Should I go for above 2200kV for Limitless motor?

[LibertyMKiii]

I did this fpv off-road below. I reckon on-road I can go faster even with vibration.

Looks like alot of fun. To me that looks like 20-30 mph max and had gone off into the grass a few times.
Tony Ignalis has a view videos as does Raz with a GoPro inside their cars going 170+ mph. Everything is a blur going by.

This example you are seeing extra blur because of the plastic body shell (which is an aerodynamics must have)

 

[secamatop]

Looks like alot of fun. To me that looks like 20-30 mph max and had gone off into the grass a few times.
Tony Ignalis has a view videos as does Raz with a GoPro inside their cars going 170+ mph. Everything is a blur going by.

This example you are seeing extra blur because of the plastic body shell (which is an aerodynamics must have)

Here's Kevin talbot cornering (11:40) with infraction. Looks fast but not sure the mph.

Here's Kevin talbot cornering (11:40) with infraction. Looks fast but not sure the mph.

Here's me on-road with 64kmh top speed of my cheap rc buggy. Blurry but fun. And certainly in full control.

That's why I'm upgrading to limitless.

 

[LibertyMKiii]

Here's Kevin talbot cornering (11:40) with infraction. Looks fast but not sure the mph.

Here's me on-road with 64kmh top speed of my cheap rc buggy. Blurry but fun. And certainly in full control.

That's why I'm upgrading to limitless.

That is only in the 30-50 mph range.
Looking forward to your project and take it in baby steps. Try it slow initially check motor temps check batteries etc. Then gear up and increase the speed in incraments.
When someone is new to speed we usually recommend 70, 90, 105, 115, 125, 135, 145 etc.

The XLX2 is the only ESC worth considering for your project.

 

[secamatop]

That is only in the 30-50 mph range.
Looking forward to your project and take it in baby steps. Try it slow initially check motor temps check batteries etc. Then gear up and increase the speed in incraments.
When someone is new to speed we usually recommend 70, 90, 105, 115, 125, 135, 145 etc.

Thanks for the advice, Sir!

 

[LibertyMKiii]

Thanks for the advice, Sir!

No problem.

You could run a HW Max 6 or Max5 ESC potentially I have seen people take those into the 120-140 mph range, but the XLX2 is the only ESC that has gone 170+ consistently.

 

[secamatop]

No problem.

You could run a HW Max 6 or Max5 ESC potentially I have seen people take those into the 120-140 mph range, but the XLX2 is the only ESC that has gone 170+ consistently.

Yup. My xlx2 is on the way. Next to order is tp power motor.

 

[Lennart]

Yup. My xlx2 is on the way. Next to order is tp power motor.

I am really interested in seeing what you will build, since I am building a 1/7 FPV onroad car for over a year now.

Your biggest upgrade concerning the drivability is probably the DJI air unit system. That was a huge improvement from my cheap analog system.

What was already said: you can't gear your limitless to much more than 90mph if you want to "race drive" it.

 

[secamatop]

I am really interested in seeing what you will build, since I am building a 1/7 FPV onroad car for over a year now.

Your biggest upgrade concerning the drivability is probably the DJI air unit system. That was a huge improvement from my cheap analog system.

What was already said: you can't gear your limitless to much more than 90mph if you want to "race drive" it.

Please share your fpv videos. But dji latency is higher than analog. For racing, that's an issue

I am really interested in seeing what you will build, since I am building a 1/7 FPV onroad car for over a year now.

Your biggest upgrade concerning the drivability is probably the DJI air unit system. That was a huge improvement from my cheap analog system.

What was already said: you can't gear your limitless to much more than 90mph if you want to "race drive" it.

And could u share what motor u used and gearing.

 

[Lennart]

Please share your fpv videos. But dji latency is higher than analog. For racing, that's an issue

I had this exact concern too, but trust me thats not an issue (I did not notice it)
In my case the analog had 25FPS, thats 40ms between each picture. My dji now has 100FPS, thats 10ms between pictures. This alone could offset the higher latency feel for me. And the dji o3 has 35ms latency or so. Thats good in my opinion.

I only have two videos uploaded at the moment. But you will see the 1/7 bigger car has less vibrations.

