adjustable Servo speed circuit [ramp control]

[olaf-lampe]

Hi guys,
I know there is a circuit at the hobbyking shop to reduce the servo speed for retractable landing gear in rc-planes.
It would be useful to reduce the startup current for our rc-ESC abusers ( like me ). Just plug it between the servotester and the ESC and find a 'servo'-speed that suits yours and the ESC's needs.
The problem is, I can't find the damn thing in the shop...
Anyone?
-Olaf

 

[SunCoaster]

Is this it?

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8863

 

[spinningmagnets]

If one of the electronics gurus sees this thread, could you please chime in with an educated guess as to how these electric 'snubbers' slow down the operation of the landing gear operation?

Is the current limited to slow deployment? perhaps the signal is chopped up? I am trying to learn, so I apologize in advance for the newbie questions, I am just looking for all the ways that the RC-ESC frying problems could be eased, and this "looks like" it holds promise, or at least it may be a viable option for some configurations of RC-drive.

 

[recumpence]

From my understanding of this (when I looked into it years ago for landing gear retracts), all it does is slowly sweep the PWM rate to move the retract servo slower. This is a simple ramp circuit. Yes, it can help reduce the ESC abuse. However, it is also annoying because every time you want to change throttle position, the ESC reacts very slowly.

It should ease the controller load under most circumstances, though.

Matt

 

[recumpence]

Is this it?

http://www.hobbyking.com/hobbyking/store/uh_viewitem.asp?idproduct=8863

Yes, that is exactly what he is looking for.

Matt

 

[olaf-lampe]

Thanks for all the infos. Yes, I guess it just ramps up the PWM signal.
My question is: does it do this in both directions the same speed or is everything adjustable? I want a slow acceleration but throttle release shoudn't be slow. If it is also slow, I'd have to brake everytime to cut off the throttle signal imediately...
-Olaf

 

[GGoodrum]

If one of the electronics gurus sees this thread, could you please chime in with an educated guess as to how these electric 'snubbers' slow down the operation of the landing gear operation?

Is the current limited to slow deployment? perhaps the signal is chopped up? I am trying to learn, so I apologize in advance for the newbie questions, I am just looking for all the ways that the RC-ESC frying problems could be eased, and this "looks like" it holds promise, or at least it may be a viable option for some configurations of RC-drive.

What this does simply, is to slow down the change in pulse width of the servo signal. The way RC servos work is that they send out a pulse every 20ms. This pulse varies from 1ms to 2ms. If the pulse is 1.5ms wide, the servo will be in the mid-point of its travel. 1ms represents all the way counter-clockwise, or 0 degrees. 2ms is fully clockwise, which I think is about 230-240 degrees. Before RC electrics, a servo was used to control the throttle on the gas engines. These typically didn't use more than 180 degrees of travel, so the servo "end points" were set via the radio transmitter, so that the 180 degrees was centered around the mid-point. When electric setups came into being, the motor ESCs simply mimicked the way the engine throttles were used. The radio transmitters have a setting "range" of 0-135%. I think the ESCs expect a range of around 100%, offset so that this 100% is centered around what would be the midpoint of the servo travel.

A servo tester is designed to operate a servo over it's full range, so its output will be a 20ms pulse train with a pulse wide that ranges from 1-2ms. The circuit is is designed so that it takes 0-5V to vary the pulse width from 1-2ms. So, what happens if you simply replace the servo tester's pot with a throttle grip. the output will vary from 1ms to 2ms, or in the terms of what the ESC is looking at, it will vary from 0 to 135%. The ESC, however, is "expecting" to see 0-100% offset 17.5%. It assumes everything below 17.5% is off, and it ignores anything above 117.5%. This offset, 100% range roughly equates to 1-4V on the input to the servo tester. This is why some RC ebike setups have "twitchy" throttles that don't do anything for the first part of the throttle twist range, and max out before it is wide open. Most modern ESC, however, have a fix for this, via an auto throttle calibration procedure. The way this usually works is that you open the throttle all the way, and then power up the ESC. It sees this maximum setting and re-calibrates the upper throttle end point. you then reset the throttle, all the way off. The ESC then will also reset the lower end point. This allows for the maximum throttle "granularity", using the full 0-135% of "travel", or in the case of our ebike throttles, the full 0-5V range.

