The E-cumbent - A project by Matt Shumaker

[johnrobholmes]

It is much more important when you are pushing the controller near the voltage limits. The voltage ripple gets worse when your battery wires are longer, which makes the ESC work harder to keep everything in phase. It occurs on the motor side as well, but I have read that it is more important to keep the ripple down on battery side. When in doubt, just use larger awg wire to compensate. What AWG wire are you currently using?

The owner of Castle has recommended such, but the lengths were probably for a specific controller. I would err on the side of super short battery wire. As voltages increase the battery wire length must become shorter or you must use larger low ESR caps:

If you are running close to the cell count limits of the controller (absolute cell count limits -- not BEC cell count limits) then its easier on the controller to lengthen the motor wires and not the battery wires.

If you are not running close to the cell count limits of the controller, then it is easier on the controller to lengthen the battery wires and not the motor wires.

Try not to exceed 30" of wire on the battery side, or 16" of wire on the motor side, especially if you are running the controller near its limits.

The reason is this: Lengthening the battery wires increases the resistance between the controller and battery, which increases voltage ripple. When running near the controller voltage limits, this additional voltage ripple can break down the FETs, and eventually cause damage to the controller. Lengthening the motor wires increases the resistance between the controller and motor, which makes it more difficult for the controller to accurately commutate the motor, which increases current ripple, which is harder on the FETs. Longer motor wires also increases the amount of radiated noise in the system more than longer battery wires.

Try not to exceed 30" of wire on the battery side, or 16" of wire on the motor side, especially if you are running the controller near its limits. Also, using heavier gauge wire reduces the effect of longer wires. (for example, using 13ga wire in a 30 amp system with long wire runs would be better than the standard 16ga.)

 

[recumpence]

I thought it was amperage that was more critical to wire length than voltage.

Matt

 

[dirty_d]

i think the reason for the short length on the battery side is that you want the inductance on the battery side to be as low as possible, when the fets turn off the inductance in the battery wires wants to keep the current going, so you get a big voltage spike that can fry the fets, the big capacitors help but i think some of the spike still gets through. on the motor side its no big deal, because when they turn off the current can freewheel through the fet's body diode.

come to think of it, the first time i blew my controllers fets i think i had my battery wires wrapped around my steel seat post because they were too long

 

[johnrobholmes]

Right, on the battery side it is the inductance of longer wires that causes the problem. On the motor side it is the resistance. High amps, shorten motor side. High volts, shorten battery side. Or just keep both short.


Long battery wires wrapped around the steel seat post? :lol: :lol: Well that will kill it!

 

[recumpence]

I understand this from my experience with SPL car audio competition. I ran 00 wire to my distribution blocks with four 1 farad caps within 6 inches of the amp inputs. But, I haven't thought much about this on my bike.

Matt

 

[fechter]

I'd balance the resistance losses a bit on both sides. The current between the motor and controller can be much higher than between the controller and battery, and resistance losses are a function of current squared, so losses on the motor side can be significant.

When running things close to the limits, some additional resistance in the motor wires will keep the peak current lower and put less stress on the circuit. This could be particularly important if the motor winding resistance is extremely low. At startup, the current limiter circuit may not be fast enough to prevent dangerously large currents if the motor looks like a dead short.

The controller already has a big capacitor across the battery input. Making the capacitor bigger will allow it to absorb more energy and dissipate more heat. I don't see how this could ever be bad.

 

[scottclarke]

Matt, I have found with my 15 inch motor wires that it really benefits the esc if you use very large gauge wire from esc to motor. When I had the desolder on the esc I didn't change the wires because I didn't have any - now I know the wire heated somewhat - perhaps 20C as you are seeing - but the currents were below 80A so there was no reason for the 125A esc to have trouble. But it did on the next run - another desolder.

I have changed the wires to something huge - they don't quote gauge or csa - weird I know - but it is very heavy. diameter of the copper core (circular) is 6mm and since doing this wire doesn't heat at all (as expected) and 26 miles on I have had no problems.

Honestly - if you can omit wire heating I would - benefits of resistance aside!

Scott

 

[johnrobholmes]

When running things close to the limits, some additional resistance in the motor wires will keep the peak current lower and put less stress on the circuit. This could be particularly important if the motor winding resistance is extremely low. At startup, the current limiter circuit may not be fast enough to prevent dangerously large currents if the motor looks like a dead short.

I can't see adding resistance as being a good way to address a setup run on the limits. If the motor is being run close to the rated amperage, longer wires will only further aggravate the amp ripple and make the ESC work harder to stay in step- which will in effect make the motor run less efficiently. A better idea would be to drop down a tooth on the pinion to reduce full throttle current and make startup easier.

Low wind resistance is what we want, and if the setup is causing amp draw that will damage the motor then the motor is either overgeared or undersized for the application. The ESC should have more power channeling than the motor needs. The battery should be able to supply more power than the motor needs. The motor should not be asked more than it can handle, but the motor should still be the "weakest" link in the chain to keep all electronics working as long as possible.

 

[recumpence]

Understood.

Yes, the battery is up to the task. The motor is just yawning here. It barely gets warm unless I do a bunch of hard launches on a very hot day. Otherwise it runs just luke warm all the time. It seems the ESC is the weak link. That is why I plan on moving up to the Power Jazz ESC.

I do appreciate all the info from you guys. You went to school to learn all this. I am at the mercy of those who had the fortitude to endure the schooling to learn it all. :wink:

Matt

 

[johnrobholmes]

I'm homeschooled on this. I started in Elec/computer engineering and switched to business in college. I decided that I could just hire the engineers, but have been interested enough to learn much electrical theory on my own.

