s e e f igure 6. You can of course order the p l u g d i rec t l y as separate piece; the size 3.5 mm x 1 . 3 5 m m (x mm length, not that important ) wo r ks b e st . Then a scrap 9 V LEGO electrical w i re i s s o l d ered to the plug. As nex t step I reco m m en d i n co r porating the bridge rectifier into the c h a rg i n g cable. The “ +” terminal is soldered to t h e c enter contact and the “–“ terminal to th e o u te r co ntact of the plug. Nex t, both “~” (or AC ) te rm i n a ls of the bridge rectifier are conne c te d to a 1 x 2 electrical plate, polarity does not m atte r, s e e f igure 6 for details. Note: For the “ p i c k- u p o n l y ” motor, see figure 4 bottom, you co u l d a l s o u s e 9 V wire with 2x2 electrical plate. W h e n you go with the “power pickup and m o to r ” ve rs i on (figure 4 top), then you need to m a ke a n o t h er wire for th e connection of the PF rec ei ve r o u t p ut to the motor “in” terminal. You ca n e i t h e r u s e a standard LEGO 9 V wire, as shown i n f i g u re 7 , o r directly use a cable with a PF termin a l ( e . g . a # 8 886 PF ex tension wire). I recommen d u s i n g t h e 9 V wire though since it is far more f l ex i b l e t h a n the PF wire and as a result, the trai n m o to r p i vo t s much easi er.
Figure 6 : P h o to g r a p h s o f t h e L i Po c h a r g i n g ca b l e. Top: Com plete a s s e m b l y. B o tto m : C l o s e - u ps o f t h e s o l d e red parts. Left: 1 x 2 ter m i n a l fo r t h e “p ow er p i c ku p a n d m o tor ” version (see fig u r e 4 , to p ) . R i g ht : B r i d g e r ec t i f i er a n d D C plug.
Figure 7 : P h o to g r a p h s o f t h e m o d i f i e d 9 V t r a i n “motor-in” cable.
c ) C onnect the LiPo to a PF receiver a n d t h e c h a rging line. W i t h the two custom cables and the m o d i f i ed m o tors we can assemble a “best of both wo r l d s ” P F/ 9 V train. Figure 8 shows the princ i p l e o f o p e ration.
O n l y t wo co m b i n at i o n s a re s h ow n i n f i g u re 8 , o t h ers wo r k a s we l l : Yo u m ay co m b i n e m o d i f i ed 9 V t ra i n m o to rs a n d RC m o to rs a s yo u w i s h , f i g u re 9 s h ows o n e exa m p l e . S i n c e t h e L i Po / P F re c ei ve r co m b i n at i o n ea s i l y h a n d l e s t wo o f t h es e o n o n e o u t p u t , t h e s eco n d c h a n n e l i s a l ways f ree fo r o t h e r st u ff.
4 ) Pe r fo r m a n c e m e a s u re m e nt s I u s e d s u c h a s et- u p to b u i l d a rat h e r co m p a c t 2 - m o to rs - P F - rec e i ve r- co nt ro l l e d “te st bed” s h ow n i n f i g u re 9 to a s s es s t h e p e r fo r m a n c e o f t h e L i Po i n a m i xed P F/ 9 V env i ro n m e nt . T h e t ra i n wa s r u n n i n g o n a fa i r l y l a rge st retc h o f 9 V t ra c k. I t p u l l ed a to ta l o f 1 0 ca rs , a s s h ow n i n f i g u re 1 0 . T h e l ayo u t feat u red t wo reve rs i n g l o o ps , e a c h e l e c t r i ca l l y i n s u l ate d w i t h o n e p i e c e o f c u r ved RC p l a st i c t ra c k a n d s o me n o n - p owe re d s e c t i o n s b et wee n t h e p o i nt s o f a 4 - sw i tc h p o i nt c ro s s ove r. Pa s s i n g t h e revers i n g l o o ps l e a d n e c e s s a r i l y to a p o l a r i t y c h a n ge o f t h e vo l ta ge p i c ke d u p by t h e m o d i f i e d m o to r. T h e 9 V ra i l s we re p owe re d at s evera l p o i nt s w i t h t ra i n co n n ec t i o n w i res ( # 1 0 0 6 7 ) to p reve nt vo l ta ge d ro ps a l o n g l o n g st retc h e s o f t ra c k. A s fa r a s I a m co n c e r n e d , t h i s re p re s e nt s a fa i r ly to u g h te st t ra c k . E x p er i m ent 1 : No p owe r o n t h e t ra c ks . T h e L i Po b atte r y wa s f u l l y c h a rge d . T h e P F o u t p u t p owe r l evel wa s s et to “ 3 ” o n b o t h P F re c e i ver o u t p u t c h a n n e l s . T h e t ra i n sta r te d re a d i l y a n d p u l l ed t h e ca rs stea d i l y t h ro u g h s e r i o u s c u r ve s a n d s o m e s e c t i o n s o f st ra i g ht t ra c k 3 . T h e b r i g ht n e s s o f t h e L E D l i g ht s n eve r c h a n ged . I m ea s u re d t h e t i m e re q u i re d fo r o n e ro u n d rep e ate d l y. We l l , i t wa s b o r i n g . A f te r 2 h o u rs I t h o u g ht I wa s d o n e , s i n c e t h e t ra i n sto p p ed . I s o o n f i g u re d o u t t h at t h i s wa s j u st t h e i nte r n a l L i Po t i m er, w h i c h t u r n s t h e el e c t ro n i c s o ff af ter p rett y m u c h exa c t l y 1 2 0 m i n w h en t h ere i s n o D C c h a rg i n g vo l ta ge p res e nt … af te r 4 h o u rs , t h e ro u n d t i m e i n c rea s e d s i g n i f i ca nt l y a n d s o o n af te r t h at t h e L i Po wa s e nt i rel y f l at . 4 h o u rs r u nt i m e, wow ! I h ave to a d m i t , wa s d ee p l y i m p re s s e d . 3 The layout is built into my office under the roof of our house; it goes “through” book shelves and underneath my desk. As illustration, see the end of this video taken with a camera mounted on a train: ( http://w w w.youtube.com/ watch?v=wTP6WtcnQbg )
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