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This is a place to share knowledge related to 1/12th scale racing. It is not to be used for conversations.

KITS:
Click links to go to manufacturer product page. If any are missing please add them!

TIRES:
Pre-mounted tires readily available in the US:
Pre-mounted tires readily available in the Europe:
  • Hot Race ??

Gluing your own donuts:
https://www.youtube.com/watch?v=hm7z1rz-74s - Special thanks to Edward Pickering!
Truing tires:
https://www.youtube.com/watch?v=8wqHOLWq6Uc - Special thanks to Edward Pickering!

The following information came from HERE, with some editing and information added. Thanks Christian!

THIS MAY NEED UPDATING FOR THE NEW BLACK CRC CARPET

Brands:
BSR, CRC, Jaco:
Pro One is no longer selling to the public, but it and the brands above are all mounted by BSR and use the same foam. The nomenclature of the BSR vs Jaco/CRC is a little different in a few instances but is otherwise the same. The BSR foam consists of three families, and can be identifed as synthetics, naturals, and blends.

Synthetics - The old school, light weight, easy to true "dry feeling" tires. These include tires like CRC/Jaco Yellow (BSR White), Black, Gray, etc. These tires offer the highest wear rate and lowest grip. Many racers continue to use these nder high bite conditions.

Naturals - These tires are usually the best alternative for low bite and asphalt. They include Pink, Magenta, Double Pink, Lilac (BSR Team Purple), Purple, and other tires. These tires provide a ton of grip, but tend to get sticky in high bite conditions. This rubber does not wear as easily, and the cars will pick up gunk and fibers from the carpet under most high bite conditions. This is especially bad if the humidity is high.

Blends - These are the tires most people run today. They were initially called "JFT foam" by some, as it was believed that the tires were the same as the JFT tires. We can divide the blends further into two groups: high rubber and low rubber content. The high rubber would be the new rear Orange and Red from the BSR family, and the low rubber would be the Green and Blue varieties. When, asked about the difference, John Foister from BSR Tires said they came from the same "family" of foam, but they offered different grip. According to John, the Green/Blue has more bite than Orange/Red, but from track testing Oranges offer more bite than Green (being equivalent to in hardness) when the grip is high and absolutely no grip when it is lower. The Orange foam has a denser pore structure and the tire is not as prone to chunking. It is also important to note is that BSR Blue rears are not the same as the BSR Blue fronts!

JFT:
JFT stands for Japan Foam Tire. They started the new wave of foam tires we are all using now (Blue/Blu, Green/Greene, Dbl Blue, etc). These tires are a little different than the BSR tire family, but work in very similar conditions. They offers four varieties A (asphalt), C (carpet), S (???), and R (???). This does not mean that those types only work on that surface, but this is what they recommend.

JFT uses the same foam for fronts and rears if the color is the same.

A: Used on asphalt, considered close to the natural rubber variety and are named consistently with other natural tires.
C: Used on carpet, considered a blend.
S: Used on carpet?, tires are ???
R: Used on carpet?, tires are ???

For setup, the JFT foam seem to generate more bite than the BSR, therefore the car tends to be a little more aggressive.

Ulti:
Ulti is another Japanese brand that offers an array of compounds. They have their own way of rating tires, and are difficult to equate to other brands. They have 4 different varieties, each in varying degrees of hardness.

J: High rubber content tire, similar to Pink/ Magenta. Soft would be close to a pink. These offer the most bite and are great for asphalt/carpet front tire. (J hard being very popular)
X: "Balanced" blend, similar to JFT Blue/ Green. Soft is equivalent to Green, medium to Blue in hardness. Great for carpet!
Y: High synthetic blend with lower grip, and is not a very popular variety.
Z: A very expensive "special" foam that is supposed to be magic on asphalt. Only make it in soft shore.
European tires:
There are many great European foam tire brands that use their own types of foam, as well as traditional foams. SOmeone with more knowledge about them will need to fill this in!

Tire Diameter:
If you are racing on carpet, you have to evaluate how much grip your track has. If your track is low to medium grip, you can run bigger tires. If you are on higher bite you have to cut them smaller, there is simply no way around it. Bigger tires are needed for asphalt, especially in the rear. The larger tires provide much needed lateral bite.