EDIT:
I use MMX8s on 8s geared for 130kmh. First I had the 1717 1650kv now I am running the TP 4070cm 1400kv.
The problem with my 1717 was the kevlar rotor wrap letting go at high rpm. The TP now has a steel sleeved rotor, but it runs hotter...

 

[rotauq]

I have many opinions about what is mentioned before. Lennart and Liberty know their stuff, trust them. I do feel i need to fill in some gaps here.

First, I think why of he original question is left unanswered. Higher KV does not equal power. It will give you more max rpm's, speed is all about gearing.
Too high or low kv will just you in the situation of awkwart gearing choices. Power is all about motor size and kv options get lower the bigger the motor.
A big 1100kv motor on 8s wont make 40k rpm, but with twice the size of pinion it will run much faster and cooler than a smaller 2200kv at 8S. The only reason to go for higher kv is when you wanna run lower voltages. A 2200kv on 3s maxes at 28k rpm and will need a very big pinion to give it some speed. 2400-2950kv is a good 4S spec as it aims for <50k rpm Motors that can deal with more than 50k rpm (excluding tiny ones) will only allow it for 8-10s max as they will quickly overheat.

I think you need to gear it for 70-100mph for best continues laps, depending on battery (voltage and weight) and motor (size and power). For fast laptimes i think you'd be supprised how much faster a light 4S powertrain can corner vs a big 8S setup.

Certainly don't go for analog fpv. Not having the stable image of flying will make it impossible to use at high speeds. Lennart's image stability is already insane good. Your initial stability will most likely be more like your offroad video. Stiff onroad suspention does go bouncy quickly.

As you mention latency of the videoyourself, but what about the radio? Radiomaster MT12 (ELRS version) is probably the only one that has the range and latency to make you do a full lap on a fullsized track. It's a karting track, so not that crazy large. But you will feel the latency difference over distance compared to the video. Alternatively the Noble NB4 has the low latency but not the (out of the box) range.

 

[secamatop]

I have many opinions about what is mentioned before. Lennart and Liberty know their stuff, trust them. I do feel i need to fill in some gaps here.

First, I think why of he original question is left unanswered. Higher KV does not equal power. It will give you more max rpm's, speed is all about gearing.
Too high or low kv will just you in the situation of awkwart gearing choices. Power is all about motor size and kv options get lower the bigger the motor.
A big 1100kv motor on 8s wont make 40k rpm, but with twice the size of pinion it will run much faster and cooler than a smaller 2200kv at 8S. The only reason to go for higher kv is when you wanna run lower voltages. A 2200kv on 3s maxes at 28k rpm and will need a very big pinion to give it some speed. 2400-2950kv is a good 4S spec as it aims for <50k rpm Motors that can deal with more than 50k rpm (excluding tiny ones) will only allow it for 8-10s max as they will quickly overheat.

I think you need to gear it for 70-100mph for best continues laps, depending on battery (voltage and weight) and motor (size and power). For fast laptimes i think you'd be supprised how much faster a light 4S powertrain can corner vs a big 8S setup.

Certainly don't go for analog fpv. Not having the stable image of flying will make it impossible to use at high speeds. Lennart's image stability is already insane good. Your initial stability will most likely be more like your offroad video. Stiff onroad suspention does go bouncy quickly.

As you mention latency of the videoyourself, but what about the radio? Radiomaster MT12 (ELRS version) is probably the only one that has the range and latency to make you do a full lap on a fullsized track. It's a karting track, so not that crazy large. But you will feel the latency difference over distance compared to the video. Alternatively the Noble NB4 has the low latency but not the (out of the box) range.

I'm clear about how kV works related to voltage, RPM and torque. I was hoping to get some experience from people on what kV you guys used and at what gearing and the output speed. I prefer not to have incompatible motors lying around. And I don't have much budget.

But no, I still think analog FPV is good enough. You'd see that analog video is stable enough when FPVing (not DVR) even on off-road. This also depends on how you mount the camera on the chassis. Obviously with big budget, one can certainly DJI the whole rig.

Nonetheless, thank you for the response. I wonder, what kV you used for your Limitless at what s and what speed you got for bashing or speed runs?

 

[rotauq]

I'm clear about how kV works related to voltage, RPM and torque. I was hoping to get some experience from people on what kV you guys used and at what gearing and the output speed. I prefer not to have incompatible motors lying around. And I don't have much budget.

