Limitless Serpent 989e Speed Runner

[fozzy71]

the 1/8 looks surprisingly small compared to my Limitless and Hobao.

Wow, I just googled 'serpent 989e wheelbase' and see that it is 'Wheel base: Adjustable 296 - 300mm +/-1.7mm' which is 11.8 inches, 1 inch shorter than a 6s Typhon. That thing should be quite the handful.

 

[dk10438]

yeah, it's gonna be a handful. That being said, @phildogg dog got his 988 up to 139 and Tony Ingall's got his Xray T4 up to 149.

Re: unsprung weight v. sprung weight, I thought that the primary disadvantage of unsprung weight was due to forces due to inertia. The lack of a flat pan on the underbody will create a lot of turbulence. It's going to be a blast regardless....

 

[dk10438]

to me it seems like a pretty clever design...
Usually unsprung weight is primarily the brakes, wheels and tires and adding weight there adversely affects braking, traction/cornering and acceleration, presumably due to rational forces. In this design, I'm thinking the aero forces bypasses the suspension and goes straight to the tires? So although there is an increase in unsprung weight, the car won't penalized in the same way that it would had there been an increase in rotational mass. IDK, maybe someone with more of a racing background or engineering/physics background could chime in.

 

[Ckrobin]

Rotational mass and unsprung weight are two separate math equations designed to perform different functions. The same parts may be used to figure them both but for different applications.

Unsprung weight is referring to the weight not controlled by the suspension. It is a minor issue but something F-1 engineers will consider as it does have a small effect on your handling. It includes parts like wheels, tires, brakes, half the weight of the control arms and springs... The basic principle is that unsprung weight is not controlled by the suspension so is going to act as its own force. It is weight you wouldn't consider when figuring your weight transfer, however you should be aware of it because if you transfer all your weight to the left you still have the unsprung weight on the right side (and left) of the car trying to fight you in a turn. In general it is believed that the lower the unsprung weight the better.

Rotational weight is not a handling issue it is a power issue. Yes the weight of the wheel and tire are unsprung and because of that they effect the handling. But they are also part of the rotational weight which has nothing to do with handling. Rotational parts would include wheels, tires, brake rotors (not pads or calipers) lug nuts, axles, differential anything that spins or is bolted to something that spins. It goes all the way to the engine and even to the accessories in a full scale vehicle your fan (on older vehicles,) alternator, water pump and other things that spin with the motor. Even the crank rods and piston are included in this weight. If you really want to get technical you need to figure out how much electricity you are using to know how much load you are putting on the alternator and add it to your rotational mass figures. All these require HP to overcome so this is why race cars measure HP at the tires vs at the flywheel. Then there is your European bHP which magically adds HP as it takes the weight of the rotating assembly out of the equation. Rotating mass is a figure to determine the amount of power the motor has to overcome the parts it is made of and get moving and to a lesser extent slowed back down as the brakes fight the inertia of the weight of the drivetrain.

So the weight of everything figured in your rotational weight also needs to be calculated separately as sprung or unsprung weights if you want to understand the handling and acceleration characteristics of your vehicle.

This design appears to allow the downforce to bypass the suspension allowing for a softer suspension at the cost of a little unsprung weight. Seems like it would be a good trade off.

 

[dk10438]

I'm very close to being done now. Installed the servo and ESC. Now I'm just waiting for a GYC470. Weight without the batteries is 2133 grams.

 

[dk10438]

I finally got the rest of my parts
I've added at gyc470 servo and a futaba temperature sensor. I didn't have a chance to drive the car on the street yet but I will say that the 470 behaves very differently than the 441. On the bench, rotating the car resulted in significant oscillations which I didn't observe with the 441 on my other cars. I actually thought that the gyro might be defective but I contacted futaba and they said that the algorithms and the hardware were significantly upgraded which resulted in a faster frame rate and that it wasn't uncommon for customers to call them thinking that the gyro was defective. So I'm curious how differently the car will drive.

 

[Dan B.]

I finally got the rest of my parts
I've added at gyc470 servo and a futaba temperature sensor. I didn't have a chance to drive the car on the street yet but I will say that the 470 behaves very differently than the 441. On the bench, rotating the car resulted in significant oscillations which I didn't observe with the 441 on my other cars. I actually thought that the gyro might be defective but I contacted futaba and they said that the algorithms and the hardware were significantly upgraded which resulted in a faster frame rate and that it wasn't uncommon for customers to call them thinking that the gyro was defective. So I'm curious how differently the car will drive.

View attachment 276379

Dude, that is sexy AF. Looking at the belts, gears, linkages, it’s like Steampunk just met F1. So cool, man!

 

[dk10438]

I modified the ESC "platform". In the stock configuration, the ESC plate is connected to the chassis via standoffs. Instead of using the standoffs, I used a few washers which allowed me to mount the ESC lower in the car. An interesting design decision by Serpent. Anyway, the car was engineered with a smaller/shorter ESC in mind so this worked out pretty good.

Dude, that is sexy AF. Looking at the belts, gears, linkages, it’s like Steampunk just met F1. So cool, man!

thanks Dan! your new street build is looking pretty awesome too!

