Efficient motors for solar-powered robot application - RC Groups
Thread Tools
Nov 01, 2017, 02:04 PM
Registered User
Discussion

Efficient motors for solar-powered robot application


Hello! I am building a solar-powered autonomous robot, and now I am searching for the right motors. The robot will have a 20W solar panel and 5000mAh 6.6V LiFePo4 battery in the 2S2P configuration. I don't know the weight yet exactly, but the motors should be able to handle at least 5kg. The robot should have 4 big 15 - 20 cm wheels. Ideally, I would have each wheel driven independently by one motor, but two (left and right) motor configuration is also possible. I calculated, that it would need about 10W mechanical power to drive upwards on 45' slope with 1 km/h speed and 5 kg mass. So, in reality, it would need 15 - 20 W mechanical power at maximum. Each wheel has to have about 100 RPM and 0,7-0,9 Nm. Because of the low power solar panel, I need the most efficient motors available. I have looked at Maxon motors, but they are very pricey. Which kind of motors is more efficient DC or brushless? Is it better to use one motor for each wheel or 2 motors with mechanical power distribution? Are there such brushless motors that can be used without any gearbox at speed about 100 RPM? Which manufacturers could you recommend to look at?
Sign up now
to remove ads between posts
Nov 01, 2017, 04:55 PM
just look at it smokin'
z-matrix's Avatar
Quote:
Originally Posted by CreFroD
Hello! I am building a solar-powered autonomous robot, and now I am searching for the right motors. The robot will have a 20W solar panel and 5000mAh 6.6V LiFePo4 battery in the 2S2P configuration. I don't know the weight yet exactly, but the motors should be able to handle at least 5kg. The robot should have 4 big 15 - 20 cm wheels. Ideally, I would have each wheel driven independently by one motor, but two (left and right) motor configuration is also possible. I calculated, that it would need about 10W mechanical power to drive upwards on 45' slope with 1 km/h speed and 5 kg mass. So, in reality, it would need 15 - 20 W mechanical power at maximum. Each wheel has to have about 100 RPM and 0,7-0,9 Nm. Because of the low power solar panel, I need the most efficient motors available. I have looked at Maxon motors, but they are very pricey. Which kind of motors is more efficient DC or brushless? Is it better to use one motor for each wheel or 2 motors with mechanical power distribution? Are there such brushless motors that can be used without any gearbox at speed about 100 RPM? Which manufacturers could you recommend to look at?
Hello!

A stock CD rom motor is driven at 10 W (but can handle 30W easily) at about 4000 RPM speed, so you can use that as-is with proper gearing, you need to connect it to delta to get higher Kv (or preferably rewind) for 2s use originally they are 12V.
So you need a gearbox that gives 40:1 reduction ratio for this motor.
Direct drive might be possible but i have yet seen a motor that was made for a similar application, it would need to be a ring motor and have 360 teeth around similar to a cd motor stator's at ~573 mm diameter, or ~287 mm diameter and double the width and ~180 teeth.


Z
Nov 01, 2017, 05:27 PM
Registered User
CreFrod
If you Google search "100 rpm motors" you will find many to do what you want. For traction installations a DC motor has much better stall torque characteristics than brushless.
Most are made in the Far East and are cheap enough but you would have to accept shipping cost and delivery times.
Nov 02, 2017, 10:16 AM
Registered User
Quote:
Direct drive might be possible but i have yet seen a motor that was made for a similar application, it would need to be a ring motor and have 360 teeth around similar to a cd motor stator's at ~573 mm diameter, or ~287 mm diameter and double the width and ~180 teeth.
I am very interested in direct drive with brushless motors because of simplicity and robustness. But if low kv motors are very big, could you recommend me some low power brushless motors?
Last edited by CreFroD; Nov 02, 2017 at 12:33 PM.
Nov 02, 2017, 12:47 PM
homo ludens modellisticus
Ron van Sommeren's Avatar
Quote:
Originally Posted by CreFroD
I am very interested in direct drive with brushless motors ...
Then better use sensored brushless motors and, of course, sensored controller. Much better startup and low rpm control.

For highest efficiency you should rewind good motors, with as much copper in the slots as possible.

BTW you do know you are one an RC e-flight (sub)forum?
Propellers and wheels are very different beasts.
Current = torque Kv.
A prop needs little torque ('=' current) at low rpm, whereas a wheel needs plenty of torque (= current) at startup.

Why not (also) ask a robot forum, or www.endlessphere.com (e-traction)?

Vriendelijke groeten Ron
Nov 02, 2017, 02:19 PM
Registered User
Quote:
Originally Posted by Ron van Sommeren
Then better use sensored brushless motors and, of course, sensored controller. Much better startup and low rpm control.

For highest efficiency you should rewind good motors, with as much copper in the slots as possible.

BTW you do know you are one an RC e-flight (sub)forum?
Propellers and wheels are very different beasts.
Current = torque Kv.
A prop needs little torque ('=' current) at low rpm, whereas a wheel needs plenty of torque (= current) at startup.

Why not (also) ask a robot forum, or www.endlessphere.com (e-traction)?

Vriendelijke groeten Ron
Thank you. But all the RC Brushless motors I've seen have very high Kv and power for my application. As I said I need no more than 5W power MAXIMUM pro motor. Is it technically possible to build (or find) brushless motors that have about 100 RPM at 5,4 kg*cm (0,54 N*m or 76 oz*in)?
Nov 02, 2017, 02:25 PM
Registered User
Quote:
Originally Posted by Ron van Sommeren
Then better use sensored brushless motors and, of course, sensored controller. Much better startup and low rpm control.

For highest efficiency you should rewind good motors, with as much copper in the slots as possible.

BTW you do know you are one an RC e-flight (sub)forum?
Propellers and wheels are very different beasts.
Current = torque Kv.
A prop needs little torque ('=' current) at low rpm, whereas a wheel needs plenty of torque (= current) at startup.

Why not (also) ask a robot forum, or www.endlessphere.com (e-traction)?

Vriendelijke groeten Ron
Thank you. But all RC motors I've seen have very high Kv (and RPM) and are very powerful. I need about 5W out (mechanical) power at highest efficiency possible and 100 RPM AT 0,54 N*m (5,4 kg*cm, 76 oz*in) torque. Is it technically possible to build (or find) such motor?
Nov 02, 2017, 09:24 PM
just look at it smokin'
z-matrix's Avatar
Quote:
Originally Posted by CreFroD
I am very interested in direct drive with brushless motors because of simplicity and robustness. But if low kv motors are very big, could you recommend me some low power brushless motors?
Stepper motors dude
they are 200 step / revolution for example, they are small and high torque without gearbox


Z
Nov 04, 2017, 03:56 PM
An itch?. Scratch build.
eflightray's Avatar
There are a couple of other RCGroup forums that may be worth looking in --

Robotics -- https://www.rcgroups.com/robotics-297/

Cars -- https://www.rcgroups.com/cars-45/ -- the 'Rock Crawlers' section may be useful owing to their low speed high power.


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Careful! Efficiency governs maximum power a motor can handle Ron van Sommeren Electric Motor Design and Construction 2 Sep 24, 2015 11:37 AM
Discussion GWS SERVOS for ROBOTIC APPLICATION gws roger GWS (Grand Wing Servo) 0 May 01, 2012 10:21 PM
Discussion Ultra Efficient Low Watt Motor for Solar Powered Planes Wrend Electric Plane Talk 13 Oct 27, 2009 02:42 AM
High Amp/Efficient Connectors (small/light/etc.. for LMR applications) eye_rc_soar Electric Sailplanes 19 Dec 11, 2003 09:29 AM