brothman01
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Buy Faster Motors

Sun Jul 21, 2019 7:34 pm

Hello, I recently finished the buggy project and it is great except the motors are very slow. I control the 2 yellow motors with a L298N chip controlled by a pi. There is a 4AA battery power supply powering the chip and motors.

I want to buy two new motors to replace the small yellow ones because they are too slow. I am ideally looking for two motors that can be used with most of the same hardware I mentioned above, although I am guessing I will need a better power supply. I am not trying to make my buggy go as fast as a regular gas powered car for humans or anything like that, but which motors and power supply will work with the L298N chip to allow my buggy to zip around like a normal RC car?

mattmiller
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Re: Buy Faster Motors

Sun Jul 21, 2019 9:21 pm

Those little yellow motors come in many different RPM varieties so you may have one of the lower RPM ones

pcmanbob
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Re: Buy Faster Motors

Mon Jul 22, 2019 5:04 pm

1. You might find that 4 AA batteries can't provide sufficient current to drive you motors under load so the battery voltage is dropping low causing your motors to run slow.

2. The L298N H-bridge motor driver boards are normally specified as being rated at voltages from 12v to 35v , so you might find that running it at 6v, the volt drop across the driver board will so so high it will cause your motors to run slow.


Get yourself a cheap digital multi meter and measure the voyage at the input to the motor driver board and the output of the motor driver board that will tell you were the volt drop is.
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blimpyway
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Re: Buy Faster Motors

Mon Jul 22, 2019 6:52 pm

yeah it could be simpler to increase voltage, e.g. use a RC lipo battery at 11,1-14.4V

brothman01
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Re: Buy Faster Motors

Tue Jul 23, 2019 12:47 am

@pcmanbob so you are saying that the weight of the car will effect the voltage consumed by the motors? If I run a car once and then run the same car a second time with a weight on top, the voltage used by the motors will be lower during the second run? I know this part is a new question, but can I (using the GPIOZero python package) control how much voltage the L298N board takes from the batteries and then sends to the motors?

@blimpyway I looked into that motor on ebay... will the L298N chip that I already have be able to use the Lipo motor as a power source?

I will get a multimeter.

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Imperf3kt
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Re: Buy Faster Motors

Tue Jul 23, 2019 1:55 am

The voltage used will be the same, but the current required to move a heavier "car" at the same speed will increase, leading to the supply voltage "sagging"

One way to observe the effect on how fast the motor spins is to simply measure the voltage with the wheel off the ground, then measure it when pushing the wheel against something.
The harder you push, the more resistance you add, the more power is needed to move the wheel at the same speed.
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brothman01
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Re: Buy Faster Motors

Thu Jul 25, 2019 10:34 pm

@Imperf3kt right that makes sense. so would the way to remedy this problem be to get a motor that is stronger (referred to as a motor with higher torque?)

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Imperf3kt
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Re: Buy Faster Motors

Thu Jul 25, 2019 10:57 pm

No, that will make your problem worse.
The solution is to get a better power supply than 4 AA batteries.
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Gavinmc42
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Re: Buy Faster Motors

Fri Jul 26, 2019 2:31 am

The solution is to get a better power supply than 4 AA batteries.
Or a better driver chip than that bipolar L298.

Those yellow motors are low voltage, high current.
It is one of my personal rants that they still put these toy motors in robot gearboxes.

You will get a lot of voltage drop in the driver chip.
By moving to a mosfet driver there is less voltage drop.
But high current motors can draw more power than AA batteries can provide unless they are NiMH or LiPo.

You are basically using crappy toy motors with a crappy driver.
I usually start with 6 or even 8 AA cells and a separate USB power bank for the Pi.

You can get higher voltage, lower current RS130 motors for about $1 each and just swap them for the toy motor in the gearbox.
You need more batteries but they will last longer and the voltage drop means less power wasted in the L298.

