Best chassis for speed runs?

[fullspectrum 97]

So I just mounted a new 2mm thick Deltaplastik body. And I have to say...Im such a hack compared to Stewart and nbTNM..lol. I suppose it doesnt help Im always in a rush because of family, work and other time constraints. I had to wait 2 weeks just to go for a speed run. 

So I took Stew's advice and dropped the gearing to 60 spur and 42 pinion from 49/46 and put the 6900kv fake Castle motor back in. I will run it on 3s and see what I get for numbers.

I kinda botched the new body install. It sits too far forward and too high. So if I cut the body out on the bottom it would sit too high. Uncut it sits good. Soooo...Im going to leave the front and bottom without cutting. All I cut out was the rear. Also I need to make a new undertray. Also would it be detrimental to not cut the wheel wells out front and back and have fully covered wheels?

[nbTMM 433]

Yep, just got to find a suitable road near me after I finish off the final details. Front posts are just regular front posts with the bottom cut off, a 2.5mm hole drilled and then attached through the spare 3mm holes in the standard bumper mount. Front bumper is just the standard tt02 foam one. Not sure if i'll keep it there but it seems to support the body well, going to make a FRP front diffuser which sets at the same level as the side trays. I need to fibreglass reinforce the shell mostly around the rear body posts and front wheel arches as it is too flexible for my liking.

60 spur / 42 pinion will have your peak power at ~125kmh
49 spur / 46 pinion will have your peak power at ~167kmh

You can work this out by finding the unloaded max motor rpm:
6900kv * 11volts (a 3S pack under significant load) = 75900rpm

Peak motor power will occur at 50% of maximum rpm = 37950rpm

Then you can work out your final drive ratio
FDR = spur/pinion * 2.6 
so
FDR = 60/42*2.6 = 3.71
or
FDR = 49/46*2.6 = 2.77

Then you can work out the wheel rpms at peak power
Wheel rpm (60/42t) = 37950/3.71 = 10229rpm
Wheel rpm (49/46t) = 37950/2.77 = 13700rpm

and finally convert that to road speeds, assuming 65mm wheel diameter
speed (60/42t) = 10229*0.065*3.1415*60/1000 = 125.32kmh
speed (49/46t) = 13700*0.065*3.1415*60/1000 = 167.85kmh

Now that assumes that your battery and ESC can provide enough juice to actually make peak power. If your battery voltage sags, or the ESC drops a lot of voltage, you may find that you go slower when you gear for peak power. Instead you might gear for 75% max rpm at the motor where you get a bit less power (coincidentally about 75% of the max power) but the motor operates much more efficiently and is less demanding on the ESC and battery. That may make the 60/42t gearing reach a higher top speed even if you're aiming for ~160kmh

Hope that helps!
 

 

[Yalson 514]

10 hours ago, fullspectrum said:

So I just mounted a new 2mm thick Deltaplastik body. And I have to say...Im such a hack compared to Stewart and nbTNM..lol. I suppose it doesnt help Im always in a rush because of family, work and other time constraints. I had to wait 2 weeks just to go for a speed run. 

So I took Stew's advice and dropped the gearing to 60 spur and 42 pinion from 49/46 and put the 6900kv fake Castle motor back in. I will run it on 3s and see what I get for numbers.

I kinda botched the new body install. It sits too far forward and too high. So if I cut the body out on the bottom it would sit too high. Uncut it sits good. Soooo...Im going to leave the front and bottom without cutting. All I cut out was the rear. Also I need to make a new undertray. Also would it be detrimental to not cut the wheel wells out front and back and have fully covered wheels?

With regard to the body mount, I am not sure exactly what you mean by it being too far forward and too high. It certainly seems to be sitting high on the chassis, but can you not move it further down the mounting posts for a more snug fit. I mean, there is nothing that says you can't have it mounted that high, but it will increase frontal area (the size of the hole the car will have to make in the air: increased frontal area means greater drag). You can always remount the shell by punching new holes and then tape over the old ones. It will be a bit untidy, but will allow the body to sit with the wheels in the correct positions and in a lower, more natural stance.

