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Old 09-08-2010, 06:23 PM   #5626
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What shock lengths are people using, I am building my car right now and was curious what the length of the front and rear shocks should be. Thanks.
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Old 09-08-2010, 06:33 PM   #5627
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What shock lengths are people using, I am building my car right now and was curious what the length of the front and rear shocks should be. Thanks.
Should be helpful. From Larry Fairtrace
Ok here is what I do when I build my shocks. I only use the V2 Shock now as they are smoother and don't have random leaking problems that some of the old v1 shocks had.

The first thing I do is not exactly necessary but I like to do it.

I cut the little nub that doesn't have threads off the bottom of the shafts. this makes me able to screw on the bottom and shorten the whole throw of the shock so the piston doesn't push on the bladder as much when fully compressed. Like I said its not necessary because you are probably never compressing the shock that much anyways but I do it none the less.

I make sure the white spacer that goes in the bottom of the shock slides on the shaft with no friction at all, I like to make sure it drops on. If it doesn't I hit it with a reamer real quick. But as of right now with the v2 shocks this problem has gone away and I haven't had to do it with the white machined piece.

I use the 40 degree o rings even with the V2 shocks all the time. I use green slime on the o ring.

I put a .2mm shim on top of the piston between the piston and the Eclip to take up the little bit of play the piston has.

As of late I don't like running any rebound at all in my shocks so I drill a hole in the plastic part of the cap right at the base of the shock mounting part that goes up from the flat part of the cap with a #57 drill bit.

Then I put the shaft in and make sure it slides up and down very very smoothly on the oring. It usually does if everything is done right. I ream out the shock bottom were the 5.8 ball goes in so it is as free as possible without any slop. This usually just takes a slight touch with a reamer. I also hit the plastic top with a reamer too, just so everything rotates smoothly.

I screw the bottom on as much as possible right before it starts binding the 5.8 ball in the bottom on each of the shocks.

Then I fill up the shock with oil. Always Losi oil, just because thats what I have used for the past 5 years so I know it well. And they have half weights which gives me more range of adjustment.

If possible I build my shocks and let them sit overnight and get the bubbles out, I don't like using a shock pump because it feels like you can always get bubbles to come up if you pump it too much. I do use them at the track once in a while if I don't have time to let the shocks sit for an hour or so.

When I am ready to finish I push the shaft 95 percent of the way in and push the bladder on with the back of my lunsford turnbuckle wrench or whatever is just about the same size as the concave part of the bladder make sure all the excess oil runs out and you keep the shock shaft pushed in 95 percent of the way. Then I screw the cap on almost all the way and push the shaft the rest of the way in as any excess oil bleeds out and then tighten the cap. If you drilled the holes right and built it right it should have no rebound at all and no contraction when you pull the shaft out.

I measure my shocks from end to end after being built and make them 61.5mm.

That is pretty much exactly what I do. The keys are making sure before putting oil in them that all the shafts slide on the orings very smoothly with almost no friction at all.

Also always make sure the pistons are clean and without burrs before putting them in.

I always use the 1.2mm pistons with 3 holes.

I think that is everything. Probably way more info than anyone needed and most of it unnecessary.
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Old 09-08-2010, 10:53 PM   #5628
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Gear diffs. I have Xray 10k CST in the rear and Ofna 120k in the front right now. I may go back to the 100k in the front for comparison testing, but they both seem to work pretty well. 80k was too soft for the front. 10k gave better steering in the rear.

Fans. I don't like the concept of heatsink fans. I realize that it's an easy way to mount a fan to any motor, but I think that the extra heatsink just traps the heat in the motor and doesn't allow it to dissipate like it should. Besides being bulky and ugly to look at, most heatsinks that I've seen run the fins in the wrong direction. To be effective the fins should run length wise along the chassis, not parallel to the motor (on a belt drive car). As the heat tries to escape the fins, the longitudinal design would allow airflow to "clean" the hot air off of the heatsink. I hope that makes sense. I haven't run a heatsink fan to compare temps, mainly because they look terrible. (I'm vain). With the BOSS fan glued to the chassis, like I have it, the motor runs 30-40 degrees cooler. Last night I hardwired a BOSS fan to the ESC instead of plugging it into the receiver and it puts out some major airflow. With the car on the table, I could feel the breeze coming from the fan. Good luck with your choices. Best of luck on the track.
Thanks for the detailed reply Tony. I've thought the same thing about heatsinks trapping the heat on the motor without a fan, I would never use one without. When I was running 540 a while back I had the fan wired into the battery/esc wires, makes a big increase of fan rpm/airflow with the higher voltage. Might have to do the same again with the brushless esc.
Thanks Again.
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Old 09-09-2010, 06:24 AM   #5629
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Fans. I don't like the concept of heatsink fans. I realize that it's an easy way to mount a fan to any motor, but I think that the extra heatsink just traps the heat in the motor and doesn't allow it to dissipate like it should. Besides being bulky and ugly to look at, most heatsinks that I've seen run the fins in the wrong direction. To be effective the fins should run length wise along the chassis, not parallel to the motor (on a belt drive car). As the heat tries to escape the fins, the longitudinal design would allow airflow to "clean" the hot air off of the heatsink. I hope that makes sense. I haven't run a heatsink fan to compare temps, mainly because they look terrible. (I'm vain). With the BOSS fan glued to the chassis, like I have it, the motor runs 30-40 degrees cooler. Last night I hardwired a BOSS fan to the ESC instead of plugging it into the receiver and it puts out some major airflow. With the car on the table, I could feel the breeze coming from the fan. Good luck with your choices. Best of luck on the track.
Just wanted to add my 2 cents worth since I was a licensed professional engineer at one point...

