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Old 12-16-2016, 08:51 AM   #46
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Originally Posted by howardcano View Post
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.)
I'd say something about being pedantic, but we are talking about measurement.

Most people don't have a 4 wire capable meter at their disposal. And at the sort of resistances we're talking, the resistance of the DMM leads is going to be a big factor.

By applying a large current, we can get a larger induced voltage on the wire, and hopefully bring the measurement into a range that the typical multimeter won't have trouble with.
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Old 12-16-2016, 08:54 AM   #47
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Originally Posted by Nerobro View Post
I'd say something about being pedantic, but we are talking about measurement.

Most people don't have a 4 wire capable meter at their disposal. And at the sort of resistances we're talking, the resistance of the DMM leads is going to be a big factor.

By applying a large current, we can get a larger induced voltage on the wire, and hopefully bring the measurement into a range that the typical multimeter won't have trouble with.
Okay, I misunderstood your point.

Using separate meters to measure the current and voltage, and applying relatively large currents, is a good way to inexpensively measure small resistances.

By the way, I just tried one of these, and it seems to work nicely. $62:
http://www.ebay.com/itm/White-OLED-F...EAAOSwbYZXXit5
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Old 12-16-2016, 09:24 AM   #48
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A shock dyno would be the easiest thing to do (one like the CSI dyno, a rotary one), I have all the parts to do it here at home. Also, as I said before using a telemetry system one could use his own car as a complete dyno (my intention), having ~on track~ information. As we speak I have the G-forces and temperature sensors part done and to be more precise I will add a humidity sensor and I have a set of linear potentiometers to measure shock stroke I intend to add later. Oh and GPS off course.
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Old 12-16-2016, 09:31 AM   #49
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Right on! I might could have some test/comparo scenario suggestions input if you don't mind. I've convinced myself there should be negligible deviation in data comparing full scale to scaled down theories. Let me know if you need any test parts/pieces/materials, I've got a room dedicated to my incessant 'tinkering', my girl informs me that this room is named a 'dining room' by 'normal people', whatever those things are...
A small list of subjects, if I may:
Tire traction comparos (sauced/old/new/treaded/slick etc.)
Test each available chassis adjustment for effect (might be exhaustive/challenging but I think ultimately worth while)
Aero (i.e. any use able down force at relate speeds, drag Co-effs, would ground effects (i.e. Lotus type 79 F1 car) work at our speeds/on carpet?)
Effects of differing spring rates
Weight bias/addition/subtraction characteristics
Measure "tweak" deviation
I'd love to come up with a way to test chassis performance between tuning with flex and tuning with the available suspension adjustments, obviously on same chassis, and with differing degrees of flex. (I've always held that chassis flex tuning is meant for pan cars that have no suspension to speak of, while today's TCs chassis are an embarrassment of riches with all the adjustment and hop up parts available. If you adjust traction performance by the stiffness of your chassis components alone why even have a TC with all this suspension? I guess I could see where, in the case of someone comin to TC after racing pans for years, they would tune with flex. Now, if I'm honest I have 5 practice sessions of 15-20 mins each under my belt, my proudest moment to date regarding running a rc car on a track is that I once almost got around our course without drifting full speed into the nonforgiving barrier on the outside of the 90 right hander at the end of the back straight, almost... so actual hands experience is very very limited. That being said, I do have some full scale racing experience. Building your own (full scale) race rig, as i did/do I know my own cars inside out, i know displacement,comp ratios, A/F ratios, exterior dimensions etc down to 3rd decimal.I named each fastener and gave them back stories (not ALL of them, that'd be crazy. I feel there's exponential advantages to be had over your opponent the more you understand your car and it's reactions to input. Now, I always went for as stiff as possible, while trying not to add undue stresses to ever narrowing points in the frames construction (or chassis structure when dealing with a unibody), then tune the suspension. By design, chassis/frames are static, the adjustment is incorporated into the suspension (or optional components with optional geometries). I feel like ignoring all the beautiful adjustments a top shelf tc offers now would be wasting 90% of all that money you spent FOR that tech! I would suggest 1/10 pan cars. But, this is completely speculation on my part, I totally could be wrong, it happened once in the late 90's. This is why we have science, prove me wrong. I'm stoked! LET THE SCIENCE BEGIN (OR COMMENCE)! thank you for your consideration, Rooster
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Old 12-16-2016, 09:46 AM   #50
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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.
I totally could see tuning flex as easier, I guess that makes sense. I often forget that not everyone is as much as a nerd as I am. I understand you can never get ALL flex out, I was speaking to adding flex as a means to gain traction, it was late last night, I'm fairly certain I just rambled through that post, the key is: the longer the post, the greater chance I kind of forgot why I was posting in the first place, and instead of erasing and wasting all those letters and words I try steering it back on course. Whoa sorry I just subjected yall to the quagmire that is my stunted thought process, I'll try and limited that exposure going forward, promise. Rooster
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Old 12-16-2016, 09:53 AM   #51
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Voltage drop testing the wire could be handy on the flywheel motor test.

