Castle 1721 Run Time?

[osuengineer]

Hello all,

I'm new here and hoping to get some insight from anyone who has used Castle 1721 motors. To preface, this is not an RC car application, I am using these motors to spin a 50lb flywheel at 2800rpm. Currently I use 2 Castle 2028 motors at 8S geared down paired with XLX2 controllers. The problem I am having is I need this flywheel to spin up as quickly as possible, and when I gun the throttle the controllers are internally limiting the rate of the current spike causing the motors to stop running when the controllers reach this limit. If I feather the throttle it spins up no issues, it just takes longer.

So I want to switch my setup from the 2 castle 2028's on 8S to a new setup of 4 castle 1721's on 8S, geared down to spin the flywheel at the same 2800rpm. I'm confident that splitting the load over 4 motors/controllers will fix this issue. But what I am not confident in is the Castle 1721's ability to run wide open for 3 full minutes without them overheating.

These motors are claimed to be for speed runs only, which I assume don't last more than about 30 seconds. I believe it's a temperature concern more than anything, has anyone ran these motors wide open for 3+ minutes under some load?

Any experienced insight on this motor is appreciated, thanks!

 

[LibertyMKiii]

Most speed runs are under 9 seconds. While they don't say this... what Castle is talking about applying 600+ amps for a long duration.
I would imagine the load is pretty minimal once the flywheel is turning at the desired RPMs?

The only limitation would be heat build-up or over-spinning the rotor's rated RPMs (1721 should be ok there).

You could always run them on 7s if RPMs were of concern.

Are you able to calculate the watts required to maintain the 2800 RPMs for this 50 lbs flywheel? I'd assume it isn't much that 1 motor alone could handle.

 

[osuengineer]

Most speed runs are under 9 seconds. While they don't say this... what Castle is talking about applying 600+ amps for a long duration.
I would imagine the load is pretty minimal once the flywheel is turning at the desired RPMs?

The only limitation would be heat build-up or over-spinning the rotor's rated RPMs (1721 should be ok there).

You could always run them on 7s if RPMs were of concern.

Are you able to calculate the watts required to maintain the 2800 RPMs for this 50 lbs flywheel? I'd assume it isn't much that 1 motor alone could handle.

Once it is up to speed each of the two 2028's draw around 80-100amps continuously to maintain speed. The spikes when I first turn it on are 400+ amps and the motors will just stop if I punch the throttle. However if I feather the throttle just a bit it will spin right up without the motors stopping.

In a 3 minute period I may have to spin the flywheel up a handful of times after it impacts an object and slows down. But the average wattage output over that 3 minute span is typically around 4 to 5kW per motor.

I'm trying to accomplish two things;

1) Prevent the motors from stopping when I punch the throttle, so I can reduce spin-up time as much as possible.
2) Get more torque to the flywheel.

Switching to four 1721's I feel accomplishes both of these goals. During spin-up it may require more power VS two 2028 motors, but once up to speed the load should be shared between the four motors and controllers. Unfortunately I don't have space for four 2028's and castle controllers are limited to 8S or below so I can't feed the 2028's more voltage; but I do have enough space for the 1721's. My motors are currently seeing temps in the 190-220F range according to the castle logs, which seems high. With how fast the 1721's run I had concerns about overheating.

 

[#ARRMArcfanboy4life]

Do you work for battlebots? It sounds like a similar application.

 

[LibertyMKiii]

Once it is up to speed each of the two 2028's draw around 80-100amps continuously to maintain speed. The spikes when I first turn it on are 400+ amps and the motors will just stop if I punch the throttle. However if I feather the throttle just a bit it will spin right up without the motors stopping.

In a 3 minute period I may have to spin the flywheel up a handful of times after it impacts an object and slows down. But the average wattage output over that 3 minute is typically around 4 to 5kW.

I'm trying to accomplish two things;

1) Prevent the motors from stopping when I punch the throttle, so I can reduce spin-up time as much as possible.
2) Get more torque to the flywheel.

Switching to four 1721's I feel accomplishes both of these goals. During spin-up it may require more power VS two 2028 motors, but once up to speed the load should be shared between the four motors and controllers. Unfortunately I don't have space for four 2028's and castle controllers are limited to 8S or below so I can't feed the 2028's more voltage; but I do have enough space for the 1721's. My motors are currently seeing temps in the 190-220F range according to the castle logs, which seems high. With how fast the 1721's run I had concerns about overheating.

Perfect Pass launch control can apply a delayed 100% throttle application over a few seconds (adjustable ). If you used something like that to ramp up the throttle slightly slower but not having to worry about doing it right everytime that will help reduce the amp load.

Another option is the noble nb4 radio has this function built in to the settings. It is adjustable down to a tenth of a second up to a 10 sec throttle application.

You can also program throttle curves/expo into the esc program through castle link to reduce the amp load at certain points of the RPMs.

Adding more motors does divide the loads as you might expect in math. (It's nice when real world matches math)
Only downside is more points of failure and possible connections to come loose if this is battle bots.

