Limitless Serpent 989e Speed Runner

[dk10438]

I'm going to enjoy this "build". I just got this roller off of RC tech, in excellent condition and am going to make it a 1/8 speed runner. Initially I was thinking of the 1/10 Natrix but the 1/8 looks surprisingly small compared to my Limitless and Hobao.

 

[real_name_hidden]

Good luck and enjoy! Can’t wait to see the results

 

[dk10438]

This is definitely a serious racecar. I was surprised at how light it is weighing in at 1364 grams. Wheelbase is 295mm and max motor size is probably a 89mm can. However, the motor mount sits lower on the chassis so a 40mm diameter can is probably the biggest that will fit.

MMX8s will fit perfectly and I've decided to go TP for this build. Since the wires exit on the back of the TP motors, I'm not sure if the 4050 will actually fit, so it's going to be a TP4040cm-2850 KV. Phillip Jolley just ran his "988e" at 139 mph on a Castle 2200. I'm using quotes because I think his car his really a 989e. I've studied his videos and his car has a 3 belt design and the 988 is a 2 belt car.

Regardless, 2850 kv should make this car scream on 6S. TBH, I'm not really quite sure how the gearing works on this car. The pulleys appear to be a set ratio so I don't have to mess around with that? The car uses a Revo style spur gear? And the options (at least from Serpent) only go down to 36 tooth.

Serpent has a nice little speed calculator to help me out which also lists possible gear combinations.
https://www.serpent.com/xcart/cart.php?target=product&product_id=11622#product-details-tab-DownLoad

Phillip Jolley said on YT that he uses a 8mm speedtek spur gear so I'm going to assume that I can use standard 8mm spurs.

 

[Dan B.]

Those are such cool cars. Looking forward to seeing it!

 

[dk10438]

TP4040cm 2850 ordered. I feel kinda guilty about using spare parts as the electronics (futaba 304, skyRC gyro, pro modeler DS630) so I think I'm going to splurge and deck it out with my usual goodies which means the pro modeler is going to go up for sale in the classifieds soon...

 

[dk10438]

tp4040 showed up today!
CB500 and Futaba 404 in transit.

 

[ColosTommy]

Hi, sorry if this is a stupid question, i know nothing of "Serpent" cars. Is there a flat bottom to go on this? Aerodynamically if you're talking about 139mp, as you mentioned someone else was doing, surely you will want a flat smooth flat bottom, I know you would in IRL car aerodynamics, i assume that transfers over to scale as well?

 

[phildogg]

Car is looking good, as we have already talked about mine is a converted 988 and not a E model. Yes I used a 8mm pinion as a spur gear. I'm not familiar with the shaft on this car (989e)

Hi, sorry if this is a stupid question, i know nothing of "Serpent" cars. Is there a flat bottom to go on this? Aerodynamically if you're talking about 139mp, as you mentioned someone else was doing, surely you will want a flat smooth flat bottom, I know you would in IRL car aerodynamics, i assume that transfers over to scale as well?

No they don't have a flat bottom, but the cars work extremely well as is.

 

[Dan B.]

tp4040 showed up today!
CB500 and Futaba 404 in transit.

View attachment 271431

Can’t wait to see that thing rip!

 

[LibertyMKiii]

Looks like that was a good call on the motor size as the belts are very close there....
I imagine a piece of tape across the bottom wouldn't be a bad idea to help keep little rocks out of the belts.

 

[dk10438]

Can’t wait to see that thing rip!

thanks Dan! Parts are coming from overseas so not sure how long that's going to take but I'm excited to get this baby on the road. I'm really interested to try out this TP since everyone seems to rave about them. I'll take some better pics of the motor bay. Although it's about 90 mm, wires on TP's exit from the back of the can so you really can't go bigger than a 4040. A 90 mm motor will fit if the wires are connected on the side of the motor such as Castle or HW. The motor sits pretty low so I couldn't use a 4985 motor like the HW or CC. I do recall seeing a video where someone used a 1520-1650 motor which barely fit but gearing options are somewhat limited so I opted for the higher kv TP.

Looks like that was a good call on the motor size as the belts are very close there....
I imagine a piece of tape across the bottom wouldn't be a bad idea to help keep little rocks out of the belts.

it's not as close as they appear in the pictures since the wires are sitting a little higher than the belt.

 

[dk10438]

Here’s the pics

 

[gotnitro]

You still waiting on china parts too? I just got an email saying mine are on the second leg, arrived in AZ last night.

 

[dk10438]

You still waiting on china parts too? I just got an email saying mine are on the second leg, arrived in AZ last night.

Yeah
Waiting on a futaba servo and receiver so the build is stalled for now…
But I source the futaba stuff from Taiwan

 

[gotnitro]

Yeah
Waiting on a futaba servo and receiver so the build is stalled for now…
But I source the futaba stuff from Taiwan

Can’t get it here in the US or cheaper overseas?

 

[dk10438]

I get all my futaba stuff from this eBay seller in Taiwan. Very reputable with 6900 feedbacks, 100 percent positive.

Just ordered a cb500 and 404 receiver for 210 which is a pretty good deal since amain has them for 200 and 110 respectively.

 

[dk10438]

Here's a quick video demonstrating the floating chassis of the Serpent.
Does anyone know if shock limiters are still necessary to prevent bloweovers since downforce created by the body is not being transferred to the shocks?

 

[LibertyMKiii]

Here's a quick video demonstrating the floating chassis of the Serpent.
Does anyone know if shock limiters are still necessary to prevent bloweovers since downforce created by the body is not being transferred to the shocks?

That is wild!
I was not aware it functioned like that.

Probably a lesser amount just to make sure you maintain the rake angle needed.

 

[Konfucius]

That car is awesome. I bet all that cost a pretty penny. Serpent cars are incredible.

 

[Ckrobin]

I wonder how that effects the handling? Typically unsprung weight is bad. That design appears to add the weight of the body and body mounts to the unsprung weight. I can see an advantage to having the aero downforce applied there. Perhaps that is overcoming the additional unsprung weight? Sure would like to hear some physics on how this effects the car.

The advantage of the chassis design not having a "belly pan" means it is lighter. Not sure what mm carbon fiber your chassis is but am guessing 5 mm. If that is the case get a piece of 1mm and cut it to fit as a "belly pan." Not only will it save you from getting rocks in the belts it will keep air out and give you something to secure the edges of the body to.

FYI one of the few places on a race car you can get downforce without adding a lot of drag is by cleaning up the air under the car. And drag is very bad for speed runs. There is an imaginary barrier depending on the aero efficiency of your car that once you hit it (excuse the full scale expression here) every mph over that speed will require double the HP it required to get there. IE if it took 100HP to push a Mazda Miata to 100 mph that is 1 hp per mph. To go faster it would take 2 hp per mph so to go 101MPH you now need 102 HP. That is a very crude explanation but every vehicle hits this wall. At that point reducing drag is as important as having downforce. Then you have to find that balance where you only add as much downforce as is needed to keep the car on the ground. if it feels like it is skating on ice the aero package is probably pretty fast.