But no, I still think analog FPV is good enough. You'd see that analog video is stable enough when FPVing (not DVR) even on off-road. This also depends on how you mount the camera on the chassis. Obviously with big budget, one can certainly DJI the whole rig.

Nonetheless, thank you for the response. I wonder, what kV you used for your Limitless at what s and what speed you got for bashing or speed runs?

My main point was, don't go crazy on high kv so you wont have an incompatible motor.

Being in to drones myself, i upgraded to DJI FPV some years ago and never looked back. Getting it purely for this build, its a big chunck of budget yes.

My limitess (v1 as a GTE with GP5 diffs/BSR foams) is dedicated on speedruns, running a TP 4070-2200 34s/30p and would do 150mph if i had the room for it.
My hobao VTE2 (also 1/7) is quite simular but running a castle 1717-1650.

For bashing/racing i prefer my 1/8 scale onroads, shorter wheelbase is better for cornering speeds (drifting is cool but not fast) My serpent Gte only has a 4068-2650 motor at 4S and is geared for 80mph. It is half the weight, has a centerdiff and grippy GRP tires.

Best investment is a big range of gears, to be able to find that sweet spot on the specific track. If you can go for a motor with a 8mm shaft so you can use the gears as both spur and pinion

 

[kaladeth]

Great points so far! I know nothing about FPV. It looks like fun. I have the el-cheapo Radiolink FPV kit that I've been meaning to stick on to the Limitless but never found time to. Can you still see through the goggles and see the entire course while viewing the feed? How do you make sure you don't hit other cars?

2950

Entire course. With fast lap times. I'm also considering going to an actual race track (short track) too to complete a lap.


I was thinking of 8s. Actually I already ordered. When you said too much power do you mean too fast on an oval track? I thought oval would let you go all out for speed.

I was thinking above 146mph top speed. Say 200mph? lol!

Btw, what gear calculator do you use? I use the Sodialed mobile app (Limitless not listed) but any better ones?

I can help you with the gearing calculation, but it's all connected. If you stick to 8S, and your 2950kV motor, using the stock motor mount, and stock spur, and your pinion selection (23 to 27), there are a couple of issues:

1. Your pinion won't work. It will be too small to reach the spur. Your total tooth count needs to be 71.
2. Your max speed will be 190 mph with the smallest pinion of 23t. Apart from what Liberty already mentioned about speed, I doubt the straight is long enough for you to reach that speed. Do you have an idea of how long the straight is? With my setup I hit ~60 mph in about 200 ft of straight.
3. You will probably run so hot anyway you wouldn't last 6 minutes. Not sure how long the course is, but if you plan to do lap after lap you need to gear down or install cryo cooling or something.

Check my math:

Suggestions:
1. Get the biggest spur you can fit. I use 46 but some people have claimed to fit a 50 in there.
2. Get a better motor mount that lets you use smaller pinions.
3. Use the smallest pinion size that will let you go fast around the corners, not the one that gives you the max straight speed. (or get the smallest that lets you get up to 71 tooth count, to start)
4. Get good fans for your motor. The XLX2 will probably be fine, I haven't thermaled it yet, but watch it just in case.
5. At some point, with the track size and all, you will probably want to get a bigger motor (and probably less kV) to take the heat.

You can always run it with whatever you've got but just watch temps etc. and adjust. Best way to learn right?

For what it's worth, I ran my car on 8S one time to see if I could go faster than 6S. Answer was no. Same lap time, same max speed. Without crashing of course.

If you haven't yet, have a look at my build thread, it's only a few pages deep so hopefully not too boring a read. Hopefully it helps you avoid some of the dumb things I did. Let me know if you have any questions!

Where is this go kart track by the way? Might be helpful to see the Google Map of it, and also be aware of ambient temps.

You should start a build thread, would like to follow this.

 

[secamatop]

My main point was, don't go crazy on high kv so you wont have an incompatible motor.

Being in to drones myself, i upgraded to DJI FPV some years ago and never looked back. Getting it purely for this build, its a big chunck of budget yes.

My limitess (v1 as a GTE with GP5 diffs/BSR foams) is dedicated on speedruns, running a TP 4070-2200 34s/30p and would do 150mph if i had the room for it.
My hobao VTE2 (also 1/7) is quite simular but running a castle 1717-1650.