I referred to keeping the wheels covered earlier and gave examples of 1:1 cars which havw found it beneficial in reducing drag and increasing stability. I am surprised nobody has tried doing it yet. It is an easy win at the rear, given you have clearance there and the wheels only move in an up-and-down axis. Just leave the wheelarches uncut and it will reduce drag, increase stability and make the shell stiffer at the back, where the removal of the rear panel is likely to make it a bit flappy. I mentioned previously that the airflow here might make the plastic at the very rear of the shell flap like a flag, but a bit of stiffening would sort that. If you look at what @nbTMM did to their shell and where they did it, then that might give you ideas (although you would not have to do such heavy-duty stiffening as in that example unless you are also planning to cut down the rear "kick-up" wing to reduce drag still further).

The front arches are a little bit more difficult, as although the body has the same width clearance here as at the rear, leaving the plastic in place will obviously cut down on the amount of available steering lock. There would be a considerable aerodynamic advantage, as with the rear arches, with lower drag and all the rest. On top of this, if you fair in both sets of arches on top of your wider, flat floorpan then you have virtually sealed up the whole of the area under the shell. There will still be holes where the wheels meet the road, but if you leave the plastic in the wheelarches then the area available for the air to bleed from under the shell to the outside is greatly reduced, and given that the whole area under the shell is now unable to leak out of the arches, both the under-shell and under-floor areas will now be at a lower pressure than the outside air. This means downforce: as @stew_mac said in a previous post, it will feel "planted" at anything over about 40mph.

Given that the idea here is to go as quickly as possible in a straight line, maximum lock may not be vital, but given that most speed runners here will be doing their runs on public roads with occasional traffic and unpredictable pedestrians, you would have to make a judgement on whether you feel the reduction in the amount of steering lock available is a worthwhile trade-off given the potentially catastrophic downsides.

You could, of course, just leave both sets of arches in place and cut them out later, or just leave the rears in.

 

[fullspectrum 97]

42 minutes ago, nbTMM said:

Yep, just got to find a suitable road near me after I finish off the final details. Front posts are just regular front posts with the bottom cut off, a 2.5mm hole drilled and then attached through the spare 3mm holes in the standard bumper mount. Front bumper is just the standard tt02 foam one. Not sure if i'll keep it there but it seems to support the body well, going to make a FRP front diffuser which sets at the same level as the side trays. I need to fibreglass reinforce the shell mostly around the rear body posts and front wheel arches as it is too flexible for my liking.

60 spur / 42 pinion will have your peak power at ~125kmh
49 spur / 46 pinion will have your peak power at ~167kmh

You can work this out by finding the unloaded max motor rpm:
6900kv * 11volts (a 3S pack under significant load) = 75900rpm

Peak motor power will occur at 50% of maximum rpm = 37950rpm

Then you can work out your final drive ratio
FDR = spur/pinion * 2.6 
so
FDR = 60/42*2.6 = 3.71
or
FDR = 49/46*2.6 = 2.77

Then you can work out the wheel rpms at peak power
Wheel rpm (60/42t) = 37950/3.71 = 10229rpm
Wheel rpm (49/46t) = 37950/2.77 = 13700rpm

and finally convert that to road speeds, assuming 65mm wheel diameter
speed (60/42t) = 10229*0.065*3.1415*60/1000 = 125.32kmh
speed (49/46t) = 13700*0.065*3.1415*60/1000 = 167.85kmh

Now that assumes that your battery and ESC can provide enough juice to actually make peak power. If your battery voltage sags, or the ESC drops a lot of voltage, you may find that you go slower when you gear for peak power. Instead you might gear for 75% max rpm at the motor where you get a bit less power (coincidentally about 75% of the max power) but the motor operates much more efficiently and is less demanding on the ESC and battery. That may make the 60/42t gearing reach a higher top speed even if you're aiming for ~160kmh

Hope that helps!
 

