Jump to content
Sign in to follow this  
Peter_B

Limiting speed

Recommended Posts

For my 3 year old twin boys I've got a Lunchbox and a Mad Bull. Both running Quicrun 1060 ESCs and standard silver can motors with standard gearing.

I've limited the speed of the cars by using the throttle end point adjustment on their Tactic TTX300 transmitters.

With the throttle end point limited the ESC is effectively only ever seeing part throttle. With a manual speed controller this would have meant a big chunk of battery power being wasted making the resistor nice and warm. Is there a similar consideration with an ESC? Is runtime being wasted by limiting the speed the way I am?

Is what I'm doing the best way to do it? Or should I look at getting a couple of crawler motors (and removing the end point limiting)?

If crawler motors is the answer what should I be looking at? I've seen other people mention 35T, 55T and even 80T in relation to these cars. But I have no idea how fast any of those would be in practice. I posted a video of the boys and their cars in another thread, see below link. I guess I'd be wanting to get the same sort of speed, and the boys would be happy if there was enough torque to get the odd wheelie happening.

 

Share this post


Link to post
Share on other sites

ESC's are far more efficient than the old resistor MSC's.. You will be getting a slight power loss running the ESC at part throttle, but I don't think that it would be enough to worry about..

When I set up a few cars for my nieces and nephews to use, I just fitted a crawler motor to the cars.. A 55t motor will run at approx. half the speed of the kit supplied 540 silver can motor.. The big thing that I noticed when running a crawler motor was that the runtime was approx. twice as long as it was with the kit 540 silver can motor..

Carson do an inexpensive truck puller motor that is very popular with the Tamiya 1/14 RC truck crowd.. 
http://tamico.de/Carson-Truck-Puller-Motor-Poison

RC4WD and HPI also produce inexpensive crawler motors..

https://www.modelsport.co.uk/index.php?search=1&search_string=55t

Share this post


Link to post
Share on other sites

Knock yourself out with mechanical limiting. Tape a piece of cardboard behind the trigger. As you said yourself, in the old days, power was regulated by letting it flow through resistors. Today. What a modern ESC does, is cut the stream of power into small chunks, so instead of a continuous stream of power, like --------------------------------- you get chunks released like:  -  -  -  -  -  -  -  -  with more and more chunks released in the same time the more throttle you apply.

 

Do I even make any sense? (:

  • Like 1

Share this post


Link to post
Share on other sites

The ESC FETs will run hotter if you are running at partial throttle all the time, because they are constantly having to turn the power on and off many times a second. Back in the day this would have put the ESC in danger of burning out, but most have thermal cut-offs these days.

 

The main issue with limiting the speed by means of the ESC is that you are also limiting the torque. A crawler motor will also limit the speed, but will boost your torque. Wheelie popping should therefore be very much on the cards.

 

Many people use 55t crawler motors in kids' cars. These are probably a good starting point.

Share this post


Link to post
Share on other sites

Thanks all. It seems a crawler motor is probably the better way to go. I'll look into getting hold of, at least, 1 and give it a try.

Share this post


Link to post
Share on other sites
17 hours ago, TurnipJF said:

The ESC FETs will run hotter if you are running at partial throttle all the time, because they are constantly having to turn the power on and off many times a second. Back in the day this would have put the ESC in danger of burning out, but most have thermal cut-offs these days.

Sorry. But modern ESCs don't use FETs - that was back in the days: 

ESC with FETs (burned through protective shrink with a 2x12):

img5934_04012006133917_1.jpg

Modern ESCs handles the output through PWM (Pulse Width Modulation) - and will actually run cooler at lower throttle than they will on full. When running on partial throttle, the motor will naturally draw (a lot) less power than it will at what.

 

Share this post


Link to post
Share on other sites

The Carson Poison motor is a good one for the money.  I run one in my rig, and even with full lights and sound on the cab and trailer, it'll run for over an hour on a Tamiya nicad.  Other crawler motors are available, but the extra torque and rebuildable design isn't really necessary for hooning in a kid's car :)

Share this post


Link to post
Share on other sites
1 hour ago, Flerbizky said:

Sorry. But modern ESCs don't use FETs - that was back in the days: 

ESC with FETs (burned through protective shrink with a 2x12):

img5934_04012006133917_1.jpg

Modern ESCs handles the output through PWM (Pulse Width Modulation) - and will actually run cooler at lower throttle than they will on full. When running on partial throttle, the motor will naturally draw (a lot) less power than it will at what.

