high RPM rc motor

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Oct 7, 2017
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6
I'd like to share a little about myself before getting into this topic. I have hip pain and can't peddle a bicycle. I have not ridden a bicycle for six years until I put a 750 Watt mid drive Bafang motor on my son's mountain bike. I had so much fun riding my son's ebike, I wanted one for myself. I'm building a custom trike using carbon fiber/foam composite for the frame and 20" rear wheels. This bike will have no crank set because I have no use for pedals.

I plan to use this motor https://hobbyking.com/en_us/assault-700-series-530kv-brushless-outrunner-helicopter-motor.html?___store=en_us .

It's a 530 kV, 4500 Watt motor. The two stage gear reduction will include a HTD3m belt with 20:120 tooth pulleys followed by #219 chain with 12:90 tooth sprockets for an overall gear reduction of 45 to 1. Speed at 80% of unloaded max RPM will be about 27 MPH which is fast enough for me. I'm more interested in hill climbing ability and acceleration than top speed. I plan to use the open source VESC controller and take advantage of regenerative braking.

I'm a retired electrical engineer but I've never tackled a project like this. I'd love to have some input and suggestions before I purchase a motor and controller. Right now I'm spending my time building the carbon fiber frame and wheels.
 
Some mechanical advice you might not need, but in case you do:

Note that unless you have really smooth roads, the small 20" rear wheels won't be much fun with the banging and bouncing, unless you use wide tires that hold a lot of air.

On my SB Cruiser delta trike, to fix my problems with that, because I already had some very wide rims, I went with Shinko SR714 16" x 2.25" moped tires
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1154498&hilit=shinko#p1154498
(ride comparison info)
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1163856&hilit=shinko#p1163856
mostly for their puncture resistance relative to bicycle tires (since they cost about the same), but partly for the bump absorption they provide on the roads around here. (there's spots bad enough to break axles; this happened on my X5304 a little while back while loaded down even though I was only at about 15MPH, and even with the Shinko's--I imagine with the smaller bike tires I'd probably have gotten a pinch flat or damaged rim (or both) as well as a broken axle).
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833&p=1311210&hilit=%2A5304+axle#p1310982
I don't know that a regular bike axle would've broken in that instance, but it would probably have bent. (I've done that before, too).

Unfortunately these are heavy tires, each weighing about 4x what a heavy-duty bicycle tire weighs, but they sure work better (for me) than the bike tires, with the motors to provide the power.


Alternately, you can build the rear end with larger diameter wheels, but put the dropouts up higher and "suspend" the frame from them, like I do on the MkIV trailer and on the new trike:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=80951&p=1325282#p1325282
The larger diameter wheels roll thru holes better than smaller ones, and have more air in the larger circumference of tire to provide more suspension even using regular bike tires. (and the wheels have longer spokes that give more suspension, too).



BTW, if you are still interested in human power either as addition to electric or as a backup in case of system failure, you might look into how "handcycles" work, if you can still use your arms/hands for that.


I don't have any sugggestions / tips about the RC motor or VESC directly, but I'd recommend looking up the various middrives and other RC-based drives for reduction info.

Kepler, Tangentdave, Lightningrods, AdrianSM, etc., all have some good mechanical stuff there. BobC and Ecyclist have RC-powered cycloidal reductions if you're up for making that sort of thing.
 
amberwolf said:
Some mechanical advice you might not need, but in case you do:

Note that unless you have really smooth roads, the small 20" rear wheels won't be much fun with the banging and bouncing, unless you use wide tires that hold a lot of air.

I'm using 20 x 2.80" "fat tires" for the rear. They came on 1.25" rims but I'm making custom 3" wide carbon fiber rims. I'm using carbon fiber more for the strength than the weight savings. I had two MINOR mishaps on my son's bicycle and bent the rear wheel both times! The front wheel and tire will be unmodified from a 20" BMX bike but most of the weight will be over the rear wheels. I like the BMX wheel for it's strength.
 
Sounds like you've got the mechanics handled. :) You should post pics of the build as you do it--you could turn this into a build thread for it (or start a separate one).

(if you're interested in mine, the new trike build in progress is here:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=80951
and the SB Cruiser trike is here:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833
though nothing I am still using is ever "finished", so it's gone thru a number of revisions as it evolves. ;) )
 
530kv means that at 12s, aka 44 volts, this motor would run free at over 23,000 rpm. Gear reduction to make a 20" wheel run at 30mph would be 23 :1. So if you had a 11t pinion you want over 250 teeth on your wheel. Or a jackshaft reducing the 11 against a 125 that turns another 11 to reach another 125. Lower voltage will reduce the rpm of the motor but increase the heat. If you were to get a Unite 24v, 36v or 48v motor they are all promised a top speed at 2,600rpm, meaning the kv would be around 110, 70 and 55, respectively. Just something to consider.

