Brushless driven beetles

[Scottie]

Greetings! Scott here. Long time stalker, first time poster. I am interested in building a beetle weight robot and I wish to use brushless dc motors to drive it. This will be my first beetle weight robot but I am under no illusions on the challenges I will face.

So anyway, my first point of call is finding a suitable motor. Around this forum I have seen forum I have seen Turnigy SK3 motors mentioned a few times. Im going to go ahead and assume that its a 2118 type? Probably these:
https://hobbyking.com/en_us/turnigy-...ner-motor.html

These seem a good choice and I do not doubt that these motors would be very capable at beetle weight. But there is this nagging voice in the back of my skull, which says "what would happen if I used more powerful motors?" There are definitely bigger BLDC motors out there that a beetle chassis could accommodate and I could still make a bot within weight limits if I used some. For an example, why not use these NTM 28-26 types:
https://hobbyking.com/en_us/ntm-prop...00kv-252w.html
Provided that I used these motors with a suitable gear box, I don't really see to much of a problem in using them.

I suppose that it maybe obvious that I am also interested in the latter motor due to its ridiculous price tag. However, I also aware of the old adage of "buy cheap buy twice". I would love to know peoples thoughts on this. As well as if im correct about my assumption that the SK3 I've link is one used in beetle weight.

Cheers

[tweedermeister]

I've used the SK3's in all my brushless setups and they've been perfectly fine in my experience with them. The biggest reason in using the SK3's over the ntm's is availability of a cheap gearbox to mate them to, as well as the weight gained from switching the standard brushed motors they come with to brushless.

[Scottie]

Thanks for the response! That sound pretty reasonable, I would likely use gearboxes for those 25mm brushed motors. This would require that I either turn down the NTM motor shaft or widen cog hole that attaches to the motor. I don't relish the prospect of either of those. I would also have to find a way to mesh the gearbox to the motor, all an expense that will quickly erode the price of the NTM motor.

[Scottie]

Hey there everyone! An update to my bldc drive activities. After some deliberation I desided to go with the Aerodrive SK3 2122 2100kv motors. I will use these motors in conjunction with some 25GA 500rpm motor gearboxes. Here is one I have assembled.

IMG_20171028_185144.jpg

It was suprisingly easy to assemble, the gear on the dc motor was a bit tricky to take off. It went flying in my room to land and perfectly camoflage on my floor! Everything i used to assemble it came with the gear box and motor, with exception to some epoxy glue and m2 washers.

IMG_20171028_165449.jpg

I placed the m2 washers underneath the gear on the motor shaft in order for it to engage with the gearbox. I epoxied the gear onto the motor shaft, the gear was a bit loose around the shaft but after i assembled everything i spun the gear box shaft as a crude way to centre the gear on the motor shft before the epoxy dried.

[Scottie]

On a different note. I found that these motors are very thirsty. I pluged one of these motors in to an afro 12A esc and enabled bi-directional control. I found that at about 50% throttle I was drawing about 7A on the DC side. I didnt see if it could go further, mostly because I didnt have a power supply that could go any higher. I am finding this a bit odd because im essentialy running this motor with no load, so I was expecting a much lower current draw.

Perhaps I should reduce the ability for the motor to draw current on the ESC. Is anyone familiar with the BlHeli suite? I believe that i would have to reduce the motor gain? im not entirely sure.

[ralf.96]

Sounds like something is wrong mechanicly. 7A is too much.

I usually just set activate "damped light mode" and "bidirectional" and it runs fine in my beetle, raptor and feather. I think I never changed the gain.

[Scottie]

hmm. worth checking for sure. luckily i have 2 motors so i can do a comparison. Mind you though I was seeing this on the esc DC link and my ESC was getting incredibly hot. It's heat shrink sleave was melting off!