gigaplex

iTrader: (2)

Efficiency values change quite drastically at different loads, timing settings etc. These values aren't really comparable.

Nerobro

iTrader: (2)

We're controlling for load, and testing a range of timing is all do-able, fairly easily. :-) We'll get there.

I need to get my hands on a pan car pod and axle. Hopefully without buying a whole digger, or eliminator.

:-)

roosterreagan

iTrader: (16)

If I may... first, imo testing shock oils would be irrelevant, there's so many different viscosities,thermal properties, shear props, break down schedules, etc. between all brands, not to mention my suspicion that none of these companies have strict testing procedures for each specific weight i.e. brand 'X's 50w today could test closer to what their 40w was last year. So, that turns into a case of preference, it'd be like testing to see what color of paint is "best".
You don't test wire resistance 'loaded' or whatever was previously mentioned. There's categories for strand count, strand gauge, wire gauge, strand composition, etc. Get a known length, select the horseshoe, touch here, touch there, do math, record it for prosperity (which has been done btw).
I am interested to see what yall do with the motors. Oh btw, I may have misunderstood the previous comment regarding a 500g aluminum disk and a magnet, if I did disregard this next statement; aluminum isn't magnetic.
I'd like some dynamic suspension testing, like: other than tires, what component/system affects corner traction most? Why is it excepted practice to incorporate chassis flex on purpose? Tons of resources are spent on race cars to eliminate flex, it makes for more consistency, if your car is not handling well and chassis flex helps, than work on your suspension, chassis flex is just softening kinetic transistion, THAT IS WHY SUSPENSION EXISTS.
There's so many made up sciences for the rc industry just to sell you shit. Race car is a race car, physics is physics, it scales (until you get subatomic and then shit gets all weird). Just some my thoughts, no offense intended, I'm actually really excited to follow this thread, hope I might could contribute an idea or two. Onward and upward.

30Tooth

iTrader: (1)

@roosterreagan Dynamic suspension is something I can do. Give me a few days to finish the code and shield arrangement on the arduino and then I can give at least G forces.

howardcano

iTrader: (37)

I've heard that regarding off-road shocks, but at the moment I'm not a believer. I predict that accurately testing a typical unpressurized, variable-volume RC shock will show a decreasing slope in the graph of force vs velocity, all the way up to cavitation (where it falls off a cliff).

If proper testing proves me wrong, then you may razz me incessantly in your preferred manner for a period of one week.

I have no predictions for a constant-volume ("shaft-through") shock.

30Tooth

iTrader: (1)

http://www.rctech.net/forum/electric...t-results.html

niznai

I always thought along the same lines, but I have a suspicion that chassis flex is used in our hobby simply because it is, oh well, simpler. To have effective suspension we need to accomodate a much wider range of transitions than our shocks and springs can handle. To eliminate flex completely and make shocks capable would mean way over engineering the cars. Which would translate in inaccessible prices.

Having measured a ton of springs, I can report their ratings are at best approximations. Some are just dead wrong, closer to completely different values. Especially "intermediate" values (i.e. between two standard values). Almost makes the ones at correct values look like fortunate accidents. Not inspiring confidence in all the setups and so on.

Measuring is also a pain in the butt, given how small everything is and the limited deflection possible with TC springs before they are coilbound.

Either way, seems like the rule is inconsistency, so I wouldn't waste my time over analysing the hardware.

It's a hobby. Take it easy, have fun.

And I think you are right, a lot of the "innovation" and "upgrades" are just rubbish for people with feeble minds, but if you try to convince anyone, they usually react like you are trying to rape their mother.

You know what they say about fools and their money.

howardcano

iTrader: (37)

Thanks, this is excellent data! It shows that, for lower velocities, the force vs velocity is quite linear. The range of velocities up near cavitation was not tested, so that question still remains.

robk

iTrader: (22)

We are not in the car to actually feel what is happening. The only feel we have is what our brain makes up relating our eyes to our hands. Therefore flex opens up the window of setup and makes the car more forgiving.

Honestly if full size setup theory was 100% applicable to our cars, we would all be running 4mm foam tire chassis on these cars with aluminum a arms.

DesertRat

iTrader: (2)

I based my statement on what I have learned and experienced racing offroad and the theory as I understand it. Several times I have had a car that I liked the handling of but there was a spot on the track where it would come down hard from a jump, bottom out, and loose control, so I switched to one size smaller shock piston and either 5 or 7.5 weight oil thinner, and it no longer bottomed out as badly.