Carpet (mm):
Low - Medium Bite
Front: 42.0 - 42.5
Rear: 42.5 - 43.00
Medium - High Bite
Front: 40.5 - 41.0
Rear: 41.5 - 42.0
Big Race
Front: 39.5 - 40.0
Rear: 40.5 - 41.0
Asphalt (mm):
Parking Lot
Front: 43.0 - 44.0
Rear: 44.0 - 45.0
Prepped High Bite
Front: 42.0 - 43.0
Rear: 43.0 - 44.0

Tire Saucing:
Most facilities have moved towards odorless traction additives such as SXT. Some of additives evaporate very quickly and some do not. This seems to be something that is also dependent on tire compound and ambient temperature. For example, saucing a Green compound seems like it never dries, especially when tjhe temperature is lower. We have found that wiping the tires off 15 minutes before we go run allows the sauce to cure, which makes the car come in much quicker with Green rears. Blue compounds on the other hand, do fine when wiped off right before hitting the track.

Saucing half front and full rear is a good initial starting point. If the front of the car is too agressive you can sauce les than half, or for a shorter amount of time. On black carpet the car may be numb to sauce changes, either a long or short sauce can produce very similar handling.
Tire Fuzzing:
In conditions of increasing grip, foam tires will somewtimes get sticky and pick up fuzz and debris from the track. This is highly dependent on the rubber sedan tire that is being run at your local track and the compound/ type of foam you are running on you car. The softer the sedan tire and the harder/higher rubber content in your foam tire, trouble with fuzzing seems more likely to occur.

There are ways to get around fuzzing under most conditions, and usually involves the selection of the correct foam compound. The more fuzz you get, the softer/lower rubber content you want to run.

Examples:
Problem: Car fuzzes with Lilac/Team Purple fronts and car starts pushing.
Solution: Use a softer front tire and or different family of foam. Replace it with Blue or Double Blue front. Alternatively you can sauce the front tires harder and tune the car for less front end bite.

Problem: Car loses rear bite 6 minutes into the run. Blue rear tires look almost clean but have small carpet hairs.
Solution: Use Green rear tires. The softer compound wears instead of getting sticky, minimizing fuzz. Possibly a longer sauce will prevent fuzzing.

Tire Selection:
Starting out, pick 2 tire compounds for the front and rear. The following should have you covered 99% of the time.

Rear - Green and Blue (BSR) or Green and Light Blue (JFT)
Front - Blue and Double Blue (BSR) or Blue and Dark Blue (JFT)

You may wonder about other compounds out there and if they might be better, trust me, they probably won't be. Even if there are other tires that can be as fast, the synthetic family wears out really fast and the high natural rubber will probably fuzz on you over an 8 minute run. The blends family seems to be the most versatile foam type available today. They last awhile, and sticking to them will make your process of tire selection simpler.
Tire Charts:
BSR/CRC/Jaco



Contact



Corally



JFT (Japan Foam Tire)



Ulti



Enneti (Xceed)



ELECTRONICS:
ESC:
As of now, ROAR is staying 1S (3.7V nominal; 4.2V fully charged) for 1/12. There are many 1S ESC's with a built in BEC so nothing else is required to power the receiver and servo.

If you don't want to lock yourself into a 1S specific ESC, you do have other options! It is possible to use your 2S ESC without a booster or receiver pack, and the ESC simply supplies the lower voltage. If that does not appeal to you, you will need to use an Rx pack or booster. The Rx pack and booster will both supply the receiver with a higher voltage than the 1S pack.

If you decide to use an Rx pack, MAKE SURE TO REMOVE THE RED WIRE FROM THE ESC PLUG THAT GOES INTO THE RECEIVER!!!

If you choose to use a voltage booster, it works exactly how it sounds. Instead of plugging the ESC into the receiver, it plugs into the booster, and the booster plug goes to the ESC, supplying the higher voltage.

1S ESC:
If there are any missing please add them!!

If anyone would like a need for a chart comparing the ESC's specs PM fenton06 and I'll get one made and put in here!
DISCONTINUED 1S ESC:
If there are any missing please add them!!