For bashing/racing i prefer my 1/8 scale onroads, shorter wheelbase is better for cornering speeds (drifting is cool but not fast) My serpent Gte only has a 4068-2650 motor at 4S and is geared for 80mph. It is half the weight, has a centerdiff and grippy GRP tires.

Best investment is a big range of gears, to be able to find that sweet spot on the specific track. If you can go for a motor with a 8mm shaft so you can use the gears as both spur and pinion

Awesome! Thanks so much. This really helps. Yeah, I've ordered a range of gears.

 

[Lennart]

For what it's worth, I ran my car on 8S one time to see if I could go faster than 6S. Answer was no. Same lap time, same max speed. Without crashing of course.

I wondered if running 8s would be beneficial. So it is heavier and not faster. But did you notice lower temperatures or something like that? Or was there no big difference?

 

[kaladeth]

I wondered if running 8s would be beneficial. So it is heavier and not faster. But did you notice lower temperatures or something like that? Or was there no big difference?

I'm thinking my speed was limited by my fingers and ability to drive the course - I was actually going at same speed / same RPM / same motor load etc etc so I expect the temps were same. Any gains probably got offset with the added weight?

 

[secamatop]

Great points so far! I know nothing about FPV. It looks like fun. I have the el-cheapo Radiolink FPV kit that I've been meaning to stick on to the Limitless but never found time to. Can you still see through the goggles and see the entire course while viewing the feed? How do you make sure you don't hit other cars?





I can help you with the gearing calculation, but it's all connected. If you stick to 8S, and your 2950kV motor, using the stock motor mount, and stock spur, and your pinion selection (23 to 27), there are a couple of issues:

1. Your pinion won't work. It will be too small to reach the spur. Your total tooth count needs to be 71.
2. Your max speed will be 190 mph with the smallest pinion of 23t. Apart from what Liberty already mentioned about speed, I doubt the straight is long enough for you to reach that speed. Do you have an idea of how long the straight is? With my setup I hit ~60 mph in about 200 ft of straight.
3. You will probably run so hot anyway you wouldn't last 6 minutes. Not sure how long the course is, but if you plan to do lap after lap you need to gear down or install cryo cooling or something.

Check my math:

View attachment 370563

Suggestions:
1. Get the biggest spur you can fit. I use 46 but some people have claimed to fit a 50 in there.
2. Get a better motor mount that lets you use smaller pinions.
3. Use the smallest pinion size that will let you go fast around the corners, not the one that gives you the max straight speed. (or get the smallest that lets you get up to 71 tooth count, to start)
4. Get good fans for your motor. The XLX2 will probably be fine, I haven't thermaled it yet, but watch it just in case.
5. At some point, with the track size and all, you will probably want to get a bigger motor (and probably less kV) to take the heat.

You can always run it with whatever you've got but just watch temps etc. and adjust. Best way to learn right?

For what it's worth, I ran my car on 8S one time to see if I could go faster than 6S. Answer was no. Same lap time, same max speed. Without crashing of course.

If you haven't yet, have a look at my build thread, it's only a few pages deep so hopefully not too boring a read. Hopefully it helps you avoid some of the dumb things I did. Let me know if you have any questions!

Where is this go kart track by the way? Might be helpful to see the Google Map of it, and also be aware of ambient temps.

You should start a build thread, would like to follow this.

Great points so far! I know nothing about FPV. It looks like fun. I have the el-cheapo Radiolink FPV kit that I've been meaning to stick on to the Limitless but never found time to. Can you still see through the goggles and see the entire course while viewing the feed? How do you make sure you don't hit other cars?





I can help you with the gearing calculation, but it's all connected. If you stick to 8S, and your 2950kV motor, using the stock motor mount, and stock spur, and your pinion selection (23 to 27), there are a couple of issues:

1. Your pinion won't work. It will be too small to reach the spur. Your total tooth count needs to be 71.
2. Your max speed will be 190 mph with the smallest pinion of 23t. Apart from what Liberty already mentioned about speed, I doubt the straight is long enough for you to reach that speed. Do you have an idea of how long the straight is? With my setup I hit ~60 mph in about 200 ft of straight.
3. You will probably run so hot anyway you wouldn't last 6 minutes. Not sure how long the course is, but if you plan to do lap after lap you need to gear down or install cryo cooling or something.

