Pimp my Ride (HPI RS4 Sport)

[DaMasha]

I have bought an HPI RS4 Sport Diablo from ebay on the cheap in kit form and I am looking for some input as whats good to put into it in order to race it as a stock beginner at my local club.

Any input appreciated, good or bad.

[WillyChang]

Be very careful with that RS4 Diablo if you take it racing, mainly 'cos as stock it is a 200mm wide chassis.

Electric racing rules now has a max of 190mm, so make sure you clarify with the organisers before the start... don't want you to get disqualified for having an illegal size and all that rot.

You can narrow the RS4 to 190mm by buying shorter dogbones, but then the narrower car don't look as nice under that 200mm Diablo shell. (Its been a few yrs but I made my electric RS4 to 190mm and donated the Diablo shell to its 200mm Nitro RS4 cousin - simple!)

[DaMasha]

OK, thanks for your help Willy. How much will it cost to convert it and where is a good place to buy to buy the parts you refer too?

Is this car any good?, I have only payed £33 for a semi complete kit, presumably the other guy bought it and hit the same problems with the 190mm / 200mm size limitations. I could possibly just get it going and use it as a mess around runner, I mainly bought it as I wanted a car to build up myself. Does the diablo shell come clear or painted?

[mr_pushrod]

If it is only club racing, there is a good chance you will be allowed to run 200mm, just depends how serious they are. As Willy says, check with the organizers!

[DaMasha]

Car arrived today, nearly complete minus a few screws, nuts and body pins. I have it running but it didnt come with a pinion or motor, I put in my 540 with 18t pinion on to test it but it was very slow (fast walking speed).

Any suggestions as to what motor pinion I should use and what pinion would be good with a 540 motor to test with until I find a good motor I can afford, it has the standard gear which is about 88t by my count. I also noticed the pinion has to be quite far out to get a good connection with the gear, do some pinions have a longer though for this so there not wedged on the end of the motor arm?

[WillyChang]

HPI supplied a 64dp (very fine teeth) spurgear in their kits, but you can use any standard spurgear to fit on the hub.

Count the teeth on the pulleys and work out the "overall gearing ratio". With a 540 you can gear to about OGR 6.0:1 ie your motor turns 6x for every turn of the wheel. That gives pretty decent speed.

Yes HPI's motor placement is quite offset. The pinions that HPI sells usually has a longer stem than others.

[DaMasha]

Its an 88t gear I counted the teeth, are you saying I actually need a gear with less teeth, I dont think anything smaller than 18t pinion would fit on dues to the motor mounts, the smallest it lists in the manual compatibility charts is 23t.

Maybe I need to start looking at other things as to why its not running fast, everything seems to move freely, I can only think the pinion wasnt connected smoothly enough to the gear wheel causing a big loss of motor power.

[DJTheo]

quote:Originally posted by DaMasha

Its an 88t gear I counted the teeth, are you saying I actually need a gear with less teeth, I dont think anything smaller than 18t pinion would fit on dues to the motor mounts, the smallest it lists in the manual compatibility charts is 23t.

Maybe I need to start looking at other things as to why its not running fast, everything seems to move freely, I can only think the pinion wasnt connected smoothly enough to the gear wheel causing a big loss of motor power.

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Am not sure if you understood correctly, but to minimize the chance of a misunderstanding, the total gear ratio should be something like 6:1, not only the ratio between the pinion and spur but multiplied to ratios of all other stages (spur to next gear, gear to pulley, pulley to end pulley etc...)

Cheers

[DaMasha]

Sorry it was my understanding, I thought he was referring to the pinion to main gear ratio, I'm not sure what the ratio is for the whole car. I will have a look tonight, I'n the mean time I'll take a guess and get a bigger pinion with a longer stem just to make sure there nothing wrong with the car.

Is there a formula for calculating these ideal ratio's for other motors?

Thanks for your help.