If anyone would like a need for a chart comparing the ESC's specs PM fenton06 and I'll get one made and put in here!

Voltage Boosters:
If there are any missing please add them!
Servos:
BODIES:
Black Art (CRC - US Dist):
  • Audi R8C - BA002 - .020 Thick



  • Black Market (Mohawk 12) - BA005 - .020



  • Lola B10 - BA006 - .020 thick
  • Toyota TS030 - BA008 - .020 thick

    Lola - black/red, TS030 - green/pink


PROTOForm:

Reflex Racing/RSD:

SUSPENSION ADJUSTMENTS:
Pan Car Front Suspension Tuning:
DISCLAIMER : The following tuning advice was written based on the tuning experience of the author and may not hold true for all cars, drivers, or surfaces. In the end the best tuning advice is to experiment and make changes one at a time so you can track your changes and find the car balance that works best for your driving style. One real world test is worth a million ‘expert’ opinions.

Front End Type:

All popular modern pan car front suspensions are very similar, with a few exceptions such as Speedmerchant New School but most of the info in this wiki applies to them as well. For the most part, they consist of a rigid bottom arm, an upper A-arm, and a kingpin with a spring. There are different flavors of this general design, such as the CRC Dynamic Strut that uses a threaded kingpin and upper pivot ball instead of the Associated style that uses a kingpin that goes through the entire steering knuckle assembly, but their operation is the same with the rigid lower arm and the upper arm controlling the arc of movement as the suspension is compressed.

Assembly:

More so than in almost any other part of the car, the front suspension of your 1/12 car must move absolutely free. Reamers and hobby knives are important here, as any binding will cause the car to corner unpredictably. A little play in the suspension is a good thing, and racers will often find that ‘worn in’ suspension pieces function a little better than new.

Springs:

Besides tires, spring rate is the most important part of deciding how your car will handle through corners, but are somewhat complicated. As a general rule of thumb, a very hard front spring will have somewhat less steering grip than a softer spring with the same suspension setup and tires, but not as much as in other classes such as touring or offroad. On carpet, springs of different tension can be used to tune how your car will maintain or lose energy through corners with the following general rule of thumb:

Hard Spring (0.55mm or harder): Less overall steering, quick reaction to driver input, less on power steering, harder turn-in with potentially lazy mid-corner and exit.

Soft Spring (.45mm): More overall steering especially at low speed, slightly slower reaction to driver input, more on-power steering, less aggressive turn-in but can ‘hook’ and give better mid-corner and exit.

It is worth noting that front springs from different suppliers are often very different, in both height, wire thickness, and coils for a given spring height meaning that a “medium” spring from one manufacturer may be the “hard” spring for another. To make accurate changes you may want to use one spring maker and stick with their line.

Another aspect to pan car springs is that they can get “blown out” and collapse, no longer as stiff or as tall as they were. These should be replaced with fresh springs to ensure consistent handling.

Dampening:

This is generally a minor adjustment, but adding dampening tube fluid to the front kingpins of a 1/12 car can give it a little more initial steering. Often unusual compounds see use here, such as Losi Smart Diff Grease or Associated Green Slime being a popular front kingpin lube.

Caster and Reactive Caster:

Caster is the angle of the kingpin, almost always angling back to the rear of the car, with a typical range from 0-10 degrees. Increasing your caster will typically result in less turn-in but a little more control, more steering exiting the corner, and somewhat increased straight-line stability with less tendency to wander because a wheel running caster will tend to straighten itself. Less caster will usually give you more off-power steering, but often with correspondingly less on-power when accelerating out of the corner.

Running reactive caster attempts to use both of these aspects to increase overall steering: when the car loads up on the outside front tire, the caster angle decreases, increasing the front end ‘hook’ as you enter the corner and then giving you the high caster on-power steering as you exit and weight is transferred off the front end. More reactive caster means more overall steering, but can mean you may have to adjust your driving style to drive more ‘ahead of the car’, needing to predict where the front end will grip.

As grip increases, less reactive caster is the normal tuning change made to keep the front end of the car from gripping too hard and oversteering and prevent traction roll. Static caster adjustments are still used to change the cars on power / off power steering balance.