-- Gary

 

[spinningmagnets]

WOW! Great answers! Thanks Matt and GGoodrum, thats just the type of information that helps me understand these parts better. It will also help me better understand the hacks that are attempted in the near future by the creative posters here.

 

[AussieJester]

My question is: does it do this in both directions the same speed or is everything adjustable? I want a slow acceleration but throttle release shoudn't be slow. f

According to one of the buyers responses in the comments on HK

"The 3 adjustment pots let you have different UP and DOWN speeds and reverse a channel"

KiM

 

[Hillhater]

Hi guys,
I know there is a circuit at the hobbyking shop to reduce the servo speed for retractable landing gear in rc-planes.
It would be useful to reduce the startup current for our rc-ESC abusers ( like me ). Just plug it between the servotester and the ESC and find a 'servo'-speed that suits yours and the ESC's needs...

Is this not what the onboard ESC "start mode" program option does ? ... soft start etc

 

[olaf-lampe]

Is this not what the onboard ESC "start mode" program option does ? ... soft start etc

Yes, the softstart option is quite similar.
But when you played with it, you'll notice that it only works when you start the stick from zero. Then it ramps up the pwm for a given amount of time.
When you only gave half throttle and the time has elapsed you better not hit full throttle, because then it doesn't softstart anymore.
I hope this gadget is different. At least there are two different speeds for acceleration and deceleration ( thanks Jester)

Even better: you can preset each of the three channels to a different speed. Then wire the white( or orange ) cable from the ESC and the 3 outputs of the timer to a 3x switch and choose which acceleration suits your mood.

 

[olaf-lampe]

Even better: you can preset each of the three channels to a different speed. Then wire the white( or orange ) cable from the ESC and the 3 outputs of the timer to a 3x switch and choose which acceleration suits your mood.

Further thinking about this feature, it would be possible to preset 4 different acceleration-reductions. Because you can also bypass the whole circuit and use the original throttle.

-Olaf

 

[Hillhater]

OL, .. i am still struggling to understand why you would need this type of throttle control / limiter ?
I can see how fast throttle action can overload the motor/controller but i dont see how you can predict the rate of throttle needed for any given situation, and it sound like limiting the throttle wont necessarily limit the current or load on the controller..
Level road starts may be one consistent situation requiring a certain "ramp" rate, but then an uphill start would require a different "Ramp" rate due to the heavier motor load and acceleration rate.
..and of course this situation changes for a steeper gradient !
ditto for downhill starts etc !
Also what do you do in "emergency" situations where you suddenly need every bit of power you can get ? ..and you are switched into one of the slow ramp modes ?
I cannot see how you can program for many of the potential combination of circumstances.
To me, the best throttle control is the built in computer and total feed back system that is attached to the throttle by your hand ! ...your brain :lol:
You should be able to think how much throttle is needed for any specific situation and adjust according to conditions. If you find that difficult, you may need a more progressive or longer throw throttle action. ( a common problem)

 

[olaf-lampe]

Actually I bought them for the pocket bike. The tracks we'll race on have different characters and with a little experience you can choose the best acceleration for each track.
Driving without any acceleration reduction on the street is also possible, just bypass the limitter.
Sure enough, you can adjust a reduction ratio , which can take every hill , but still reduces the risk of a fried controller.

-Olaf

 

[spinningmagnets]

If an RC builder fries a 65A ESC under the loads he occasionally applies, the common remedy now seems to be to upgrade to an 85A ESC (then up to 100A, and so on...). I recall a 150A RC-car ESC that claimed 150A continuous and 1,000A burst (for 10 seconds) that cost $120. My 85A ESC (I am waiting for delivery) was only $40.

