I am new to bot building, and i really apprecaite your videos and other resources provided. The one stopping point i have hit is being unsure of how to pick out motors. Ive found lots of information on matching ESC's to motors and this is a great guide on batteries, but so many of these builds start with "i have these xxxx motors sitting around so im going to use them for drive and..."
As an aerospace engineer im very curious: have you considered or tried making the rotor more aerodynamic? Especially with bar spinners I can imagine that making a substantial difference
For sure. I personally don't pay too much attention to this. Making it more aerodynamic can often decrease the bite or the actual impacting surface. Sure, it will take more current/power to spin, but you only need to last 3 minutes, and at the lower weight classes, battery capacity usually isn't a big deal. If you watch my battery video, I explain that higher capacity batteries generally equal higher current delivery. In short, you're going to want more capacity to get that higher peak current for initial spin-up, so making it more aerodynamic just leaves you with more battery capacity at the end of the match, which doesn't gain you anything.
Can you make a video explaining sensored vs sensorless brushless motors? I understand the differences but others might not. Also, is there such a thing as a “castle” system that switches between sensored and sensorless?
All the competitions that I go to don't allow LiPo batteries, so buying batteries is a very different story. Most of the time I use Li-Ion batteries and I have a pack for my weapon system and a pack for my drive system. These batteries typically have a much lower discharge rate and their capacity depletes a lot quicker. So trying to find a battery for my weapon system, which draws 90 amps at full speed, is very difficult because I would need a 3.6 Ah pack with a high discharge rate in order for my weapon to run for 3 minutes.
@@RobertCowanDIY I am located in the Mid West but I make 15 lb robots with my school club and all those competitions don't allow LiPo batteries. I use Li-Ion batteries for the drive and I am using a Zippy 3s 4200 mAh LiFe pack but they are discontinued so idk what to use for the weapon now.
Have you worked out how many mah just for the drive you need for Crippling depression. to isolate if you were to say change weapon specs. run without a working weapon and use a lighter battery and bolt on another mod or something?
The Lipo should not go below 3.7v per cell, is your calculation taking into account that it would end up at 3.7v after the 3 minutes using 30a per minute? Is there something I'm missing about the Lipos in this situation?
Well, the voltage will sag quite a bit when the motors are on. We're not looking for an exact number here, we're looking for a sanity check. If you're worrying about the final voltage, you're most likely cutting it too close. Does that make sense? Matches are 3 minutes, but if you have something that binds up the weapon or drive, your current draw can be significantly higher.
@@RobertCowanDIY Thank you very much for your answer. I didn't know how a LiPo battery worked and I feel a bit dumb not checking before asking. I found that a LiPo calculates capacity differently than other batteries. In short I can use the whole 1400ah of my 1.4 battery without troubles since it's meant to be at the 3.3v nominal voltage after this much use. (I thought I'd have to monitor the battery to not drop below the nominal voltage after like 20% of the capacity, from 4.2v to 3.3v. When in fact I could use 100% of I before it reaches nominal. Really dumb me...) I found low voltage alarms for my LiPo for testing, really useful.
If the 20a is the rating of the esc wouldn’t you need to double it since both sides of drive are probably running drawing power or am I missing something.
Correct, each is drawing power. But realistically, unless you use crazy magnets or are just pushing against the wall the whole match, you won't use much power on the drive.
You want your drive motors to be able to accelerate at the same time, so you find the max amount of current of both of the motors. If you have a weapon like a spinner, you can either try to spin it up before you begin to drive or get a larger battery. If you need to be able to run 3 motors you find the max draw current, let’s say 90 amongst the motors. A 3ah battery with 30c plus would work well.
I am doing a 6wd beetle each draws 16A max so I am getting a 60A continuous ESC. So then I get a 2200mah 75c battery. But do I need the 60A ESC making the battery so big? Or would I be okay with a 45A. Each ESC is for each drive size.
It doesn't matter how many wheels you have, they will lose traction well before the 16A is hit, and that will probably be distributed through the whole side. If you're doing a brushless ESC, I'm not sure you'll have good luck hooking them up to multiple motors either. Consider the load distributed from each side, not necessarily a single motor.
@@edsrobots9107 Ok, so why is there a 13kg load? that's way more than a beetle would normally see, and if the current draw is only 4.5A, you shouldn't need an ESC rated for much more than 10A. It might be good to just work this problem out with common sense. A beetle won't push much more than it's own weight, or double that. So in that case, how much load do you have with ~3kg? then, what's your current draw? then base everything off of that. Good luck!
Would making the blade more aerodynamic help at all with idle draw? I remember a beetle called Best Korea experimented with downforce blades with some interesting results. ruclips.net/video/I7PCn-V7yZ8/видео.html
Eh, I could probably save a little bit, but I don't want to bother with it, it sounds good and I'm not worried about spending a few extra amps. I've gotten it drastically lower with different ESC settings.
One of my favorite series right now. That was a really aggressive calculation, man
ALL my calculations are aggressive.
The best series explaining this subject. Exactaly what i needed. Just wanna thank you. ❤❤❤❤
You're very welcome.
Very fun and helpful demonstration of power throughout a match haha
Sweet build Robert, thnx for making videos.
I am new to bot building, and i really apprecaite your videos and other resources provided. The one stopping point i have hit is being unsure of how to pick out motors. Ive found lots of information on matching ESC's to motors and this is a great guide on batteries, but so many of these builds start with "i have these xxxx motors sitting around so im going to use them for drive and..."