Also, what people don't think about in shocks is the mass of the oil. For the piston to move through the shock, it must accelerate the stationary oil to a speed much faster than the shock piston, have it flow through the shock hole, and then stop it on the other side. Each part takes energy and the energy needed to accelerate something is dependent on the square of its velocity. I believe that this energy to transfer mass becomes more important than absolute viscosity at high speeds.

30Tooth

iTrader: (1)

Exactly, flex is a something that adds a lot of margin to account for driver/mechanic errors. We could run stiff chassis with stiff arms (they aren't needed though) if we knew everything about our car handling performance. The more you know the less flex in components is a help. 1:1 setup theory applies 100%.

Nerobro

iTrader: (2)

Well, testing would prove that out. If one brand runs light, and one band runs heavy, that's something ~we should know~. That's critically useful when say, you're at a new/strange to you track, and you need to buy shock fluid that's not your usual brand.

It feels like you're saying "we don't know, so we shouldn't test it". When to me, this means "we really, really, need to test it." Even if it is to say "you can't trust shock oil."


When I design things, I use lookup tables. I've never gone back and measured things myself to verify them. If anything, testing wire is a good way to prove out that I/we are doing measurement right.

By applying a measured current to the wire, we get around needing to do 4 wire measurement, and that brings the testing more into line with things anyone here could do. It's not a high effort thing, and is worth the time to demonstrate you're getting things right.

Worst case, if your multimeter gets some stupid result, you then have a bright orange flag saying ~something~ is wrong with your setup.


so far, 500g is a number pulled out of my butt. It's about a pound, so should dampen some of the rotor impulses.

Aluminum is highly conductive. and if you put a magnet near a conductive surface, it generates a magnetic field. That eddy current resists the movement of the magnet. Look up "magnetic braking". There are some really cool links on youtube demonstrating it. Lots of bicycle trainers (think bike dynos) use it too. If you're the sciency sort, magnetic braking is used on balances to provide stiction free damping of the balance bar.


This is covered really well in existing books. Here's the one that "really made it make sense" to me.

https://www.amazon.com/Chassis-Engin...0GRC1KT2XG805N

My only hesitation, is a testing rig that will do that justice, would not be even vaguely inexpensive. Consider it put on the list, if this gets popular, maybe we can try to figure out how to do it well. It's the same reason I hadn't suggested testing shock oil in a shock, with a shock dyno. Those too, aren't even vaguely inexpensive, or easy to run.

Shock dynos are ~very cool~ though. So are suspension dynos. I've never actually seen on on a r/c car scale though.... There's always a first.

Engineered flex is soemething r/c cars have done for decades. t-bar suspensions are a good example. Motorcycles are big on that too, because suspension does not work well when leaned way over.

R/C cars also have some interesting unsprung weight issues. When unsprung weight is high, suspension spring rates need to be even higher, which pushes "suspension" into the chassis itself.

That's going to take some time to read.... Thank you.


You gotta start somewhere. If the industry is feeding us BS, lets measure it. They did it in paintball. We can do it here. Better products come of it.

Measurement IS a pain. But it's something that should be done. And i'm aiming at low hanging fruit for now. Good test rigs are expensive, but make collecting data a lot easier. That'll come later if anything comes of this.

Getting rid of flex is rarely the best option. Understanding it, is what we need to do.

What I've seen with the setup of r/c cars, is people aim for "a little push" and a linear response to breakign traction in their setups. While the fastest cars are closer to neutral.

Flex, on a motorcycle, almost always leads to more traction, but the cliff where you lose traction becomes much steeper.

The stiffness of most R/C setups, really does push the suspension work to the chassis. Less so for off road cars, but the on road cars...

You're describing packing. It's not about mass, but about pressure, and mach number in the fluid. It's a useful performance tuning tool for off road.

Off road shocks, on things that do jumps, is darned near voodoo. :-)

DesertRat

iTrader: (2)

Mach number is the speed of sound in a fluid, which in shock fluid is on the order of 1500 meters per second, and is not a meaningful value when simulating the fluid dynamics of a shock absorber.

You are right about the this phenomenon being referred to as "pack" but the mass is very important. I had test questions on this shit,

https://en.wikipedia.org/wiki/Turbulence

At high flow rates the Reynolds number becomes large and flow is dominated by inertial forces, causing eddies and turbulent flow.

Nerobro

iTrader: (2)

I wish I had a thumbs up button on this forum, or something like that. Thank you.

howardcano

iTrader: (37)

No.

Four-wire (Kelvin) measurement IS the process of applying a current to the wire, then measuring the voltage drop across it. (Actually, that also describes two-wire resistance measurement. The difference is that four-wire measurement uses one pair of contacts to supply the current to the wire, and a different pair of contacts to measure the voltage drop.)