I like the "position 4" turbo bypass idea, and this little speed controller is very cheap. I think ramping up acceleration will keep the ESC heat down. I also believe it will make life easier on the battery's health and help the bikes battery range. As far as heat goes, I imagine a hot controller is more fragile than a cool one (when an amp-spike hits it). The last thing anybody would want in an emergency, is for the controller to fry just when you need it most.

 

[olaf-lampe]

In general it helps to smooth the sometimes erratic signals of these hall sensored thumbtwist throttles.

I removed the spring from my throttle to have kind of a cruise control.
Sometimes in stressy situations I hit full throttle instead of pushing the throttle to zero. The ramp-control (as I'll call it from now on ) helps here too...

And you are right, the FETs get more sensitive when they heat up. Thats why multi FET controllers (should) try to keep their temperatures on an equal level.
-Olaf

 

[ioio1]

Hi,

New on the forum. Very impressive work what you have done.
I am just starting building my ebike. From the begining, I have been thinking of ramps for motor control. I work in the electric motor industry, and when powering electric vehicle, we control the following parameters, amongst others:
- set torque
- set speeds
- ramps
I am builing an electronic controller for my ebike. As model controlers only have a set speed input, I use a micro controller circuit to adjust the set speed according to the various parameters.
I have designed micrcontroller circuit with graphic touch screen, and I want to implement one on my micro controller circuit.. It will require two micros: one for PWM control of the motor, and another one for screen, sensors and so on. It will send set speed to the pwm mircro through serial comms.
I believe torque control is necessary to preserve the brushless motor. I will use curent measurement on the motor to evaluate torque.
When pushing the trottle, internal set speed increase following a ramp, and torque set point is calculated according to throttle deviation. Full throtle will give full torque when speed is above a certain level.
Transforming internal set speed and torque into RC controller set speed is the difficult thing I am working on.

I am at the begining of the concept and build process, conducting both electronic and mechanical design and build at the same time.. If you are interested (and patient!) I could make a controller for you to try out. At the momment electronic trials are conducted on a test bench, as my ebike is not build yet (still machining transmission and fixings..)

Regards.

Lionel

 

[olaf-lampe]

I got the ramp control circuit yesterday and tested it.
Unfortunately it is not a 3-channel reduction. It's more like a one-channel reduction with three outputs.
The first two potmeters are used to adjust the ramp speed ( back and forth seperately adjustable )
The third potmeter is meant to reverse the direction, but it doesn't work in my setup with the turnigy servotester.
It's useless anyways, so I don't care.

The positive thing is, that it works exactly as I hoped: you can raise the throttle to a certain position, the ESC will follow with the adjusted rate. When you accelerate more, it will follow again with the same speed. ( Thats what the ESC's internal 'softstart function' doesn't do)
When you release the throttle at any moment, the ESC will react instantly.

My plan to adjust three different ramp speeds and switch them is still possible, but you'd need three of these circuits.
I happen to have ordered three, so I'll come up with a PCB where I mount and wire them to a 4-way switch and put it in a box. Pictures will follow soon.

-Olaf

 

[spinningmagnets]

The 85A ESC I am about to attempt to use on a 6S (22V) friction-drive is only $40 and is very small. I will add caps, and I am hopeful for success. The next upgrade would be a $65 K-force 100A, then a $100 150A RC-Car ESC, then finally, the big-dog $270 Castle Creations 160A (many features besides high amps, high quality, data logging, higher voltage, etc).

Most people simply don't want to be bothered gently ramping up the throttle every acceleration cycle (like me), and a simple, reliable amp-ramp gadget creates an added layer of insurance to help an affordable ESC survive.