 

That helped tremendously! Thanks.

Im pretty crappy with the math part of RC which is pretty important...lol.

Yeah I think I was way overgeared and over motored in kv's which was why I did worse getting up to even 90mph which I was able to do before on a 5700kv motor, 4s and 49/46 gearing. Like Stew told me it takes too long to get up to speed and you need a very long run at it.

[fullspectrum 97]

Thanks Yalson. The body is 2mm Delta Plastik so its stiff even cut out at the back. Its also 200mm so the wheel arches still allow full steering at full lock so I guess I will keep them covered.

With this body I cant put it any lower on the front because its literally sitting on the front shock tower so thats as low as it goes but if I dont cut the bottom off the body the ground clearance is pretty low.

[Yalson 514]

1 hour ago, fullspectrum said:

Thanks Yalson. The body is 2mm Delta Plastik so its stiff even cut out at the back. Its also 200mm so the wheel arches still allow full steering at full lock so I guess I will keep them covered.

With this body I cant put it any lower on the front because its literally sitting on the front shock tower so thats as low as it goes but if I dont cut the bottom off the body the ground clearance is pretty low.

I just had a look at your image at greater magnification and I see what you mean about the mounting. It is a bit high, but you could theoretically leave it completely uncut and the flare all the way round the shell would act as an air dam. Try running it with the wheels covered and see how it handles. If it bottoms out or if the front arches do negatively affect the steering lock, then consider cutting some of the shell away in the affected areas. It's an intriguing compromise, though. And that flare all the way round might be very helpful.

[Yalson 514]

2 hours ago, nbTMM said:

Yep, just got to find a suitable road near me after I finish off the final details. Front posts are just regular front posts with the bottom cut off, a 2.5mm hole drilled and then attached through the spare 3mm holes in the standard bumper mount. Front bumper is just the standard tt02 foam one. Not sure if i'll keep it there but it seems to support the body well, going to make a FRP front diffuser which sets at the same level as the side trays. I need to fibreglass reinforce the shell mostly around the rear body posts and front wheel arches as it is too flexible for my liking.

60 spur / 42 pinion will have your peak power at ~125kmh
49 spur / 46 pinion will have your peak power at ~167kmh

You can work this out by finding the unloaded max motor rpm:
6900kv * 11volts (a 3S pack under significant load) = 75900rpm

Peak motor power will occur at 50% of maximum rpm = 37950rpm

Then you can work out your final drive ratio
FDR = spur/pinion * 2.6 
so
FDR = 60/42*2.6 = 3.71
or
FDR = 49/46*2.6 = 2.77

Then you can work out the wheel rpms at peak power
Wheel rpm (60/42t) = 37950/3.71 = 10229rpm
Wheel rpm (49/46t) = 37950/2.77 = 13700rpm

and finally convert that to road speeds, assuming 65mm wheel diameter
speed (60/42t) = 10229*0.065*3.1415*60/1000 = 125.32kmh
speed (49/46t) = 13700*0.065*3.1415*60/1000 = 167.85kmh

Now that assumes that your battery and ESC can provide enough juice to actually make peak power. If your battery voltage sags, or the ESC drops a lot of voltage, you may find that you go slower when you gear for peak power. Instead you might gear for 75% max rpm at the motor where you get a bit less power (coincidentally about 75% of the max power) but the motor operates much more efficiently and is less demanding on the ESC and battery. That may make the 60/42t gearing reach a higher top speed even if you're aiming for ~160kmh

Hope that helps!
 

 

This is great. The maths side of gearing was always a bit of a closed book to me, so thank goodness someone knows what they're doing!

