Go kart clutch? Has this been discussed?

[PWJM]

Been lurking some time, and have been really interested in the developments in the RC motor route...

I just read a post on the tech board that linked this this:
http://www.youtube.com/watch?v=vwODx028_Jw

Ignoring the fact that he has 3 motors on a common axle, he's using a go kart clutch... with a fairly small gear reduction to the drive axle which enables a very fast top speed. It seems very simple and compact... albeit noisy...

Has this idea been overlooked for Ebike applications for some reason?

 

[dimitrib90]

I was thinking of doing the exact same thing for my ebike. The reason that he uses the clutch is because of the high amp draw to get the go kart (or bike) moving.

Once the go kart or bike is moving, I dont think that there is a problem.

The main reason that the clutch has been overlooked is because we could just pedal to get the bike moving. Cant do that on a go kart.

 

[buzzfirst]

I couple of other reasons could be that a)you will notice that he smokes that clutch later in the video. You would have to be very very careful not to do the same as electric motors have a flat torque profile, and b) wasted energy when the clutch is not totally locked up.

 

[TPA]

I don't think even Karting clutches are rated for the rpms that rc motors produce.

Perhaps you could put the clutch on the first gear reduction axle.

 

[AussieJester]

Large RC helis (nitro and petrol) use a centrifugal clutch this might be an option?

 

[PWJM]

I don't think even Karting clutches are rated for the rpms that rc motors produce.

Perhaps you could put the clutch on the first gear reduction axle.

RC motors spin faster than kart engines and on a centrifugal clutch the faster it spins the harder it grips.... unless its spinning so fast it flies apart, then thats no good!

Check out the video link. There's 3 RC motors on a common axle attached to a tiny little Kart Centrifugal clutch. As stated by another poster, it helps with the current draw, and seemingly negates a 2 stage reduction.

Would a CVT type drive from a moped be plausible?

 

[PaulM]

I don't think even Karting clutches are rated for the rpms that rc motors produce.

Perhaps you could put the clutch on the first gear reduction axle.

Some of the big RC motors don't spin all that fast. The 130 kV HXT from Hobbycity is rated for up to 48 volts, making max rpm less than 7 grand. A small two-stroke ICE can easily spin 10 grand and more.

I would be more concerned with excessive slipping at low rpm. The average go-kart clutch engages around 2000 rpm. If you geared a minibike (or whatever) for a max speed of 50 kph at 7K rpm, The clutch won't fully lockup until you are going 14 kph, which is pretty fast on a steep hill, tight trail, or if you are stuck somewhere. The electric motor has enough torque to overheat the clutch in a hurry.

 

[AussieJester]

Some of the big RC motors don't spin all that fast. The 130 kV HXT from Hobbycity is rated for up to 48 volts, making max rpm less than 7 grand. A small two-stroke ICE can easily spin 10 grand and more.

Eeeeeasily more i had 3.5cc motors in my Serpent rc race cars that hit 35 000rpm We used centrifugal clutches in those with no springs, the simple centrifugal action was enough to bend the solid mounted clutch shoes to make contact with the housing of the clutch...

 

[etard]

Are they still using the same noisy clutches I remember as a kid with that high pitched pingy sound? I would hate to have that on a bike. I do see the value of having one. I would think as the motor picks up speed, the clutch should counterbalance the inefficiencies of having the motor pull alot of amps, instead the clutch slips until rpm matches efficient speed. I would rather see the rear wheel slipping though.

 

[AussieJester]

Are they still using the same noisy clutches I remember as a kid with that high pitched pingy sound?

HAHA i started racing the 1/8th nitro buggies and on road cars when i was ~15 along with I.C Helicopters then again in my late 20's with the 1/8th on roads again and oonly a year ago i was back into electric Helicopters.....the buggies of the 1980's had some classically bad clutches, my old man turned up a custom shoes from a teflon type material (forget exactly what it was now) Mounted the shoes solidly on one end, the centrifugal force flexed the shoes enough to make contact with the bell housing, no springs were used at all was also not clangy like the original and didnt wear out like the originals where you actually had to glue in a lining on the bell housing for the metal clutch 'shoes' to slip/grip on LoL The 1/8th scale nitro on roads i raced had a 3 shoe clutch setup in the same vein as the old fella made for the buggies, i couldn't see why it wouldn't work on the rc motors albeit in a slightly scaled up level which is why i suggested the larger I.C Helis...i would prefer to see the rear wheels :: cough :: "slipping" also though ....some tire smoke rather than clutch burning out smoke would be a neat touch t