Reactive Camber and Front Roll Center:

Reactive camber or camber gain is how much camber is added the front wheels as the suspension compresses. This can be increased or decreased by changing the angle and length of the top arm. Short, angled arm = more. Long, flat arm = less. More reactive camber will typically cause the car to “roll up” on the outer front wheel, transferring more weight in a turn and give more steering up to the point at which the tire is overloaded. This is generally more front grip and weight transfer than wanted on carpet, and as a result most cars run a flatter longer front arm.

Roll Center is the point on which the car will twist laterally or ‘roll’ during cornering. This can be raised or lowered by changing the angle and length of the top arm, with a short angled arm raising is slightly and a long flat arm lowering it. From what I have calculated most modern 1/12 cars meant for carpet have a roll center somewhere around the height of the chassis plate or just below it, but due to the lower arms being rigid and flat the roll center cannot be under the bottom of the tires like it often is on a touring car.
These two are inexorably linked in pan cars. Top arm length can be changed by the top arm mount in or out using shims or a CRC Long Arm kit, but is generally a minor tuning choice. Tuning of roll center with shims is usually a minor tuning choice in a pan car with a rigid bottom arm due to how the car cannot gain extra mechanical advantage on the lower arm as you can in a touring car, while reactive camber can be a significant driver of the car’s performance. In a modern car running on carpet the kit setup is usually perfectly fine.

Front End Alignment:

Static camber is the angle of your front wheels at rest, typically somewhere from 0 to 1.5 degrees on a pan car depending on surface, tire choice, and other factors, but a good starting point is usually somewhere around 0.5 degrees. More camber will typically give more steering, but many racers use static camber to ensure that their tires wear flat even if that means not having exactly equal camber on both sides of the car. This is adjusted by threading in and out the upper turnbuckle or pivot ball.

It is also worth noting that when running on high grip the flex and deformation of your chassis, suspension parts, and front wheels can become significant and cause uneven front tire wear. Some troubleshooting of the right combination of static camber, camber gain, caster, and tire/rim choice may be necessary to ensure even front tire wear.

Toe-In:

The front toe is one of the more easily adjusted aspects of the car and can have a significant effect on the attitude of the car due to it being a quick way to moderately adjust Ackerman without making significant other changes. With nothing else being adjusted, going from zero toe to toe-in will give a car a harder turn-in and will tend to scrub speed with the front end as opposed to using drag brake. This can be necessary when racing in Super Stock or higher power classes and will allow you to drive more aggressively, and can help the car track straighter under power. Toe-out will tend to make the car coast more through corners due to reducing the steering angle of the outer front tire. If a car has too much off-power steering but is otherwise stable, adding toe-out can calm the car but may the car to wander on the straights especially if the front end setup is very soft.

Ackerman:

Ackerman is the difference in steering angle between the two front tires during a turn. It is the result of how during a turn the inside of the car experiences a tighter circle and needs correspondingly more steering angle, but is also an important tuning tool. More Ackerman means having more inside wheel steering angle relative to the outer wheel, less means that the difference in steering angle is smaller.

To add or remove Ackerman, using a servo horn that spaces the links further apart (such as a Kimbrough Small Servo Saver, the outer holes on a Tamiya or Xray servo saver) will have more Ackerman than a servo that puts the links close together (Kimbrough Medium inner holes, Tamiya or Xray inner holes.) The rule of thumb is that a servo that puts the ball studs close together but spaced away from the servo horn will have less Ackerman than one that spaces them far apart and close to the servo horn. Ackerman changes will have the same effect as changing toe with more Ackerman being effectively toeing the wheels out and less toeing them in, but will not affect the straight-line attitude of the car.