 

If modern ESC's don't use FETs, then what do they use?

I believe that older FET (MOSFET) ESC's also work using Pulse Width Modulation, its just that some ESC do it at a much lower frequency..

Share this post


Link to post
Share on other sites

PWM refers to the means of throttle control.

 

FETs are still used to switch the current to the motor.

 

Varying degrees of throttle are indeed achieved through pulse width modulation (varying "on" time versus "off" time) however in every ESC I have ever pulled apart, this rapid "on" and "off" switching is still achieved with good old FETs.

 

See below video:

https://youtu.be/22CpRl2_TRI

(Just ignore the repeated references to AC - he should be referring to commutated DC.)

 

 

  • Like 1

Share this post


Link to post
Share on other sites

I've ordered a couple of the Carson Poison motors to give them a try. I've ordered them from Amazon so, if they don't work out, I can easily return them.

Share this post


Link to post
Share on other sites

It's school holidays, took a fleet of XCs out to the track with the kids & their friends. Most were silvercan with QuicRun.

For the less experienced drivers, I tried limiting ch2 epa which worked ok at first... but after a few on/off cycles, they've reprogrammed themselves to go full throttle again on the limited EPA! something to watch out for ;) these ESCs are smarter than me

 

Carson Poison is a sealed can, cost around EUR10 or US$15-20ish? 

Wouldn't the Yeah Racing Hackmoto (35/55/80T) be better value at about same pricepoint, it's got replaceable brush endbell 

Bought some last yr but haven't installed, didn't buy enough for today's 5 cars so didn't bother trying them today. Haven't looked if it's got bushing or bearing.

 

Share this post


Link to post
Share on other sites

Yep Carson Poison have cost me £11 each.

I don't really care if they're replaceable brushes or not. Plus they're not going to get used day in, day out so I'm not worried about them wearing out before the boys have got to grips enough to switch back to silver cans.

Good point about the ESC re-calibrating the end points. Probably another argument for restricting speed with the motor instead.

Share this post


Link to post
Share on other sites

If the motors are rebuildable, I can maintain & use them in my crawlers later on, right? :) 

 

well, I now know to limit EPA only on ESCs which need a button press to initiate programming, not auto sync like QuicRun ;) (originally I thought the 5yo had worked out how to undo the EPA limiting... nah kiddies aren't that smart, hah)

also my cheapy TXes don't have EPA... I had to sacrifice a Spektrum for the 5yo 

this might become a regular thing (trying to addict next generation into RC), so thinking of ways to make the speed-limiting easy to add & remove - like when friends arrive unannounced & they spot my RCs

1, a mechanical limiter to TX trigger... hard to equalise across different TX

2, an additional resistor/trimpot to trigger (electrical EPA)... need to hack TX

but most simplest, was thinking

3, what about adding on a resistive load inline with motor? Next time I do soldering I'm going to experiment adding a suitable load via male-female bullet connectors... just plug into 1 side of motor to ESC lead, everything else stays same, done!

 

Share this post


Link to post
Share on other sites

I ran an 80t in the madbull for my two when they were about three and then went to 55t at about 5. At 7 my oldest is running a 10.5t brushless and doing better than me :-(

  • Like 2

Share this post


Link to post
Share on other sites
4 hours ago, Nobbi1977 said:

I ran an 80t in the madbull for my two when they were about three and then went to 55t at about 5. At 7 my oldest is running a 10.5t brushless and doing better than me :-(

Join the oldman club, daddy-o! :P

My 2 aren't too bad; trouble comes when their friends dropin... majority of today's kids haven't driven RC before.

Or worse, more likely they've flown a toy quad... which as we all know has enough gyros to fly itself - the only purpose of human intervention is to steer it into a tree! ;)

Share this post


Link to post
Share on other sites

One of the Carson motors arrived today. Fitted in the Lunchbox.

Speed seems spot on and there's enough torque to spin the wheels and pop the front up about on take off.

Another should arrive tomorrow for the Mad Bull.

  • Like 2

Share this post


Link to post
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
Sign in to follow this  

×
×
  • Create New...