The heatsink doesn't "trap" the heat. In fact, if the heat sink is warm or hot, then you know that the heat that would otherwise be at your motor is now transferred to the heat sink. The more "fins" or surface area metal on the heat sink the better it is at dissipating (drawing the heat away from) the motor.

When you say the fins should be running in parallel to the belts is theoretically fine. However, I would bet all my cars on it that the difference is negligible. You have airflow inside the car already. So long as there's airflow, it's blowing the heat away from the heat sink regardless of the fins orientation. It's not like the fins are 5 feet tall where the air in between them gets trapped.
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Old 09-09-2010, 08:30 AM   #5630
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Have you guys been keeping up with the Photon in Vegas? Looks like its doing fairly well with all that comp!

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Just wanted to add my 2 cents worth since I was a licensed professional engineer at one point...

The heatsink doesn't "trap" the heat. In fact, if the heat sink is warm or hot, then you know that the heat that would otherwise be at your motor is now transferred to the heat sink. The more "fins" or surface area metal on the heat sink the better it is at dissipating (drawing the heat away from) the motor.

When you say the fins should be running in parallel to the belts is theoretically fine. However, I would bet all my cars on it that the difference is negligible. You have airflow inside the car already. So long as there's airflow, it's blowing the heat away from the heat sink regardless of the fins orientation. It's not like the fins are 5 feet tall where the air in between them gets trapped.
Might i ask a question then? What transfers heat best, a solid metal object... or two solid metal objects made from two different metal types touching each other?

Lets add to that. If the first metal object in the latter half of the above question had holes that allow natural heat exchange with the outside air, and you covered those holes with the second metal object, would heat exchange from the first metal object increase or decrease than if it was left alone? Which would be more efficient?

Now while i know there are a lot of variables NOT mentioned here for an accurate answer, surely you can get the idea of where im heading. Molecules transfer heat best when part of the same object. Two objects just touching each other, adds a break in efficiency of transfer (conduction). Adding a thermal paste can improve transfer.

The most efficient way to transfer heat from an electric motor would be with a one piece finned motor casing, like you see in some of the 1/8th scale motor designs. Not an attached heatsink that may plug motor case holes specifically designed to remove heat from the motor. Adding a fan to the equation is a whole nother set of variables.
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Old 09-09-2010, 09:01 AM   #5631
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Might i ask a question then? What transfers heat best, a solid metal object... or two solid metal objects made from two different metal types touching each other?

Lets add to that. If the first metal object in the latter half of the above question had holes that allow natural heat exchange with the outside air, and you covered those holes with the second metal object, would heat exchange from the first metal object increase or decrease than if it was left alone? Which would be more efficient?....
It depends on the 2 types of metals (or materials) for that matter. In an extreme case, if you lit something on fire and put something which was more flammable next to it, the item that is more flammable "takes the flame away" from the less flammable object." Regarding the motor metal and the heat sink, I don't know what kind of metal is on the BL motor (I don't have one yet), but I assume the heat sink is aluminum. Thus, I don't know what the heat conductivity specs are to be able to tell you if the aluminum heat sink "draws" the heat away or not.

Regardless of how many holes are on the can, I would take the addition of the heat sink any given day of the week. About 30 years ago, the first heat sinks came out for brushed motors. The manufacturers claimed we go up at least 1 or 2 teeth on the pinion gears because of the reduced heat. So we did a little experiment... hooked up a motor to a battery at room temperature with no load and ran it for 10 min and took a heat measurement at the end bell. Then we did the same with a heat sink on. I don't recall the exact numbers but I recall it was huge and significant. We then added load to the motor and the difference with the heat sink was even larger. So from that point forwards, I always had a heat sink on my motors.
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Old 09-09-2010, 09:40 AM   #5632
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Now while i know there are a lot of variables NOT mentioned here for an accurate answer, surely you can get the idea of where im heading. Molecules transfer heat best when part of the same object. Two objects...
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Regardless of how many holes are on the can, I would take the addition of the heat sink any given day of the week. About 30 years ago, the first heat sinks came out for brushed motors. The manufacturers claimed we go up at least 1 or 2 teeth on the pinion gears because of the reduced heat. So we did a little experiment... hooked up a motor to a battery at room temperature with no load and ran it for 10 min and took a heat measurement at the end bell. Then we did the same with a heat sink on. I don't recall the exact numbers but I recall it was huge and significant. We then added load to the motor and the difference with the heat sink was even larger. So from that point forwards, I always had a heat sink on my motors.
I found quite the opposite. Brushed motors remove a large amount of heat through the cooling holes with the air coming off the armature as it spun. Once i covered the motor up with a clip on heatsink, that air was trapped inside the motor mostly allowing conductive cooling. This actually forced hot air through the endbell shortening brush and commutator life and raising overall temp.