Turning Circle / Steering Angle:

In offroad or even touring car you can set up the car to use the full angle of the steering 100% of the time. You will almost certainly not be able to do this in 1/12 scale. It goes without saying that as you turn up your steering angle you will gain steering often to the point of the car being undriveable. The quickest way to set the steering correctly is to set the sub-trim in your radio such that the car tracks straight and the servo horn is straight up and down, then set the endpoints equally such that they don't quite hit the steering bump-stops, then turn down the dual-rate or total throw from there. A typical starting point is somewhere between 45 and 60% of the total steering throw, or a 4-5' turning circle.
Pan Car Rear Pod Tuning:
Modern pan cars are all link cars with a center pivot ball and solid rear axle. This suspension system is required by ROAR rules and has the advantage of being simple, lightweight, and inexpensive compared to other more exotic methods of rear suspension, but it has some complicated movements that can be unintuitive.

Motion of the Rear Pod:

Due to how the rear pod is a solid axle, the only motion the pod itself sees is the main pivot up and down, but due to the main chassis being independently sprung it will feel the lean, dive, and squat of the main chassis as the car is driven. The lateral forces of the main chassis during cornering is transmitted through the main pivot ball and side links, the roll through the side springs and side dampeners, and the squat and dive through the main shock and spring. In addition, the torque of the motor against the pinion gear both during acceleration and braking is significant enough to cause a change in attitude even in low-powered classes. The motor pinion will try to “climb” the spur gear, lifting the center pivot of the car and countering the “squat” of the main chassis weight being transferred backward by the acceleration or the opposite under brakes.

Main Shock:

The adjustment of the main shock of a pan car is one of its more important tuning parameters. Spring, dampening oil, and pod droop are all controlled by the main shock.

Main Spring:

A soft main spring generally means more rear grip and more forgiving off-power, while a stiffer spring can mean more steering especially off-power, but the main spring must also be stiff enough to prevent the chassis from dragging when running on high grip. For most cars the kit spring is a medium weight spring that is a good starting point.

Main Shock Dampening:

The weight of the main shock oil will determine how fast the car will react off-power. 30wt or roughly 300cps shock oil is a good starting point, going up in weight will increase initial off-power turn-in, while going down will generally make initial turn-in softer. Often a heavier shock oil can make the car transition from entry to mid to corner exit smoother, where a car with light fluid may have a more pronounced ‘hook’ in the mid corner.

Side Springs:

The side springs transfer the roll motion of the main chassis to the rear plate via spring tension. Softer side springs give the car more rear grip and can make the car have a smoother steering feel. Stiffer springs promote the cars rotation and give more steering. You can either pre-load side springs or let them float, due to all side springs being progressive beehive shaped springs pre-load makes them effectively harder and will give more steering, but a small amount of pre-load can also make the care more predictable and forgiving. In conditions of extremely high grip, it may be possible to run no side springs at all due to the steering afforded by the tacky running surface and helps prevent traction-roll, likewise in extremely low grip when rear stability is absolutely necessary. Generally 1/12 cars run soft side springs but stiffer ones can be very common in Pro 10, WGT, or WGT-R.

Side Dampener Tubes:

Heavier tube lube will keep a car flatter at corner entry, initiating quicker. It may also make the car square off the corner entry when the grip gets beyond med-high. Going lighter will reduce steering initiation and maybe preferred on higher grip. This parameter is really unique to the driver preference, as some drivers are very fast and consistent with heavily dampened cars while others prefer softer setups.

Droop:

Controlled by the length of the shock, adjusting the rear pod droop is extremely important on high-grip surfaces. Reducing droop prevents the car from transferring weight during cornering and will give more rear stability and prevent traction-roll or problematic lifting of the inside rear tires during cornering, low droop can also give the car slightly more on-power steering. Increasing will allow the car to transfer more weight and dive harder into corners, but by allowing the center of the car to rise you will be more prone to traction roll issues. A typical starting point is 1-2mm of droop from ride height, but 0mm is often used on high grip.

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Old 06-04-2003, 07:20 PM   #3091
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question

what is a good servo for 1/12?
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Old 06-04-2003, 07:23 PM   #3092
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Went to the track tonoght.
I was working on geting rid of the car's twitchyness, and I ended up doing something completely different. I ended up setting up the car based on how much foam dust was left on the body after the run. Initially, the fronts were wearing more, so I added caster, and it made the wear a lot more even. Not to mention laptimes were down.