 

[#ARRMArcfanboy4life]

I am not saying you are involved in battlebots or anything like that, but their designs sound like they would work in your "project".
I am guessing (by looking at your username) that you are a professor or student at Ohio state, and are making this for either a senior design project, or a robot fighting competition.

I have heard a few people had problems running multiple 1721s, but most times it works fine. It might be worth looking into.

 

[LibertyMKiii]

I am not saying you are involved in battlebots or anything like that, but their designs sound like they would work in your "project".
I am guessing (by looking at your username) that you are a professor or student at Ohio state, and are making this for either a senior design project, or a robot fighting competition.

I have heard a few people had problems running multiple 1721s, but most times it works fine. It might be worth looking into.

Oklahoma state University is also know for their engineering programs.

I don't know of any other applications where you spin up a fly wheel to speed and it might hit obstacles and need to quickly get up to speed again in such a rush.
Other applications are for gyro effect and balance. You don't run those flywheels into objects

 

[osuengineer]

Yep this is for a Battlebot

The perfect pass launch control you describe sounds like something in OpenTx called SLOW, I believe they do the same thing. This is in fact one way to solve this issue that we have been considering, however we still need to find a way to get more torque to the flywheel without sacrificing speed in order to self-right. The additional torque would also presumably solve the spin-up issues as well, killing two birds with one stone per say. We want to stick with all Castle components, and we could fit four 1721's in the space that our two 2028's currently occupy...it's pretty crammed! We should have enough battery capacity on board to support the four 1721's.

Mostly just looking for history on this motor since there doesn't seem to be a lot of information floating around on them. Given they do not come under warranty it could end up being an expensive experiment if it doesn't work the way we hope. These spin at 3X the rotational velocity as our 2028's which currently run hot, so the additional heat generated by friction at those RPM's might be a problem. However on the other hand having the load shared between 4 motors should allow them to run cooler. I'm just trying to get a good idea on what motor temps people are seeing running these motors rigorously, or what known problems they might have.

 

[LibertyMKiii]

Yep this is for a Battlebot

The perfect pass launch control you describe sounds like something in OpenTx called SLOW, I believe they do the same thing. This is in fact one way to solve this issue that we have been considering, however we still need to find a way to get more torque to the flywheel without sacrificing speed in order to self-right. The additional torque would also presumably solve the spin-up issues as well, killing two birds with one stone per say. We want to stick with all Castle components, and we could fit four 1721's in the space that our two 2028's currently occupy...it's pretty crammed! We should have enough battery capacity on board to support the four 1721's.

Mostly just looking for history on this motor since there doesn't seem to be a lot of information floating around on them. Given they do not come under warranty it could end up being an expensive experiment if it doesn't work the way we hope. These spin at 3X the rotational velocity as our 2028's which currently run hot, so the additional heat generated by friction at those RPM's might be a problem. However on the other hand having the load shared between 4 motors should allow them to run cooler. I'm just trying to get a good idea on what motor temps people are seeing running these motors rigorously, or what known problems they might have.

I agree the 4 motor approach will help spread the load out and should result in lower temps and more total power.

You will also pick up some gearing torque due to the extra rpms these motors can output.
Hard to say how that compares against the 2028 motors torque.

 

[#ARRMArcfanboy4life]

You will also pick up some gearing torque due to the extra rpms these motors can output.
Hard to say how that compares against the 2028 motors torque.

The problems with excessive gearing is it creates another weak point. Maybe a custom wound TP motor would be best for this application.

Given they do not come under warranty it could end up being an expensive experiment if it doesn't work the way we hope.

Just a guess: battlebots damage isn't covered by warranty.

We want to stick with all Castle components,

Edit: I didn't see this when I suggested TP motors.

 

[Diem Turner]

Yep this is for a Battlebot

The perfect pass launch control you describe sounds like something in OpenTx called SLOW, I believe they do the same thing. This is in fact one way to solve this issue that we have been considering, however we still need to find a way to get more torque to the flywheel without sacrificing speed in order to self-right. The additional torque would also presumably solve the spin-up issues as well, killing two birds with one stone per say. We want to stick with all Castle components, and we could fit four 1721's in the space that our two 2028's currently occupy...it's pretty crammed! We should have enough battery capacity on board to support the four 1721's.

Mostly just looking for history on this motor since there doesn't seem to be a lot of information floating around on them. Given they do not come under warranty it could end up being an expensive experiment if it doesn't work the way we hope. These spin at 3X the rotational velocity as our 2028's which currently run hot, so the additional heat generated by friction at those RPM's might be a problem. However on the other hand having the load shared between 4 motors should allow them to run cooler. I'm just trying to get a good idea on what motor temps people are seeing running these motors rigorously, or what known problems they might have.

Since these motors are marketed to and generally used by speed runners and a pass is typically 10-12 seconds of full load with a bit of low amp taxiing before and after, it's going to be difficult finding anyone running this motor flat out for 3 minutes. I'm not saying people like this don't exist, I'm just saying that they're going to be a rare find.

