would normally be and drill the hole.  Then mount a guidepin on the car and place the car on the box with the guidepin in the hole.  Make sure everything lines up right, mark a spot just in front of the shoes for the power taps, and drill your holes.  I had been using 1/32 slot car braids for the power taps, but that's a timeconsuming proces so on this box I tried just using wire.  The power comes through fine, but the wire does not lie as flat as the braid, and I will probably rework this one.

   

( Dyno 39 )

(Dyno Photo 40)  Cut off the posts on the bottom section as shown.  Also cut off the two shown at the very top of the photo as they may interfere with the power jacks. (I'm not certain any of them are really needed, but they may help if you accidently step on it) Look closely and you will see a small area above the speaker and slightly left of it that I grooved with a dremel ball bit.  The box comes with a groove above and to the right of the speaker for gear clearance.  When you move the big white gear, there MAY be contact with the bottom of the box once you reassemble it.  I never noticed it before, but on this box it did rub.

  

( Dyno 40 )

(Dyno Photo 41)  Almost done!  Put the electronics plate back in place, making sure the small glass piece stays aligned (you may have noticed it is not attached when you pulled the box apart).  Also make sure you get the buttons back in the right holes.  Once the plate is installed, secure the optical reader piece in place.  Then close up the box, making sure not to pinch the wires.

  

( Dyno 41 )

(Dyno Photo 42)  The completed Dyno / Speedchecker.  You'll need to add two AA batteries for the electronics to work.  I also add a small plexiglas piece just to keep things from falling into the open hole behind the rollers.  All you need to do now is hook up a power supply/transformer.

   

( Dyno 42 )