Sure resistance is fine and dandy and all, but it won't tell us if the 18g wire we use in 1/12th scale is too small and overloaded. A voltage drop test will lets us know if we're pulling more current than the wire can handle, for real, not just book stats.
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Old 12-16-2016, 09:54 AM   #52
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I don't think I need anything, but if I come across an obstacle or improvement I will speak.
So, I can do tire comparations, sauced and unsauced. I got slicks from various brands and ebay specials (that are proving as good as the other ones!); chassis adjustments are a roll distribution/slip angle management thing so I think with a read in servo angle from the Rx and front-rear shock stroke vs roll motion I can come up with something, will need a thermometer to read tyre temps; aero is easy, running ride height change vs speed; weight bias again is roll distribution so add that too; what is this "tweak" deviation you speak of?

Flex vs grip is easy to do once I have the provisions to use the telemetry on the car, same car (with everything the same between runs), record track conditions (temp, humidity) then remove or add flex and record the run. Should have different roll front to rear regarding the other runs. Also some adjustments like neutral roll axis make chassis flex less noticeable. So it's only the tweak deviation I don't know what is the others consider them on the TODO list.

Speaking of that list, a bit more of organization would help a great deal. @OP, how about creating a TODO list, with jobs assigned to each contributor?

@zerodefect: my intention with the telemetry is to read total voltage drop, easiest and a rough estimate but with more doing this we can draw some conclusions.
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Old 12-16-2016, 10:10 AM   #53
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Tweak is a common R/C term for bad corner weighting. (IIRC) If you put your chassis on a tweak board, it will show some twist in the static set of the suspension. This leads to inconsistant left-right performance. And can cause one or more wheels to lose traction before you really want them to.
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Old 12-16-2016, 10:45 AM   #54
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Originally Posted by Nerobro View Post
Tweak is a common R/C term for bad corner weighting. (IIRC) If you put your chassis on a tweak board, it will show some twist in the static set of the suspension. This leads to inconsistant left-right performance. And can cause one or more wheels to lose traction before you really want them to.
Oh I see, static and dynamic similarity in tire load. Easily doable only have to buy another set of linear potentiometers. Good thing I've got this Pro4 I can say if and how torque steer happens.

My TODO list:
-torque steer and tweak deviation;
-simple shock dyno;
-tire grip comparison (hopefully tire slip angles can be known);
-roll vs traction;
-flex as adjustment;
-aerodynamics and effects;
-blue wire on the motor sensor harness is temp so I can piggyback and record motor temp;
-acceleration vs time graphs.
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Last edited by 30Tooth; 12-16-2016 at 10:58 AM.
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Old 12-16-2016, 10:58 AM   #55
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Pots are probably not the best option. If I were to try an instrument a "live" r/c car. I'd use some magnets glued to the suspension arms, and hall effect sensors. That way you're not adding drag to the suspension, and if you mount the magnets close to the pivot, they won't significantly alter the unsprung weight either.

Alternatively, some printed clear plastic with a quatrature pattern on it, or even just a gradiant printed, and some photodiodes. Both are non-contact methods, and would cause less testing gear interference on the suspension.

... I love DAQ gear.
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Old 12-16-2016, 11:19 AM   #56
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I'll have a to-do list written up by Monday. And our first datasets. :-)
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Old 12-16-2016, 11:30 AM   #57
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The hall effect sensors I searched only have 2 states, yes and no, nothing in-between I thought doing with infrared to measure distance to ground but they aren't accurate nor work at that low distance. Maybe laser?
The pots I have are 75mm ones (the biggest I thought would do it, they are a bit too much but I intended to use them on 1/8th buggies) and they weight around 7gr (a bit but not much) but they do have drag (feels like they used silicone grease). 45mm ones would be enough for 1/10th TC and those are the ones I am ordering next.

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I'll have a to-do list written up by Monday. And our first datasets. :-)
Thank you.
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Old 12-16-2016, 01:10 PM   #58
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Hall effect sensors can be analog too. Gotta find the right ones. Like these: http://www.allegromicro.com/en/Produ...s/A1318-9.aspx

You're right, going to the ground is a fools errand. You could put a reflective sticker on an arm, and measure to that... The gradiant sticker on a sheet of plastic and phototransisor/photoresistor/photodiode/photocell method might be cheaper... but it will take more work to make work consistently. As ambiant light could be an issue.
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Old 12-16-2016, 01:13 PM   #59
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Quote:
Originally Posted by Zerodefect View Post
Voltage drop testing the wire could be handy on the flywheel motor test.

Sure resistance is fine and dandy and all, but it won't tell us if the 18g wire we use in 1/12th scale is too small and overloaded. A voltage drop test will lets us know if we're pulling more current than the wire can handle, for real, not just book stats.
But math using known quantities will tell you what you need to know, most the time, but hey I'm all about confirming data myself so have at it. I guess I just find out the data and plus size for wiggle room, can't use too big but can go too small.
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Old 12-16-2016, 04:37 PM   #60
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Originally Posted by Nerobro View Post
Pots are probably not the best option. If I were to try an instrument a "live" r/c car. I'd use some magnets glued to the suspension arms, and hall effect sensors. That way you're not adding drag to the suspension, and if you mount the magnets close to the pivot, they won't significantly alter the unsprung weight either.

Alternatively, some printed clear plastic with a quatrature pattern on it, or even just a gradiant printed, and some photodiodes. Both are non-contact methods, and would cause less testing gear interference on the suspension.

... I love DAQ gear.
What if we chip in for a FPV setup? Then use gradients and locators and the like visually for shock/arms/link movement. Plus it'd just be cool to watch the action in real time.
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