Thanks for posting this! Please add pics when you finalize the design. What would you charge to make up a batch? you could easily and quickly sell 10 units for beta testing...(count me in for one, if its less than $20 its cheaper than the next ESC upgrade)

 

[Hillhater]

Ditto what SM said re testing.
Also SM, I have one of the 150a car ESC's in the post ( $70 ..with sensor capability also ) so i will report back on its effectiveness.

 

[olaf-lampe]

The only RC setup I could test the circuit with in real life situation is the pocket bike. I focus on that build to collect some testmiles before winter comes.
I will make a simple PCB and document it with pictures. Everyone with a solder iron can copy that.
-Olaf

 

[olaf-lampe]

While I was taking a picture with three ramp-controls a big turnswitch, the turnigy servotester and a 3.7V_to_5V voltagebooster, I came up with a much simpler idea:

Just use one ( instead of three ) ramp-control and replace/rewire the relevant smd-potmeter with a standard-potmeter. Mount it on the 'dashboard' where the switch should have been located and we've got a stepless ramp-control

I still could make some marks on the dashboard with useful ramp-speeds for dry/wet/snow/ice conditions
The critical part is, that the useful range of ramp for my application is pretty small. I don't need a 10s ramp from 0 to 100%.
The replacement potmeter would therefor have a much smaller value ( eg 1kOhm instead of the original 10k) but there will be a resitor in series to spread the useful ramp-range to a full 270° turn. ( I hope I'm not confusing anyone )

-Olaf

Anyway here is the picture how it's not gonna be

 

[olaf-lampe]

BTW, here's a tip for everyone who is using the same servotester: replace the resistors beneath the LED's with 4k7Ohm. Your eyes will love it
-Olaf

 

[liveforphysics]

Holding it in partial throttle longer is absolutely the worst thing for the poor ESC.

You don't have to believe me though, this is straight from Castle Creations own website:

http://www.castlecreations.com/support/faq/faq-mamba_max.html

Question:
2. Can I control how much current passes through my speed controller by limiting full throttle travel on my transmitter with endpoint adjustments/trim? In other words can I use a 25 amp speed controller with a motor that will pull 45 amps but lower my top throttle endpoint on my transmitter so my watt meter only shows 25 amps at full throttle? Will this be OK?

Answer:

NO!!! A speed controller controls power to the motor by turning full throttle current on and off really fast, 11 to 13 thousand times per second (Pulse Width Modulation or PWM). The percentage of each on/off pulse that is off compared to the part that is on determines how much power the motor sees. I.E. With a pulse that is 50% off and 50% on the motor will see 50% power*. Because each on pulse is 100% of full throttle current, a system set to pull 20 amps at full throttle through a Phoenix 10 will not last if you are throttled back to the point where you only see 10 amps on a wattmeter. The ESC in this case is still switching 20 amps, which it can’t do for long. Actually it is worse than the simple example above. Because an electric motor will always to try to pull as much power as is available to get to its rpm (volts times Kv), when you are running the motor below its Kv speed by switching power on an off, each on pulse will actually be way over the full throttle amp draw. That is why ESCs work harder at partial throttle than full throttle and why we underrate our ESCs. We underrate not so they can handle more current than their rating at full throttle, but so they can handle extended partial throttle operation with no problems.

 

[liveforphysics]

This is why when folks wana power motors with extremely low resistance/inductance, there is no magic control box solution to let a controller not up to the task perform like a suitable one.

Fechter's box for RC throttle signal backing down as current creeps up. = Poor motor performance, glitchy response, and exploded ESCs.

EV logix box for backing down the throttle signal to control current. = Blown ESCs unless you disable the current limiting function (but otherwise works at least).


You could make the Olaf box, which if I'm reading correctly, would be designed around making sure maximum heating goes into the controller during throttle position changes, and stripping away the riders ability to have instant and direct control over the vehicles throttle, an attribute that gasoline engine designers work so hard to try to achieve as best as they can, and electric users often like to dismiss. It's a puzzle to me.