If you want to have fun you can pull the motors apart and rewind them with more turns of smaller wire.
That is the main difference between a 3V toy motor and a 12V robot motor.
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brothman01
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Re: Buy Faster Motors

Fri Jul 26, 2019 11:27 pm

Ok, here is my new power supply:
https://www.ebay.com/itm/Battery-Holder ... 0500ab82e2

and this is the driver board:
https://www.ebay.com/itm/Dual-Motor-Dri ... Sw301dF4CK

1. with the L298N there was this useful diagram with it to show what each port was for:
Image
the MOFSET does not have a similar useful diagram, but on the product picture has positive and negative ports for each motor, and then other ports 'DIR1', 'PWM1', 'DIR2' and 'PWM2'. The two GPIO pins associated with each motor need to connect to the DIR and PWM for that motor? Rephrased that is, if a motor is declared on the pi as

Code: Select all

 ...Motor(17, 18)
then GPIO17 and GPIO18 on the raspberry pi connect to DIR1 and PWM1 respectively? (I already have working code from my past project, don't worry about the syntax of the code).

2. Although no one said to get new motors outright, you both seemed to look down on the little yellow motors, haha. Should I get new motors or do you think the changes I am already doing with the board and the power supply will be enough to fix the sagging problem and make my buggy faster when carrying the raspberry pi? I did look at RS130 motors but they all seemed very expensive so if I can avoid this step I want to.

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Gavinmc42
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Re: Buy Faster Motors

Sat Jul 27, 2019 12:56 am

Going to higher voltages has many benefits.
Those little yellow motors are not bad gearboxes, it is just the motors they put in them are a low voltage high current versions.

The L298 can go up to 4amps at 35volts, that is a quite a bit of power.
Over a 100watts. but those toy motors might be 3V 1 amp, only 3 watts.
If you push higher voltages into them they can draw much more power but then the brushes have to handle the current and they burn out quick.

The brushes for motors can be of metal, carbon or precious metal.
The cheapest have metal ones, they wear out quick, carbon can handle more power and last longer.
The more expensive longest life ones use precious metal.

I think you will find the higher voltage battery pack will make a big difference.
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Imperf3kt
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Re: Buy Faster Motors

Sat Jul 27, 2019 6:39 am

The L298N is actually rated for 2Amps, but you can bridge two together to get 4Amp output. Note that at that current, the included heatsink is inadequate and should be replaced with something bigger.


Don't use the 5v on the L298N, it is limited to a bit less than 0.5A and isn't sufficient to power a Pi (maybe a Zero) nor noise free.

I have several myself. Here's the one attached to my Pi3b running off a lithium polymer battery (2000RPM geared motor powered by a separate 12v supply)
Image
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brothman01
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Re: Buy Faster Motors

Sat Jul 27, 2019 8:35 pm

I do recognize and appreciate the time gavin and imperfect spent answering this question, but I do need to know if the above equipment will work with my existing pi and motor configuration or if the new board and power supply will need new motors if I want to have a faster buggy that does not sag under a little bit of weight?

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Imperf3kt
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Re: Buy Faster Motors

Sat Jul 27, 2019 9:51 pm

As I see it, you've got two choices, get some higher quality motors (and higher voltage/better current capability power supply), or give your current setup more power.
Those motors should run okay at up to about 12v. They'll get pretty hot at that voltage though, might not be a good idea to run them for too long like that.
A better option is to double the batteries you use and parallel them. (use batteries at the same voltage when paralleling them, don't mix new and old/used batteries.)
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Gavinmc42
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Re: Buy Faster Motors

Sun Jul 28, 2019 2:36 am

Those metal gearmotors are good ones. A step up from the plastic yellow ones.
But I see you are using a single LiPo and a battery boost circuit.
That should be ok for powering the Pi but don't try to power the motors from it.

Motors and gearboxes are tricky - torque, weight, speed, voltage, current are all connected.
Then you need to factor in the efficiency of the drivers, the internal impedance of the batteries, wiring gauges......

The best way to get a handle on all this is just mess about chassis, wheels, motors, gear boxes and batteries and worry but the electronics later.
Just use a switch? Add some extra weight to pretend it's the Pi.
If you don\t have enough torque to move you can use smaller wheels.
If you want more speed then bigger wheels.

In the real world of electric vehicles, lawn mowers and cordless drills you might have noticed a trend.
Voltages are increasing, cordless drills used to be 7.2V now they are 20V or even more.
The simple solution - More power = more voltage.
If you cannot move with 8-10 NiMH AA then you can try 8-10 AAA cells to save weight.
Or three x Li-ion or 4 x LiFePO4.

