7 replies to this topic

[Xhosant]

After a round of questions over at the electronics stack exchange (linked below), I have 2 ideas for peer review.

My limited experience says that the standard way to decrease rev-up delay is the use of stronger batteries,but that comes with some downsides, like cost.

Idea #1 was presented by the top answer in SE, the use of capacitors to have the same battery deliver a bigger burst of speed on rev-up.

Idea #2 is a spring-powered pullcord, primed as a spring blaster, revving the wheel mannualy.

Thoughts?

https://electronics....t1121166_446848

[Meaker VI]

The respondents are all missing some crucial information relevant to our interests:

• These motors are too small for a pullcord to be of any use
• These motors are spinning ridiculously fast.
• These motors already spin up in fractions of a second.

So a pullcord is right out. That'd work as a novel completely redesigned system, but not as a modification to an existing wheel system, and likely wouldn't have great performance characteristics.

 

I don't know enough about capacitors to know if they'd work or not, but what I do know is that they'd still take power from the battery to charge so you still need a battery capable of charging them.

 

The best route to faster spinup is to just use lighter wheels and torquier motors; which leads to higher amp demands from the motors which leads to larger (but still fairly small) batteries. If you're willing to monitor batteries more closely, it'll likely mean more damage to smaller/less well specc'd packs. Asking around recently, you could likely undersize a NIMH or alkaline pack and safely get the same spinup until voltage sag gets to you.

[Xhosant]

The pullcord could attach to the flywheel, so size isn't an issue, though the question of speed is valid.

As for a capacitor, the battery's power is not an issue. The short of it is, the capacitor can take its time charging, which in this case means that it can double the battery's output - briefly - after charging for an amount of time comparable to this boost's duration.

Does the theory make sense?

[KaneTheMediocre]

So I don't do flywheels, but I know a few things about electronics and feel I need to explain some things.

 

The capacitor you need to do this probably costs more than the bigger battery, without giving you any increase in capacity that you would get with a battery.  This is kind of a weird edge case where it's probably not absurdly expensive, but still more expensive than just using a bigger battery. 

Neither solution means you'll have a fast spinup time, it just means it will be as fast as it can be for those motors and wheels.

 

The pullcord solution might be viable with larger-than-normal flywheels or a geared system, but making it work will again cost more money than a big battery.

Edited by KaneTheMediocre, 08 July 2019 - 07:20 PM.

[Meaker VI]

The pullcord could attach to the flywheel, so size isn't an issue, though the question of speed is valid.

Yeah, standard wheels should be doing 35k RPM; big wheels have been more like 25k RPM but either way thats way faster than a pull cord will get quickly.

[Xhosant]

Welp, here I was, thinking I was contributing.

[KaneTheMediocre]

Yeah, standard wheels should be doing 35k RPM; big wheels have been more like 25k RPM but either way thats way faster than a pull cord will get quickly.

I think you and I mean different things when we say "big".

[Tactical Butter]

So I don't do flywheels, but I know a few things about electronics and feel I need to explain some things.

 

The capacitor you need to do this probably costs more than the bigger battery, without giving you any increase in capacity that you would get with a battery.  This is kind of a weird edge case where it's probably not absurdly expensive, but still more expensive than just using a bigger battery. 

 

Now, we have ready access to supercapacitors, which are still fairly inexpensive, but can deliver a ton of current.

 

Here's an example of a website selling them, as you can see, they have rather high energy density and fairly low pricing.

 

https://www.richards...=Ultracapacitor is a retailler local to me, and judging from the specs, you would need a small array to boost voltage to 14.4 V (3S) but it seems to check out.