 

[recumpence]

Very cool.

I am self taught on machining. I know what you mean. I was an early homeschooler (I am 37 years old as of yesterday). My wife and I homeschool our 3 kids. So, learning on my own has been the halmark of my life. However, it has mainly been the mechanical side. I am green on the electronic side of things.

But, I have had a car I built featured (5 page spread) in Auto Sound and Security magazine and a bicycle I hand made featured in BMX Plus. So, My mechanical side is strong enough to get noticed. I just feel retarded when it comes to the electrical side of things.

So, again, I appreciate all the help I can get.

Matt

 

[recumpence]

Oh, I also may have a line on a Power Jazz ESC. A friend of a friend is a pylon racer and may have one to get rid of. So, I may get a deal on one. If not, I have at least half the money for a new one from my birthday yesterday. :wink:

Matt

 

[johnrobholmes]

I have always been an electrical type. Knew all the basics of electricity at 10 thanks to a smart stepfather that got me interested in it.

Now I am learning the mechanical sides of things. I have been welding for a few years on and off, but I need a lot more practice to get a nice looking bead with proper depth every time. Corners still get me, it seems the filler vaporizes before I can hit the metals to be joined (too hot?). I should probably just bite the bullet and get a nice Tig instead of fooling with sticks and flux core mig. I bought a mini mill and 12x24 engine lathe a few years back as well, mostly so I could build my own electric motors. I haven't gotten to that point yet, and my time is generally more valuable than the time it takes me to machine so I end up hiring out machinists to do most of my custom fabbing. If I want a custom motor I just hire the professionals, but that is an advantage of having multiple factory contacts.

 

[recumpence]

Cool.

I was tired of using a hack saw and drill press to "Machine" parts. What a pain. So, I sold a used car and bought most of my equipment all at once. It took a couple years to figure it all out. But, now I am rolling.

I have a bench top CNC, manual 5 axis bench top mill, bench top lathe, drill press, band saw, gas MIG welder, etc. I need a TIG next.

Matt

 

[recumpence]

I ordered my Power Jazz ESC today. It should be here Tuesday or Wednesday.

I am excited to get this. I found out the Jazz line of controllers have a throttle ramp program. So, I can program a soft throttle response to lessen the hard slam on the driveline. I believe it is a delayed ramp up feature. That is something I have wanted but could not achieve with the Castle Creations ESC.

Matt

 

[dirty_d]

you can find some decent tig welders on ebay for around $400, they are no-name brands made in china. thats where i got mine from, it works just as good as the $6000+ tig i learned on in school. it doesn't have AC output though so you cant weld aluminum, the AC/DC ones are 500-600 i think.

its got a arc welder and plasma cutter in the same unit also, both work great.

 

[johnrobholmes]

I ordered my Power Jazz ESC today. It should be here Tuesday or Wednesday.

I am excited to get this. I found out the Jazz line of controllers have a throttle ramp program. So, I can program a soft throttle response to lessen the hard slam on the driveline. I believe it is a delayed ramp up feature. That is something I have wanted but could not achieve with the Castle Creations ESC.

Matt

The CC controllers don't have a throttle ramp feature in the air controllers (yet), but they do in the ground controllers.

The Jazz ramp feature is a sort of throttle delayer. It only allows a certain % change in throttle over time, same effect of slowing down your throttle hand. The more you soften the throttle, the slower it reacts to your input. I like to compare it with hydrolic lines with a choke installed.

 

[recumpence]

Exactly. I ran a Mamba Max ESC in a scratch built RC truck (untill I smoked it). I loved the ramp feature. I used it as a wheelie control. :wink:

Matt

 

[scottclarke]

Its real funny you should mention this at all Matt since on Wednesday of this week I gave a 'servo slow' device a trial - it did pull the peak amps down a touch - but it also worked on the decel ramp meaning delayed stops!!! Maybe a newer one is programmable both ways - will have to have a look around.

 

[recumpence]

The ramp up is only a ramp up, not a ramp down.

That would be annoying.

Servo slowers are designed for things like landing gear retracts that should operate slowly to look scale.

Matt

 

[scottclarke]

Servo slowers are designed for things like landing gear retracts that should operate slowly to look scale. Matt

Yeah I know - I took it off my spitfire flaps just to see what effect it would have on amp draw. My meter is good to only 100A and it normally pulls 120A from 5-10mph or so. It did push the peak down - on one run out of 3 it showed a max of 98A - the other two were off the scale.

 

[recumpence]

Cool.

I know a ramp up feature is good for lowering amp draw. That is cool. For me, I am looking for reduced shock on the driveline. The amp limiter will lower my amp draw and increase efficiency alot further.

Matt

 

[Miles]

One-way hydraulic damper on the throttle, anyone?

 

[scottclarke]

Matt, you have a lathe so why don't you turn some parts and make a cush drive? It would be a lot simpler than the slipper - require no adjustment - never wear out and best of all they are silent in operation!

I would turn my own but my lathe isn't big enough since I want it on the back wheel.... hence paying a machine shop

Scott

 

[recumpence]

A cush drive is good for innitial shock, but not for sustained (more than the few mm a cush drive absorbs) slip. The driveline is not capable of handling the huge power my motor cap put out in bursts. But, it can handle the sustained output of the motor assuming the system has an outlet for the overtorque of a hyper spastic throttle thumb.

Matt