 

[Pete1961]

An idea I had was to use a variable belt drive contaning a centrifugal clutch element, after seeing electric milk delivery trikes work fine on the flat (20+mph) but totally die when travelling uphill (2mph) and use a fixed single speed drive.
I had seen the Comet industries Torque-a-verter on small IC fun bikes & looked into them, made by http://www.hoffcomet.com seems there is quite a range including TAV2
rpm responsive & the 340 which reacts to torque requirements from the road wheels without dropping engine rpms. These units are designed to work with small Honda or Briggs IC engines (TAV2 actually bolts on to the SAE 'A' bolt circle round these motor's output shafts)... BUT found this elec motor as suppled by Brett White
http://www.users.bigpond.com/solarbbq/newproducts.htm
Pity there are no torque graphs for the motor but max speed of 3200 rpm & power of 4Kw would put this motor right in the speed & power ballpark for the Comet variable drives. One thing to note is that the Comet clutch take up rpm can be varied by swapping an internal spring in the driver pulley at anywhere between 1200 & 2200 rpm
so could be optimised according to the motor's torque curve. A case could be made for using variable belt drive without the clutch element (and possibly under manual control)
but the company does not offer this configuration (may be poss to limit movement in the driver member so the belt never fully slips). Having the clutch does mean that the motor would never stall hence always has 'back emf' and protected from burnout.
Brett shows the planetary reduction box removed from the motor, this would be needed so as to have the correct rpms to use the system. might be poss with some machining to re introduce this reduction box downstream of the 'torque converter' as makers insist on calling it. This idea for load carrying trike rather than a light ebike, hope its not too foolish (& not too off topic). More tech info on motor & trike weight etc would be poss to predict hill climbing ability PETE

 

[GGoodrum]

Clutches are used with IC engines because these need to spin up in rpm before the torque kicks in. Electic motors have all their torque at time zero, so why would you want to use a power and efficiency robbing clutch?

If you are worried about too much current, initially starting out under a heavy load, you can use the ramp-up feature, now available on pretty much all RC controllers. This is needed on higher power RC helicopter setups, because the initial torque on startup was snapping the main blades around enough that it would strip the main gear. It actually took two years to get patrick to include this feature in the CC controllers, the first being the HV series, when they first came out.

Anyway, this is completely programmable on the HV110, the PowerJazz and most everything else I've played with, and is really nothing more than a programmable current limiter.

-- Gary

 

[rgx]

I think another reason for the clutch is that they are using a sensorless controller.

 

[GGoodrum]

I think another reason for the clutch is that they are using a sensorless controller.

All RC controllers are sensorless.

 

[gogo]

Electic motors have all their torque at time zero, so why would you want to use a power and efficiency robbing clutch? -- Gary

Centrifugal clutches can facilitate a quicker launch acceleration by allowing the motor to spin up to a higher power output (engagement RPM) and then act as variable reduction gear until complete engagement.

Are quicker launches worth the expense? For me it can save me from having to get off my bike and sprint across a busy intersection. If you're sticking to the legal limit of 750 watts and only have one gear, centrifugal clutches may be a consideration.

 

[Diamondback]

All RC controllers are sensorless.

not so....

Novak controllers are sensored.....

 

[gwhy!]

Would a CVT type drive from a moped be plausible?

I keep thinking the same thing Yes I think it would but you will not need the clutch part of the drivetrain just the front variator and the rear variable pulley geared directly to the rear wheel. I dont know why peeps havent picked up on this ( unless there is something I am overlooking) . It will always have the correct gearing for the load ( as long as the roller weights in the variator are matched with the motor power ). I have played around with many a auto scooter/moped drivetrain from 50cc scoots to monster maxi scoots. I think the only real draw back would be the overall weight/complexity of such a drivetrain could possibly make it not practical for use on a pushbike . but I would love to see it done

 

[liveforphysics]

The same Kart was later re-done to eliminate the clutch, and run direct drive. It was much faster, much more efficient, and smokes the tires from a start rather than smokeing the clutch.

RC motor speed controllers seem to be shockingly good at starting a motor from a stop, even under load. Don't ask me how they are able to do that, but they do.

 

[dimitrib90]

The same Kart was later re-done to eliminate the clutch, and run direct drive. It was much faster, much more efficient, and smokes the tires from a start rather than smokeing the clutch.

RC motor speed controllers seem to be shockingly good at starting a motor from a stop, even under load. Don't ask me how they are able to do that, but they do.

Wouldnt having a direct drive ruin the internal bearings of the motor from a start-stop position?