I am in the process of making a remote controlled lawn mower. For the cutter, I purchased one of these 775 DC motors, which work between 12-36v. The idea being that I would attach some strimmer wire to it and use that as the cutter.
However, in my simple tests, with a bit of strimmer wire attached to the motor. At only ~6v, it is drawing 6 amps! and that is without load, as soon as it comes into contact with the grass, it goes up even higher, 10-15 amps.
Having it draw that much current isn't going to work well with the power supply which I planned on using, which is a 12v 10Ah Cyclic Lead Acid battery. It will probably only last 10 minutes.
So my question ... is this going to be the case with most 12v high rpm motors? can I do better?
As for why I only used 6v, it was because the RPM was already scary high at that point, I dare'nt go higher
tunacheese:
So my question ... is this going to be the case with most 12v high rpm motors? can I do better?
That is a big motor and you will need a high power motor if you mean to cut real grass. To be honest I would not be surprised if you discover that you need a more powerful motor.
The link you gave mentions 0.16 amps. I wonder if that is a typo for 16 amps?
I would expect a motor of that size to take a large current so you are correct to conclude that your 10Ah battery is not suitable.
tunacheese:
I am in the process of making a remote controlled lawn mower. For the cutter, I purchased one of these 775 DC motors, which work between 12-36v. The idea being that I would attach some strimmer wire to it and use that as the cutter.
However, in my simple tests, with a bit of strimmer wire attached to the motor. At only ~6v, it is drawing 6 amps! and that is without load, as soon as it comes into contact with the grass, it goes up even higher, 10-15 amps.
Having it draw that much current isn't going to work well with the power supply which I planned on using, which is a 12v 10Ah Cyclic Lead Acid battery. It will probably only last 10 minutes.
So my question ... is this going to be the case with most 12v high rpm motors? can I do better?
As for why I only used 6v, it was because the RPM was already scary high at that point, I dare'nt go higher
You need to characterize what's needed for strimming before choosing a strimmer motor... Checkout the
power and rpm of an actual electric strimmer motor.
MarkT:
You need to characterize what's needed for strimming before choosing a strimmer motor... Checkout the
power and rpm of an actual electric strimmer motor.
I did take a look at the electric ones and they're about 350w with an RPM of around 12k. The cordless ones tend to have an RPM of around 8K. Not sure on the power rating.
All the cordless ones are 18v. I can find 18v cordless tool motors on ebay for around £15, but I then need to find the battery, and they're not so cheap, as well as needing to buy a charger too.
Sounds like at least 100W, and 10krpm are good places to start. That probably means the cheapest option is
an RC motor + ESC, rated for 3S LiPo pack should be fine to also run from 12V SLA.
Given the off-balance nature of a strimmer as light a motor as possible mounted on anti-vibration mounts
is probably a good idea to reduce the load on the bearings - the longevity of bearings might be the weakness
of an RC motor approach, but then they are cheap enough to replace on failure.
MarkT:
Sounds like at least 100W, and 10krpm are good places to start. That probably means the cheapest option is
an RC motor + ESC, rated for 3S LiPo pack should be fine to also run from 12V SLA.
Given the off-balance nature of a strimmer as light a motor as possible mounted on anti-vibration mounts
is probably a good idea to reduce the load on the bearings - the longevity of bearings might be the weakness
of an RC motor approach, but then they are cheap enough to replace on failure.
Ah ok. So by light RC motor, do you mean something like a drone brushless outrunner motor?
That one would certainly do it, but you probably don't need a 38A motor, something half the power with Kv of around 1000 should do. Remember these motors are very powerful for their size, and never make the mistake
of trying to handle them when running, can take chunks out of your fingers easily at 12,000 rpm