Is this a decent way to set your car up, based on even tire wear?
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Old 06-04-2003, 07:27 PM   #3093
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Quote:
Originally posted by CypressMidWest
Actually, the Six-Pack and CarpetKnife from CRC can also be ordered with the old front-end. They call it "retro"
my bad....maybe it's because all the kit i see at my LHS are Assoc. strut
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Old 06-04-2003, 07:40 PM   #3094
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This thread is busy tonight.

On the Dynamic strut front end, in order to free up the kingpins to make the steering block move freely, what sized reamer do you use?

And do you ahve to use a reamer, or could I just usae a drill bit? I understand you shouldnt use a power drill, but how about a drill bit in a tap handle? Would that work?

Thanks
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Old 06-04-2003, 09:58 PM   #3095
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Default Re: Discharging 4-cell packs

Quote:
Originally posted by mushu
I'm getting ready to do some 1/12 scale racing and I have a question. What's everyone using to discharge their 4-cell packs. There are plenty of choices for discharging 6 cell packs down to .9v per cell @20-30 amps, but what about 4-cell packs. The only things I've been able to find are the high-end Integy chargers and the Competition Electronic chargers.

I asked the same question about ten or twenty pages ago! And the same basic answer. Seems like Deans or somebody would make a 4-cell specific cut-off device. The one I use on my 6 cell packs don't seem to take the 4-cell packs down very far.

Think I'm off to the electronics store to see what I can build or come up with......I'll keep you posted.

By the way, a guy on here posted a home-made discharger diagram.....seems to me I saved it.... Hmmmm
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Old 06-04-2003, 10:01 PM   #3096
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Quote:
Originally posted by dg8one
question

what is a good servo for 1/12?
I'm going to use the Airtronics 94145 servo in my 1/12 car. I think thats what the number is, it's metal geared and has good specs. You can get them from Hobby Ect. for 65 dollars. I've heard this is what a lot of people use, and since it's Airtronics you know it will last .

I think you could use any drill bit to ream it out, not sure what size though. Just put it in a pin vise or something, that's what I've used before. I'm going to order my car tonight and I was wondering if any 1/12 springs advertized on the CRC site would fit the old style and dynamic strut front end, there's not difference right? Thanks!
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Old 06-04-2003, 10:08 PM   #3097
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Hi Guys, A little off topic, but I was just cruising the net and I saw that SpeedMerchant has an online shop now. http://www.teamspeedmerchant.com/index1.html No more waiting for my LHS to order for me.
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Old 06-05-2003, 12:50 AM   #3098
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Mushu: I found it! Someone (sorry, can't remember the name to give you credit) posted this for me when I asked the 4-cell/discharge question. In reading it you will notice a resistor. Looks to me like the text at the end discussing how to size the resistor says that without a resistor it discharges to about 3.5 volts.....that sounds about right to me for 4 cells. There is a drawing and picture that go with this, but I can't seem to get it to copy from the file to this thread. If the guy who originally posted this could re-post the drawing, it would sure help out! Thanks! and good luck with your discharger project Mushu!


Auto Cut off

Once you have built a bulb discharger you should build an auto cut-off device to protect you cells from reversal which can be very damaging. The device simply switches the load off once it reaches a predetermined voltage (usually about .8 volts per cell). To build the device you will need:


1 x High current 12 volt relay (A 30 amp Bosch automotive horn relay is what I use but anything similar will do.)
1 x Momentary push on switch (where the switch is on only while you press it and is off at all other times)
1 x About 1 foot of battery wire
1 x Pair of battery connecters
1 x 1/4 watt or larger resistor approx 30 ohms (more about this later)
A few pieces of small hook up wire (any small wire will do)







The first step is to wire up the main current loop using standard battery wire, locate one of the coil terminals and solder two pieces of wire (black) to this (one to go to battery negative and one to go to the discharger load negative). Then locate the common terminal and the normally open terminal of the relay (these terminals are open circuit when the coil is not activated and short circuit when the coil is activated) and solder one piece of wire (red) to each of these. Each pair of red and black wires can now have their battery connectors attached.

To check the first stage of the circuit, first measure the resistance between the pair of wires that plug into the battery and the pair that plug into the load they should both be infinite (open circuit) if they are not recheck the circuit and fix any problems.