Oh, there are 10 motor poles. If you're planning to run it with an RC controller this one will handle 2 pole at 200,000rpm so it should be good there. https://hobbyking.com/en_us/turnigy-dlux-250a-hv-14s-60v-esc.html
 
People who are developing RC motors for E-Bikes are getting lower KV motors, Like 150 KV and under ,

I started to research this a few months ago, but do not have the machine tools or place to make my own, So I am waiting for Lightingrods , Ecyclist , to start making/selling complete kits.

Here is a RC motor Mfg that I found that does good quality RC Motors, they have a wide range of motors with different KV 's , You can even get them to make a motor for you with the KV you want.

https://www.kdedirect.com/

https://www.kdedirect.com/collections/uas-multi-rotor-brushless-motors/products/kde7208xf-110


I have allot of interest in your tirke, you are going to make it with suspension on all wheels ?

Tad Pole or Delta Design ?
 
amberwolf said:
Sounds like you've got the mechanics handled. :) You should post pics of the build as you do it--you could turn this into a build thread for it (or start a separate one).

(if you're interested in mine, the new trike build in progress is here:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=80951
and the SB Cruiser trike is here:
https://endless-sphere.com/forums/viewtopic.php?f=2&t=67833
though nothing I am still using is ever "finished", so it's gone thru a number of revisions as it evolves. ;) )

The main difference between your new trike design and the trike I'm building is that I sit lower and further back in between the rear wheels.
 
I would agree with Scooterman.. the motor you have posted a link to is quite high kV (rpm per Volt) so would require two stage reduction to the back wheel. Each reduction stage costs money, adds weight, produces noise, uses up some of the power and adds to the build time and future maintenance.
If you use a motor with a low enough kV that only a single stage reduction is needed, you could afford to pay more for the motor as you will have one less reduction stage to build.
The motor will be heavier, but on a road-going trike that probably isn't critical, and you will have lost the weight of the second reduction stage.
The motor will be bigger, but that probably means it can dissipate heat more easily and absorb temperature spikes with less stress. (Heat dissipation is a major issue with motors on high performance electric vehicles).
As far as RC motors are concerned, in theory I like the "pancake" style of motor being developed for heavy lift multirotors, as they have low kV and would have great heat dissipation. I don't have practical experience with them however.
Matt S ("Recumpence" on this forum) has built some awesome drives using Astro RC motors. They are well worth studying if you are thinking of doing something similar. He has achieved extreme performance and good reliability through good engineering and a lot of personal experience, however there is a lot of engineering work involved.

At the other end of the scale of price and complexity, but still achieving great performance, check out Gman's trike using a Cyclone 3000W drive.. a simple, cheap bolt-on kit with a large motor and direct-coupled planetary reduction.. all it would need would be mounting brackets and it would be ready for single-stage chain drive to your back wheel.
(Gman is currently active on the Cyclone 3000 thread on this forum.. find one of his posts and hopefully you will be able to find his build threads from there).

But if you enjoy experimenting, please go ahead and build something new.. it's what many of us would do.. and share the journey here.

Whatever you end up doing, remember that for your application, even more than normal, you need good torque at zero rpm and good reliability.

Best of luck with your build.
Dave
 
20" wheels are perfect. Throw a moto tire on a 24mm or wider rim and add a suspension seatpost ( if the frame design allows ).. all the fat rubber of a moto tire will do a good amount of the work on suspending bumps.

I would not go with that motor. Cut hobbyking's maximum power ratings by a third to get an approximate continuous wattage on a bike, which has far less air flowing through it than a RC helicopter doing 50-100mph!

I have no expertise so i cannot guide you on what motor to select.. but i would check some RC builds around here before selecting a motor.. for sure. Controllers and RC motors are also finnicky on an ebike so find a setup someone's already done and riff off that..
 
You might want to check local laws to see if what you are building is legal. The addition of a pedal system may be necessary just to to pass legal muster. I suspect that a trike will be more likely to catch the attention of Johhny Law than a typical e-bike conversion.
 
I've built a few delta trikes.

1. Weight distribution is critical on delta trikes. ideally, 33f/66r.

2. For safe and predictable handling at speed, the CG should as low as possible on Multi-track (non tilting) vehicles. And the rear track should be no less than 30" (wider is better to improve roll stability).

3. A wheel base much below 50" becomes very sensitive above 25mph.

4. Check state & local laws before eliminating the pedals. Technically, it's no longer a ebike (etike) or moped without pedals.
 
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