Brushless motors have very little air generated by the spinning rotor when compared to brushed designs. BUT the wire core is closest to the can making it easier for the windings to shed their heat. You do the math, brushless is best for SO many reasons.

As previously mentioned, air under a TC body shell is likely turbulent at best, and essentially becomes its own enclosure from cooling air. If you doubt this, then you have likely never run a 1/10th 4wd buggy, nor struggled with the heat issues they are so commonly faced with. This environment is completely different than your open air bench test that allowed heat to dissipate to a much larger volume of cooler air. Of course you will see much lower temps with a clip on heatsink in those conditions... even under load. The results are not comprable.

My years of testing have been countless dyno hours, and in car at the track comparisions. Every day at the racetrack is one big test session for me... and yes i DO take notes. lol

The purpose of this wasnt to take things off topic. Just sharing a little bit of info for those wanting to do a little daily thinking. PM me if ya wanna continue the conversation...
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Old 09-09-2010, 10:59 AM   #5633
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Originally Posted by M3Armand View Post
Just wanted to add my 2 cents worth since I was a licensed professional engineer at one point...

The heatsink doesn't "trap" the heat. In fact, if the heat sink is warm or hot, then you know that the heat that would otherwise be at your motor is now transferred to the heat sink. The more "fins" or surface area metal on the heat sink the better it is at dissipating (drawing the heat away from) the motor.

When you say the fins should be running in parallel to the belts is theoretically fine. However, I would bet all my cars on it that the difference is negligible. You have airflow inside the car already. So long as there's airflow, it's blowing the heat away from the heat sink regardless of the fins orientation. It's not like the fins are 5 feet tall where the air in between them gets trapped.
+1 from another formerly licensed engineer

Also, if your heat-sink mounted fan is blowing air onto the fins, just turn it over and it will pull air away. That's what I do.
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Old 09-09-2010, 04:35 PM   #5634
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Im amazed at the use of fans/heat sincs buy some club drivers,especialy those who thinks its a quick cure for high temps,Yes they may help if you are running your motor to an inch of its life and can aford to replace motors often,But its pointless blowing fans on your kitchens oven if the Roast beef is getting burnt,all this is doing is cooling the allready damaging dissipating heat.
IMHO if you need large fans/heat sincs to lower temps to a safe level your profile and gearing are wrong. gear and profile with out them then maybe fit "to be safe " and preserve motor life!....besides clip on heat sincs do next to nothing (very little surface contact unless a heat paste is used,plus why try to cool just 30/50% of the heated area,thats not good engineering practice at all!!)No doubt the tiny air gap between a poorly fitted heat sinc and Can casing may prove to be an insulator,next time you remove a clip on heat sinc from your motor take note of the tiny scratches left on the Can as these are the witness marks of the ONLY points of true contact to dissipate heat into the sinc ..Hmmmm......Another diagnostic Engineer
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Old 09-09-2010, 06:21 PM   #5635
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I should have just said that heat sinks are ugly and been done with it. Great bit of info and arguements from both sides though.
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Old 09-09-2010, 08:47 PM   #5636
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This might sound dumb but I'm having a heck of a time trying to get my servo in. It seems like I might have to cut the top Ear off of it... does this seem right? Ehhh its been a long day.. hahaha but the car is just about together and starting to look pretty sick!!
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Old 09-10-2010, 12:37 AM   #5637
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Shouldnt have to cut it. Post a pic.
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Old 09-10-2010, 02:26 AM   #5638
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This might sound dumb but I'm having a heck of a time trying to get my servo in. It seems like I might have to cut the top Ear off of it... does this seem right? Ehhh its been a long day.. hahaha but the car is just about together and starting to look pretty sick!!
Hi
It depends what servo mounts You are using, what servo and what holes in the chassis You are using. I wanted to have my S9550 forward so I had to dremel the servo house and move the top left ear.
Now I have changed to another servo that is very low, so the problem is solved.

Good luck
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Old 09-10-2010, 04:01 AM   #5639
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Hello

5 place in the 4 round of National Championship Stock class , My Setup

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Pedro Silva

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Old 09-10-2010, 05:00 AM   #5640
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Congrats Pedro.
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