If this checks out ok the battery can be plugged in. At this stage nothing should happen (if there are flames explosions etc. something is wrong). By using short piece of small wire energise the coil by connecting the unused end of the coil to the positive of the battery (where the switch is on the diagram). When this wire is applied the relay should turn on and the load wires should have 7.2 volts across them, as soon as the wire is released the relay should go off and the voltage across the load wires should go to zero. Once again if the load voltage does not go to zero when the wire is removed check and fix the circuit before continuing. If this works ok the switch can be soldered into position between the two terminals just used.

The next step is to calculate the size of the resistor needed, to do this first measure the resistance of the coil (it should be about 100 ohms). Then the voltage at which the relay releases has to be found, this is done by soldering a temporary piece of wire in place of the resistor and discharging a battery while monitoring its voltage (press the switch to start discharging). The battery voltage at the moment the coil releases should be around 4 volts.

The resistor value can then be calculated using:

R = Rr(Vc/Vr) - Rr

Where:
R is the resistor value
Rr is the resistance of the relay coil (around 100 ohms)
Vc is the cut off voltage required (I use 5 volts for a six cell pack)
Vr is voltage at which the relay releases (around 3.5 - 4.5 volts)

This size resistor can then be placed in the position shown on the diagram in the place of the temporary wire used in the previous step. The discharger should now switch off at around the voltage calculated. All you have to do to use the device is plug in the load and battery and press the switch once to start discharging. Alternatively a variable resistor can be used in place of the resistor to trim the cut off voltage. If you have room in the case of the relay the resistor and switch wires can be placed inside (as I have done), this makes the devise much neater and less prone to damage. The switch can also be mounted on top of the relay.

The excess terminals on the relay can then also be removed leaving only three (negative, bat positive and load positive). Once the cut off trips the battery is completely isolated so it can be left connected for extended periods of time, however as always the load should not be left unattended while it is operating as it could set fire to something due to heat build up. I find mine very useful for racing as it only takes a few seconds to plug in after a race before going out to marshal the next race, when you get back the battery is dumped and ready to be recharged.




Last edited by Graphitedust; 06-05-2003 at 12:56 AM.
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Old 06-05-2003, 03:26 AM   #3099
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Cool I built one!

Instead of using all the formulas, I just bought a 1/2 watt pot, built the thing, and adjusted it and tried it until it cut off at my required voltage. Then I measured the resistance of the potentiometer and bought a resistor to match it. I then gave all the parts including the resistor to my son and he built him self another one. My son is 11. Different relays have different coils so this seemed the simplest way for me. It has to be a low resistance pot, like 500 Ohms or lower if you can find one. I think I ended up with like 150 ohms for 5.0 volt cut off.

I also used a digital meter with a min-max function so I could see exactly where the relay opened up. Made it easier than watching it.

By the way they both work flawlessly.

David Root
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Old 06-05-2003, 04:59 AM   #3100
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The website for that info is http://users.chariot.net.au/~samstain/howto.html

They also have all sorts of other good stuff, like tire warmers.
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Old 06-05-2003, 06:02 AM   #3101
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Quote:
Originally posted by dg8one
question

what is a good servo for 1/12?
Call Mimi, she has the proper Airronics servo for $60..... Just let her know you need a 1/12th servo and she'll knw what you need......
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Old 06-05-2003, 06:04 AM   #3102
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Quote:
Originally posted by racerdx6
. I'm going to order my car tonight and I was wondering if any 1/12 springs advertized on the CRC site would fit the old style and dynamic strut front end, there's not difference right? Thanks!

The springs work on both frontends.....They are all Associated frontend springs......
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Old 06-05-2003, 06:55 AM   #3103
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Quote:
Originally posted by dg8one
question

what is a good servo for 1/12?
Airtronics 94145Z
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Old 06-05-2003, 07:25 AM   #3104
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The KO 947 is an excellent servo, as is the 3025 from JR. The Airtroncs referenced above is also great.
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Old 06-05-2003, 09:10 AM   #3105
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DavidRoot and RC Paperboy: Thanks for the assist!!!!

David: How low could you turn down the voltage? Could you get as low as 3.5 volts?
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