[fullspectrum 97]

Thanks for the input. The weather is getting colder here. Going down to zero degree Celcius so my mad dash for 100mph will probably be halted until spring. I may give it one more try if I get a dry day but its going to kill me waiting 5 months of winter...hahahaha 

[Yalson 514]

5 minutes ago, fullspectrum said:

Thanks for the input. The weather is getting colder here. Going down to zero degree Celcius so my mad dash for 100mph will probably be halted until spring. I may give it one more try if I get a dry day but its going to kill me waiting 5 months of winter...hahahaha 

Five months? Ooh, harsh.

[fullspectrum 97]

Yeah Nov to beginning of April

[Yalson 514]

We have a similar seasonal range in London, except in our autumn and winter it usually just rains a bit more than in the spring and summer.

[fullspectrum 97]

I could deal with rain for winter instead of snow...

[stew_mac 326]

On 11/2/2019 at 5:37 AM, fullspectrum said:

Wow that thing looks awesome Stew!

Well I went out to my new spot today and did some runs. It was cold and very windy and the TT02 didnt do well today.

I had trouble seeing the car and lining it up and drove off the road a bunch of times just lining it up. The 6900kv motor on 6s with my Arrma blx185 was kinda lackluster probably because it was overgeared. The motor didnt get fried however. My aerodynamics werent good enough and it did a backflip on one run. 

On other runs I wiped out into the weeds and I lost the car on a few different runs.  I lost a dogbone on one run. The best I got was 76mph. So I swapped the 5700 kv motor back in and on that run I lost a wheel...hahahaha. Not a good day for my TT02.

  But my high gravity slash 4x4 did well today. It was a reversal of luck with my cars. After putting 2 million weight diff fluid in the rear, putting a wing on, cutting the back of the body out and installing Arrma Hoons tires on it she was planted on the road. It didnt go airbourne once...which surprised me. I forgot to put foam on the front bumper to support the front of the body so it dragged on the ground at speed but I still managed a personal best of 93MPH. So the Traxxas saved the day from total disappointment....lol.

So after all the running down the road and looking in the weeds for tires and my cars Im pretty tired to say the least. Im glad I made it to 93mph but 7 more mph to 100 eluded me. Then my GOPro died so that was it...hahaha.

At this point Im not sure where to go with my TT02. Im wondering if the BLX185 slowed it down compared to my OcDay cheap 120amp esc which got me to 90mph. And the 6900kv motor may not have the torque. Should I keep the 6900kv motor in and drop the gearing? Or should I go back to the 5900kv motor? 

 

I would think the BLX185 with the 6900kv on 3 would be more than enough to get you 100 with the right gearing. The BLX185 is just a rebranded hobbywing 8bl150. A mate ran good numbers with his TA07 with that esc and I think a clone castle 5700kv motor. 

[stew_mac 326]

On 11/4/2019 at 11:28 AM, fullspectrum said:

So I just mounted a new 2mm thick Deltaplastik body. And I have to say...Im such a hack compared to Stewart and nbTNM..lol. I suppose it doesnt help Im always in a rush because of family, work and other time constraints. I had to wait 2 weeks just to go for a speed run. 

So I took Stew's advice and dropped the gearing to 60 spur and 42 pinion from 49/46 and put the 6900kv fake Castle motor back in. I will run it on 3s and see what I get for numbers.

I kinda botched the new body install. It sits too far forward and too high. So if I cut the body out on the bottom it would sit too high. Uncut it sits good. Soooo...Im going to leave the front and bottom without cutting. All I cut out was the rear. Also I need to make a new undertray. Also would it be detrimental to not cut the wheel wells out front and back and have fully covered wheels?

I never trim the lower part of the body. I also keep that little bit of plastic on there too to act as a splitter. 
 

also the further forward you mount the body the more downforce you will get on the front wheels.

not sure if you can see with my pic but the body is about 5mm forward when the wheels sit in the body. 