As for the shutting off, I assume you're probably hitting the ESC's amp limit when you're gunning it, so your plan to distribute the load across four motors is surely a good idea regardless. This sounds like a fascinating project. I know you probably won't want to reveal anything about your battlebot before it competes, but if you could post some pics at some point when the coast is clear, that would be dope.

 

[#ARRMArcfanboy4life]

I know you probably won't want to reveal anything about your battlebot before it competes, but if you could post some pics at some point when the coast is clear, that would be dope.

I have wanted to build a battlebot for years. I would love to see some BB internals.

 

[#ARRMArcfanboy4life]

Would 3x2028 motors work better than 4x1721s?

 

[osuengineer]

Would 3x2028 motors work better than 4x1721s?

From what I understand at 8S the 1721's are pretty on par with the 2028's in terms of raw power. The 2028 is actually a 12S max motor, but Castle controllers only support it up to 8S, whereas the 1721 is an 8S max motor. So on an 8S system, having four 1721's would be about the same as having four 2028's, they just require more gearing. The unknown is how long can the 1721's run at a given power draw without overheating.

The height of the robot won't allow me to stack two 2028's, so I can't get even get three inside. I can however stack two 1721's per side within the height of the robot.

 

[LibertyMKiii]

From what I understand at 8S the 1721's are pretty on par with the 2028's in terms of raw power. The 2028 is actually a 12S max motor, but Castle controllers only support it up to 8S, whereas the 1721 is an 8S max motor. So on an 8S system, having four 1721's would be about the same as having four 2028's, they just require more gearing. The unknown is how long can the 1721's run at a given power draw without overheating.

The height of the robot won't allow me to stack two 2028's, so I can't get even get three inside. I can however stack two 1721's per side within the height of the robot.

It seems like all limitations considered the 1721s would be your best option for moving forward.
I know teams try to preserve how much time the flywheel is turning. This conserves both lipo energy and reduces heat build-up. With an enclosed case and no airflow the motors certainly won't cool off during the 3 min battle.

 

[osuengineer]

It seems like all limitations considered the 1721s would be your best option for moving forward.
I know teams try to preserve how much time the flywheel is turning. This conserves both lipo energy and reduces heat build-up. With an enclosed case and no airflow the motors certainly won't cool off during the 3 min battle.

Ideally it's spinning the full 3 minute match, with a handful of spin-ups mixed in after impacts. Otherwise we would never want to turn it off short of a rare circumstance. We could do certain things to aid with cooling but there's not much airflow inside the bot itself, the components get pretty warm and are all close to one another.

I will likely end up buying one and running a smaller scale bench test with it and go over the Castlelink logs. At least nobody I've talked to so far has said "no chance in hell that will work with that motor", so I suppose that is good.

 

[LibertyMKiii]

Ideally it's spinning the full 3 minute match, with a handful of spin-ups mixed in after impacts. Otherwise we would never want to turn it off short of a rare circumstance. We could do certain things to aid with cooling but there's not much airflow inside the bot itself, the components get pretty warm and are all close to one another.

I will likely end up buying one and running a smaller scale bench test with it and go over the Castlelink logs. At least nobody I've talked to so far has said "no chance in hell that will work with that motor", so I suppose that is good.

As you noted the motor runs well on par with the 2028 in car applications.
The key is using the 1721 motors' RPMs.

Because you will be gearing this to retain the 2,800 rpms on the flywheel you will have a nice gear ratio off the motor given the approximately double KV value. That gearing torque gain of around 2x and having 2x the motors should result in a solid setup.

 

[osuengineer]

As you noted the motor runs well on par with the 2028 in car applications.
The key is using the 1721 motors' RPMs.

Because you will be gearing this to retain the 2,800 rpms on the flywheel you will have a nice gear ratio off the motor given the approximately double KV value. That gearing torque gain of around 2x and having 2x the motors should result in a solid setup.

Per 'amp' the torque at the weapon will be the same for a given motor whether I use 2028 or 1721 as long as the weapon is geared to spin at the same RPM in each case. The torque constant of the 1721 is lower than the 2028 (Kt*Kv=1352), but when geared to the same rotational velocity it should work out the same. The additional torque would come strictly from the addition of two more motors.

 

[Sirkensirlot]

Per 'amp' the torque at the weapon will be the same for a given motor whether I use 2028 or 1721 as long as the weapon is geared to spin at the same RPM in each case. The torque constant of the 1721 is lower than the 2028 (Kt*Kv=1352), but when geared to the same rotational velocity it should work out the same. The additional torque would come strictly from the addition of two more motors.

This is totally out of my wheelhouse but at the same time fascinating

 

[StephenSchandelmayer]

@osuengineer you came to the right place and talking to the right dude @LibertyMKiii. Hope we get to see something of this bot down the road as well this is a cool thread.

@Sirkensirlot right there with ya buddy