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There isn't enough going on here in the Losi section so I thought a good discussion of the hydradrive would be welcome. While I have owned one, I never drove it. It was on an LXT that I had bought on a whim then later sold when I got buyers remorse. I've seen the info on vintagelosi.com about it and know how it works on paper. What I'd like to know is how many of you drove one/still drive one, and what your thoughts were/are of it? How do you feel it stacks up performance wise against modern offerings such as the VTS system and others?

Quite! The Losi Forum is in need of some much needed......stimulation

In my opinion, the Hydra-Drive was/ is one of the great RC innovations. Unfortunately, due to manufacturing tolerances, it had the habit of leaking unless you spent a fair amount of time fine tuning it. The Hydra-Drive that came with my original XX back in '93 or '94 has never leaked, even to this day, which I am very surprised at. However, I did spend much longer on the preparation of the moulded parts prior to assembly, which the build instructions make no mention of.

As I remember, most of the time was spent preparing the mating faces of the actual Hydra-Drive housing. Basically the preparation involved using fine grade emery paper to remove any mould marks and imperfections so that the two halves, when joined together, would form a really tight seal with no 'air' gaps. A friend that I raced with back in the '90s did none of this 'fettling' to his Hydra-Drive and his leaked quite soon after he started racing his, then new, XX.

Also, as I recall, you were supposed to set the Hydra-Drive quite loose to allow it to do its job but in my personal experience most drivers abandoned it in favour of the basic single sided slipper using the additional parts in the kit.

Now, if someone were to make a CNC'd version of the Hydra-Drive housing out of aircraft grade aluminium, the performance of the unit would no doubt improve dramatically. However, since the standard these days is the dual disk slipper, this is unlikely to ever happen but it would be interesting if it did.

Making one out of aluminum would add a considerable amount of mass to the rotating assembly.

fredswain wrote:Making one out of aluminum would add a considerable amount of mass to the rotating assembly.

A few grams....maybe....but probably not as much as you think. It would certainly be interesting to find out.

When I spoke with Gil Jr last October he said the Hydradrive was dead now. He believes the power in todays brushless motors would destroy the rubber o-rings in the middle real quick in a real 10 minute or more main. Might last a couple races at best. The friction for that long would be bad. It would have to be redesigned with better material for the seals.

I wonder if he believes that under all circumstances? Certainly in open class but what about 17.5 blinky mode? We also have much better oils today in a far wider range of viscosities.

I have been running my original hydradive unit since I got my xx in 94 (I think). I haven't raced it in years, but did a fair amount back in the day. I always prefered the hydradrive to the now standard slipper clutches. I agree that it was and still is a great design, however development never contiued past the first version. So yes, todays high power brushless systems of today would probaby tear it up pretty quickly. However I have had some pretty hot motors in my xx over the years and never had problem.

I am sure if development continued on the Hydradrive along side with current technology it would be able to handle the power of todays systems. It's to bad, but understandable why it wasn't continued. The current slipper systems are far easier and less expensive to maintain/produce/and develop then the hydradrive.

For me that's part of it's apeal is the maintaining, I enjoy to wrench on my cars as much as I do driving them. One thing I found that the hydradive is far smoother, and I think it's got "cool" factor.

I've always loved the Hydra since it was so very different. Using some different O-ring materials and types could beef it up for higher output use.


And an aluminum one would be very cool. No one yells at the RC10 guys when they build an all aluminum RC10

knixdad wrote:No one yells at the RC10 guys when they build an all aluminum RC10

i could start to......

I get distracted by the shiney metal

Pretty sure that the Hydradrive oil was silicone to begin with. The unit was great overall, added a ton of rotating mass (one reason it was so good at smoothing out a car) and the hydrostatic nature of a fluid means it's dynamic in resistance to the amount of force exerted upon it, so it's...well, fluid. Gil Jr was quoted saying (paraphrasing) that one issue was lack of heat dissipation, and that the best solution was to machine the entire unit out of aluminum, which was insanely cost-prohibitive.
I think that even a blinky 17.5 (timing is still allowed to be adjusted and a strong 17.5 can still pull 25,000+RPM with 85% torque at initial throttle... would be equivalent to approximately a strong 19t RPM with a 10t torque number & why you can run such a "tall"gear) with such a constant average voltage via LiPo battery (instead of 8.9v for 6 sec, then 7.0v for 30 sec, then 6.0 for 45sec etc, from NiCads) would severely tax the unit from heat, pressure and the constant combination of both. I'm sure that it could still be used, and unless you were trying to run high-level races it would work fine. Newer slippers will still prove more consistent with little maintenance on todays (ie, locked slipper) tracks.

Shumacher visco-drive unit on the other hand....

In the late 80's, I remember a guy on the south side of Houston who owned a local hobby shop. He was holding parking lot races on weekends. It wasn't smooth enough for pan cars so it was really just lots of buggies. There were a couple of direct drives running around and the owner's car was too. However his was unique. It was a hydraulic direct drive. There was no diff or mechanical connection to the wheels from the motor. It was much like the hydradrive on it's own in principle. It was neat turning one wheel while the other did nothing. His car was pretty quick.

He had two big problems. The first was that it leaked. Horribly. Probably due to the o-rings wearing quickly. The other problem was that it got hot and the viscosity dropped badly. The car noticeably slowed down due to constant slipping which only made the heat issue worse. He was using shock oil of the day since that's all he had so the viscosity was probably fairly low. When it worked, he was untouchable in corners. He could put the power down in a turn like no one else. I have no idea what his name was or what he did later. The shop is long gone and we don't have a hydraulic direct drive.

Charlie don't surf wrote:Pretty sure that the Hydradrive oil was silicone to begin with. :

http://vintagelosi.com/Articles_files/HydraDrive%20Patent.pdf

And as it states in that document, ethylene glycol is the fluid of choice. It was found that 5 and 10 weight have little anti-slip effect. The range they found was 20-120 weight. So go order yourself up some ethylene glycol. According to Wikipedia "It is an odorless, colorless, syrupy, sweet-tasting liquid. Ethylene glycol is only weakly toxic, but cases of poisonings are not uncommon." Sounds like the perfect dessert at dinner.

Ethylene Glycol is the chemical compound that changed the freezing point in automotive anti-freeze. Odd substance to use!

Charlie don't surf wrote:Ethylene Glycol is the chemical compound that changed the freezing point in automotive anti-freeze. Odd substance to use!

They used it because it's so delicious and smells like maple syrup when it burns