[WillyChang]

Ok, I'm now at home & have had a chance to pull my RS4 off the shelf for a closer look. (these old RS4s can be setup to take Tamiya body shells - same hole positions!)

The purple HPI spur gear is a 122 tooth 64dp.

The supplied HPI pinion is 35 teeth.

Sorry it was too hard to count the pulleys. (Its 1am and I'm working in darkness...)

If you have a 88t spur gear, there's a good chance its a 48dp (coarser pitch) gear. If so, to get the same OGR as HPI's 35/122 you'll need about 25t on the pinion.

[DaMasha]

Your on the money Chang, I took it down the model shop, its had the gear placed with an 88t and as you suspect it is 48dp.

What dp is a standard tamiya? I'm going to give it another trial tonight, the guy said its not in too bad shape but a rebuild and bearing clean wouldnt hurt.

I'll let you know how it goes later. I have actually got a 30t pinion though so it wont be quite to the spec of the standard gears.

[mr_pushrod]

Tamiya is different, 32dp I believe. It's certainly a lot coarser and will do a good job of lunching your spur gear!

[DaMasha]

Set it all up and its running well, 30t 48dp pinion, battery didnt last ages but seemed quite fast and runs well, I think I'll go for a full rebuild and clean now I know its all running ok to try and loosen the steering up a bit and smooth the running gear.

Cheers for your help fella's, now the question is whether I keep this as my touring car runner or the tamiya tt01 I ordered off ebay which is waiting for me at the post office, whilst I do love tamiya this car looks like it may be less prone to breakage's...what do ya think guys?

[WillyChang]

quote:Originally posted by mr_pushrod

Tamiya is different, 32dp I believe. It's certainly a lot coarser and will do a good job of lunching your spur gear!

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no... 32dp, 48dp & 64dp are imperial measures.

(literally they mean that eg 64 tooth gear at 64dp should measure exactly 1" in diameter)

32dp is usually used in gas cars, its a big chunky tooth.

Tamiya uses "METRIC" gears.

Typical metric Tamiya gears are either 0.4m (fine teeth) or "AV" 0.6m (coarser teeth). Tamiya TRF & PRO cars usually use 0.4m; the AV 0.6m is used in your normal kits.

Metric gears are not interchangeable with imperial gears.

(although 64dp & 0.4m are small enough to be cross-mistaken)

[DJTheo]

Just to complete the list most Tamiya cars of the (g)old "58050+-" or mid 80s Tamiya era use AFAIK 0,8m which is very similar and according to some experiences interchangable to 32dp...

Cheers

[mr_pushrod]

quote:Originally posted by DJTheo

Just to complete the list most Tamiya cars of the (g)old "58050+-" or mid 80s Tamiya era use AFAIK 0,8m which is very similar and according to some experiences interchangable to 32dp...

Cheers

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Thats what I was thinking of[:I] Getting my sizes for new and old mixed up, honest!

[WillyChang]

Theo just means everything pre-AVante. []

[mr_pushrod]

WillyChang, king of comedy, lol.

[DJTheo]

quote:Originally posted by WillyChang

Theo just means everything pre-AVante. []

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... and after Wild Willy (with few exceptions before and after)

Cheers

[DaMasha]

My TT01 arrived at the weekend, and I do like it, so I have decided to stick the HPI back on ebay. Its all running now so I can sell it with confidence.

However I did take my TT01 down the local outdoor race track last night and it does seem to be lacking in the top speed department, the guy who I bought it off says he's fully ballraced it, and the propeller shaft has been replaced with an anodised one and it has a sport tuned tamiya motor in it. What do I need to do to get this baby running a little faster, I presume a bigger pinion will be order of the day, not sure what it comes with as standard though at the moment? The 27t motor track record is about 16 seconds and I am currently hitting about 20 seconds with a perfect lap, I would like to get a little closed to the club level times before unleashing it on an official club night.

I have some CVA mini shocks ready to put on it which should improve the handling, not that there seems to be much of a problem in that area of things at the moment.