 

[gotnitro]

Did you stay 40/26? I ordered the 36T, I could probably get 36/29 to fit before dremeling out the mount holes.

 

[dk10438]

40/26 for now but I have a 38T on order.
Using the serpent calculator on 6S (20V)
projected speed would be 135 mph. Realistically I usually get about 75% of the projections so probably 100 mph is what I'm thinking the setup will do. I want to take this slowly and not crash into a curb so I'll test on 3S and 4S before jumping to 6s and then work up to 120-130 mph. I've read that these motors run pretty hot which is why I threw on the futaba temperature sensor so I'll have to watch the heat too.....

 

[LibertyMKiii]

Just throwing this out there incase you want to go to the 10th degree
I use these on most of my builds to hold the servo wires. I scuff the CF and add a drop of CA glue then put a small piece of the tidy strip on.

https://www.chiefaircraft.com/map-sw-tidy-strips.html

You can also see in this picture I use spark plug wire holders for the motor wires when they run near moving parts:

 

[gotnitro]

Just throwing this out there incase you want to go to the 10th degree
I use these on most of my builds to hold the servo wires. I scuff the CF and add a drop of CA glue then put a small piece of the tidy strip on.

https://www.chiefaircraft.com/map-sw-tidy-strips.html

You can also see in this picture I use spark plug wire holders for the motor wires when they run near moving parts:

View attachment 276424

Lol!! I use that black 3 wire holder for my subwoofer runs

 

[phildogg]

Car looks good. But please tell me you have locked the front 1 way?

 

[dk10438]

Car looks good. But please tell me you have locked the front 1 way?

not sure. I have the one way front axle. Is there a locked front one way? Or do I lock it myself?
I guess if I do speed runs with a one way, braking would only be rear wheels only?

 

[phildogg]

not sure. I have the one way front axle. Is there a locked front one way? Or do I lock it myself?
I guess if I do speed runs with a one way, braking would only be rear wheels only?

Stock is a one way axle. I would be very careful braking with a one way as like you said rear brakes only. People lock the one way by drilling into it and adding flat spots on the axles. adding a grub screw to lock the axle. the guy who did minr removed the one way bearings and inserts a bushing then drills and adds a grub screw. Def. worth looking into.

 

[Dan B.]

Stock is a one way axle. I would be very careful braking with a one way as like you said rear brakes only. People lock the one way by drilling into it and adding flat spots on the axles. adding a grub screw to lock the axle. the guy who did minr removed the one way bearings and inserts a bushing then drills and adds a grub screw. Def. worth looking into.

The number of experienced people and the wealth of knowledge on this forum never ceases to amaze me.

 

[dk10438]

Stock is a one way axle. I would be very careful braking with a one way as like you said rear brakes only. People lock the one way by drilling into it and adding flat spots on the axles. adding a grub screw to lock the axle. the guy who did minr removed the one way bearings and inserts a bushing then drills and adds a grub screw. Def. worth looking into.

@phildogg
Thanks for the reply! I didn’t really think about the one way axles before you mentioned them but now that I think about it, it’s a pretty big issue since all the mass is the car will be loaded onto the front axles which means that a) rear wheels won’t have much ability to stop the car and b) this will create a severe oversteer condition and spin outs at high velocity!

I’m wondering if the gyro will be able to compensate for the oversteer? I’ll have to look at the one way axle more closely and see what the best way to lock it would be. Is welding an option??

 

[phildogg]

@phildogg
Thanks for the reply! I didn’t really think about the one way axles before you mentioned them but now that I think about it, it’s a pretty big issue since all the mass is the car will be loaded onto the front axles which means that a) rear wheels won’t have much ability to stop the car and b) this will create a severe oversteer condition and spin outs at high velocity!

I’m wondering if the gyro will be able to compensate for the oversteer? I’ll have to look at the one way axle more closely and see what the best way to lock it would be. Is welding an option??

Never heard of anyone welding them. the main issue is the actual one way bearings. Like i said there are people you can send them too and the will lock them. ive had several done.. i usually buy a spare axle and send it off then switch them.

 

[dk10438]

Car looks good. But please tell me you have locked the front 1 way?

@phildogg
I've got a lot more respect for what you've done with your 988 now. I took mine for a maiden spin (haven't locked the front yet so nothing too crazy). These little guys are so much harder to control than a limiltess or hobao. Since it's so light, traction is an issue and it seems to catch air with any pebbles or gravel on the street. Getting to 120-130 is going to be challenging!

 

[phildogg]

@phildogg
I've got a lot more respect for what you've done with your 988 now. I took mine for a maiden spin (haven't locked the front yet so nothing too crazy). These little guys are so much harder to control than a limiltess or hobao. Since it's so light, traction is an issue and it seems to catch air with any pebbles or gravel on the street. Getting to 120-130 is going to be challenging!

yeah the smaller cars take some getting used to. I started speed running with 1/10 touring cars and still have a 150+mph 4tec 2.0. they are a little more twitchy on steering but the more you do it the easier it gets.