Check my math:

View attachment 370563

Suggestions:
1. Get the biggest spur you can fit. I use 46 but some people have claimed to fit a 50 in there.
2. Get a better motor mount that lets you use smaller pinions.
3. Use the smallest pinion size that will let you go fast around the corners, not the one that gives you the max straight speed. (or get the smallest that lets you get up to 71 tooth count, to start)
4. Get good fans for your motor. The XLX2 will probably be fine, I haven't thermaled it yet, but watch it just in case.
5. At some point, with the track size and all, you will probably want to get a bigger motor (and probably less kV) to take the heat.

You can always run it with whatever you've got but just watch temps etc. and adjust. Best way to learn right?

For what it's worth, I ran my car on 8S one time to see if I could go faster than 6S. Answer was no. Same lap time, same max speed. Without crashing of course.

If you haven't yet, have a look at my build thread, it's only a few pages deep so hopefully not too boring a read. Hopefully it helps you avoid some of the dumb things I did. Let me know if you have any questions!

Where is this go kart track by the way? Might be helpful to see the Google Map of it, and also be aware of ambient temps.

You should start a build thread, would like to follow this.

You said it. FPV car racing is super fun and really gets your heart racing! Because you're viewing lower from the ground, you can't see that far ahead. But far enough to race. I mean it's like F1 driver sitting on the floor of their car. You avoid like how you avoid other cars when you drive a full-scale car. It's literally the same. The faster you drive, the less time you can react.

The quality of video feed depends on FPV camera. Yeah, comparing analog vs. DJI digital, digital gives better feed but way more expensive. DJI is like the Apple of FPV - it only works with its own parts. You need DJI goggles with DJI air unit. And they cost like $1k per set vs. $300 for an average analog set. And some analog cameras do come with digital recorders so you will get HD quality recordings too. More info here -> https://rcgrid.com/how-to-fpv-your-rc-car-comprehensive-guide/

Thanks for the gearing insights. I'm not based in the US, btw. But I'm sure some go-kart tracks in the US will let you RC it. Try to find one that has proper lines along the track. That helps a lot when FPVing.

 

[LibertyMKiii]

My recommendation would be to start slow and see if you can go faster later on.
My list of how this would go:

1. 80 mph max
2. Probably GRP tires but could do foams
3. Retain high downforce wings on the car for grip
4. Confirm Heat is within safe specifications for the electronics. Below 175 f. (79 c)
5. Confirm you can keep the car on the track at "full speed"
6. Confirm the LiPos can handle one full lap before LVC.

As your speed increases the wattage needs increases significantly. Assuming the setup is running efficiently the data trends in a straight line.
I had done some tracking of this in my Hobao VTE2. Once you get to the point of pulling over 6kW your total run time is very short. You can see based on my data that running around 100 mph would be roughly 3x the run time of 146 mph. (although I believe heat management will be the biggest challenge)

Off shore electrics has a nice calculator page for run time based on amperage https://www.offshoreelectrics.com/conversion.php

 

[secamatop]

My recommendation would be to start slow and see if you can go faster later on.
My list of how this would go:

1. 80 mph max
2. Probably GRP tires but could do foams
3. Retain high downforce wings on the car for grip
4. Confirm Heat is within safe specifications for the electronics. Below 175 f. (79 c)
5. Confirm you can keep the car on the track at "full speed"
6. Confirm the LiPos can handle one full lap before LVC.

As your speed increases the wattage needs increases significantly. Assuming the setup is running efficiently the data trends in a straight line.
I had done some tracking of this in my Hobao VTE2. Once you get to the point of pulling over 6kW your total run time is very short. You can see based on my data that running around 100 mph would be roughly 3x the run time of 146 mph. (although I believe heat management will be the biggest challenge)

Off shore electrics has a nice calculator page for run time based on amperage https://www.offshoreelectrics.com/conversion.php
View attachment 370609

View attachment 370608

This is super. Thanks! Btw, where do you usually buy your GRP tires? I googled and there are just so many sites selling. I saw a few on AliExpress and wonder if they are genuine. AliExpress ships in a week to my place.

And why GRP and not Hoons?

 

[rotauq]

GRP's are better both in grip and wear
GRP hq is based in italy, https://www.grpgandini.it/en/grp-bigger-shop/

AliE sources likely are genuine, question is more if they have the same QA.