What kind of bot are you building and in which category?
ant/beetle mostly beetle right now (us not uk)
As an aerospace engineer im very curious: have you considered or tried making the rotor more aerodynamic? Especially with bar spinners I can imagine that making a substantial difference
For sure. I personally don't pay too much attention to this. Making it more aerodynamic can often decrease the bite or the actual impacting surface. Sure, it will take more current/power to spin, but you only need to last 3 minutes, and at the lower weight classes, battery capacity usually isn't a big deal. If you watch my battery video, I explain that higher capacity batteries generally equal higher current delivery. In short, you're going to want more capacity to get that higher peak current for initial spin-up, so making it more aerodynamic just leaves you with more battery capacity at the end of the match, which doesn't gain you anything.
Can you make a video explaining sensored vs sensorless brushless motors? I understand the differences but others might not. Also, is there such a thing as a “castle” system that switches between sensored and sensorless?
MAYBE, I would need to learn more on the subject.
Nice work against Gruff!
All the competitions that I go to don't allow LiPo batteries, so buying batteries is a very different story. Most of the time I use Li-Ion batteries and I have a pack for my weapon system and a pack for my drive system. These batteries typically have a much lower discharge rate and their capacity depletes a lot quicker. So trying to find a battery for my weapon system, which draws 90 amps at full speed, is very difficult because I would need a 3.6 Ah pack with a high discharge rate in order for my weapon to run for 3 minutes.
You should look at other competitions... Where are you located? Most every major competition in the US allows LiPo batteries. Do you use LiFe instead?
@@RobertCowanDIY I am located in the Mid West but I make 15 lb robots with my school club and all those competitions don't allow LiPo batteries. I use Li-Ion batteries for the drive and I am using a Zippy 3s 4200 mAh LiFe pack but they are discontinued so idk what to use for the weapon now.
gotta love all-offense designs :D
the weapon serves as defense as well ;-)
Have you worked out how many mah just for the drive you need for Crippling depression. to isolate if you were to say change weapon specs. run without a working weapon and use a lighter battery and bolt on another mod or something?
Nice
The Lipo should not go below 3.7v per cell, is your calculation taking into account that it would end up at 3.7v after the 3 minutes using 30a per minute? Is there something I'm missing about the Lipos in this situation?
Well, the voltage will sag quite a bit when the motors are on. We're not looking for an exact number here, we're looking for a sanity check. If you're worrying about the final voltage, you're most likely cutting it too close. Does that make sense? Matches are 3 minutes, but if you have something that binds up the weapon or drive, your current draw can be significantly higher.
@@RobertCowanDIY Thank you very much for your answer. I didn't know how a LiPo battery worked and I feel a bit dumb not checking before asking.
I found that a LiPo calculates capacity differently than other batteries. In short I can use the whole 1400ah of my 1.4 battery without troubles since it's meant to be at the 3.3v nominal voltage after this much use.
(I thought I'd have to monitor the battery to not drop below the nominal voltage after like 20% of the capacity, from 4.2v to 3.3v. When in fact I could use 100% of I before it reaches nominal. Really dumb me...)
I found low voltage alarms for my LiPo for testing, really useful.
Power =/= energy.
Power = energy per time.
LETS GO COPPERHEAD
If the 20a is the rating of the esc wouldn’t you need to double it since both sides of drive are probably running drawing power or am I missing something.
Correct, each is drawing power. But realistically, unless you use crazy magnets or are just pushing against the wall the whole match, you won't use much power on the drive.
What's the model of his Power analyser?
I'm not sure if you can still get this exact one. You can look on Amazon or Hobby King for 'watt meter' or 'power analyzer'. They are pretty generic.
What about discharge rate? What is its significance ? And how do i determine which is appropriate?
You want your drive motors to be able to accelerate at the same time, so you find the max amount of current of both of the motors. If you have a weapon like a spinner, you can either try to spin it up before you begin to drive or get a larger battery. If you need to be able to run 3 motors you find the max draw current, let’s say 90 amongst the motors. A 3ah battery with 30c plus would work well.
@@bldjln3158 oh okay, got it
Glue the calculator to the front if you're gonna bash it like that. :)
I have that shirt
I can tell you first time driving copper head was different.
I am doing a 6wd beetle each draws 16A max so I am getting a 60A continuous ESC. So then I get a 2200mah 75c battery. But do I need the 60A ESC making the battery so big? Or would I be okay with a 45A. Each ESC is for each drive size.
It doesn't matter how many wheels you have, they will lose traction well before the 16A is hit, and that will probably be distributed through the whole side. If you're doing a brushless ESC, I'm not sure you'll have good luck hooking them up to multiple motors either. Consider the load distributed from each side, not necessarily a single motor.
@@RobertCowanDIY Okay, so would a 15 A ESC be okay for each motor?
When there is a 13kg load 4.5 A is draw. Or would a 10A be more appropriate?
@@edsrobots9107 What weight class is this? I feel like you need to do way more testing.
@@RobertCowanDIY Beetle
@@edsrobots9107 Ok, so why is there a 13kg load? that's way more than a beetle would normally see, and if the current draw is only 4.5A, you shouldn't need an ESC rated for much more than 10A. It might be good to just work this problem out with common sense. A beetle won't push much more than it's own weight, or double that. So in that case, how much load do you have with ~3kg? then, what's your current draw? then base everything off of that. Good luck!
Would making the blade more aerodynamic help at all with idle draw?
I remember a beetle called Best Korea experimented with downforce blades with some interesting results.
ruclips.net/video/I7PCn-V7yZ8/видео.html
Eh, I could probably save a little bit, but I don't want to bother with it, it sounds good and I'm not worried about spending a few extra amps. I've gotten it drastically lower with different ESC settings.