Cheap RC BMX build

[flanders]

Looking to put together a cheapish RC build with an old bmx I have
Not done much like this before, except add outrunners to a couple of scooters, so any help appreciated


already have a 6374 180kv motor
I am hoping to make a mount out of some 6mm angled aluminum and bolt it to the frame with either some U-bolts or exhaust clamps
I am lookin to put a 10-13T 6mm sprocket(6mm not 25h as this is not too easy to get hold of in UK) on the motor driving a 40T sprocket,
this will be attached to a 12mm steel rod mounted with 2x 12mm Bore Pressed Steel Type Pillow Block Bearing. Then have a 10-13t 1/2" sprocket
driving the rear bmx 20T sprocket.

If things work well, I will see about adding halls and a freewheel crank later on.

Can anyone give me an idea what sort of top speed and acceleration this would give me? I would be happy with anything over 15mph. Or do I need to adjust my gearing?

 

[Thud]

Sounds like you intend to run on 24volts? (6 cell lipo?)
from the hip, you are still over-geared.

using 4-1 priamry & a 2-1 secondary to the wheel you are spinning the wheel 540rpms on 24v....thats 33mph in a 20"wheel.

You need to get your gearing down into the 13-1 range if you want any kind of reliability with RC components.....speed controllers especialy.
good luck & have fun.

 

[flanders]

Hey Thud, thanks for your help

yeah I am going with 6s lipo.

was hoping 40t would do it, they jump up in cost over that I think I will go for a 57T instead of the 40 and will try for a 8or9T on the 1/2" sprocket.

 

[gwhy!1]

Hey Thud, thanks for your help

yeah I am going with 6s lipo.

was hoping 40t would do it, they jump up in cost over that I think I will go for a 57T instead of the 40 and will try for a 8or9T on the 1/2" sprocket.

Not sure if you tend to go for a rc esc but I have just bought and tested a 200A £22 ( delivered from LH) 6s controller , it works reasonable well as long as the gearing is not to high ( like Thud has already said ) , I was running it on a 26" bike ( using a 6374 ) geared for a top speed of only 14mph ( using a 12t and 40t 6mm initial reduction ( this was part of a 3 stage reduction ) ) and it had no probs syncing at this load , it will be better ( less load with a smaller wheel ) so the top speed maybe could go upto around 20mph before you get sync issues ( but I haven't tried ). But I did find that if you tried putting a lot higher load onto the controller it would draw upto 250A-300A while it was trying to sync so there is plenty of potentional for the controller to let out the magic smoke if you get the gearing wrong, a very good investment to help protect the controller with these sort of not syncing /high current situations would be to use a CA as a current limit setup. I have used the 6mm chain and sprockets ( initial reduction ) with good success on many of my builds upto 4kw without problems.

 

[flanders]

I have a 200A mystery controller I got off ebay for £23, also a 100A skywing one that was about £9, I will see how these work out.

I see you are also in the UK gwhy, can I ask where you got your 6mm sprockets from? was going to use technobots, but they are closed for hols now, so will have to wait a bit unless I can find somewhere else that sells them.

 

[gwhy!1]

I have a 200A mystery controller I got off ebay for £23, also a 100A skywing one that was about £9, I will see how these work out.

I see you are also in the UK gwhy, can I ask where you got your 6mm sprockets from? was going to use technobots, but they are closed for hols now, so will have to wait a bit unless I can find somewhere else that sells them.

I used a 100A mystery controller for a while ( experimenting with it ) I was surprised how high the current can go before they blow up, I was regularly getting 180A peaks from the 100A controller without it popping !, I finally blew it up by forgetting it was only a 6s controller and plugging a 12s battery onto it they dont like it :lol: .
I get my sprockets from technobots they have quite a quick turn around and offer the option of different size bores and also the option for grubs as well, not sure where else you can get them with the bore size options, bearingboys sell them with standard bore sizes and they are about the same price as TB.

 

[flanders]

Hey, in the end I went for a single 130T sprocket, I have had this laser cut in 3mm steel looks ok but need a little bit of tidying up with a file.

I have a 12T sprocket for the motor, so will give me about 10.8 reduction, was hoping for a little more, might try for a smaller sprocket on the motor or even try to rewind my 6374??

just waiting for some drill bits so I can try and bore out my 12T sprocket from 8mm to 10mm then I can put this together