[fullspectrum 97]

Ok thanks Stew. Its looking like I have to wait until next spring. Temps here in Toronto are going to go down to -3 Celcius. I guess Im asking for trouble doing speed runs with the temps so low. My tires wont grip well. Im going to run foam tires though. Maybe one more try at 100mph?

[fullspectrum 97]

Hey guys...well I made it close to 100mph....only 3mph shy.

 

[fullspectrum 97]

Hey guys...well I made it close to 100mph....only 3mph shy.

 

 

[museguy 39]

On 8/18/2019 at 3:22 PM, fullspectrum said:

Hey guys I was thinking of getting a modern Tamiya to build for speed runs. Any ideas what chassis would be best to start with that will allow tall speed run gearing? 

 It seems around me(Toronto) Tamiyas and parts are a little scarce. Mostly all I can find is TT02 kits. But then I need to upgrade shocks, driveshaft, turnbuckles...etc. And can this chassis accommodate tall gears? 

Dear @fullspectrum

Great thread and great videos !

I am new to RC, trying to learn as much as I can and I enjoy watching your videos.

Cheers

[Dakratfink 967]

Great thread so far. 
I’ve never tried to build a speed run car myself, but from threads I’ve seen on the Delta Plastiks bodies are popular choice for speed runners.

I’m surprised no smart alec has pipes in and said “ I want to see a 100mph Lumchbox !” 
so I’ll say it lol 

[Fabia130vRS 2098]

Who ever said a TT02 is a good chassis for speed runa probably never had a professional touring car.

 

I guess you would be better off with a 416 or Xray T4 then anything else.

 

I am using a FF03 and got to 103km/h, my buddy with a AE TC6.1 got 113km/h much easier. 

[museguy 39]

6 hours ago, Fabia130vRS said:

Who ever said a TT02 is a good chassis for speed runa probably never had a professional touring car.

 

I guess you would be better off with a 416 or Xray T4 then anything else.

 

I am using a FF03 and got to 103km/h, my buddy with a AE TC6.1 got 113km/h much easier. 

Dear @Fabia130vRS

Thank you for the post, had to look up the links to understand the differences;

• Tamiya 416 Chassis
• Xray T4 with Hobbywing
• Tamiya FF-03
• Associated Electronics TC6.2

Cheers

P.S. I am interested in learning more about the Arma Limitless (fun video). 

[legooolas 11]

12 hours ago, Fabia130vRS said:

Who ever said a TT02 is a good chassis for speed runa probably never had a professional touring car.

 

I guess you would be better off with a 416 or Xray T4 then anything else.

 

I am using a FF03 and got to 103km/h, my buddy with a AE TC6.1 got 113km/h much easier. 

I think it's all about that challenge

Also a Tamiya forum here

(People have got to > 150mph with a Hobao Hyper VSe off-road 1/8 buggy...)

Edited September 4, 2021 by legooolas
add 1/8th buggy reference

[Fabia130vRS 2098]

4 hours ago, legooolas said:

I think it's all about that challenge

Also a Tamiya forum here

(People have got to > 150mph with a Hobao Hyper VSe off-road 1/8 buggy...)

416 and FF03 are also Tamiya.

I am just saying… it takes a loT of effort to make the tt02 speed run ready. 
 

any pro TC from Tamiya would be a mich greater starting point. 
 

but I like the idea… had same thoughts.

for me, I am using the FF03 for speed runs, havent done a lot to it lately. Still at 103km/h

[hIghQ 149]

On 9/3/2021 at 1:29 PM, Fabia130vRS said:

I am using a FF03 and got to 103km/h, my buddy with a AE TC6.1 got 113km/h much easier. 

You do realize however, that this thread is about getting past 100 miles per hour (which is around 160km/h)?

[Fabia130vRS 2098]

5 hours ago, hIghQ said:

You do realize however, that this thread is about getting past 100 miles per hour (which is around 160km/h)?

And so what??

still the chassis I have mention,  are  capable of that kind of speed. For us it was enough to reach 100 km/h