hpi s plastic transmission gear set (18€ or 13$) are not suitable for use with powerfull brushless motor systems. read below to rectify this issue with a relatively small budget.
this would be unnecessary if only RC4WD had not discontinued their steel hardened gears!
thanks to "Snoopmax" for the online informations provided about the gear sizes available.
1) 15Tooth Mod1 5mm shaft gear. (available for other rc cars) (30 € in france, 10 $ in usa)
2) 22Tooth Mod1 5mm shaft gear. (available for other rc cars)
- find a 5mm shaft to attach the 22 tooth gear on. be carefull to cut it to the most appropriate lenght. i cut it too short and place some common small 5mm hollow metal discs on both sides to adjust the position of the gear with the other gears of the tranny.
3) the 28 tooth plastic gear in the bottom could last longer but i am preparing a home made metal version of it in soft steel from a random stick:
-make the shape of the metal very roughly round with a saw and tough file and dig a 6 mm hole in the centre with an exact 90° angle shaft drill system.
-screw it tightly onto a screw bolt (as shaft) and attach it onto the vertical immobile drilling system. I rotated the drill-fixed-metal-gear applying pressure on the edges with a hard file. The file being immobilised in such a way it applies pressure on the metal being circlized. This lasts hours before the circle comes to perfection. This way you make sure it is perfectly circular instead of elliptic if you were holding the file by hand.
-once the filed up "gear" has the appropriate size, dismantle the round piece of soft metal and glue a paper printed real scale picture of the original gear (you can find on hpi website as a pdf manual) on the metal round shape just done taking care of the alignment. carefully cut the paper to the exact shape of the gear.
- use a hand metal hard saw to drill the teeth of the gear in to approximate shape taking care not to dig too deep.
- use a small handy driller with a small grindstone attached to it. Grind the tooth to perfection very slowly so you don t do mistakes.
BE PATIENT. This process takes hours of work.
4) i purshased the 48p 96 tooth spur gear and a 15 tooth 48p pinion gear from HPI and it was a bad idea. with the high power 7700kv brushless motor i have, the carbon fiber spur gear got destroyed in 15 min. i adapt a KIMBROUGH 32P SPUR 64T and a 15 T 32p pinion instead for durabilty. you only need to drill 2x 3mm holes in the plastic to fit it onto the hpi original spur holder.
the next gear problem: the bevel gear in the rear differential broke after 2 months of fun, wheelies, etc.
i believe this is another clicking sydrome of the wheely king.
- will be fixed by heavy duty bevel gears (18$)
quick sum: 140$ WK + 30$ steel trany gears + 18$ *2 bevel gears + 20$ tranny gears (plastic, bad choice) + 20$ new servo saver kit = 246$ total cost so far in 2 months.
what s next? any other low endurant gears hidden on the hpi wheely king?
----------------i had to replace the aluminium differencial gears with heavy duty steel gears from Integy. i had also to buy their shafts, because the original hpi shafts they are not compatible with the steel gears. well i am very disappointed as it broke on the 2 use, all the 4 new shafts giving power to the wheels. i spent more than 50 $ on brand new shafts. what a waste. thank you Integy, you seel very bad material or is it only made for slow users?
here is the reference not to buy: Universal Drive Shaft (2) for HPI Wheely King (use with #T8126)
i will try to adapt my original shafts to the integy heavy duty bevel gears ( really HD ?)HD Bevel Gear Set for Wheely King (use with #T8118)
picture: broken integy shaft parts T8118. broke in crawler gearbox mode. the 3 others shafts broke soon after with the 7700 kv motor installed after 3 minutes use. i did not even do a burnout ...disappointing...
EDIT : 19 -9-2010
broken again. nevermind, let's fix it!
i tried to recover the integy shafts but it was not a great success as the longer metal stick transmitting power to the wheel axis became "wobely" as shown below.
back to the original shafts modification to be working with the bevel gears from integy. i drilled a 2 mm holes carefuly enough making sure the holes do not look like a funnel, otherwise the metal stick would never hold. NB: hit the centre of the small metal stick with a hammer to slightly alter it so it stays in position in the shaft. do not hit too hard as hardened steel breaks (i tested for you, thank god i wear glasses!) final assembly of the original shafts modified.
I have experienced some trouble with the adaptated shafts from HPI and INTEGY. I thought that it would be stupid to buy the same material again that would break after a short period of use. so I had this idea of using a standart Inox/stainless steel screw and to modify it so that it would be able to enter the space of the original shafts (cost 0.2 €). just have a look at the picture below. it is very simple you just have to cut/adjust the head of the screw into a "T"and to alter the diameter of the shaft from 6-7 mm to 5 mm in order to allow the ball bearing to be inserted into the shaft. when that is done, one just has to drill a 2 mm hole at the tip of the shaft so that the little 2 millimetre bar would fit into the INTEGY "HD" bevel gears and transmit the torque to the wheels of the car. be careful when you drill the hole for the little bar because if it is not perfectly in the centre of the shaft you will experience tremendous problems to insert the device into the Bevel gear.
IT works !
i adaptated a piece of aluminium and a 17 kg.cm servo to my rear transmission axle to control the direction there too. see picture. My wheely king has 4 direction wheels and 4 wheel drive :) see the video for some fun twists! NB: avoid to turn only with the rear direction while at high speed, it does not forgive!
temporary fix of the small bevel gear:
shortening the small gear in order to shift it s position in the bevel gear box.
BIG DISCOVERY: one of the ball bearing of the small bevel gear was broken and it was the reason for the gears to brake because it induced a misalignment of the teeth when a force was applied. i wish i had seen it before i have to buy another set of HD bevel gears.
jumps and passing on Chiara
7700kv - CC MMP
stock HPI bevel gears (HD bevel gears from integy don t like fast brushless)
integy transmission mobile trees
homemade shafts (from steel screws)
5000mAh lipo 20C
hardened steel trany gears (forget about plastic gears)
4 wheel direction
Super short turning radius!
so far the only thing i know will break for sure are the bevel gears, i have another spare pair, lucky it s not too expensive!
Wheely king as a snow plower!
a toy for those that like to stay warm inside...
i know the lesft side is protruding more by 1cm ish, initially a mistake from my measures, it might be a good thing to optimise the equilibrium of the machine. the snow is being pushed to the right side of the plower shovel and therefore the amount of now accumulates more on the right side (shorter shovel).
Test of the prototype in real conditions soon...