If you want to get serious about batteries then visit HobbyKing and get a LiPo charger and some 3S cells.
And a flame proof bag.
Those chargers are computerised and can charge lots of types and up to 6S?
There is a good reason drones use LiPo packs.
If you want some serious usage and expect long life then the new Graphene cells are worth the extra money.
The number of recharge cycles is important.
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brothman01
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Re: Buy Faster Motors

Sun Jul 28, 2019 6:28 pm

Ok then awesome, thanks, I am going with option 2 and using 8AA batteries instead of 4AA batteries to increase the power. The single LiPo battery was from another answer, that part is different than my setup.

I think for my next project I will use a lipo because currently the pi is powered by the wall outlet and the motors are powered by the batteries. With a lipo maybe I would be able to power the pi AND some motors, but I will have to buy the right one along with a charger.

That HobbyKing site is a gold mine, thanks for that, just going on the site and seeing what they have gave me ideas for future projects. I can't be too hasty with new projects though, I will finish this project first.

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Gavinmc42
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Re: Buy Faster Motors

Mon Jul 29, 2019 12:22 am

A small USB power bank will power the Pi and the AA's for the motors.
That's pretty much the usual way.
Motors, especially these toy ones are nasty spike generators that can kill electronics.

Optical isolation to the motors drivers helps.
Always put spike suppression caps across the motors brushes.
Three caps, across the brushes and from each brush to the motor case is not uncommon.
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brothman01
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Re: Buy Faster Motors

Tue Jul 30, 2019 12:14 am

oh nice I was about to ask about a separate battery for the pi but you already told me, haha do you have a specific battery in mind or how many watts are needed to run the pi? (a number and a link to an ebay page would work)

I am also unable to find "spike suppression caps" and am not sure what they are.

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Gavinmc42
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Re: Buy Faster Motors

Tue Jul 30, 2019 12:53 am

I am also unable to find "spike suppression caps".
A ceramic cap from 0.01 to 0.1uf X7R 50V or or more should do.
The X7R is the important bit.

No point having a big Pi battery when the motor battery goes flat much faster.
Some of the small 2600MaHr USB power banks only deliver 1Amp.
Look for 2.1Amp ones if you are going to use USB things in the Pi.
USB PS2 Eyecam etc, I have got these as low as $2

I look out for USB banks on special at local shops, I don't buy from ebay, shipping costs are high here.
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brothman01
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Re: Buy Faster Motors

Tue Jul 30, 2019 1:28 am

ok, I am able to find battleries that are 2600MaHr USB power but why are these batteries described in MaHr or a/hr as opposed to wall plugs which are described in volts?

-------- UPDATE ----------
I just found one with both:
Image

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Gavinmc42
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Re: Buy Faster Motors

Tue Jul 30, 2019 1:47 am

Never seen a pack like that before.
It must be a LiPo, Lithium Polymer cells are flat.
Because of the thickness it might be a 2P pack.
Two cells of 1800MaHr wired in parallel.

HobbyKing packs have heavy duty connectors for motor powering.

2600Mahr Power Banks normally have a single 2600MaHr 3.7V Lithium Ion 18650 - 18mm dia by 65mm long cell with boost circuit.
A 5000MaHr pack can be two 18650 Li-Ion cells wired in parallel.
The 18650 is a common size cell, you can get them for LED torches etc
Three of these is about the same as 8 X AA NiMH, but lighter.

Wall plugs have unlimited capacity ;)
You only need to worry about Voltage and Current.
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Imperf3kt
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Re: Buy Faster Motors

Tue Jul 30, 2019 1:55 am

Lithium polymer isn't necessarily flat just like lithium ion isn't necessarily cylindrical.

Given that the voltage is 3.6v, it looks like an old portable device Li-ion battery. Possibly a toy RC device, camera or phone?

The mAh rating is its capacity, how much you can get from it before it's "empty"
Beware that many batteries bought on ebay are fake. Either recycled laptop batteries, or new batteries but with clearly nonsense capacities
https://youtu.be/hIMMYJ97BjM

Such batteries not only rip you off, they're also potentially dangerous.
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